Dedicated to the Promotion of Electric Propulsion in all types of Aeromodeling

Das Fun Cub

  Multiplex took full advantage of the potential of energy absorbing foam/plastic and light weight,  powerful out of the hole electric power to produce a distinctive performing,  fun to fly,  slow airplane the likes of which has never before been available.  As the owner and pilot of a “full size” Piper Pacer who flew the Alaskan Bush with his father,  this is a “scale” flying RC Piper Cub,  until you put that power to use at which…  If you have average to slow reflexes,  want to express your RC flying originality and can enjoy an airplane with landing gear which needs only a semblance of a landing spot,  the Fun Cub may be for you.



This is an original year 2012 for the SEFSD article.  Portions of it are in opposition to any other report known to the author to be public.

Since the Multiplex Easy Cub was a simpler version of the same airplane,  it will be commented on.

Cub in Field

The Multiplex Fun Cub is a moderately priced, easy to build,  soft Elapor foam,  scale RC airplane,  in a bigger flies better size (without getting too big for the back seat),  slow speed (it’s wonderfully entertaining for our longest lived pilots who’s reflexes and eyesight are fading,  provided they fly in no more then twice walking pace wind),  graceful to clumsy flight playfully interacting to wind and inputs from the pilot,  including the potential for outrageous scale like landing stunts using the flaps and some entertaining,  if awkward looking,  aerobatics.

By the standards of the Easy Star,  Twin Star II,  Mentor and similar,  the Fun Cub is not a “modern” beginners airplane,  it’s too fragile to hold and too light in the wind,  it has to be put down on it’s landing gear,  which also restricts it’s general purpose use.  Although it will fly well with a basic four channel radio (or even on three),  it benefits from five channels,  if you have six or seven or eight channels it helps to have a computer assisted transmitter to get the best out of this one.  The Fun Cub needs to be kept light,  if you weight it down too much,  if you just have to build in all kinds of accessories,  if you need to fly in the wind,  if any of the previous applies and you don’t just have to have a scale Piper,  then get a Mentor instead.

This can be a Butterfly like RC Airplane. You can see the adds,  read and video all about it in the Inter net,  and still be completely off the mark in you expectations,  or at least I was.  This is a sport pilots airplane,  in the sense that,  although stable,  you can/need to fly it.  The Fun Cub is neither so hectic you have to keep it under control at all times,  or so docile you have a free flighter which only needs that you steer it back to the starting place.  Although except for landing it,  a “second airplane” beginner can enjoy flying it,  to get the best out of it you as the pilot should have control over all four axis (maybe half of the Mission Bay sport pilots can coordinate all four at the same time),  with a fifth (in the form of flaps) there are some cool tricks available,  for which you get the satisfaction of having a big butterfly at your disposal.  No,  not the neutral stability of the Parkmaster,  and not the fly straight and true,  just steer it around of a Mentor (or common sport plane),  either.

For decades this size was “standard”  partly because it harmonized with then available equipment.  Even today the four foot wingspan has a lot going for it,   like being able to see it,  adjustments so big you don’t have to already know what to do and just the pleasantness that size brings with it.  Take the wing off and split it,  reassemble it at the field in one minute,  the Fun Cub may be easily transported.  Of all my airplanes this is the one that spectators identify best with,  it’s as if a pilot were inside this looks like a “real” airplane and they could experience it harnessed in next to him.

The hardest to set to words, 
and not visible on an Internet video,  let me try to describe some Fun Cub flight characteristics not available on any similar looking,  scale like,  RC airplane:

Using full rudder,  the ailerons in the opposite direction,  to turn flat a Fun Cub Lite around in the width of a room!  Even the Parkmaster can’t do that.

A Fun Cub Lite is so slow speed controllable that you can fly past the edge of lifting flight into a stall,  give it amps,  and fly back out of it,  in the length of ten  to twenty feet,  provided you kept the weight down.  Probing the edge of the flight profile at head height,  I’ve done that with my variously different propulsion(ed) Fun Cub fifty times (it became a standard for how well a motor/prop/battery combination functioned),  which is about fifty times more then with all my other airplanes combined.

Cruise in high,  deploy the flaps full for a controlled decent at from forty five degrees to vertical like you were aiming for a sandbar,  with the fuselage held level,  then at head height either retract the flaps for a precision touch down,  or (to really woo the crowd) pull the flaps back to one quarter travel,  hit the amps of that big flat pitch propeller and power it on to the landing strip.  Either way,  depending on available power,  hit the amps hard and come right back up.

Find and play with every little puff of air the airplane encounters.  Amaze your friends by flying in the wind anyway.

Go ahead and do some acrobatics.  Despite of,  or because of,  being clumsy,  they are fun.  The diameter of the maneuvers is speed dependent,  although even straight down this is a slow airplane,  it DOES have a range of speeds (lacking in many similar looking airplanes),  the control response varies with and is proportional to airspeed,  something lacking in a vast majority of RC airplanes that look like it.

Although neither a dedicated thermal soarer,  and by no means a slope soarer,  I can think of lots of places and times in the San Diego Back Country where,  thanks to the long landing gear and big wheels so it could be put down on a dirt road or bare field,  it could be used where slight up hill breezes and occasional thermals with the pilot sitting there on a hillside would make this a very entertaining airplane.  But not Point Loma or Cowels Mountain,  because of it’s size it’s too bushy there for this one.  Bring one along in case the wind dies at Torry Pines.  One of the Internet reports where the author flew it enough to know what he had,  his favorite place to fly was the beach.  He reported nose standing when landing on hard surfaces,  but not on lawns,  something I didn’t encounter.  But then maybe I ran more toe in on my landing gear and kept the Center of Gravity at (80) mm from the leading edge.

The best comparison to the Fun Cub I can think of,  is a type of RC airplane that has fallen out of fashion,  called the Fun Flier.  They look like a control line combat airplane as an RC airplane reduced to the absolute minimum with a big thick wing and the tail hung off a rod.  Magnelli had one,  even if I saw the motor tear loose to independence one day,  he probably still has it.  Our Editor even marketed a kit for one “The Butterfly” a while back.  Both were electric of course.

If you wanted a traditional flyer,
the Fun Cub isn’t it.  There are plenty of same size,  same looks,  airplanes available,  the Mentor from Multiplex being a best,  utterly predictable,  choice.  A vast majority of airplanes in this configuration track stable,  do predictable aerobatics and just fly.  Pick your same old same old,  the rest of them are all more alike then different. For a vast majority of look alikes all you have to do,  and all you can do,  is just guide them around. The Fun Cub difference originates in the lower wing loading along with never before realized low speed thrust to weight.  Load a Fun Cub heavy though and that wing flex makes it less predictable then other airplanes intended for the higher loading.  Unless you specifically want a “Bush Plane” with it’s really only flies slowly characteristics of a lower wing loading and can accept the relative fragility,  get something else.

A while back at a swap meet,  because it was framed up,  but not finished,  bought for the price of a 40 ouncer,  I built up my first traditional “standard high wing” balsa/spruce/heat shrunk on covering,  nearly identical looking airplane converted to electric power.  With it’s Clark Y flat bottom airfoil and full house controls I started getting bored with it part way through the first flight.  For my twelve hours to finish the building I had what amounted to a well powered,  armored,  electric,  folding propeller,  fragile,  Senorita without landing gear.  Slightly over minimal weight because of added fiberglass over balsa/foam armor on the motor mount,  belly ,  wing tips and inboard third of the tail,  I sold it after just five flights,  the new owner thinks it’s a great airplane.  Even more so since as a vintner he got for a case of local white wine.  At least this time I didn’t wake up at the flying field the next day wet,  covered with grass and hung over.  As a Tao of Poo thing,  I’d never had a “Standard”,  now I knew.  If I had it to do over I’d have just bought a six pack and a Fun Cub instead,  but they didn’t exist yet.

Nothing in my Real Flight 5.5 simulator (with the 2011 updates) flies like The Fun Cub,  not even after fiddling with the software settings.

I spent two hours assembling a great,  maintenance free Fun Cub wing (that includes flaps,  optional spachtel,  tape,  fiberglass and paint) which,  because of it’s semi-symmetrical airfoil flies great.  Anybody can put together a Fun Cub.  It took eight hours to build an easily torn and broken balsa/Depron/fiberglass and foil one that,  because of it’s flat bottom,  made for a dull and inefficient flier.  I’m a proficient builder,  what a beginner can do would taken longer and not fly as well,  to recreate the flaps in that format would have taken a lot longer.

Just Because they Spec’ed it that Way
Let’s get a few things straight,  I don’t automatically like everything that flies and I’m not easily satisfied with an RC airplane.  I expect a minimum of a hundred flights out of any airframe,  often mine last far longer.  To get that much use I’m willing to spend more care and money on materials initially.  I’m willing to take advantage of the exquisite ease of changing propulsion combinations in Multiplex airplanes to determine what I like best,  the results are often a surprise,  even to me.  My Multiplex airplanes get reinforced or armored as required (which can only be determined from really flying,  and landing,  the things),  I use non standard propulsion components (both smaller and lighter or more powerful,  often at 4S LiPo and higher battery cell counts),  most of my stuff has folding propellers for which the nose was clearanced.

This isn’t a review of a “stock”  Fun Cub,  the Internet is full of gee,  I’ve made three flights with it and everything is great reports that omit way too much.  How could they possibly have determined the truth,  the whole truth and only the truth from so little flying?  I made over fifty flights with mine before reporting,  even with fiberglass reinforcement there were both disagreeable and entertaining aspects to The Fun Cub not mentioned in the adds,  the magazine reviews or the Internet reports.

The Fun Cub has some designed in weaknesses (soft foam,  inadequate airflow motor cooling at the cowl for most motors,  with the standard motor setup the battery blocks the airflow outlet),  mine and many others suffered from an single part’s invisible loss of manufacturing quality control at the landing gear wire.  Multiplex airframes cost twice as much as their competitors,  Multiplex based airplanes are worth even more then that.  RC airplanes based around Multiplex airframes have the lowest net cost per flight of any RC airplane.  This was my first time in dozens of Multiplex airplanes of an under specification part showing up.  But that soft landing gear plagued my use of the Fun Cub for the first thirty flights.

Since the Fun Cub looks like some other airplanes in the Multiplex lineup,  and the difference couldn’t/wasn’t described in words or adds,  the different flight profile of The Fun Cub caught me off guard.  Mine has more in common with The Parkmaster then The Mentor.

I had given up on my Fun Cub,  except I kept seeing other ones with stock landing gear,  which,  despite being quite a bit heavier from all kinds of Schnick Schnack (zu English,  doodads)  didn’t collapse on every single landing to beat up the nose and wreck propellers.  Mine was remarkably agile,  since I kept the weight down,  a  flying friend kept commenting that mine flew slower and more gracefully then any other.  Of all my airplanes The Fun Cub was the one that casual watchers enjoyed seeing fly the most.  I finally caught on,  although they enjoyed watching the,  higher thrust to drag and weight aerobatic planes,  what they enjoyed about the Fun Cub was the butterfly like “I can see the pilot controlling it”  right down low there in front of them was what looked like a “real” airplane character that made it interesting.  Those pop up off the ground tricks were fun to watch.

Be careful though,  I have been branded a “Bad Example” as too many beginners have wreaked their airplanes trying to fly like me,  your results may vary.  Maybe if I flew an F3A or F5B airplane people would take me seriously.  It may have to do that I use ordinary looking airframes with simple finishes that anybody could field.  My airplanes,  and flying skills,  aren’t as ordinary as looks would suggest.  The Fun Cub has a different flight profile then what I was expecting,  my anticipation was a scale like Mentor or Twin Star II,  which it isn’t.  I kept fiddling with and flying The Fun Cub out of a refusal to give in (or out) before getting things right.

After sitting around in the way for four months,  the acquisition of a Blizzard and a DogFighter (that’s the way it’s written in German),  including for the first time a pair of HiMax 35 series (135) gram motors,  on a day where I threw away four old obsolete airframes,  I finally got with it and,  after thirty frustrating flights,   bent up a new landing gear wire.  Unwilling to believe that the new one was that much stiffer,  I taped the old one to the new one.  The landing gear was now too stiff,  but I was finally flying the airplane without expecting to trash it,  or break a prop on every single landing.  Steel isn’t just steel,  evidently for a while the 2,5mm diameter wire landing gear was under specification,  so soft that it drove pilots to all kinds of modifications to make up for it.  I was able to tune the stiffness of my landing gear by varying at what length the additional steel rod was taped to the main one.  And,  although the Blizzard motor is higher turning then the one specified for the Fun Cub (1130 kV verses 850)  it was close enough to be worth a try,  on both 3S and 4S LiPos.  I also used a lighter (100) grams Plettenburg 800 kV motor,  it should be better performing then the specified HiMax one,  it costs more then twice as much.

Although small,  medium and large are relative terms,
let’s identify the Multiplex Merlin and Fox as small,  the Multiplex Cularis as large and the Fun Cub (along with the Twin Star II and Mentor) as medium size.  Unlike the Twin Star II and Mentor that may be tossed in the back seat,  The Twin Star II can be landed on nearly anything,  The Mentor requires a runway,  both can buck the wind,  the foam of The Fun Cub is about two thirds of their density,  it’s dent prone and it gets blown around.  That renders it less suitable for beginners,  since you can’t grab this thing,  or cartwheel it,  without automatically damaging it.  Still,  set up light (use the Parkmaster/Gemini propulsion kit) for a pilot with slower reactions to whom it’s really important that it look like something he’s seen fly at a general aviation airport…  It’s almost,  but not quite (don’t laugh until you hold one of these things in your hands) like going back to the bad old days of balsa,  plywood and shrink on covering.  I was so frustrated that I kept the wings in their original box for their own protection during transportation.

Knowing that I suffer from greasy fingers 
and land in weeds,  that pure white foam of the nose hatch and all hand holds along with the underside of the wing from the tips in a handbreadth and the bottom of the horizontal stabilizator were covered with a layer of (6) ounce per square yard fiberglass held on with easy to work with water based hardwood flooring paint.  The wing and horizontal stabilizator leading edges were covered with heat shrunk on packing tape,  the whole nose,  inside and out was (repeatedly,  as the landing gear kept bending up so far the fuselage hit the ground on landing) fiberglassed with two component epoxy resin.

Servos and Control Surfaces
Although I used (18) gram HiTeck HS-81s,  the nearly identical Multiplex Tiny  (which may have better quality control,  among other things they all center at right angles to the case,  important for ailerons if your transmitter can’t individually zero each servo) are the servo of choice for the elevator and rudder.  Expecting low speeds,  and short on cash,  I used inexpensive (8) gram HiTeck HS-55 servos for the ailerons,  with no regrets,  this isn’t a precision handling airplane no matter how repeatable the control inputs are translated.  I used even more inexpensive (8) gram servos for the “all or nothing” flaps,  again satisfactorily.

If you were wondering how durable those servos are;  I first used this pair of HS-81s ten years ago in a Twin Star II for (60) flights,  until pilot foolishness trashed the airframe.  They were then installed in another Twin Star II for (26) flights,  until an overloaded BEC shredded that airframe through a tree.  They were then installed as aileron servos in a third Twin Star II that went (421) flights,  until a radio failed.  That’s (600) flights now and still performing perfectly.  My pair of Mini Mags with HS-55s currently have (250) and (350) flights on them (including many crashes that would have blown apart a conventional built up out of wood airplane),  they are still flying well.  It’s hard to define the boundary between inexpensive and cheap,  even more so with too small a sampling group.  These Euro6/$8- ones installed for the flaps haven’t had a single defective one out of the twenty I’ve used.  None of them improved over a hundred flights (double centering HS-55s from a while back did),  but they haven’t gotten any worse either.

Unless you are using a computer radio where you can assign separate canals to the flap servos,  you have to turn one around within a newly cut indentation in the wing to run both flaps servos on a single channel with a “Y” cable. It is inconvenient to mechanically perfectly set the flaps to up position,  over-traveling them slightly at the transmitter took care of that.

The mechanical linkage and aerodynamics of the flaps are actually quite well laid out,  I’ve read reports where pilots wanting flaps on unrelated airplanes used these,  for good reason.  I wish I had had a variable dial like setting for the flaps so I could do some of the stunts in Internet videos.  In the end I set them for half the available travel (about (45) degrees) and used them just about like I do in my 1:1 size Piper Pacer.  ?
I mostly used the flaps as brakes to get a steep decent,  then retracting them to flare for landing on Lite versions.  There are some neat tricks that could be flown with the amazing low speed acceleration of the big motor/big low pitch prop combinations,  if the servo for the flaps were a dial instead of just a switch.  But most of my flights were with higher turning,  higher pitch props then the great big flat pitch one specified by Multiplex,  because I’d have had to replace the prop every single flight until I got the landing gear sorted.  Get the airplane together as specified from Multiplex,  with a computer radio and the required skill,  the motor and flaps can be used together for some entertaining close in,  down low,  stunts.

Those channels at the wing underside from spars and such get filled or covered with tape on my airplanes,  which may account for part of why mine flies better.

Although my five channel “just above basic” radio was sufficient for decent flights (both ailerons and flaps on “Y” cables) ,  things went a little better when I used the tuning available of a six channel computer radio for separate aileron inputs.  You can build in some mechanical differential at the ailerons,  I made use of being able to tune differential at the ailerons for more differential then Multiplex recommends for the Fun Cub.  Because getting the throw on the ailerons balance is speed dependent,  and it has a reasonable range of speeds,  between that and the dihedral,  semi symmetrical airfoil and flexing wing you don’t get nice round aerobatics.  Truth is,  that’s part of the charm.

No,  it isn’t reasonable to stiffen up the wing.  At even (1100) grams in a gust the whole wing flexes enough to flatten out then bend back up.  Part of that is the necessary clearance between the spars on one side and the joiner,  but mostly it’s just not all that stiff a wing.  From somebody that has stiffened,  strengthened and armored a lot of EPP,  Elapor and Solidpor,  if you need a stiffer wing get a different airplane,  or take up aeromodeling and add struts like the full size one.  I’ve flown RC airplanes with completely flat wings,  you have to constantly use the ailerons to keep them level,  fine for the F3A and Acromaster pilots,  but irritating and tiring for sport general purpose use.

The trim does NOT change with the flaps extended,  at least not out to the maximum of 70 degrees I used and not in wings level flight.  Light weight configurations of the Fun Cub just kind of climbed a few feet to settle back to just about where it was with them retracted,  medium weight ones just went slower.  In case you were wondering,  the big ones (140 horse power,  aluminum and  fabric covering,  you are betting you life on your own skill and the airplane) change pitch on moving the flaps.  You have one hand on the flaps lever and the other on the control wheel,  with practice you learn to compensate at the elevator for the change in trim of flaps as you don’t have a third arm for the trim wheel in the ceiling and couldn’t move it as fast as the lever for the flaps anyway.  You have to fly the Fun Cub too,  in the end that’s part of the fun of it.  Even without the flaps,  even with smaller then specified motors and higher pitch props,  provided you kept the weight down,  this is one of very few airplanes where you may fly it into,  and back out,  of a stall!

I’d start with the Multiplex throws on the control surfaces.  For my personal Fun Cub I went to a lot more up travel on the ailerons and nearly the physical maximum on the rudder,  after which I went back to about (20) degrees right and left,  the elevator I left as it was.  The Germans use exponential on EVERYTHING.  I’m old school,  I made ten thousand flights with just three channels,  and no extra adjustments…

My Fun Cub has some of the “old” style of control horns,  the ones with only one side to them where so many otherwise competent builders over-tightened the nut.  From experience with Twin Star IIs the area of glued contact from the control horns to the control surface is insufficient,  they tear out over time starting around fifty flights.  Mine have additional fiberglass over the control horns,  which also adds some needed beneficial stiffening up to centers of the aileron/elevator/rudder(s).  Although not strictly necessary,  I taped the hinges.

Worth Mentioning
Even when using simple inexpensive combinations the resulting flights continued from twenty minutes on up.  With the high performance combinations that went to half an hour on up.  What’s with the magazine reports of seven to twelve minutes of flight time?  Maybe I glide more?

One of my standards for evaluating changes can be performed with no equipment of any kind.  With the airplane slowly gliding by,  give maximum amps and do a maximum climb for a count of ten,  then count how long it takes to glide back down.  Figure a one to seven ratio for typical affordable Fun/Easy Cub combinations,  the higher climb of the more powerful combinations glides back down faster because of the increased weight,  until you go to 4S and (350) watts-out at which ten seconds of straight up results in a three minute glide back down.  Ah,  but what a controllable climb it is,  what a relaxing glide back down.  Who cares if less expensive Reinforced Hot Rod Mini Mags and Howling Fun Jets with the better combinations have one to fourteen ratios,  the Fun Cub is for just enjoying flight,  not maximum performance.

Flying with fixed propellers windmilling (because the brake in the controler wasn’t selected) reminded me of my PA-20,  currently rotting at Corona Municipal Airport,  although it screws up the handling and increases the drag,  after a while I liked it.  When I wanted to balance in the breeze I just left a couple of amps on to turn the prop with the wind.

Although I have difficulty understanding it,  the FPV,  or remote video piloted,   RC community in Germany considers this a suitable airplane.  I can only relate that maybe,  to a portion of them (overconfident about their flying skills and all),  that flying something that looks like what you would see on TV and at general aviation airports all over the world with a couple of grand of additional equipment has an aesthetic value.  Then again,  they usually only fly in really still air and I like wind as an opponent…  The Fun Cub just isn’t suitable for carrying a lot of weight around,  there are other RC airplanes for that.

I reinforce my Twin Star IIs and Easy Star Is wings out beyond the wing spar,  otherwise they develop a “hinge” there.  The Mini Mags,  being smaller and lighter,  don’t need that.  For my Fun Cub I went light,  just a thinnest layer of fiberglass with the lightest attachment,  hard wood flooring paint,  for the outside hands breath on the wing and the underside of the horizontal stabilizator.  But then I didn’t load the Fun Cub down  heavy or land it hard,  and not for hundreds of flights (yet),  the expected hinge in the foam just past outside of the spar (or right at the wing servos) started showing up about flight seventy.

The soft foam and landing gear why,  I had to treat it more carefully,  that pure white foam with just accents of color stayed new looking.  Go ahead and paint your Fun Cub all you want,  but if you can’t duplicate my results,  all that paint adds a lot more weight then you might have thought.  Check with our indoor pilots and DW Models Mike Morgan about that.

Since I treated my Fun Cub a lot more gently then my Zagies,  Sturmoviks,  Easy Stars and Twin Star IIs,  things like not landing in weeds,  refrozen snow,  plowed fields,  standing wheat,  oleander bushes and the like,  maybe,  despite the soft Elapor,  the wing will hold up without the leading edge tape I always use,  but hit just one stiff weed with that lowest density Elapor and you are missing a portion of the leading edge.  Then too,  I had to get used to landing on roads and places the rest of you would recognize as landing spots.  The low wing loading and sensitivity to wind of the Fun Cub cut back on my “he has to be a Fool to be flying in this much wind”,  but only some.

To the enthusiasm of many of the reports,  having an airplane that looks like a “real” airplane under radio control may be important a lot of sport RC pilots,  even without their putting it to words.  Partly due to the (expletative deleted) problem with the landing gear,  but mostly incorrect expectations (because nobody mentioned otherwise) it took me a long time to appreciate the Fun Cub for what it can be,  it’s not just a routine flying experience.

What About the Bad Things
Take note,  I actually list things that didn’t work or suite me,  both equipment and flight profile(s),  something missing or censored from a vast majority of reports.  If we listed out the stuff from most other manufacturers,  in comparison to Multiplexes go right together and everything works fine,  the list could be a lot longer!  And sometimes a single huge problem,  which is censored out by commercial magazine editors,  like the too soft Solidpor foam from Graupner,  or an airplane having only a single realistic speed range,  renders an otherwise good airplane nearly useless.

The Fun Cub is a staggeringly inexpensive,  durable if used reasonably,  airframe.  The outlay,  be it purchase price or the time spent to build/assemble it attributed to the airframe makes any comparison with balsa of years gone by a joke.  There are seemingly equal airframes from other manufacturers out there made of junk foam,  that the magazines reports don’t dare offend their advertisers by telling about it.  I’ll fly with anything Graupner,  except their foam airframes.  Multiplex will willing sell you any and every part of all of their airframes for a reasonable price. You break that neat,  it came with everything for the same price as just the Multiplex airframe kit airplane,  good luck,  often they won’t sell you anything but an entire airplane.  I’ve tried the other manufacturers,  you get what you pay for,  the