The Short Nose, Reinforced, Multiplex Fun Cub Propulsion Experience

By Carl Murphy

One Airplane, Two Batteries, an Hour of Carefree Flying

(0) to (750) Feet At a Count Of Ten (5S) or Thirteen (4S) or Fifteen (3S)

This is an instruction by examples of electric propulsion choices for a four foot wingspan, molded from impact resisting foam, reinforced, light wing loading, semi-scale RC Piper Cub.  Chronicled are testing, things gone right and wrong, and, RC flying as a whole experience.  From light weight one and an eighth inch diameter outrunners, light to medium (37) mm diameter outrunners through geared competition inrunners, four combinations were selected as optimal.  From relaxed to outrageous, flight times start at twenty-five minutes on just the motor and battery.  Altitude gain at maximum climb for count of ten ranges from three hundred to seven hundred and fifty feet, glide back down from a seven to one ratio to fifteen to one.

Tuning Is Worth It

Where I started RC flying in Orange County, CA, back in the mid 1990s it was next to the current F5B world champion and six other current or former thermal, slope soaring and pylon RC pilots.  At San Diego’s Mission Bay my company includes a former F5B world champion who manufactures the worlds best RC racing motors plus several more national and international ranking F5B, F5D and F3A precision aerobatics RC pilots.  As a friend in low places (I gave up my Piper Pacer at the start of the second great depression, for ten years I was almost, but not quite, broke) though the experience with getting a RC airplane set up right was not lost on me.  Significance; Nobody has ever seen a Fun Cub fly this well, when I loan my RC airplanes to other pilots they don’t get as much performance or duration.  Part of that is having flown enough to be “one” with this airframe.

This article is paired with articles about The Mentor Propulsion, a larger and heavier airframe and an article about The Cost of Flight, Outrunners verses Inrunners. 

An Introduction To Selecting a Propulsion System

The most often heard exclamation where ever I fly is; “What do you have in that thing!,”?, followed by “how do you get it to stay up there that long?”.  Real world testing including stuff that failed, adjustments to get the best out of components and net economic analysis.  With experience extending back a decade and over twenty different motors in Fun Cubs, the outrageous performance from a geared down racing motor was still something new for me.

A lifelong pilot (both RC and full size), once CNC machinist programmer and a civil design engineer with the confidence to bet the public’s safety and his license on dozens of numerical decisions every work day; Even with nine semesters of university mathematics, when I look at the calculations related to flight, the complexity is mind boggling, I give up.  Ask the Editor, he majored in aeronautical, the rest of us at the SEFSD include electronic and mechanical engineering degrees.  Let the airframe, propeller, electronics and motor experts do their part, I’ll fiddle with what they created to get the most out.  I can’t do a thing about what is inside the motor-controllers, radio or servos, so why concern myself beyond how to operate them as intended to get the best out of them?  I can’t build as good a wing as they can cast in foam either.

From experience I knew that the twelve year old NeuMotors 1105 with the Maxxon 4.4:1 gear box (fitted last year 2019, seventy-five dollars for the transmission plus paid the labor in fresh lobster) on 4S 2250 LiPos swinging a wide blade Aero-Naut 12X6.5 folding propeller wasn’t quite enough for the five foot wingspan, two kilos, Mentor.  It was like putting a sports car’s overhead cam V6 in a full size pickup when a pushrod V8 was needed.  The Mentor needs a more powerful motor.  The Fun Cub weighs half as much at a two-thirds the wing loading. 

NeuMotors are all out competition quality, which in that configuration weights (135) grams and is operating at a calculated (91)% efficiency less a nominal (5)% loss through the transmission.  More average values for sport quality are (60)% efficiency until at about seventy flights when the motor’s bearings start giving out.  I estimate that three out of four RC pilots are operating their electric propulsion at about (40)% efficiency.  My flight durations start at twenty-five minutes and go up to an hour, on just the motor and battery in still air at from sea level to about five hundred feet.  An unexpected conclusion is that if you aren’t often slamming your RC airplane into the ground that the high initial price of this seemingly exotic combination had the lowest net cost per hour of flight as outrunners costing half as much required half again more amps for two-thirds of the flight duration and used up batteries much faster.

Current similar 1105 series motors from NeuMotors are rated at continuous operation at up to the boiling point of water at sea level at (200) watts-in.  Maybe run that way in a pylon racer.   Average motors at that temperature a NeuTronics motor can withstand the magnets demagnetize.  And for a short burst at up to (400) watts-in.  That (400) amps is for a “drag race” to altitude.  F5B (seven horse power) they use a trigger switch, two seconds is a long burst taking them from level flight straight up to about two hundred miles an hour. 

For use in a Fun Cub most of the time is flying at fifty to a hundred watts, a quarter to a third of the time it is coasting with the propeller folded.  Correlation, after you make sense of all the inputs, of the modern (3,000) kV equal with the at the NeuMotors web site virtual dyno is excellent.  Correlation at trying to model a Fun Cub airframe in the computer simulators is lousy, none others have such low wing loading.  From experience in a twice as heavy and quarter bigger Mentor an approximate in flight output of (200) watts-out in flight was about the useful limit of this motor plus transmission at that airframes duty cycle.  Although decent performance could be had with propellers as small as ten inches diameter, the Mentor airframe flew best with propellers from twelve to fourteen inches.

Having determined that the Fun Cub flies best with propellers in the ten to twelve inch width (nominal, the carrier bar width figures in too), there might just be some improvement in running that motor/transmission combination on 5S LiPos although that requires a smaller diameter propeller.  It’s a net efficiency thing, would more efficiency from the motor be more than offset by the smaller diameter propeller, in this airframe?  Although that 12X6.5 folding propeller on 4S LiPos provided outstanding performance in a Reinforced Fun Cub, at the November show I picked up a single 5S 1200 mAh LiPo.  That 5S is uncommon as is the smallest capacity.  Only a fool would want one…

5S 1200 mAh LiPo (179) grams including connectors

4S 2250 mAh LiPo (229) grams including connectors

Propeller pitch is by no means standardized, and, from Aero-Naut there are two choices.  Average would be 11X6, wider and thicker is the 11X6.5.  They cost about fifteen dollars a pair.  To that add the width of the bar connecting them, which can be varied.  There are more effective propellers in carbon-fiber.  If you are really into it different carrier bar angles can be tried too.  If that isn’t enough NeuMotors can custom wind a motor…  I used an ordinary Castle Creations Talon 2-6S (25) amp motor-controller with the lead set on automatic and the brake activated.

11X6.5  (17.7) Volts (23) Amps (!)  Volts 5S LiPo 1200 mAh  (410) watts-in  too many amps, start lower than more than the maximum

11X5  (17.7) Volts  (19) Amps  1200 mAh LiPo  (330) watts-in on the bench  At (91-5)% that is (290) watts-out, on the bench and about (215) watts-out in flight, at full amps.  Somewhere above (20) amps this motor heats up too much.  Although full amps will only be for seconds on launch, better work up to it.  With modern motors and batteries you don’t need to run them on the edge of failure.

I fly an odd profile, intended to approximate slope soaring, without a slope, this combination will not be flown at full amps for more than a count of ten, maybe fifteen now and then.  A count of five with this combination will take this Reinforced Fun Cub from a hand launch to higher than the law allows at Mission Bay.  I glide my Fun Cub at least a quarter of the time.  Knowing this combination is prone to running hot and that it has about the limit of power I’ll be flying mostly at part amps.  It’s going to be tested, it could well be that a ten inch propeller with a higher pitch would perform better.  And that 5S LiPo weights (50) grams less than the available 4S LiPos.

11X5 (14.8) Volts  (15) Amps  4S 2250 mAh LiPo  (220) watts-in on the bench.  One battery isn’t enough for a decent flying session, this was with a 4S 2250 LiPo, of which I have three.  The outputs of the three batteries don’t quite match, despite having been bought at the same time and operated just about the same.  Precision testing would require a controlled voltage source and a wind tunnel or telementary, neither of which I, or a vast majority of RC pilots, have.  Let’s see what we can do with nothing more than the manufacturer’s instructions, a watt-meter, the virtual dyno, our fingers as a heat sensor and experience.

Flown back to back, on 5S the system had way more power than on 4S, which, in still air, only made a difference in how big a loop you wanted to fly as both combinations can climb way up there quickly.  Any airframe can only use so much power and both combinations are at about the limit.   

It was a beautiful December day, a nice overlook out over the Lahn River where, when the wind is from the other direction, slope soaring is possible.  Looking out over a vast expanse of grass, forest and soccer field.  When a older couple was out for a walk the gentleman had to tell me it reminded him of Stukas, that in a dive with the sirens howling scattered.  He was old enough to have been there.  Any veteran I’m interested, but, I have a let them tell it if they feel like it, just the same, I didn’t want to be reminded of what happened in connection with Stukas.  Although the Fun Cub often invites comment, I can count on my fingers how many times WWII was discussed and he must be one of the last of them.  I helped restore a Free French Piper Cub observation plane from that era, any resemblance of my little RC airplane though must be the climb, hang out up there and dive I often do.

Four Generations of Fun Cub

Originally assembled for an acquaintance the winter of year 2017, by the time I returned two years later the first “full house” Fun Cub (there were previous versions) in Elapor impact absorbing molded foam, had, after a decade in production, been replaced with the considerably stronger (heavier, more versatile and slightly more expensive) Fun Cub NG. 

I first saw the Fun Cub Next Generation and watched it being demonstration flown at the biggest model show of the year in German speaking Europe, early November year 2019.  I planned to buy two of them, one the Radio Ready (€289/$320-) and one a kit (€130/$143-).  A clue, buying the RR version you get balanced, usable quality at a price lower than you can buy pieces and assemble it yourself.  My reason for wanting a kit was to model a front motor mount (the NG has a rear mount) to use a high performance NeuMotor inlinner with a transmission.   After a decade of being almost, but not quite, broke, I could buy new, full price.

One of the Multiplex factory buildings burned down while we were all off at the show!    At which, after determining the mail order houses listed the Fun Cub NG as unavailable for at least six month, I decided to order a spare set of wings foam and another whole kit from new old stock for a Fun Cub.  And later the kit for the indoor/outdoor Funny Cub, for me a new direction.  Although distributed by HiTek, for now Multiplex stuff is not available in the USA, they are alive and doing well in Germany and Europe.

Except that Corvid-19 as of March year 2020 reduced me to idle and nearly broke, again.

A Dozen Fun Cubs

I’ve assembled a dozen Fun Cubs in all, flying them in both San Diego CA USA and Rhine-Main Germany.  In SoCal usually with landing gear, in Rhine-Main usually without.  As usual I assembled the first as per the manufacturer, then I reinforced the weak stuff.

Semi-scale (increased tail area) be it the Pico (year 2000, Styrofoam, ruder and elevator, speed 450, direct drive 6X5 propeller on six NiCad cells) or Fun Cub NG (year 2019 impact absorbing Elapor foam plus reinforcement) are a near visual match to the Piper Pacer I used to fly. 

With the exceptions of three Fun Cub airframes (original and two for others) I considered the flaps unnecessary weight and expense.  If pilot cannot place his landings (a vast majority), or, if the pilot has sufficient concentration and has the radio to use them, flaps are worth their weight, drag and complexity, more so for heavier versions.

I spent enough on basic quality servos that they follow control inputs, don’t break easily or wear out long before…  Other simple stuff like setting up any ARF right.

The Fun Cub, “full house” with rudder, motor, elevator, ailerons and flaps, great big main wheels, too weak main and tail wheel landing gear, as a flying assembly, was a (continuing) transition away from build it yourself (at least forty hours for this size) and just barely flying with brushed motors and Nickel-Cadmium batteries, to modern Almost Ready to Fly (out of the box).  The original was offered first as a kit with the matched propulsion of an (80) gram outrunner and 3S LiPo at (150) grams, they took about four hours to put together (plus decals or paint and setting up the radio) for which they held up for about fifty flights at an average of ten to twenty minutes a flight, in still air at near sea level.  They were so light that a puff of turbulence on landing threw many pilots.  Starting with my second Fun Cub mine were substantially reinforced. In Southern California I (usually) flew with landing gear, in Rhine-Main (mostly) without.

My final two Fun Cubs I shortened the nose (about two cm/most of an inch) to ease the Center of Gravity (balance) problems. 

I have never seen a Fun Cub flown with the (135) gram motor and the APC 13X4 propeller, which was the final Radio Ready configuration intended for use on a 3S 1600 mAh LiPo, flown.  That’s kind of a shame as the promotional video was some really interesting close in flying.  Special for Multiplex, from APC, easily broken (the landing gear was insufficient, leading to prop strikes) most were replaced with a 10X6 fixed propeller and nose heavy with a 3S 2200 mAh LiPo.  At which you had a (misunderstood) medium-light weight, Cub like RC model.  Misunderstood as without exception the dozen RC pilots I met flying them were confused by the light wing loading and soft foam that contributed to keeping the price and weight down, they way loaded them down.  These really flew best at lightest weights.  No amount of reinforcement or ballasting them made for standard flyers.  They couldn’t even be modeled on the simulators correctly.

That odd choice in propeller continued with the Fun Cub NG.  Although that (135) gram motor on a 3S 2600 mAh LiPo will hover a nearly three pound airplane, that might explain the eight minute flight times the manufacturer cites as a reasonable expectation. 

See my previous articles where I reworked other airframes bought slightly used which appeared to be in flying condition.  Almost Ready to Fly turned into almost flying for way too many inept assembler/RC pilots.  I lost track of how many times somebody commented; “I didn’t know those could fly that well”.   

Performance, Reality and Expectations

Typical ARF flight times cited for similar (1.4) meter/four and a half foot wing span sport RC electric powered airplanes are in the eight to twelve minute range.  Anything under twenty minutes from my stuff and something has failed.  I expect and get from twenty to thirty-five minutes of Ersatz (zu English replacement) slope soaring out of my Fun Cubs with twice that easily available if flown for duration.  And that is landing with a quarter of the charge of the LiPo battery left.  My personal Horizon Hobbies Apprentice, E-Flite tuning motor, replaced the propeller (I used the original to mix epoxy) battery and motor-controller, it flies half an hour on up, per flight.

All it took to take a RR Fun Cub straight up three hundred meters/a thousand feet (full amps for a count of ten) was replacing the motor-controller with a 5S/(40) amp motor-controller, a 5S 2200 mAh LiPo and a 9X6 fixed propeller with the Multiplex specified HiMax (135) gram motor.  From that height, with the propeller stopped, it took about five minutes to glide back down.  Pulling back hard on the stick with stock wings, at that power level, would fold them off at the outboard servos.  If you hadn’t doubled up the main landing gear wire at that weight the wheels hit the wing, the tail wheel mount gave out quickly too.

No Equipment Performance Measurement

As a simplest standards, requiring no equipment, I cite the diameter of an inside loop starting from level flight to compare power to weight, and a starting from “coasting” in level flight maximum power climb for a count of ten to glide back down ratio.  The “lightweight” (two ounce) motor configurations will loop in twenty meters, ten seconds of full power climb to glide back down (propeller folded) is in the seventy range.  The “heavy” systems loops run sixty to eighty meters (for as long as the battery charge lasts) climb to glide is in the one hundred and thirty range.

All of these combinations have durations of at least twenty minutes, even if the propeller will not fold and it windmills.  Most of them will go half again more although average landing are at twenty to twenty-five minutes with the battery charge at about a quarter remaining.  A guess puts a flown for duration only flight with the medium configuration on a 3S 2200 mAh LiPo at about an hour.

Using energy management, the economical and well matched propulsion from Multiplex, a HiMax (80) gram motor with a 10X4,7 APC (fixed) slow fly propeller flights on a 3S 1600 mAh LiPo went about fifteen minutes.  Use used up batteries, mangle the servo instillation, fly uncoordinated, forget that there are amp stick positions between all down and all up, fly in more than walking speed wind and times went to half that.

Light Wing Loading Won’t Simulate

Even with (135) gram propulsion the Multiplex Fun Cub had a wing loading so much lower than the any other Piper Cub as model that the simulators, even ones where you can go in and change everything (even designing your own system) could hardly be configured to model as The Multiplex Fun Cub.  As compared to a vast majority of other Cub models, which have a much heavier wing loading.  It figures in that this is an under-cambered wing, not the typical flat bottom Clark Y.  That’s quite the effective set of flaps, they and folding propellers aren’t modeled, you’d have to turn aeronautics engineer to do so.  I tried building other wings, a conclusion is that the factories can mold a better wing then I can reasonably construct myself.  We used Real Flight version 5, way behind the current version, until bored with simulators.

I have had to adjust my understanding of “reality”.  It used to be the simulator was a simulation.  For many today that computer screen is real, and flying outside doesn’t match that reality.  There are now two realities!

Multiplex offers a combination of their “affordable” six channel radio transmitter and receiver combined with their own flight simulator for €100/$110-.  As it contains some of their airplanes I just might spend the money.  A limitation is that although you can get the experience of flying a RC airplane from a single position, only the simulations in which you can fly around within a computer generated landscape were interesting.  A case of I’d like another radio system anyway. 

Sport First, Trainer Second

Most of my personal Fun Cubs, as the airframe aged out, were refitted with inexpensive propulsion and given away at their end phase with worn out propulsion to help a beginner RC pilots get the hang of it.  For €10/$11- I had a (125) gram motor configured to turn a ten inch propeller on 2S LiPos in the 2200 mAh size that with it’s (5) mm output shaft would take some nose in hits before giving out. 

In the here and now of year 2020 probably the Horizon Hobbies Apprentice system is a best first RC airplane, but I liked the Fun Cub.

A couple of years ago in SoCal, at the club flying field on Mission Bay, I stood next to a retirement age beginner, who like me, also flew full size.  I later found out he’d just wrecked another (of, so far, five) RC airplanes.  My Reinforced Fun Cub was fitted for (450) watts-in on 4S LiPos with a three blade folding propeller.  For him I put in a 3S LiPo, launched it, trimmed for a slight climb and let him fly for twenty minutes.  I landed it.  That twenty minutes with an RC airplane set up right got him some confidence back.  Later that day a mid-forties beginner flying it commented it didn’t seem to have much power.  Even on 3S I showed him otherwise.  On 4S it could take off straight up and was still agile enough to chase it’s own tail. 

A Stronger, Heavier Replacement

The Multiplex Fun Cub NG looks about the same as a Fun Cub, is however considerably strengthened inside.  It is correct for the mounts at the rear outrunner in the (135) gram size.  A bunch of weak stuff was corrected.  Multiplex insists on selling decent quality systems, in an era of cheapness.   Want to experience ARF really right, buy a Multiplex RR.

Multiplex, an established six decades ago RC stuff company, is centered in South-West Germany a couple of hours drive further upstream on the Rhine River from where I live half the year.  At Mission Bay in San Diego CA they are most likely best remembered for the Easy Star (1) although I spotted a Rock Star being flown by a club president recently.  Multiplex is owned by and they were distributed in the USA by HiTek.  Multiplex has disappeared from the USA, their superior quality was misunderstood during the decade long Second Great Depression, when “cheap is as good as real” took over.  Despite the setback of a burned building, Multiplex is alive and doing fine.  They may arrange for an alternative distribution in the USA.

Out Of Twenty Propulsion System, Four Motor Weights

I tried motors ranged from (40) grams to (185) grams with the Fun Cub.  I used 2S, 3S, 4S and 5S LiPos.  Most of the time I used Aero-Naut folding propellers, depending on power (and continent) APC fixed or Graupner and Aero-Naut were also used.  Currently I mostly use Talon motor-controllers, any modern motor-controller, when the timing is set on automatic, can be a good choice.  It helped that the lighter power combinations also fit and function in the Mini-Mag (now the Fun Man), Gemini, Park Master and Twin Star II.  A couple of combinations that were underpowered in a Mentor (a quarter more wing area and half again higher wing loading) did well in a Reinforced Fun Cub.

Lightest (reasonable):   outrunner

(58) gram outrunners, (25) mm width, (3) or (3.17) mm shaft  lowest available kV, on 3S 1500 to 3200 mAh LiPos with seven to ten inch propellers.   Figure on up to (200) watts-in (maximum on the bench) at (65)% efficiency.  That falls off about a quarter in the air, follow the manufacturer’s recommendations.  In Germany Hacker (Sport) (€65/$72-) each and in the USA brand Scorpion at about fifty bucks each.  Figure on fifty to seventy flights before the bearings are giving out.  Roxxy also has an economic motor which also did well for €30/$33-.  Everything cheaper was not really sufficient, at this weight, to be enjoyed.

At this weight with lighter batteries the Fun Cub was a butterfly, too light for most pilots, there wasn’t much requirement for the flaps.  Flights in still air ran fifteen minutes (average pilot) to half an hour (me) and that wasn’t just cruising around either.  When most recently used I enjoyed thermaling my Fun Cub so much I gave up on burst to glide measurements as it kept staying up five minutes on just a count of ten climb, the transmitter battery gave out first… 

If at Mission Bay the new height restrictions limit RC flying to (200) feet/(65) meters this would be a most interesting combination.

Hacker has their affordable quality motors manufactured for them, in China, their Sport series are a most reasonable quality.  Hacker rates these size sport motors to be operated on 2S and 3S LiPos.  I’ve run Hacker Sport motors rated for 2S-3S on 4S LiPos, that mostly that just wears them out faster.  As in verses about seventy flights for the 20 series before the bearings go rough to less than half that.  You need more power out of this series of Hacker Sport motors; Either get a bigger motor, or, a more expensive one.  Be it Hacker or Scorpion for this configuration this about the best quality you are going to find.  A vast majority of what you get costs less and is junk.  Both Hacker and Scorpion sell replacement bearings for their stuff.

Take note that the same case size, at higher quality, price and too high rpm (kV) for direct drive propellers are also used for helicopters.  Hacker also sells their better quality one inch diameter motors factory assembled with a Maxxon 4.4:1 transmission in the €125/$140- range.  Reasonably enough priced that I canceled my plans to send in some Hacker and Scorpion helicopter motors in this size motors to Reisenauer to be fitted with 6.7:1 transmissions.

For their sport motors Hacker does not make any claim to efficiency.  On 3S systems with cheap(er) motors (a vast majority of what I observe in sport fixed wing use) when run on 3S LiPos I estimate (0.65)% efficiency, if you get one that is straight.  These Hackers and Scorpions are better, I estimate (0.70)% efficiency (on 3S), if configured well. 

Much of what I see being used in the “cheap is the same as real” era is way down on efficiency and wears out quickly.  I doubt that (165) gram Dxxxxx I tried puts out as much of half the power to the prop it takes in and weights half again more than quality stuff.  It didn’t, as a system, perform as well as sporting quality outrunners weighing (105) grams.

Medium/Light:   outrunner

The seldom seen (70) gram, wide (37) by shallow Hacker (€72/$81-) or recently available from NeuMotors.  Using a 3S 2200 mAh LiPo on a 10X6 folding propeller with 2S, 3S and 4S was my favorite combination in still air.

Two of these in a shortened motor gondolas Twin Star II would be “killer”.

The original offering for a propulsion package in the Fun Cub was the same as for the original Park Master as a (80) gram outrunner (longer then it’s diameter) which turned a 9X4.5 Slow Flier APC just fine on a 3S LiPo.

Bought as Hobby People went out of business, were a pair of cheap (8) gram servos that fit the flaps pocket of a Fun Cub.  I went ahead and put them in as their known to be failure prone, poor positioning accuracy and wearing out quickly would be OK for flaps.  In the USA we are usually satisfied with a basic (5) channel radio, for which to operate the ailerons a “Y” cable is required.  You lose some there as even decent quality servos the centers are seldom identical.  Operating the aileron servos on separate channels they can be “matched” and the end adjustments can be worthwhile.  As for flaps, they could be run on a “Y” cable, but, getting the adjustments for the Fun Cub and Fun Cub NG just right for the surprisingly elaborate flaps of a Fun Cub or Fun Cub NG is tedious.  It’s easier to get them close then adjust the center of the servo from the transmitter.  And it saves the price of a Y cable. 

At this light and medium weights I didn’t necessarily consider the Fun Cub with a two position switched flaps (up or down) justified the weight.  Oh, every once in a while, even I can’t always perfectly place a landing in swirling wind, deploying the flaps saved running into a rock.  Part of the issue is that using the flaps as an emergency brake is having to let go of one stick to hit the switch and that with folding propellers, even with landing gear, landing on a too beat up and rocky place for most pilots if the flaps were deployed the folding propeller sometimes hung straight down and broke the tip off. 

In Germany, they aren’t believers until their transmitter has more switches than the law allows.  I use a Graupner MZ-12, they use Graupner MZ-18.  From a professional published flight review of a stock Fun Cub NG (FMT December year 2019), that author also flies elaborate, at the limit RC stuff, using the computer ability of an expensive, he programmed a delay between when the flaps switch is thrown and when the flaps deploy.  That lets the pilot get his fingers back on both of the control sticks before the flight profile changes.  Oh, and from the pictures he is flying at a reasonable, grassy, place.   

Run a heavier combination with a selectable from the transmitter flaps and a wide flat propeller and there are some fun possibilities with flaps.  Of a dozen other Fun Cubs I’ve seen none flew as well as mine, with our without the flaps.  But those factory videos…  When I get a RR Fun Cub NG I’ll report back on the flaps.

Medium:   outrunner

Easily sourced from Hacker or Scorpion, (105) grams at about €100/$110- on either 3S 2200 mAh or 4S 2200 mAh.  With a 10X4 or 9X6 these were what most people would most enjoy.  With the standard length nose they were also all the weight that would make balance with the battery all they way at the back.  It was also about the limit of what a standard Fun Cub could use as far as power goes, fact is run at under maximum was better.  What a blast of carefree flying these combinations made.  At this weight slight wind was an allie, an opponent to be spared against.   Covering most of the belly air outlet with a 3S 2200 mAh LiPo all the way back had no observed heating issue.

Heavy:   outrunner

(135) grams from HiMax (former Multiplex supplier), Permax (current Multiplex house brand), Hacker or Scorpion at €100/$110 on up.  Anything cheaper is mostly a disappointment.  At this weight getting a Fun Cub to balance was a problem, even with the battery all the way back.  Although good motors at this weight are more powerful than needed, most often they were set up to pull (30) amps.  They could be run on 2S (down-rated for use as a trainer) 3S 2200 mAh, 4S and even 5S.  Power could range from a ho-hum (300) watts-in/(165) watts-out to climb straight up (450) watts-out.  Flights from eight minutes to half an hour depending on…

Heavy:   geared inrunner

(135) grams from NeuMotors.  Lowest kV 1105 series (3,000) with the Maxxon 4.4:1 gear box.  Effortless power at (18) amps and (91)% efficiency (!) less slight loss through the transmission.  Set up with a 12X6.5 folding propeller with either a shortened nose or notch the foam to push a 4S 1500 to 4S 2200 LiPo further back, flown hard, they flew for half an hour. 

A short burst of thrust is enough airflow over the tail to change maneuvers.  Too much swirl under the clouds of the walking speed wind to do climb glide tests.  Ten seconds of full amps though takes it even further, way up there, than the previous combination. The first flight with this combination was stopped at (38) minutes. 

For the second flight some fine tuning, I moved the battery half an inch further back.  Wrong direction, it was too sensitive to the turbulence, not worth the slight improvement in agility.  By now the wind had picked up, the second flight was stopped at half an hour by cold fingers.  By the walk back to the station wagon though the clouds thinned out, the wind quit, temperatures came up and it was too soon to go home.

Unexpectedly, they had a lower cost per hour of flight than the outrunners at the same flight performance when durability and reduced using up of the batteries was taken into account.

Hacker offers factory assembled motors with the Maxxon or Reisenauer transmissions too.  Guess watt(s-out)?  They cost more than cheap stuff.  About the same as NeuMotors.

Standard Equipment, The Best Examples 

The influence of the competition pilots I fly next to, we aren’t satisfied we determined optimum until both sides of the curve(s) are demonstrated, these are effective “net” systems.  My personal “bell curves” include optimizing for net efficiency at a reasonable cost.  Reports at three flights that everything is perfect; I regard as censorship, by omission.  In case you were wondering, I fly the stuffing out of my RC airplanes and can land right at my feet, even in wind only a fool would take to the air.

My Fun Cubs the aileron differential (twice as much up as down) as set per instructions (a vast majority have equal up and down throw, often even the factory RR), throws are equalized by individual trim at the computer transmitter, the attachments set up correctly and the connection to the foam secured with additional fiberglass.  Thows changes makes it handle correctly and increases the duration during flights with aerobatics.  You don’t have to be an F3A pilot with a three thousand dollar airplane (plus transmitter, batteries etc.) to enjoy getting an RC airplane “right”. 

When there are F3A pilots at the field, for their few minutes of perfection in flight I clear the air for watch them fly, or go way out to the end of the field so they can concentrate.   

“Ordinary” Fun Cubs, with decent system durable components, have a net cost to fly of about six dollars for a fifteen to twenty minute flight.  Anything cheaper than what is detailed in this report (or the RR) and the cost, the real net cost; Cheaper costs more and doesn’t fly as well! 

I must have a more efficient flying style then most as reportedly nobody stays up longer, from having others fly my stuff only part of that is having optimized everything.  A former slope soarer (so my systems are optimized for climb, the highest power combinations over-speed the propeller at full amps in level flight) using lift, coordinated flying and coasting with the motor off and the propeller folded may be part of it.  I yawn at pure thermals lift, but, will use them if available as is the case with the detailed (55) and (70) gram motor combinations. 

Take note this was from testing flying at near sea level on up to about (300) meters or a thousand feet.  For a majority of pilots even “heavy” Fun Cubs should not be flown in more than about walking speed (for the SEFSD OK to the 10 O’clock wind tunnel) or maybe a little more.  Fixed propellers have an advantage if you fly only on the motor (they glide ok anyway, the drag is an advantage for beginners) and that if you are flying at higher elevations things have to be adjusted.  If where you have to fly is subject to constant winds; get something else as the Fun Cub is a still air airplane.  The two lighter systems (motor plus battery about (175) to (250) grams) anything much above five miles an hour is too much, the two heavier systems, if the Fun Cub will lift out of your hand holding it into the wind, if you have to ask, you had best fly something else. 

Yes, I have slope soared a reinforced (main landing gear removed for that flight) Fun Cub in a twenty mile an hour wind with gusts to thirty-five mph, but, for good reason they call me “The Bad Example”.  Three combustion pilots wrecked their airplanes that couple of hours we were there.  Transmitter failure, eighty flights later (flight 143 on that airframe) finally took mine out.   Closer to home and my previous record for encouraging by (bad) example was on a rare day of onshore breeze at Mission Bay.  My Easy Star (I) had a NeuMotor putting out (270) watts (same motor as used twelve years later with a transmission fitted) and the rudder area doubled.  I used quality servos and had the necessary flying skill.  Four standard (40) watts-out Easy Stars tumbled to destruction, launched from behind me.

The most expensive and heaviest, two (135) gram systems are a subject of a separate article detailing the net cost per hour of flight of geared competition inrunners verses good quality direct drive outrunners.

Hacker 20-20L (55) grams 3S 2200 mAh LiPos   (28/3) diameter/output shaft  maximum (200) watts-in for (15) seconds  €65/$72-  timing (20) to (25) degrees  Graupner or Aero-Naut 9X6 folding propeller   Talon (25) amp motor-controller with the timing on automatic, brake activated

The recommendation from Hacker are an APC Slow 10X4,7 (19) amp (209) watts(in)   ACC 10X6 (16) amps  (176) watts(in) Both at about (7.5)k rpm

On the bench   (10.5 ) volts under full load (185) watts-in  (18) amps  all included flying weight (780) grams  estimated (130) watts-out, on the bench, estimated (100) watts-out in flight

That is enough power to whack your fingers, but not tear them off.  Other than a direct hit to the head the danger a Fun Cub represents is secondary issues, as in a horse rears up and throws its rider or a car swerves to avoid it.   

That was not the maximum power this motor could have been configured for.  Why not run it even harder, as with a 10X4 (folding) propeller?  From using the same in a Gemini (two screws, unplug and plug back in, two screws was all it took to do the swap, about fifteen minutes) that was pushing this exact motor too hard.  It’s an average load and how long do you want the bearings to last thing.  The motor was more efficient at a slightly lower maximum power and the bearings last longer.  For this specific Fun Cub it turned out slinging it around hard with the heavy propulsion combinations was causing flex creases in the wing sooner than expected, using this lighter and less powerful combination was the best use.  It was later fitted with a 10X4, too close to call, better climb but not as good part amps cruise.  If I had only one RC airplane I’d vary the propeller and battery size according to the wind. 

I’ve worn out the original stock motor for the Fun Cub, a HiMax at (80) grams (identical to the Park Master) the bearings give out at about seventy flights on 3S, this is a better, and more expensive, combination.  This Hacker (Sport), motor (which included a good quality collet, X mount and mounting screws) costs €65/$72- (in Germany).  A no longer common (3) mm output shaft (a vast majority are 1/8 inch or 3.17 mm) eliminates problems with using cheap/inexpensive collets.  Aero-Naut still supplies collets for the folding propellers in the (3.0) mm size.  For which a reasonable life of the bearings with it proped for near the limit on 3S LiPos at 1500 mAh to 2200 mAh (near the (200) watts-in maximum, about (135) watts-out) is in the seventy flights range.  Hacker sells replacement bearings at a reasonable cost.  With me at the controls half an hour a flight, most of the rest of you; A little less.

Take a look at the published efficiency curves for most electric motors, their efficiency peaks at about a quarter of the maximum input, then slowly falls off.  Typically the efficiency, if they report on it at all, is taken at the maximum output. There is some tuning here, net use of a flying system, with results hard to quantify for a RC airplane.  Running this motor as configured at a quarter under the limit of what it could the watts-in maximum was where it was best configured for my personal, short nose, reinforced, landing gear omitted, Fun Cub. 

As an example it was best accelerated for a maximum count of ten altitude gain by coming from “float” speed (coasting in level flight with the propeller folded) by using one count of full amps in level flight before curving up to about a (45) degree climb.  A count of ten seemed to take it up about two-thirds of the height of the outrageous combinations, which was still great performance.  At the start of a vertical up loop from level flight cutting the amps back at the middle then going to maximum just before the apex and then cutting back just past there gave round loops.  Endless round loops, as many as you could stand.  Outside loops and Figure 8, abet a little oval on the transition, too.  Much of the time I flew the Fun Cub, for the half of the in the air time when the motor ran at all, with this combination at about half amps.  That put the motor right at where it was most efficient and kept the rpm down for decent bearing life.  That cuts the wear down on the LiPo too.   

Electrical watts-in never equals mechanical watts-out! 

Don’t expect a $35- motor, with the timing set at (5) degrees and a “it still takes a charge so it must be ok” LiPo to function half as well.  Even before the bearings of lesser quality wear out, if they were any good to begin with, they don’t put as much use of the power in to moving the airplane.  Use a cheap, inexpensive, or the bearings are shot motor (if you can feel it drag flipping it through with your fingers, at seven thousand rpm it is just heating up the bearing, not turning the prop) the tips beat up of a combustion propeller (fuel pilots often just don’t get the hang of electric power, they do that kind of stuff, really) powered by LiPos exhausted by being run into the BEC limiter for twenty flights results in a typical ARF eight minute, just wallow around, flight. 

An improvement, evidently currently the best choice sport quality motor-controllers, the Talons from Castle Creations, they gave up on letting the user set the timing and just run on automatic. 

Running retarded timing is throwing a fifth of the performance of an outrunner away.  When I ask about what the timing is set at most converted fuel pilots look at me like a cow at a passing train.  When I ask about their LiPo they proudly show me that with their meter it is at (94)% right off the charger and so must be OK.  I pull out my power meter and a healthy LiPo to show them the difference.  Sometimes I let them fly my stuff, so just once, they get to fly an electric RC airplane set up right.  That has, on several occasions, resulted in my getting a case of wine (no tax stamps) in exchange for propulsion. 

Do not fly after dental surgery nor with a hangover.

Flights 32 through 35  Entrance to the Middle Rhine  late November 2019  cool, sunny with just a trace of wind up the hill  Flying and weather conditions are, for this time of year with the sun peaking at just (18) degrees above the horizon at ideal.  All alone, on what may be the last day for months to hang out up here surrounded by vineyards, far away from most industrial noise, with a fine view out over the Rhine River, in physical comfort.  That is typical of this club, The Rhine-Gau, they really only fly about five months of year and only in great weather.  At the club over the other direction, too close to S. Fraport, freeways on two sides and no view, they will park a km away and walk through snow a foot thick to fly.  Better five months of the year and a longer drive to be among people we like then…

At first it seemed low powered, partly because the first two flights the batteries were giving out and subjectively I had been flying with outrageous power and duration.  Vertical up loops with (250) watts-out and the better “couple” of the twelve inch diameter propeller can be eighty meters in diameter, this combination the vertical up loop of about twenty meters is the limit and use of the amps stick is required to keep them round.  Subjectively rate of climb was way off and still a count of ten at maximum amps takes it way up there.  There was so many thermals and the prop-fold flip wasted a second of full amps that a glide down comparison was not made.  As in if thermals were used five minutes at a time with only a hundred yards of glide down…  Flights with “intact” 3S 2200 mAh LiPos appear would be in the half an hour range if flown into the BEC low voltage limiter.  The nominal performance of the first two flights confirmed what simplest testing on the bench indicated, the voltage under load of LiPo batteries with just thirty flights on them was way off (135 watts-in verses 185) with the resulting watts-out in flight dropping off.  Although the power with seemingly worn down LiPos seemingly wasn’t (initially) as far off as it might be (because full power isn’t needed much in these near still air conditions) duration was way worse than the bench testing had me expecting.  The run down LiPo flights would have been about fifteen minutes.  Just the same, because this combination is well matched and with the landing gear omitted somewhat lower drag, both pairs of flights had plenty of power.  At this lower weight, about (140) grams less than the previous combination, something I had learned the week before, if the sun is out there are weak thermals up about fifty meters, which were enjoyed the third and fourth flights.  That was two hours of continuous flying taking just long enough on the ground to change batteries.

Getting the propeller to fold was even worse than the previous combination.  It took a vertical up “flip” to get it to fold.  Although if the propeller didn’t fold this combination evidently freewheeled better, even so it cut the glide back down time by a third.     

At this current draw on medium discharge LiPos it is not clear when the battery is about discharged, although climb at maximum amperes drops off, not until full amperage puts the battery into the motor-controller cutting out is it evident the battery is about empty.  There still remained enough power to position the landing at this spacious field surrounded by vineyards.

The batteries of the first two flights were later discarded.

Just down the hill starts the section of the Rhine River with a castle in sight the whole way to Koblenz.  And I was feeling so cheap after tanking up that I almost went home.  A forty km trip costs a net twenty Euros of motor vehicle expenses.  What a great drive after a break of two years.  The sun shining in, I put in out at a hang out.  The world is getting warmer, back in the 70s and 80s we only rode motorcycles for the brighter six months of the year. 

Part of this series of flights was to test old LiPos.  Of a dozen on hand, none newer then three years, some a decade old, only two were fully serviceable.

Although not noticed on the bench, this combination vibrates some in the air.  I later changed to Aero-Naut propeller blades which ran smooth.

Graupner, one of the first model flying stuff suppliers in post WWII Germany, for decades one of the largest suppliers of everything in models, was reduced to bankruptcy a few years back.  The company manufactured nothing itself, their administrative and distribution facility (was) at a great place to fly, Kircherheim Teck, south east of Stuttgart.  What was left, in a legal sense, was bought up by the Korean company they sourced their radio controls from a few years back.  The end of year 2019 a second bankruptcy ended Graupner as a general company with the expectation that the Kircherheim location be dissolved.  Their radio transmitter and receiver systems, maybe the latest servos, may continue to be available.  Here is hopping so as we in Angle all have them…  A good thing Aero-Naut is still functional for folding propeller stuff.

Although I have flown the Multiplex Fun Cub with Hacker Sport outrunners in the (40) gram class, trying to keep the weight to a minimum using small 4S LiPos proved pointless.

NeuMotor 1105/3,000kV   Maxxon 4.4:1 gearbox (135) grams   Aero-Naut 12X6.5 folding propeller  4S 2250 mAh LiPo  (400/200) maximum/constant watts-in  Talon motor-controller timing set on automatic, brake activated   

The NeuMotors virtual dyno was right on.

That is the power of a hand held grinder, which can tear tendons out of your arm, shred fingers, rip open your face and land you in the emergency room with “it happened so fast”…

On 4S 2250 LiPos this combination drew (300) watts-in on the bench, estimated watts-out is (275) less (5)% taken as loss through the transmission.  Let’s take a better look at that.  Efficiency is (91)%!  All it takes to make a Fun Cub rip with this combination is (18) amps (maximum for a count of ten at a time) on 4S 2250 LiPos.  This combination is as outrageous as it is expensive, about $250- for just that motor plus gearbox (verses about a hundred-ten for an equal weight outrunner turning the same propeller) which more than offset though by the in flight duration and longer lasting batteries. 

I been flying next to the manufacturer in San Diego (I barter fresh lobster to afford his stuff) since year 1997, nobody has reported wearing one of his motors out.  If there was a way to get more of an electric motor, NeuMotors would already be making them that way.

Flight 31  Pea Acker  late November 2019  For this time of year it was warm.  My wife was with me, one of the benches has gone missing.  Still, these fields had another bench and has a decent view out over the fields and hills beyond.  There was a slight wind adding lift, if the airplane was up there a ways, at ground level it is turbulent coming through the trees.  The freeway and highway background noise are irritating.  Winter is late on it’s way, we had to dress half warm.  The field had been harvested and ploughed, landing here requires a strong airplane and pilot skill few have.  Into the wind I landed on the grass of the track at three steps wide, across the three steps.  The alternate was to walk over, the Fun Cub in the air, about fifty meters for a grass field in the sort of lee of some trees, or put it in the mud.

Flights 29 and 30  Where I rode into the Rhine River Flood Basin   late November 2019   The day started out almost sunny, then it went to overcast.  Wind still, I flew for the enjoyment of being there.  Loads of space although the area is building up.  Polite behavior among German youth was demonstrated when three twelve year olds (two boys and a girl) pushed their bikes up the side of the grassy dike to watch the show.  With the short nose, reinforcement, landing gear omitted, and exactly too much power from that geared NeuMotors 1105 and 4S LiPos this is an outstanding combination, they may not see something like it again.

Flights 27 and 28  The Corner under the Village  mid November 2019  Two days in a row of the weather being mostly sunny, well above freezing and in general quite a bit better then the prediction.

I flew for the pleasure of being out and about.  No radio problem at all.  I wasn’t dressed warm enough, standing for an hour was enough for my knees, back and cold fingers.  A month after getting back from a year in Way Northern California and a year in SoCal I’m still having moments of; This isn’t real.  How much of my adult life have I spent here and some of right on this seemingly insignificant curve of an asphalted farm access road with people enjoying being out on foot, bicycles, electric bicycles and horses? That quarter of a mile walk gets us away from (most) road noise, walking by two different farm sheds, one of which includes outside horses, cats, geese and pigmy pigs.  The last outdoor flowers have given out, on the way home I’ll go by the greenhouses and get my wife some.  Quite a bit of when a “where” matters I’ve spent here.  Unusual, as most of us our internal “ID” is where we were a teenager, I am in my second internal, this where things are “right”, something few people who move experience, this is my adult center.  I’d been waiting for this moment, mostly recovered from jet lag, my wife at work, a friend busy earning a living, just me doing something worthwhile before its over, for the first time in a decade not concerned about working or money, for a little while.

Flights 25 and 26  Fallen Soldiers Monument above The Village   early November 2019  It had been gray all day and the cold I brought from SoCal just won’t quit, when I finally got going late that afternoon.  On the ground it felt like a slight wind.  Two crashes, both something wrong with the radio as it slow rolled over the right wing not responding to transmitter inputs.  There was some slight damage to the leading edge of the right wing from landing in a tree and mud in the spinner.  Later I realized that the fuselage had been creased too.  The propeller collet is set up so that under thrust it just clears the mounting screws, the play of the bearings transferred the hit to the motor mount plate and fuselage saving the propulsion assembly on impact.  The additional ironed on decal mostly saved the wing’s leading edge, the additional fiberglass the fuselage.  Practice, even crashing, makes perfect.  This RC airplane was configured to withstand exactly what happened, right here.

This site both the huge S. Fraport airport, (2,000) flights a day and the US Military airport at Mechtildshausen are in line of sight.  The combination of Graupner MZ-12 and MZ-12 receiver (single antenna, park flyer type) has functioned well everywhere else before (up to a kM away) so this may be electronic smog.  Another possibility is with the ground wet there may have been some kind of radio reflection although the roll occurred even fifty meters up.  The most recent flights, almost two years ago, I used a twin antenna Graupner (full range) receiver with the same Graupner MX-12 transmitter.  I’ve been flying here a few times a year since year 2007, neither I or the other pilot have had radio problems there previously.

Flights 24 through 26  Nearest Slope Hill   end of October 2019   

I’d flown hardly at all the previous two years while in Way Northern California and SoCal.  A Dutch professional airline pilot at a club’s flying field really put on a show with it.  I was surprised, the pilot delighted, the rest of them impressed.  Despite still being plagued by jet lag and the wind being from exactly the wrong direction, a slight uphill sitting on a berm between ploughed fields proved to be just the place to fly.    I later sat in the midday sunshine (not to be taken for granted in Germany) where two flights at forty-five minutes each eased me back into my other reality. 

Hacker (Sport) A30-28S (70) grams, or NeuMotors

Hacker A30-28S   1140 rpm/Volt  €72/$80-  (70) grams   (20) to (25) degrees lead at (8) kHz recommended lead and switching frequency   (250) watts(in) maximum for fifteen seconds  (37/5) mm diameter of the motor and output shaft   

That (5) mm output shaft is a whole lot more crash resistant than a (3) mm one.  That may be why Hacker includes a spare motor shaft with their smaller motors, but not with this one.  If I can have just one RC airplane I prefer the (105) gram outrunner systems, but, if I can reserve a Fun Cub for just near still air days this is my favorite.

These are the lightest of any (37) mm diameter motor available, about half what you expect in that diameter.  One fifth more power than the (55) gram motor at negligible weight increase (plus (15) grams/three-quarters of an ounce), this is a delightful combination, provided the pilot can make use of landing it this light.  As compared with the lighter (one inch diameter) combination the airframe must be able to accept the one and a half inch diameter of the motor.  What isn’t quickly evident from the numbers and running it up on the bench is that this combination has more torque, it not only swings a larger diameter propeller, it accelerates from glide better, over the top thrust for completing a loop is better.  Flight duration is about the same as the smaller motor, just a little longer.  Bottom line, use the larger diameter motor if you can.

As I have a range of similar sized RC airplanes and can match them to the wind this was my personal favorite on still air days.  Of all the RC airplanes I fly this combination is what the casual observers enjoy watching the most. 

I left for Way Northern California the spring of year 2018 with a minimum on board my camper.  I had 2S, 3S and 4S 1100 mAh LiPos for a Reinforced Fun Cub with me although the propeller was optimized for 3S.  The performance on 2S was ok for a trainer, 3S was correct and 4S would almost take it vertical.  I was a little surprised it ran OK at short duration on 4S as I’d lost the 3S LiPo. 

I only flew a couple of times up there.  One session on the sand spit west of Eureka on a nearly deactivated runway was with four other men, all older than me (and I’m at six decades) we all started this as teenagers, one other also flew full size.  At first politely checking my seemingly simple stuff out, when it lifted out of my hand to go near vertical (on a 4S) and just kind of drifted around for half an hour, endless loops, inside and out, rolls, come to an almost stop and power out of the stall; They realized just who knew what was what.  It was a (170) mile round trip to get there (not much in between though) and I just wasn’t interested in flying on a place that flat.  I wasn’t interested in much of anything up there.  In SoCal the summer of year 2019 I worked directly at the beach, I rode my bike or walked barefoot on the sand every single day.  In Eureka I was on the beach just three times that summer year 2018, all alone.  Other than the playing field for the school back in the way steep and too dangerous hills there was nowhere to land.

Two of these in a modified Twin Star II (shorten the motor gondolas, rear mount the motors, see the previous article) would be “killer”.

example configurations from Hacker

10X5 fixed propeller Xoar (27) amps at (309) watts(in) (10.5) krpm   3S LiPo

10X6 fixed propeller ACC (26) amps at (320) watts(in)  (11) krpm   3SLiPo

What?  Hacker recommends running them over their maximum rating!  Yes, at least as measured on the bench, because they know in the air the system unloads to a lower power draw.  That’s a (28)% overrating of bench power input verses their maximum input rating.  Which, from telemetry, is just about what you expect the power draw of a typical sport RC airplane, in the air, to be, when compared to measurements on the bench.  Hacker knows that, they want you to know how to get the best out of their motors.

Many of us have power meters.  By citing their propeller and what it could do, the user is still left to verify their own configuration, has however, a reference to start from.  With hundreds of configurations that is all they can do and probably the most effective reference a vast majority of RC pilots can use.  Want more information, use the virtual dynos.  Even I have to concentrate and contemplate to get usable results out of computer estimates. 

9X6 Graupner folding propeller blades

(11.1) volts (15.5) amps  (170) watts- in  estimated (120) watts-out  Depending on battery choice and without or with landing gear about (800) grams to (1000) grams all up flying weigh.

I wasn’t satisfied with that:

Switch to a Castle Creations (latest) Talon (25) amp motor-controller

(11.2) volts  (220) watts-in (20) amps (145) watts-out 

That is a (29)% increase!  I downloaded the programming instructions for the Multiplex motor-controller and advanced the timing, at which the power evened out. 

That is part of why my airplanes fly better than most.  And a warning, go swapping parts around without taking measurements and burn stuff up.  Just putting in modern high discharge LiPos into an older system can get a one fifth increase too.

That Multiplex motor-controller is their here and now standard, we’ve used them in various Radio Ready Multiplex airplanes (Twin Star II, Panda) in which going in and resetting the timing could result in flights with more power and one fifth longer flight duration.  For something which takes five minutes to perform and costs nothing that is a huge improvement!   Although the financial, size and weight cost of over dimensioning (bigger than needed) the motor-control is nominal, the best efficiency of the motor-controller itself is when the motor-controller is matched to the load.  It is complicated, what it comes down to is that the losses through the transistors are at a lowest when they are switched wide open.  That’s why they are called semi-conductors.  In this case a propeller the bench load will be reversed to max out at either (22) amps with the motor-controller setting the upper limit.  That’s after going in and setting the timing.  See above, this is applied engineering, how to get the best out of what you have.     

Scorpion (105) gram motor   Fallen Soldiers Monument over the Village spring year 2017

A problem with the Fun Cub was that this (105) gram weight is the heaviest motor in front which will not cause it to be nose heavy with a 3S 2200 mAh LiPo all the way at the back.  Another was that a majority of pilots had difficulty flying and landing with the lighter weight propulsion, this was enough to make it more stable.  For a majority of pilots, running on a 3S 2200 mAh LiPo this is the happiest combination.  Effortless power at a nominal initial financial outlay.  We liked it in the (obsolete) Gemini too.  You don’t always want to prop a motor for maximum output, both airframes flew well with 10X4 and 10X6 folding propellers on 3S LiPos.

Scorpion (135) gram motor   Mission Bay San Diego CA (USA) spring year 2016

Depending on if you believe Scorpion, their weight outrunner can be run at up to (600) watts-in, more common for (135) gram outrunners is a maximum of (450) watts-in.  I figured mine, using a three blade, folding Aero-Naut propeller, 3X12X6 on 4S 2250 LiPos at (40) amps was excessive.  At this weight in the nose the battery must go all the way back, mostly covering the cooling air outlet hole in the belly and it is still nose heavy.  By just changing it a 3S 2200 mAh LiPo it was used helping inexperienced pilots get the hang of it.  For most people proping it for (30) amps on 3S or 4S LiPos is great.  The RR HiMax at the same weight did just fine too.  Either combination output about the same, at thirty amps, as the geared NeuMotors at eighteen amps, both on 4S 2250 LiPos.  Flight performance was about the same, just the duration of the ordinary stuff less.  About fifteen minutes for the outrunners, about twenty-five minutes for the competition quality geared inrunner, landing with a quarter of the charge left in the battery.  If you don’t have the high performance geared inlinner to compared to, they are great.

I have two Scorpions in the (37/5) at (135) grams weight.  As part of checking things out the (1050) kV motor didn’t seem right.  Somewhen between when I last used it most of three years ago the front bearing had given out.  Nothing specific, just a flip through feel that something was dragging.  I ordered two sets of bearings.

Obsolete, over twenty years old and almost, but not quite, never used Multiplex Permax 480/4D with Maxxon 4.4:1 gear box   Reinforced Fun Cub with landing gear over the forested (if dry) river wash SoCal year 2015 and again at On the Curve under the Village (landing gear omitted) Rhein-Main late November 2019.

This hung out behind the counter in Orange County (SoCal) for almost two decades.  I paid $60- for it including a fixed timing motor-controller, most of a decade ago.  It weights a bit, about (170) grams for just the motor plus transmission.  It is so old you can feel the magnets flipping it over, they used better quality magnets in sport motors back then.  Just luck, whereas I had to make a custom plate motor mount plate for the three screws holding the current Maxxon transmission, this old one with a four bolt pattern matches the small circle Multiplex motor mounting plates also used with the Park Master.

Due to my scrounging I have half a dozen mounting plates (the plastic ones warp, they were straightened with fiberglass) and even more folding propeller carriers. 

I first ran the geared Permax in another Fun Cub, in SoCal, four years ago, on 3S LiPos.  Although it flew the Fun Cub, it wasn’t all that effective and too heavy.  If I remember right the maximum amps at 3S Voltages of about twenty amps and no more than 3S LiPo voltage (back when seven to ten Nickel Metal-hydride cells was still front line) limited the output.  Multiplex rated it at (80)% efficiency, maximum 300 watts(-in) on maximum (10) NiMH cells or the then new 3S Lipos at up to (50,000) rpm, from the specifications still found on the Internet.  I ran it two years ago in a Mentor where it just didn’t have enough power.  About like the 1105/4.4:1 (also just too low powered for that airframe) what to do with it?  Give it another try in something else. 

Bench testing, values after the ten second or so “burst” and the LiPo voltage settles down.  With an Aero-Naut 12X6 folding propeller:

(11.5) volts  (18) amps   (205) watts-in   3S 2200 mAh LiPo   At (80)% efficiency that would be probably a ho-hum (160) watts-out.  Ho-hum because of the weight.  It could be loaded down by a 13 inch propeller, except that might be too many amps.  Maybe go ahead and use higher voltage instead.

(14.0) volts  (24) amps  (325) watts-in   12X6 folding propeller   4S 2250 mAh LiPo   At (82)% efficiency that would be (270) watts-out, on the bench, a quarter less in still air.   A little high on amps, as maybe the motor-controller is limiting it, but that same motor-controller just “flashed” (32) amps.  As for limiting the voltage to 3S, the wires in the NeuMotors are thinner and they are rated for up to 6S, might as well try a little more current in this Permax.  It’s not like it is under warranty…

At the same volts and lower amps, the geared 1105 NeuMotors pulls (300) watts-in, (265) watts-out (on the bench, less a quarter for in flight) at (50) grams less weight on a 12X6.5 folding propeller.

There is some fine tuning possible with the propeller.  The Aero-Naut 12X6 is a standard width folding propeller, the 12X6.5 is a little wider and likely a better match for this combination.  And the width of the bar holding them can be varied a little too.  Check the F5B stuff for what you can do if you are going for the win, if after you have everything else just right NeuMotors can custom wind a motor for you…

I didn’t want to change the motor-controller, the Talon is rated for (25) amps.  Note the increase in expected efficiency by going to the higher voltage of 4S. That has it’s limits, the whole motor has to be configured for the correct voltage.  This Permax has full power magnets and the high performance bearings to use the required high rpm, might as well give it a try.

Flights 36 and 37   On the Curve under the Village  start of December 2019  gray, a little above freezing  Not much wind on the ground, but above some.

I wasn’t expecting much out of this combination on 3S, in truth it flew fine.  The extra weight was an advantage with the wind above this little valley although with the turbulence just above today this location was more of a Twin Star II or Mentor day.  Something odd, the top three klicks of the amps stick on 3S LiPo do not result in more power?  The extra weight proved to be about right for conditions, the prop folded most of the time, but I wasn’t impressed.  I thought after fifteen minutes of mostly on the motor it was time to land.  As it turned out I’d run the LiPo way down, about a 2,000 mAh charge of (2,400) available.

With these high effectiveness combinations I’ve been intending to land with a quarter of the battery charge left.  Even having set the motor-controller for the highest voltage cutoff available.

A young family, the father carrying a three year old, had enjoyed the show, we talked for a little.  Bottom line to get started for outdoor flight here is about €600-.  And that my stuff was hand modified to withstand the landing conditions, that my propulsion is well tuned and the airframe correctly set up, being flown by a pilot who likes the “difficult” unpredictable conditions aloft.  He may not see the likes of this again anywhere else.

The 4S LiPo woke this combination up!  Back and forth, around, I enjoyed being there and flying.  Four youths out riding bicycles held a respectable distance to watch the show.  Inside loops from level flight go to forty/fifty meters.  I headed home about when it was getting too dark to focus on the airplane, about three-thirty in the afternoon.  Just one battery, a twenty minute flight landing with a quarter of the charge left, wasn’t a full test.  I later again flew this combination again.  It has plenty of power, the weight wasn’t as much of an issue as I thought, the duration is down a bit compared to the competition motor. 

If there are still behind the counter when I get back to Orange County, I’ll buy them.

A provisional consideration is that the wing is showing stress creases (this was reinforced as a beginner airframe, expected to be destroyed early on, not flow the stuffing out of it for many flights) and that lighter combinations should be preferred.  What to do with this old, obscure, slightly heavy for it’s output motor plus transmission combination?  Make a Fun Cub NG for it!  Longer than the (135) gram outrunner that newest Fun Cub NG is configured for (and no way to bolt it on at the rear), so, fiberglass on a front mount and use the rear mount, bored out, to hold this combination.  Multiplex “fixed” the wing and landing gear, they added struts to the wings for the Fun Cub NG too.  I might have to fiddle some with the location of the battery to get the balance correct…

Scorpion 22-12 1050 kV (58) grams  maximum (15) amps continuous  maximum voltage 4S   timing (5) degrees  (28/3.0) diameter/output shaft   maximum power (220) watts(-in)

I had a pair of these motors, left over from a Twin Star II with Graupner 8X6 fixed propellers (not the E or slow flier propellers from the Scorpion table) running on a single 3S 2200 mAh LiPo in which they provided fine power, until transmitter failure at Flight 57 trashed the airframe.  I might as well run them up in the Short Nose Fun Cub and determine if they are still any use.

The table from Scorpion (Internet) lists combinations, for 2S and 3S LiPos, all E or Slow Flyer propellers.  Listed are a series of propeller combinations, ending at too much.  The Scorpion measurements are likely as run up on the bench.

8X8  (11.1) volts  (15) amps  (168) watts-in at too much continuous, use an 8X6

9X7.5 (11.1) volts  (17) amps  (190) watts-in at too much continuous, use a 9X6

10X4.5  (11.1) volts  (17) amps  (185) watts-in at too much, don’t use a 10Xx  I have a pile of 10X4 folding propeller blades as that was a favorite size for dynamic aerobatics. 

When you figure it through it looks to be a little less power than the Hacker 20 series, which cost (40)% more although the Hacker package includes more accessories.  A visual comparison has the external dimensions about the same, it looks like more windings in the more expensive Hacker.  Scorpion lists a maximum of (220) watts-in.  Hacker lists a maximum of (200) watts-in, provides a recommendation for which the run on the bench measurements are well over that, evidently taking into account  that in the air the system unloads about a quarter.  Also the same choice, the odd, (3.0) motor shaft, for which Scorpion includes their own fixed propeller collet.  To run (durable, more expensive and slightly less efficient) Graupner or Aero-Naut fixed propellers required a specific Aero-Naut collet.

That (5) degree timing though is Scorpion unique, every other motor manufacturer, if you look it up, if they admit to it at all, requires at least (20) degrees lead.  The motor-controller is set on automatic, let the motor-controller’s electronics decide on the leed. 

These motors provided fine performance previously on Scorpion brand indoor motor-controllers as used in a Twin Star II.  If you are going to run either easily broken APC full speed fixed propellers, or the much more durable Graupner and Aero-Naut full speed fixed propellers (not quite as efficient) eight inch is what doesn’t get hung up in a Twin Star II.  It figured in I had a pair of Scorpion ultralight speed controllers limited to ten amps.  I pulled the input power from both of them and used a voltage step down to power the airframe.  That combination of affordable equipment provided great performance.  Something always sets a limit, in this case wanting to fly carefree landing of grass as a crop farm fields that include mole piles with rocks that are sometimes frozen, down rating the motors to match that propeller size and capacity of motor-controller was great.

Part of what defines a folding propeller is the blades, to which the separation between them also figures in.  To get them to clearance the nose in the big for this motor size Fun Cub, even with the nose reworked, they are going to be used with a wide for application bar.  To that, under load, the before motor-controller voltage often falls off a little.  And how much of the time at maximum power is for a Fun Cub not ordinarily more than a count of ten.  To that the cooling airflow is as good as it gets.

It took an hour sorting through my collection of screws to find a pair of just the right length.  That is important.  A screw too long cuts into the windings and your motor is history.  A screw too long which presses on the motor wires works for a little while, until vibration in the air cuts through the insulation and trashes things.

To mount the motor and propeller, then on the bench measurements, took fifteen minutes. 

Graupner 9X6 folding propeller on a wide bar, no spinner.

(16) amps   (11.1) volt  (180) watts-in on the bench   The same folding propeller combination as the same weight and configuration from Hacker, about the same input.  What I can’t on the bench measure is output. 

For the second motor of the pair I changed to Aero-Naut 9X6 folding propeller blades, no change, on the bench, except that ended the vibration.

This was expected to be a light-weight, lower time cost to assemble airframe, the fuselage bottom is showing it’s use in scrapes and a few dents.  That single layer of lightest fiberglass was insufficient for the actual use.  There are three stress creases from those two hard landings, without the additional fiberglass (most of inside) this fuselage would likely have broken in half.  Although the propeller collet was carefully positioned so that under power it pulls forward just enough to clear the motor mount screws an impact like that would likely trash the little (3.00) mm shaft.

Flights 34 through 36  At the Curve under the Village  early December 2019  It rained all night, the sun came partly out, a slightest breeze from the North which can hardly be felt in this little valley on the ground.  These are the conditions best suited to a Fun Cub, if you can afford a different RC airplane for days with more wind.

The two flights with 3S 2200 mAh went well, about twenty-five minutes, mostly on the motor, as run into the low voltage limit.  I had taken advantage of programming in the cut off at the highest of the three voltages available.  Fact is although not near as powerful as the other combinations, in it’s own way, this is impressive.  Optimal would likely be a lighter 3S 1500 mAh LiPo.  For fifteen minutes a 3S 3600 mAh LiPo was tried.  It flew, but I’ve always maintained the Fun Cub is best flown light, this was a little sluggish, the minimal amps required to maintain level flight was three klicks higher.  With the LiPo less than half discharged at a fifteen minute flight the amps were set at maximum for a count of twenty-five and landed.  No component felt even warm.

The Scorpion and Hacker motors are a direct comparison.  Something odd, although difficult with the Hacker, with the Scorpion the prop just would not fold from level flight.  It took doing a vertical up to stall to get the propeller to quit turning with usually one blade pointing forward from the backwards tumble to recover to level flight.  Without any measurement device, subjective evaluation, it would take at least a (10)% difference to be definitive.  There might have been a little less acceleration with the Scorpion.

At this price we are comparing a Scorpion with (60) flights (of an expected (70)) to a new Hacker.  And there is the matter of insufficient sampling.  Two just isn’t a statistically large enough sample to base a decision on.  Even more so as, unlike a competition motor, at this price there is likely some variation between seemingly identical  motors.  That number of flights isn’t strictly the only quantity, this pair of motors were being operated well under maximum because they were operated in a Twin Star II where on 3S LiPos eight inch propellers were the choice.  One motor has a little more felt bearing wear, both draw identical power on the bench.

If I were in the USA and had a source for Scorpions, that’s what I buy.  Hacker was unable to get established in the USA, in Germany that’s what I buy.

Brand Roxxy (once again available) has a very slow turning (58) gram outrunner which would turn a 10X6 on 4S LiPos, at way more then the (7) amp maximum the manufacturer rated it on for 3S LiPos which, if flown in exclusively still air, made a nice combination too.

Down Rated To a Trainer

The light weight Fun Cub wing, even with my added reinforcement, just doesn’t last forever.  A previous (I flew the stuffing out of it, with landing gear and often heavy, way powerful propulsion) Reinforced Fun Cub the wing was giving out by (140) flights, the “house brand” servos (I won’t do that again) the two that went the distance, were worn out.  For a beginner with a “mean time between crashed” of about ten landings, pull the motor and keep going. 

The only way to learn to fly is to fly.

Efficiency, Less than (100)%

The upper limit on the outrunner configuration efficiency is about (85)%.  Inrunners can go to (95)% efficiency although there are some losses through the required transmission.  About the only competition where both maxed out quality outrunners and maxed out inrunner with transmissions are both being used is the International Aerobatic Pattern class F3A.  They estimate that as compared to inrunners that outrunners output about (5)% less power (losses through the inrunners transmission included in that) for the same watts-in at (5)% more weight for just the motor.  That does not include a different weight of batteries.  There are other factors such as partial load efficiency , possibly flywheel effect and they want the motor to work against some drag otherwise unnecessary for geared inrunners to keep the speeds nearer constant.  For the F3A net (flying) systems, outrunner verses geared inrunner; It is too close to call.  Keep in mind the exotic, programmable motor-controllers those, going for the win, pilots use costs more than a RR Fun Cub NG.

Some of that seemingly low efficiency, lower than the manufacturers claim for their motors, is real net engineering.  Use a virtual-dyno and you quickly realize that considerations of a best match of propeller/motor/timing/battery/airframe and the efficiency of just the motor is usually under optimum for the motor alone.  Ya can’t get the perfect pitch on the propeller and the perfect voltage from the battery (which continuously changes dependent on load and charge) to run the motor at it’s best all the time.  Even if you could, as soon as you switch from level flight to climb (I shut the motor off, the propeller folds for dives) or start doing aerobatics, that changes.

With it’s big, blunt front end and thick wing a Fun Cub is in the F3A high drag range.  What is clear cut, for all out speed (F5B, F5D) and on the limit thermal (F3J) performance the less frontal area of the geared inrunner is the choice.  Go up slightly in frontal area though and it’s outrunners that are the vast majority.  But, maybe they didn’t do net cost analysis… 

Hacker in Germany also manufactures competition motors, which are second only to NeuMotors, at a commensurately three times as expensive as their sport stuff. 

2S verses 3S verses 4S verses 5S

At the size of the Fun Cub there is no current reason to continue with 2S LiPos, at least not buying new, except for possibly detuning a 3S system for a beginner.  3S seems to be stuck in a “time warp”, higher voltages are more effective.  A time warp as what previously limited affordable systems was the wasting the excessive voltage of (11) volts down to the typical (5.5) volts of the receiver and servos was done by burning off the excess power, that could not be extended to 4S.  Modern motor-controllers use a much more effective means (switching) and can easily use 4S LiPos.  4S proved to be just fine in a Fun Cub although sourcing sizes under 2200 mAh was a problem.  5S worked too.  If starting from a twelve inch diameter propeller was about optimum, working backwards, using the NeuMotors virtual dyno, a higher kV on 5S might have been an advantage.  Might because even down rated from maximum the geared 1105 put out so much power it didn’t matter much.

Graupner Compact (8,4) Volt version (125) gram motor  2S2P LiPo 3200 mAh 

Aero-Naut 10X6 folding propeller  (6.7) volts  (145) watts-in  (22) amps  estimated efficiency at (0.65) (100) watts-out in flight.

This was a new, old stock, motor that had been laying around for at least ten years.  I paid €10/$12- for it three years ago.  Back over a decade ago, when it was front line, I used one like it, run on 3S 2200 mAh LiPos with an 8X4 propeller for seventy flights.  By which time the bearings were rough.  For use by a beginner pilot the (5) mm output shaft is far more durable than a (3) mm one.

Flights 10 and 11  North End Overlook.  Five days before Rose Monday year 2018, the big parade in Mainz and me getting on the flying bus to “The World” a.k.a SoCal.  Zero wind, the sun shining under a thin layer of clouds, just a trace of thermal action.  I was landing on foot long grass laid down for the winter, over ice cubes.  The lightly hardened belly showed a couple of scrapes.  It’s a trade off, I could have put in some used servos for the flaps plus a reversing “Y” connector to run them on an off and on switch, but didn’t.  The real cost of flaps though is carrying around the increased weight and drag as to slow the Fun Cub down for landings you is slow it down for all of the flight.  Those dramatic tricks of the videos Multiplex made for the Fun Cub, for which the flaps and a weird, way wide and flat propeller (13X4) are required are real, but not my thing. 

The goal was a second trainer for use around Rhine-Main, at no more, and no less, then nominal cost, was met.  Truth is far better climb, as in over a hundred meters from a count of ten altitude gain (nearly straight up at that) good agility, not a lot of power for aerobatics, however, in this stillness it can do half outside roll from inverted to upright with the diameter being not much more then the wing span.  Count of (10) climbs to glide back down ran (50), (90), (65) and (55).  That (90) is why multiple runs are necessary, either it caught some slope uplift or flew in a thermal.  That counts of sixty average aren’t as good as the motors weighing half as much run on half again more voltage.  The flights went ten and twelve minutes, verses double that for the fragile (in a crash) lighter motors.  As luck would have it, one of the batteries was supplying all the power.  Flown again on a (2S1P) 2200 mAh LiPo duration at twenty minutes was quite reasonable.  Dream like flights during which with the low wing loading you can let your thoughts wander, performance we never would have believed, from an airframe originating ten years ago, a ten year old affordable motor, only the batteries and motor-controller are modern.  A larger capacity battery would up the flight and duration, for most the expense would be worth it.  For an observer used to ordinary performance this would have pretty good.

He had to get out of the house, two daughters (one now a teenager) and his wife exceeded his understanding.  Not that human experience doubted it, he reports they have determined that things in the MCP aren’t yet coordinated plus hormone surges…   Decent flying weather, as in wind still if the puddles are frozen we met near where he lives.  Months ago the wife and I figured we’d someday meet again the farmer who’s field we cut some onion like vegetables from, he was there, we paid up.  I assembled the airframe of his Fun Cub for the friend, he put a Scorpion (105) gram motor and folding prop in it, with a 3S 2200 mAh LiPo it heaves around a lot harder than mine.  In light wind, I like my slower version better, his has an advantage at walking speed wind.  Duration, if mine is flown on the motor without the propeller folding was about the same.  He was a little surprised I have about twenty hours of assembly in each of these two airplanes.  Ah, but if general purpose, carefree flying was a goal this hit it exactly.

I’ve been wondering about that 3S 3400 LiPo, flights seem to be getting shorter as the recharge declines, I don’t think it’s just the near freezing temperatures.

Current production 3S systems at half the motor weight, provided you buy decent quality and set them up correctly, deliver count of ten to glide back down ratios in the one to seven ratio, the flights go on for a quarter longer.  Hit the ground with a (3.17) output shaft and write it off.

Although this was an economical, sport, motor, you can feel the magnets flipping it through.  The cost of the rare earth material for magnets went up so much that the manufacturers “thinned” it out for economical motors.  A decade ago, a vast majority of what is in print, the rest of them gave up on mentioning any level of efficiency or durability.  Flip a older motor, or an expensive one, though, and the magnets were so much more powerful you can feel the motor “cog”.  That provides a simplest, first order, estimate of an unknown motor’s basic quality.  That and if you can feel the bearings.  Even sport quality Hacker and Scorpion motors of the last few years you no longer notice the magnets on flip through although the bearings are just fine and thanks to decent quality control fit correctly.

My assembling a Funny Cub (semi-indoor on 2S 500 mAh LiPo) had been put off by missing a little tiny part to use my watt-meter.  I wasn’t too concerned as the system should be matched, I just want to know.  Something decided from this Reinforced Fun Cub operation of let’s determine what still works; Don’t bother with the way old 2S 350 and 500 mAh LiPos I had. 

Something else decided from a junker of a new flying airplane (see my previous report on the DT-80); Spend the money for better electrical connectors.  No luck, stuck with what came with the batteries.  On a whim, I bought a bigger 2S LiPo.  At fifty flights I did about three hours of patching up the fuselage, about what I would have done for a personal Reinforced Fun Cub.  And I worked over my motor selections again.

Hold it, was that really all there was to get out of this Graupner combination?  I ran the same motor type at much higher rpm at thirty amps on the bench for seventy runs, why not try a higher capacity motor-controller and battery both.  It was run up on the bench again on two (split the pack) 2S1P 7.4 Volt 2S 1600 and with a new (bought to try that motor again) 2S 2200 mAh LiPos

Graupner 8.4 Volt outrunner (35/5) motor/shaft diameter 10X6 Aero-Naut folding propeller  (23) Amps  (7.0) Volts  2S 1600 LiPo  (165) watts-in on the bench, same for both available 1600 mAh batteries  (24) Amps  (7.1) Volts  2S 2200 mAh LiPo (170) watts-out with the bigger, 2S 2200 mAh, new battery.

At which an older 2/3 LiPo Multiplex (54) amp motor-controller replaced the Talon 2-6S (26) amp motor-controller and the measurements were repeated with no change.  That smaller, modern motor-controller was near it’s limit and too valuable for a “beginner” system.  I was a little surprised that the older motor-controller was that good.  Next up was, although Aero-Naut 10X7, 10X8, 11X4, 11X5,  11X6,  11X7 and 11X8 blades were available, to try the 10X8s.

(31) Amps  (7.1) Volt 2S 2200 mAh LiPo (210) watts-in on the bench.  That thirty amps or so on the bench might be a little low for this motor, work up to it though.  Times (0.62)% efficiency makes for 130 watts-out on the bench.  Times (.75) for unloading in the air estimates (100) watts-in flight.  Although the motor is a little heavier, the battery is lighter, if (58) gram motors on 3S LiPos move a Fun Cub OK at one hundred watts out, there might be something in there with a (125) gram motor on 2S LiPos, it is time to fly this combination again.  And the car RC people have a much bigger 2S battery which exactly fits a Fun Cub, this might be “right”.

Flights 53 and 54  On the Curve Under the Village  End of December 2019  It rained hard the night before, hardly at all during the day  A previous rainy day the fuselage was freshened up covering the belly dents from landing on rocks and applying a couple of layers over the forward half of the fuselage on the sides to correct for the compression ridges from that hard landing a while back. 

The Friend and I hadn’t seen each other in two years, we had a lot more to discuss than just flying.  He arrived with a Reinforced Fun Cub I had custom assembled for him.  The standard length nose, the “tuning” HiMax (135) gram motor with a 10X6 Aero-Naut folding propeller running on 3S 2200 mAh LiPos.  One battery was shot (died sitting three years) and the inexpensive receiver suspect.  He’d spent four hundred bucks on a radio ready, fast motor-glider, only to stall it to destruction four minutes into the first flight weeks before.  It had been a while since either of us had done that.  Both of us hard stalled Blizzards to distruction and I lost a Dog Fighter in the sun.  Up went his Fun Cub into an off and on breeze.  You could see his just below competition flying skills and confidence return during the twenty minute flight.  Light and slow, tremendous power, easy handling and good agility, if you know how to fly and need to relearn, a Fun Cub is ideal.  As with turbulence, unpredictable swirls, that day at that location required a pilot who could respond to the unexpected.

The surprise was my combination.  Loops to forty and fifty meters and a twenty minute duration on the new 2S 2200 LiPo.  Not quite as good on the 2S 1600 LiPo, duration about half.  I’ll shorten the flights to save the batteries.  Carefree flying the way we wanted it, despite the breeze.  It was hard to believe how much difference going to a bigger battery and from a 10X6 to a 10X8 made.

It made me want to reevaluate four motors I’d schrounged years ago in San Diego, two pairs of one inch diameter Hacker outrunners.  One Hacker at (80) grams can reportedly turn a 16X8 propeller at (38) amps on 3S LiPos, when fitted with a 4.4:1 gear box.  A clue, Hacker rates it at (30) amps max on 3S using a 4.7X4.7 propeller.  Nope, neither of them is the least use in anything but a pylon racer.

You Want To Fly, Or Talk?

From the cost per hour of flight analysis, more expensive, more efficient, more durable motors are less expensive overall in terms of net cost.  That being dependent on your personal mean time between crashes.  That can move the choice to less expensive i.e. beginner RC pilots.  It would also justify the more expensive (5) mm output shafts of more expensive motors. 

Buying new; You get what you pay for.  As the Speed Shops put it; Speed costs money.  How fast do you want to go?  You got it cheaper, you brag about it, I’ll stay up there flying.

Guess what?  The better motor-controllers are more efficient (among other things better quality transistors plus operated better by the rest of the electronics), more expensive and require more skill to take advantage of.  For carefree RC sport flying Castle Creations Talon or Multiplex motor-controllers will do just fine. 

Time to Build, Plus Radio Programming

Not including programming your radio, a RR (radio ready) Fun Cub NG (the newest one, Next Generation) can be ready to fly in about an hour.  I’d take a couple of hours to put some water based hard wood flooring paint over mine to seal the foam.  And although the latest covering is really “spiffy” reinforce the wings leading edge and run some fiberglass over the nose and belly.   Then I’ll enjoy the propeller it came with, until I break it and then refit it with folding propeller. 

Following is what it took me to get build up a short nose, reinforced, Fun Cub, including fiddling and programming the radio.  A look ahead, it wasn’t three flights and everything was perfect on the first try.

4 Hours on the bench   late January year 2018

Although the intention was to use a medium range (single antenna) Graupner receiver, after hours, four different tries, of not being able to bind two channels for the ailerons and no “Y” cable on hand, the long range receiver (the two antenna receiver pulled out of the Mentor) was installed.  The motor-controller could use an extension.  A surprise, I knew that this new fangled (to me) Graupner system had built in telemetry from the receiver back to the transmitter, for the first time I I found which buttons to push for the information.  Neat!

Although the originally intention was a lowest cost and still usable as a secondary trainer, so configured for a (125) Graupner motor in (35) mm diameter on 2S LiPos, I also have two pairs of medium performance sport (70) gram Hacker motors in (25) mm diameter.  The intended use was gearing them in helicopters at relatively high RPM, as such they are better quality then ones intended for driving a propeller.  The pair wound for (3500) kV was just too hot to be useful with a propeller.  The two of them wound for (2500) kV might go well in a 2S Twin Star II, might as well try them in a Reinforced Fun Cub. 

One was mounted with a fixed propeller, (21) amps at (6.8) volts or about 2/3 of the burst capacity.  Figure (140) watts-in at (70)% (of (80)% possible, way better than standard) for this combination on a 2P1S 3200 (net) mAh 2S LiPo is (100) watts-out .  This is a good way to run in a motor (the shields in the bearings need it) from past experience what works well in a Fun Cub or Fun Man as a single motor works well as two in a Twin Star II.  Originally $82/Euro65- each, I paid fifty-two USA dollars per pair.

Since I’m going to fly it myself, this Short Nose Reinforced Fun Cub received my “standard” recognition color scheme.  Half an hour with masking tape and spray paint at the tail.  Igit, on starting to head out for a test flight the rain, it went on for the whole day, again, started.

Flights 1 and 2  Looking out over the state capitol to the north  end of January year 2017  A wind out of the north communing up the hill at maybe eight mph/12 kmh.  Thermals way up there, two different hawks riding them.  After months of mostly around the house (rain or snow every other day) it feels great outside in the cool sunshine.  As I learn how to use the return telemeter from the receiver it also gives the temperature, (10C/50F).  I’ve stood here in the snow at this time of year too.  They are having fits logging in the forest, too much mud.  They used to get at least weeks if not months of frozen ground.

Although the (80) gram Hacker is fitted with a too small for this airframe 8X4 folding propeller to operate on a 3S 2200 mAh LiPo, I pushed it into the air, after a couple of seconds of over controlling (the Mentor and Panda I flew the previous day require more forceful inputs) up it went.  Unexpectedly, full amps is loud.  I drifted around at mostly one third amps, even did some simple aerobatics landing at fifteen minutes.  It feels about like flying with a Cox 0.15 (two stroke combustion run on alcohol, nitro-methane and castor oil as fuel) did long ago.

Well, that high revving motor and tiny propeller weren’t right for a Reinforced Fun Cub anyway.  That is an old speed propeller on an indifferent quality carrier turning up medium rpm.  That combination goes well in a speed oriented flying wing, not this floater.  At least that motor should have cost $82/Euro65-, I paid $27/Euro22-, the high revving helicopter outrunner motor is now broken in.  Maybe try it again later with a bigger propeller at full rated output.

Going through everything again the vibration was caused by something just a little off on the bar that holds the two blades, it was discarded.

It has only been the last few months I’ve been using inrunner motors again, some never before encountered problems showed up.  As in the motor and transmission cutting out at higher rpm, another similar combination bought used making death rattle sounds.  I’d determined that some of the problems I was having with the geared down in-linner motors was slip on connectors that weren’t making enough electrical contact.  One connector (of six, three pairs) was changed, now all three are tight.  The used, way old geared inrunner, the transmission gave out.

Installing the medium range receiver and a “Y” harness for the ailerons, plus the soldering, the latest attempt to program the motor-controller by amps stick, the motor and propeller the swap took less than two hours.

same place a couple of hours later  The felt wind speed at the ground doubled, the clouds have more gray to them, they are lower, moving twice as fast and now at a thirty degree shift to the north swirling up and back down a forested hill then up across this little ridge. 

The air is really clear, you can see all the way over across the Rhine River to the Donnersburg (Thunder Mountain) a hundred km away.  When Paris occupied that side of the river they rename the administrative district Germany calls the Pfalz to Donnersburg since it can be seen from their (usual) side too. 

Reportedly, from reading on the Internet, there is a site there for slope soaring.  It costs two and a half Euros for the five km, twenty minutes, round trip to fly here.  Five hours round trip drive and a hundred Euros are enough that I’ve never even tried to fly at the Donnersburg.  If it weren’t for the curvature of the earth you could see all the way to Heidelberg too.  The ridge of the Taunus Hills is to the rear. 

This light wing loading RC airplane should not be flown under these conditions.  Even at two hundred meters up it is a turbulent mess, at ground level utterly unpredictable.  There were even thermals to confuse things more.  Figure long wave turbulence as the wind direction changes direction (and with it the ground turbulence), medium size turbulence and micro turbulence, all at the same time.  The determining factor though is right at ground level, if the pilot knows how to handle it up higher. 

This was a Twin Star II moment.  What was needed was something agile, without too high a landing speed and able to withstand a rough landing.  So will my Reinforced Mentor, but the landing speed is too high for here.  Although without setting the ailerons to work as brakes, in no wind and if anybody else is there the Mentor is too big for this location, with this much headwind it would have been right for here and now.   Later in the day I did put the Mentor up, what a fine flying sport RC airplane!

The fields are so saturated the water can’t sink in, the low spots are puddles.   

This location is next to the snottiest horse stable, very little motor vehicle traffic backed up to forest, not even tractors going by, the horses aren’t used to anybody or anything else.  Fly on the side of the ridge away from them and the public road, avoiding being seen, has been the solution.  This is often a pleasant place to fly and the closest location to where my wife and I live.

After two months of constant rain and snow the World (my territory around Wiesbaden) is a mud hole.  At least this track, a farm access road, has been filled in with rubble and gravel to make it passable.  I walked down the paved public road for a hundred meters (too muddy on the trail), this half-big, gaudily collared flying machine under my arm, risking the royalty of Wiesbaden objecting to my existence.  They aren’t all wrong at that, a horse will buck at the sight of anything unfamiliar, including this airplane. 

Where I more often fly, open fields, if a horse and rider come by (often there, every other flying session) I step off ten yards to the side if I can.  Holding the RC airplane as if left sitting on the ground a horses intelligence evaluates it as something waiting to pounce.  More so here as back in SoCal where horses are a forgotten past. 

To the uphill to the ridge, when an, even older than me, bicyclists paused at the top twenty meters away.  I ride a bicycle, a similar street oriented one with fenders, here a couple of times a week too.  We both knew it wasn’t reasonable for him riding downhill in the churned up muddy wheel ruts at just a meter wide in between he or I don’t both fit.  Slipping, getting splattered with mud and at our age increasingly dangerous, a likely fall, either in the ruts or the trail to his left (I couldn’t safely walk it) wasn’t a reasonable alternative.  I carefully stepped off to the side (my plastic slippers aren’t suitable for mud, I wore my work boots with angled soles the day before) and tucked into the edge of the forest to let him use the middle.  mutual courtesy 

Up it went, to get buffeted around for fifteen minutes.  This Reinforced Multiplex Fun Cub is set up correctly, I have loads of experience flying them, this latest one  flies right too.  Except that my latest try to get the Talon motor-controller brake set on failed again.  You can screw up the folding propeller blades and the rest of the RC airplane landing with that twelve inch propeller spinning.  As in either scrape the propeller up or snag it in the here scraggly winter grass.  Do a short dive to get some speed, a ten foot vertical up to stop, the propeller then folds.  Just pulling up from level flight to a stop won’t do it. 

The Talon motor-controller instructions seem well written, there is even a blinking led on the motor controller to confirm the tones from the motor being pulsed, I’m missing something as this is the third try.  With that transmission I can’t determine on the bench if the brake, the electronics of the motor-controller force at no amps the motor to stop turning, on the bench.  I’m going to get the programming stuff when I get back to San Diego California in a few days.

Although once a combination is sorted out, I prefer to fly with some wind (wind, how, and why, do you fly without it?) under these conditions evaluating the power wasn’t reasonable.  I have loads of experience with Fun Cubs, flying a Fun Cub at all under these conditions wasn’t reasonable, had there been anybody to watch I’d have confirmed my reputation as a Bad Example.  At (125) watts-out, even with the excellent couple between the propeller and airframe (past experience, ya know) you aren’t expecting vertical out of a Reinforced Fun Cub, more like a decent climb and longish duration.  It was too loud from the wind to hear the motor from a distance, and too turbulent to fly low.  Important, there was none of the seemingly breaking up sounds from the electric motor being abruptly starting and stopping as the (sensor-less) latest production motor-controller lost contact, maybe getting a better fit of the slip on and off connectors did it.

You’d have to have been there, the landing (perfect) after rearing up and on edge twice in the final ten meters, the Fun Cub caught a downward swirl just right, setting down gently, level, with no forward speed from one meter up, was a real exercise in skill and luck both. 

The re-charge on the battery was only a thousand mAh, the flight could have gone on for twice as long.

Flights 3 and 4  I finally figured out the sequence to get the motor-controller to brake the motor so the propeller folds.  The first flight, with the heavier 3S 3800 mAh went on for forty-two minutes.  With the lighter 3S 2600 mAh LiPo I stopped at half an hour, (2000) mAh recharge.  From my first Fun Cub I’ve always maintained they fly better light, half an hour with the smaller battery was preferable to three-quarters of an hour with the heavier one.  This was the RC airplane for the conditions.  That big, slow propeller allows a vertical half loop up from inverted level flight even.  Not an endless loop, the radius is about ten yards, just elegant.  This combination is quiet, just a little hum from the transmission, effortless power.  Way unpredictable ten seconds of maximum climb to glide back down.  As in fifty to three hundred. 

I’m working out the possibilities before soon returning to SoCal.  Although I had settled on a sport Hacker outrunner, that wide for it’s (70) grams on 3S LiPos turning a 9×6 folding propeller is fine combination, this is better.  It also costs twice as much.  Depending on the height of the clouds there is two different basic wind directions plus the chaotic swirl at ground level around the hills.  No computer simulator can prepare a pilot to enjoy this.  On the ground and up to three hundred meters up constantly changing directions as there was a fair amount of thermal action.  The low wing loading made exploring up there fun.  This was exactly the RC airplane to be flying here today.  Uh oh   Way off in the distance black dots of big migratory birds, heading north!  Too early, we might still get cold winter weather, not the near spring of today. 

The first bump, although the landing went perfect, a stick put a slight dent in the belly.  I’m out of two component resin, maybe add a couple of layers with water base hardwood flooring paint.  Clear, as my try with brown on a different airplane  looks like censored.

Although the climb with the 12X6 is great, it could use a little more pitch in level flight at the loss of some maximum climb.  I’d have installed a set of 12X7 propeller blades, except I don’t (yet) have any.  On went a pair of old style Aero-Naut 12X6.5 blades, wider, they have higher power draw then the newer types at similar pitches. 

Over to Under the Village where I flew for half an hour.  What a show for the people out for a walk, this is a perfect RC airplane for here today.  Down in the bowl at ground level hardly any wind, I took advantage of the power to fly both close in and high up, where it is turbulent.  However, as the battery ran down increasingly there were cutouts as the motor-controller looses track of the motor.  At first I thought it might be the transition at very low amps from the propeller is pulling to pushing, changing the direction of load on the transmission, more amps took care of that, until it increasingly took more amps to get the motor to run smooth.

It was standing room only at the Thermal Pool, so I went on home.  Minutes after getting back to our apartment snow/rain started again.  All considered I was going to be back in SoCal out hunting off shore for the Super Bowl soon. 

Recharge on all three batteries was in the 1800 mAh range, just right.  If you are reading this back in warm and sunny SoCal there are some considerations to be reminded of; The cold.  Although air density and humidity make zero changes to the output of an electric motor they have some effect on the airframe and the propeller.  Here in Rhine-Main we are flying at not all that much above sea level, but it is some.  The power available out of a LiPo drops off with decreasing temperature, their optimum is about human shirt sleeve temperatures, maybe a little more for competition.  So, even if they start out warm on flights this long the batteries are quickly at air temperature.  These modern high discharge batteries have been holding up fine at (40) amps, at this power draw they did ok too.

Flights 16 through 18  24 October 2019 (Th.)  Gone for twenty (20) months and back seven (7) days I haven’t slept well in weeks.  Perfect flying conditions.  Not warm, but not cold either, foot long grass, clear skies with just a little clouds, zero wind just a few people out and about.  The sugar beat harvest is going on in the next fields over.

I had left a note inside the fuselage:  4SLiPo 2250 mAh  Bench (21.6) times (14.5) volts on a rated (18) amps maximum.  That works out to (320) watts-in and about (250) watts-out, about (190) watts-out in flight. 

After remembering that the radio and receiver must be set for each other (I used the Gemini settings) up it went.  Three (3) carefree flights over the course of an hour.  Effortless power even if not enough for straight up.  These flat and wide blades make it so the prop doesn’t fold from level flight.  No evidence that the system is overloaded. 

Afterwards I went over and bought Dahliens (flowers) for my wife.

Model Piper Cubs

Of course they were modeled as soon as they came out, with balsa wood, glue, paper with shrinking paint as free flight models with rubber bands for power.  In the “peanut” size for indoors they are still great fun. 

Scale Piper Cubs are notoriously difficult to fly with radio control, at model sizes the tail surfaces are too small.  One of my first semi-scale RC airplanes I was built from a kit (Great Planes) with ruder, motor and elevator (two full size (45) gram servos, an on/off RC switch) using a brushed Speed 500 motor, 8X5 fixed propeller and seven NiCad cells on direct drive.  Just about the same size as a Fun Cub.  An estimated twenty ounces of thrust for two minutes, for the thirty or so, five to maximum ten minute flights after the brushes were worn in to when they wore out.  The airframe had to be built light to fly at all, in fact they were close (too close) to a old school free flight with a lot of wing “V” (polyhedral) that could be steered around.   I refit mine with the then just available 3:1 transmission and a brushed sixteen turn double wound car motor on seven cells.  Of the five among the Silent Electric Fliers of San Diego back in 1998 mine was the only one to get fifty flights on it at which I traded it. 

I’ve wrecked two Reinforced Fun Cubs to elevator servos gone bad and almost trashed a wing replacing another servo.  One elevator servos (a HiTek HS-81) was past reasonable service expectancy (six hundred flights, three different airframes) and the other was an inexpensive “house brand” which failed at fifty flights.  Use new either HiTek or Multiplex servos and they can be removed when the foam of the Fun Cub gives out and used in another airplane.  The cheap stuff, at a hundred and fifty flights the “house brand” servo, the one of the two that went the distance, was near failure.  Any savings of five bucks a servo was lost when one elevator servo broke during transport at just flight twenty-six. 

Airframe Cost   Costs are in Euros (for USA dollars add one fifth) for new stuff.  The entries are in reverse order i.e. newest at the top.  All considered a Fun Man kit would have been more economical, but they didn’t have one and (Reinforced) Fun Cubs are great fun, I walked out of the store with the kit.

7 174 “Y” the two aileron servos on one channel cable.  If you are contemplating purchase of a basic radio system, the difference between simplest four and five channel radios in analog verses those with computer mixing, maybe more channels too and intend to fly a Fun Cub NG; This kind of additional expenses here and there might influence your choice.  Want flaps on a Fun Cub with an analog radio and you need a Euro11- (have to be ordered) reversed servo and other “Y” cable too.  In addition to the ease of balancing the ailerons, flaps, getting even throws on the rudder that would justify the additional purchase price of a computer radio.   

22 167 new Multiplex Tiny servo   good enough for a beginner’s elevator

5 145 two new servo extension leads for the ailerons

20 140 two new “house brand” metal gear aileron servos  The best of the inexpensive, I hope, as the fifty or so of the plastic gear servos have held up fine.  Remember, the target is fifty flights, not the three hundred flights the more expensive (and couldn’t get that rainy day) Multiplex or HiTek servos could be expected to last.  The two euro each extra cost and trivial weigh increase for metal gears are for the intended beginner use.

10 – two serviceable, if used, aileron or flap servos, veterans of fifteen flights  eight years old  They were rejected as unsuitable.  This Fun Cub has a potential life expectancy of a hundred and fifty flights, that is seventy-five hours of flight, why put inexpensive, used, servos in it.

10 – Used house brand rudder servo out of a previous Reinforced Fun Cub.  With the tail gear omitted the loads on the rudder servo aren’t that much, in flight it also isn’t all that loaded or used much.

15 120 fiberglass, sandpaper and spray paint

5 105 glue

100 100 Multiplex Fun Cub kit

Fiberglass and Glues

The glass cloth itself doesn’t seem to vary much between manufacturers.  I use the lightest (3/4) of an ounce per square yard (really follows curves, sneeze and you start over though) and a little heavier at (2) ounce.  In metric units that is (25) gram and (75) gram per square meter. 

I previously used hobby grade German two component fiberglass resin.  The same chemicals, when certified, can be used for man carrying aircraft.  It was very difficult to sand.  As in it took (80) grade sandpaper, which shredded anything else it touched.  The aircraft grade stuff had a pot life (how long after mixing for a couple of minutes it can be applied) of about forty-five minutes.  After that it needed a whole calendar day at shirt sleeve temperatures to set up enough to sand.

Lately I use American sourced two component resin (Hobie-Poxie, lately available in Germany too and at a reasonable price, no need to weight down my luggage anymore) which isn’t as strong, but is a lot easier, a whole lot easier, to sand.  Pot life is twenty minutes, so over a typical most of an hour fiberglass application you are constantly mixing small quantities.  It is overnight cure before sanding (start with (240) grit) works out. 

That first application of (thin) fiberglass is just to make an inherently flexible, and not all that precise, foam to stabilize.  The fiberglass has to be layered anyway, after you sand the first coat you realize these aren’t precision models.

If you hit the ground hard you realize the bond between the Elapor and resin isn’t all that good.  Then go buy another airframe kit and start over.

Lighter, as in a net approximately (55) grams per square yard with (25) gram per square yard fiberglass (verses more like one hundred grams) and not as strong, is water based hardwood flooring paint.  Thin water based paint has the considerable advantage that, with the use of a heat gun (the same as used for drying your hair is fine) you can just keep working minutes after painting the fiberglass on.  That gets used at places such as hinges, wing tips and leading edges where just getting a little bit of abrasion resistance is enough.

In addition I use CA (cynoacrilate) instant glue, in foam safe.  The stuff marketed by Multiplex for their Elapor is worth the couple of extra Euros more than the other brands (if you can get it) in medium thickness.

For joining the fuselage halves and the tail was always a problem using CA, the foam parts would drift just enough before the glue set to cause an inconsistent fit.  So, this time, I used UHU Poor contact cement, that will be the standard for those connections  from now on.

Paint and Glues and the Multiplex Decals

Not only do I suffer from greasy fingers, I am often landing on mud.  So, the whole airframe gets a couple of light coats of hardwood flooring paint.  In this case after thirty days and thirty nights of rain and snow the whole airframe outside was painted once, light sanded and painted again.  Although the foam cells look closed, wipe mud off and you find out otherwise, you can’t get the mud back out.  I just sanded my Mentor after (45) flights on it.  Even with fiberglass and paint some of the mud is embedded and won’t sand or easily wash out.  I’m in it to fly, you don’t notice the dirt stains in the air.

Some color, so you can see the orientation in the air, and it looks nice, is required.   Although the provided decals are great material, at “way out there” the RC pilot needs to be able to easily discriminate right from left too.  For color I use a good quality of spray paint available in German hardware stores at about Euro8/USD10- a can.  Some gloss paints over the Elapor brings out all the imperfections, the worst is paint intended for hot fuel proof like what the fuel burners use, that swells the surface cells up.  What I get in Rhein-Main at Euro8/USD10- a spray can that isn’t an issue.  Consumer paints in Germany are in general more expensive than in the USA, however, the quality goes up some too.

When you go to use the big area decals supplied with the kit you realize why Multiplex stuff costs more, the material is great!  I used to use clear packing tape to protect the wings leading edges from abrasion.  The tape I can get lately doesn’t work out, now I use the decals.  Left over from heat shrink on covering plastic, I have covering irons.  Run the iron over the decals activates the glue, it seems to suck the decal sheet right into the foam.  After which the decal material will outlast the foam. 

For the wing tips and horizontal stabilizator hardening the leading edges with fiberglass and flooring paint seems to do better as I can coax the cloth around compound curves better than the decals.

The rudder hinge foam was too thin, often a problem with Fun Cubs.  Although in the past I heat shrunk on clear plastic packing tape, this time I used (25) gram per square meter fiberglass with paint.  The rest of the hinges the foam was fine, not always the case.  As great as Elapor is, these inexpensive airframes are injected foam which expands into the moulds, the foam pieces aren’t exactly the same from one box to another.  You want spiffy?; Get something else, pay way more, make endless repairs and land on a runway!

In particular the elevator, but also the aileron control horns, are not strongly enough attached to the foam.  Further the foam compresses under input loads.  The easy, if ugly, solution is a couple of layers of fiberglass at the foam to control horn.  The newest from Multiplex, as in Fun Cub NG, Solius, Heron usw. they cast in a pocket and glue in a stiffener. 

For a first time (dozens of Multiplex kits) the fit of the “cowl” the windshield and forward of there which removes for access, was so tight that finger access was cut and the whole cowl reinforced so it had a chance.

Servos

That elevator servo is critical.  Although they had “house brand” metal gear servos in Mainz (the only source closer then Frankfurt) at first I decided against them.  Too almost, but, not quite, broke.  The airliner pilot wouldn’t want me to save five bucks on aileron servos that broke though, in went metal gear house brand servos.  At fifty flights, when the fuselage was “freshened up” they were doing fine.  The wing though is showing flex creases.  Compared with the fix the covering after almost every flight of a built up from sticks wing that is near trivial.  Even at Mission Bay, when I last flew with a “traditional” covered balsa with heat shrink plastic I figured on having to recover half the airframe about every twenty-five flights. 

The rudder servo gets little use, a USA “house brand” servo, used, was installed.  A seemingly identical servo at the rudder failed at fifty flights for the elevator (that cost two hundred dollars worth of propulsion and twelve hours of repairs plus a $23- replacement servo) this one has (134) flights on it, so far.  It can reasonably fail in flight with no crash, it can easily be removed and replaced.  That would have been fine for use as a trainer, reduced throws reduce over-controlling.  Since I kept this Fun Cub and have become more proficient at difficult maneuvers, someday I’ll replace this servo with stronger one and double the rudder throw, all that fits.  With nominal rudder throw at (200) flights it is still doing fine. 

I tried “house brand” (8) gram servos in Fun Cub at the ailerons, once.  Failure at (26) flights due to transport damage.  Most non-builder RC pilots, would have ruined the wing getting the old one out and a new one in.  The one that went “the distance” ((143) flights) movement was jerky due to the worn down variable resistor inside and the gear train was worn down to near failure.  You can’t by wing spares anymore, damage a wing and buy a whole new kit.  As an alternative, installing the next larger servo ((18) grams) with re-cut pockets does OK. 

A big weak part of the Fun Cub was that both the wing main spar and the servo pocket are an abrupt loss of rigidity, a “hinge” in the foam develops there.  Although ugly, the performance of the wing can be greatly extended by “scab” on patches both over the servo on the underside of the wing, and above.  Multiplex fixed that for the Fun Cub NG.  The latest Fun Cub NG they completely redid the wing internal design with a full width wing spar and a brace most of the length of the fuselage.  To even out the heavy nose the moved the tail servos further back.

The latest designs from Multiplex are moving away from inexpensive foam replacements for the time consuming, had to be constantly patched and so flown gently wood and iron on covering, to; Let it rip.  I’ve met some of Multiplexes people, it was never a expectation that an Easy Star (I) or a brushless Fun Man fly three hundred flights.  More like fifty was the expectation, back then.  Their customers of today is willing to pay more for improved quality and durability.  My Solius, a friends Heron, a Fun Ray semi-hotliner, you don’t need to improve the wing.  The Fun Ray even has a from the factory hardened wing leading edge!

Airframe Build Log   I decided to keep track of time on this one.  Entries are rounded to whole hours. 

1 23 Mask off the tail, spray paint two colors.  My simple paint scheme for the wing(s) just sprays on.  Since the foam is white that makes for three colors.  Gaudy on the ground, it makes for recognition in the air. 

As the epoxies for fiberglass resins quickly turn yellow and I’d like a color to match the mud I often land on, instead of clear hardwood flooring paint to hold the belly fiberglass on (that’s not strong enough for there), but, I tried using brown hardwood flooring paint on a Panda.  It turned into the worst looking paint job on anything I ever did.  I’ve landed in horse censored that had a nicer color.  If I smeared an Elapor airframe with censored and painted clear hardwood flooring paint over it that would have looked nicer. 

Since over the life of a Fun Cub used this way the belly has to be patched now and then (about the only repairs) spraying paint on, since fiberglass then won’t stick (the spray paint won’t sand off) won’t due.  See above, you want spiffy…

It was time to test fly it.  Or so I thought.

2 22 Install the new rudder servo. 

2 20 Even using the thinnest fiberglass and paint it is a trick getting it to form around that wing leading edge.  The second half I got it, the first some of the “bubbles” had to come off.  I cut up some of the decals for use at the wing leading edge as experienced based that gets beat up during our rough field landings.  It was raining again.   

3 18 It has been raining forever and it will never stop.  Although undecided about the aileron servos, and it will be a day or two before I get an elevator servo, the rain started at ten, I stayed put in the basement and did the fiberglass with paint hardening of the wings, except at the wing servos.  Another couple of layers of this very thin, and so light, paint to seal it some against mud.

3 15 Wind with some rain.  There was something odd with getting the wing spar to slide in and out of the center joiner, and Fun Cubs break the wings right at the fuselage, although I might have otherwise left the wing to split, so the wings could be stored in the box they came in, the decision was to make the wing one piece.  I ran out of two component epoxy, from here the weaker, but much easier to apply, hardwood flooring paint (water based) will have to do. 

I decided to use what I already had in the basement, the servo extensions I had were for soldering on, so they were soldered.  If I had the luxury of buying new I’d have used push on connections.

2 12 New Years day, the wife and I went for a walk, when it started to rain I hit the basement.  First I worked over the tail surfaces individually with thinnest fiberglass held on with paint.  Lighter and good enough hardening back there.  This is winter, the horizontal portion got some extra fiberglass and paint to help with mud.  Did I mention I’ve done a dozen of these?  Then some more fiberglass on the fuselage just in back of the wing as that’s where my greasy fingerprints first show up.  Then paint, lightly sand and paint again all fuselage foam, except back at the tail, there where the tail attaches as that gets more fiberglass with two component resin.  Fiberglass can takes up some fit problems, usual at the tail if using CA.  That’s why at the tail and the fuselage halves I switched to contact glue.  Uhu Poo is great stuff, I don’t know what comparable we can get in SoCal.  Pack it in the checked bag or get it taken away though.

Wing tips in SoCal, where I fly with landing gear and land on sandpaper with rocks, get worn down, so the fiberglass is put on there with two component resin.  The wing tips take a lot less abrasion in Rhein-Main, so they get fiberglass held on with paint at less weight and effort. 

2 10 The rain started at four in the morning, it was unnecessarily dangerous going anywhere on wet, melting snow.  I finally focused and got going in the basement.  Oddly enough, for as many of these as I’ve built, this was the first time I really made a determined attempt at getting the nose rounded to the folding propeller really folded flat.  It took an hour with a hand grinder and a sanding block to get the 10X8 on a (20) mm center bar to mostly fold.  I was really determined, but getting a ten inch folding propeller to fold flat there where it is needed most, straight down the belly, would take a whole lot more of grinding and sanding, my patience gave out. 

The initial fit was done with a (135) gram (37/5) mm HiMax motor on the modern stamped aluminum plate.  On pulling the Graupner motor and it’s small bolt circle, hard plastic mount, out of the Gemini, the fit was no longer just right as the mounting plate is thicker.  I had to do some “old school” modeling to get it all to fit.  After that re-fiberglass the nose, more fiberglass on the canopy, fiberglass on the elevator horn and use the resin to glue in one side’s wing spars and joiners and fiberglass the motor plate as they all warp. Which makes for problems with the motors in that they vibrate.  Sanding the white plastic flat (the plastic shrinks warping them) doesn’t work as it is really tough so it takes forever.

2 8 General fiberglass and sanding.  It rained almost the whole day

3 6 Patch the four “ring” castings on the underside of the wings with lightweight spachtel.  Fill, but not glue in (so flaps could be added later) the flaps pockets.  Fiberglass the inside of the fuselage, this time without removing the foam ridge bracing.  Begin clearancing the nose for an 11X8 folding propeller on a (20) mm carrier.  That is a tedious task with a sharp knife and sand paper, however, it has to be done.  First realization that I moved one frame rail (2) mm further back then the other, that is going to be a problem.  Or so I thought, that right thrust is built in.  Why can’t they cast in enough down thrust too?  After letting the two component epoxy harden back to the workshop in the basement.

1 3 Unpack the wings, horizontal and vertical.  Sand off the leading edges, which is the most important five minutes in the whole build up.  That remaining casting “lip” otherwise really screws up the airflow.  I can’t convince the other pilots how important that is.  Sand off the casting points.  Not that they make any difference to the flying, however, fiberglass, decals and paint go a lot better without them.  It is also contemplative while examining the individual components, the foam of which is not perfectly identical from kit to kit.  This is low density Elapor, even with (320) grit sandpaper it takes care.   The elevator hinge is fine as is, the rudder hinge will have to be improved. 

Two (8) gram servos were removed from a flying wing that has had almost no use and evaluated.  Cycled a hundred times they are serviceable. 

2 2 Pack out.  Survey the small parts.  Lightly sand the fuselage.  Move the motor mount rails back.  Cut out and fit the window decals, without which somehow the Fun Cub doesn’t look complete. 

2 0 Although not strictly part of this project, an original goal to reuse servos was evaluated and mostly, three out of four, rejected.  In particular the elevator servo has to be reliable.  It’s going to be Tuesday before I can get anything new, the fuselage servos can be installed afterwards.  Although if one of the three servos for rudder plus ailerons ceases functioning you can usually get back to the ground in one piece, my “as cheap as possible” inclination/necessity gave way to; We are flying around people and horses, saving a few Euros isn’t saving.  I just couldn’t hand an RC airplane I knew to be unreliable to anybody.

The Four Foot Cub, Semi-Scale, Multiplex History

Back about year 2000, the Multiplex Company came out with a simplest ARF, a  sort of scale Piper Cub, for ruder, motor and elevator, in molded in forms Styrofoam, the Pico Cub.  Back when we flew on Speed 450 motors and (6) or (7) NiCad cells they flew.  I did not see one myself. 

About year 2008 the Easy Cub, in impact absorbing Elapor (similar to EPP), ruder, motor and elevator, became available.  They flew about the same as the Pico, but, withstood impacts way better.  Elapor is great stuff, a modified EPP.  I helped convince many of them to fly as if the components weren’t “right” they wouldn’t.  In an era where many did not believe in electric powered flight or ARFs.

Year 2010 the Fun Cub became available.  If you had one set up correctly you could amuse yourself and others for hours.  Many of us made modifications.  The original motor weighed (80) grams, which performed quit well.  The biggest issues were the decision to use a (135) gram motor, which made them nose heavy and was too much weight for the main landing gear, then the wing reinforcement was insufficient.  I’ve always maintained the Fun Cub was misunderstood.  They are best flown light in still air, every other one I ever saw was loaded way down.

Year 2015 a bigger version, The Fun Cub XL, (1.7) meters or most of six foot wingspan, became available.  At the time the first easily available “big” Foamie.  Unfortunately, much of the USA and World in depression, with “cheap is the same as real” and Multiplex continuing with quality, they slowly became unavailable in the USA. 

At a model exhibition in Southern Germany, West Austria and North Switzerland November year 2019 was also my first sighting of the way improved, if heavier and so a higher wing loading, The Fun Cub NG (Next Generation).  Even if they changed to a rear motor mount they “fixed” the weak stuff.  I’ve got to get my hands on one…

What I could get was the newly introduced, indoor/outdoor in EPP (instead of Depron) Funny Cub.

End