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

The Acromaster Pt.2

Continued from Pt. 1

An Economic Analysis

Before I buy something used,  I first need to know what it costs new.  And,  since I commute between Wiesbaden Germany and San Diego California,  two prices,  one for each end of the flight.  I can carry propulsion and a few batteries in my suitcase,  the radios and airframes stay where they are.

In San Diego,  when it comes to Multiplex I buy at SureFlite,  so their website was used,  where applicable.  Yes,  Hobby People will sometimes sell you the same stuff,  but good luck getting Multiplex replacement parts out of them,  they don’t want to be bothered.  At SureFlite they either have the Multiplex parts right there,  or will get you them (from Poway) for you in a week,  and the owner of the local store is a member of the SEFSD.

California taxes are computed in at (9)%.  In Germany any taxes are included in the posted price.  The Germans are puzzled by our American practice of adding the tax(es) at the checkout counter.

Acromaster airframe kit                           131-  The Multiplex kits I get in Germany are made in Germany,  the ones in the USA come from the Philippines.  I’m not current on comparing the two,  most likely if there is any difference it’s hidden in the quality control of the parts.

My pair of year 2011 Fun Jet kits,  one bought on Convoy Street in San Diego CA,  the other in Lampertheim Germany,  seemed identical,  except that the German kit no longer includes the Speed 400 brushed motor.

The German production Easy Star I may have had better matching of fuselage sides and wing halves then the ones out of the Philippines back in 2009.

The Fun Jet and Easy Star I have been discontinued in Germany,  where the Fun Jet Ultra and Easy Star II are now available.

Two HS-81s at 15.50                           34- As the current issue HiTeck (18) gram servos are the HS-82,  I take SureFlite is selling off their old stock.  I wouldn’t let the slight difference between HS-81s and HS-82s determine where I bought the servos.  Although they list the HS-82 as being digital,  if it’s that much to you,  please research the difference and report it as my Acromaster will be my first use of HS-82s.  I expect my airplanes to last,  at least fifty flights if not a lot more.  If I were building it new an Acromaster it would get a Metal Gear servo for the rudder.  The better impact capacity is why as from examining the movie made by a SEFSD members Telemaster with the camera facing rearwards that tail wheel really gets jerked around.

Two HS-65s at 33.95                           74- I had considered using my already sitting around HS-81s as an economy measure were I to start with a kit.  Saving (9) grams per servo would be worth less to me then seventy four bucks.  I’d gladly carry the extra (18) grams of on hand HS-81s in exchange for the better accuracy.  That keeping the airframe light is a good thing,  but not the whole picture.

Glue                                                        5-  If I built it new add ten bucks of fiberglass reinforcement to that.  Even the used one will get “beefed up” so it can withstand our landing on grass as a crop fields around Wiesbaden.

Prop (APC) 11X5.5 and collet                             10-  APCs are the standard included in Multiplex Germany kits both for Germany and the USA,  where they cost a lot less.  I prefer the Aero-Naut and Graupners even if they cost more.

All my airplanes now fly with Aero-Naut collets at thirteen dollars on up each.  See my book for beginners “So,  You Want to Fly RC” for details.  I’m neither embarrassed,  or proud,  about having to do everything possible economically.  If five dollar collets worked well enough,  I’d still be using the cheap ones.  If ten dollar Graupners were as good as Aero-Nauts…  To me propellers and their hubs aren’t the place to cut the budget.  As cheap and beat up looking as my airplanes first appear to be,  they fly well,  good components set up right where they matter,  and the skill to use them,  are why.

Extensions,  two at twelve inches         11-

Motor         (available mail order)                  81- That (105) gram motor costs $75- plus shipment in the USA,  or half what my same weight sport Plettenburg outrunner costs.  One benefit of the used Acromaster purchase,  comparing different motors and controllers, the Extreme proved to be poor quality i.e. poor efficiency to begin with,  the bearings quickly wore out ect.  Effectively by buying used I paid less for a motor then really good quality replacement bearings for my (125) gram Graupner.  I’d put new bearings in it anyway,  the replacements available from Boca Bearing are much better quality then the originals,  but the magnets broke lose too.

Motor controller (45) amps                  76- It’s not strictly fair to compare the German Robbe (40) amp motor controller included in the purchase of the used Acromaster with the (45) amp Hifel,  but if I were buying new in San Diego at SureFlite that’s what I’d likely get.  On reviewing the information,  and looking at the picture of the programming card ($10-),  the Hifel controller can control 2 to 6S LiPos,  it has a tacked BEC and has adjustable timing.

You have to watch it with the older non-tacked BECs,  as a consequence of having to dump excess voltage into heat the available amperage to the radio and servos at 4S was way down from the ratings at 2S and 3S,  as such they are not necessarily sufficient for the four servos of an Acromaster being put through it’s paces.  Everything could go along for a while,  and then you put in a new,  low internal resistance high Output C battery resulting in higher voltage at the motor controler,  the motor puts out like never before,  until the BEC quits,  taking the whole airplane down with it.

That being able to increase the lead from fixed 5% to an outrunner correct 20-25% makes about a one fifth increase in duration even with “sport” quality motors.  Although I’ve enjoyed thousands of flights with 3S LiPos and fixed timing,  to date,  Castle Creations oh so reliable and affordable motor controllers won’t go to 4,5 and 6S,  and the timing is fixed for inruners.  That could well change in the near future.

It looks like,  no doubt missing some bits and pieces (like paint),  about $430- to field a “stock” Acromaster with about the same equipment back in San Diego California.  Add to that the receiver and battery(s).

I’ve always maintained that if you are starting with nothing just go ahead and get the whole Multiplex package.  Hobby People’s website didn’t have everything individually packaged by Multiplex for the Acromaster,  Tower Hobbies did:

Acromaster Airframe kit                  $145-

Motor,  Prop and Controler           153-

Servo Pack with extensions          131-

Glue                                                  5-

Looks like $444-,  or about the same.  The HiMax is a little heavier motor (135) grams verses (105),  the servos aren’t exactly the same,  HS-85s verses HS-81,  but it’s a good match.  As luck would have it,  I have the specified HiMax motor and latest Multiplex controler already.  On thing I determined with the Fun Cub,  the big HiMaxes didn’t overheat despite the motor mount blocking off the airflow at the motor,  the lighter more powerful Plettenburg did.  I had to clearance around the motor of the Fun Cub and glide more to keep heat at the motor under control.

In Germany I used the Multiplex Deutschland suggested prices.  Since the majority readership is Americans,  who are not used to Euros,  the prices are adjusted.  If the Euro/Dollar rate is different over reports,  it’s because the exchange rate changes daily,  I report the prices at the time of the transaction.  As I write this,  dejectedly next to the window,  where outside it looks like a perfect sunny day (in Germany if it’s sunny go outside and play,  you never know when that might happen again),  except that with the mornings 12F and afternoons 23F,  it’s too cold to function,  the exchange rate for banks (what you see on the TV news and the fine print of the print newspapers) is Euro/Dollar (1/1.30).  Add five cents to that for the rate an individual gets for (1/1.35).

Multiplex Germany publishes suggested prices.  They are in fact what my local hobby store needs to stay in business.

Airframe         Euro140/$189-

Power Kit         Euro142/$192-  Two APC props,  different sizes,  a timing settable 2-6S (55) amp motor controler.

Nano Karbonites Euro28- each Euro56/$76-  Not exactly the same as HS-65

Karbonites,  the leads are longer,  all of them to date have centered to each other.

Tiny-S Euro17- each  Euro 34/$46-  Again,  not exactly the same as HS-82s

Or HS-85s,  longer leads.

Two twelve inch extensions Euro8/$11-

Glue         Euro5/$7-

It looks like Euro395/$520-.

But,  they have Internet mail order places here too.  Where you can always get a better price right up until the neighborhood hobby store closes.  They don’t all carry the whole program.  For reference,  one of the bigger mail order RC offerings was:

Airframe         Euro120/$162-

Airframe plus motor/controler/prop package  Euro252/$340-

They mention a super package,  which includes the whole radio ready package and a Multiplex receiver,  but they didn’t give a price.  Shipping for orders above Euro90- is free,  but saving Euro20- on an airframe means I soon will have no choice but to shop in the Internet.

The Package Arrived a Week Later

Well,  I hadn’t seen one in four years,  and nobody nearby stocked the kit,  so the size and proportions were a surprise.  A big thick symmetrical pair of wings that look stubby assembled to a surprisingly voluminous fuselage.  I E-mailed the seller back thanks,  it was exactly as described and began examining it.  Maybe attribute it to having started out with balsa,  and when I discovered that I could selectively strengthen EPP and Elapor foam with fiberglass,  which won’t structurally bond to the foam over the paint,  I immediately started sanding.

People show themselves in everything they do,  I wonder what somebody would think of me if they ever find that Easy Star I with the Aveox motor and fiberglass reinforcing sixty feet up in that tree somewhere in the Santa Ana river bed where it crashed on radio failure five years ago.  Or that found set out for the garbage,  balsa wing (paper and dope paint sanded off,  ailerons added and re-covered with heat shrink covering) with the a Depron/fiberglass body and brushless motored Graupner Taxi that went missing near the Rhine River somewhere between Bingen and Rüdesheim.  The original build quality of the Taxi indicated the owner did it without help or prior experience (never finished,  it wouldn’t have been able to fly as found),  that it sat in the attic for an estimated thirty years and was carefully set out on the street along with worn out furniture in front of a million dollar residence,  where a scrounger like me could find it,  and maybe make use of it,  said something about the first owner.  Both times three hundred bucks worth of equipment just gone.

It Started in a Mould

From the add description where the valuable servos (a hundred and fifty bucks new) have only five flights on them,  and oversize control arms,  the few dents on the leading edges and the tension crack in the paint on the fuselage right behind the main landing gear mount.  I wish I could have flow next to the previous owner.  He could have pulled the motor and controller in one minute,  and chopped the servos out for use in another project in five minutes more.  Either just the servos or motor and controller would cost new as much as I paid for the whole airplane,  which,  if it has the same number of flights on it as claimed for the servos,  only flew five times.  I wonder why he sold it,  but a thanks to him.  It has the older issue plastic motor mount.  It looks like about the same tail wheel mount that proved too fragile for extended use in a Fun Cub.  But,  I’m beginning to realize that my hundred flights airplanes aren’t typical.

The bottom of the nose was slightly cracked and repaired,  most likely from hitting the ground on a nose over.  It was decently painted in two tones.  Either the original builder used a primer,  or the paint reacted with the Elapor as sanding both the blue and orange resulted in an icky green mess that irritated my lungs and stank.  The wings leading edges were slightly dented up,  for no more then five flights the outer edges abraded.  Had the airplane had been used in a  crime (contributing to the delinquency of an adult wouldn’t count) there were debris embedded in it which could be analyzed. The right wings lower foam section didn’t evenly match the upper.  After flying with typical “minimal” level servos it’s always a surprise to see how much smoother and exacter even slightly better servos function.  The original assembly and painting was plenty competent,  if I was putting one together stock I would have done no better.  Things like not getting a perfect match between the Elapor components are determined by the staggeringly economical net cost of the kit and that’s just the way it goes gluing together a material that is inherently flexible and compressible.  Initial examination and sanding took three hours.

For reference sanding,  spachtel,  a layer of heat shrunk on packing tape at the leading and outside edges and fiberglass with resin reinforcement at the control arm and adjacent foam of the aileron took the right wing from (120) grams to (121) grams. That working over the wings after cleaning them up took an hour.

I had been paying Euro8/$11- for worthwhile name brand cans of spray paint that gave better results then any consumer level spray paint I ever used in the USA.  Just a thin coat covered well,  it stuck great to Elapor and the cans coverage went a long way.  I took the Euro6/$8- cans of the house brand back to the hardware store for a refund.  I wanted paint with pigment,  not clear with an accent of icky color.  The local artists spraying graffiti murals on approved places use Euro3- a can paint that’s better.  A Tau of Poo event,  how else do you determine the level of financial expenditure that provides satisfactory results?  The new paint, only a third of the area,  added (8) grams.  The wings are now clean and smooth,  however the mix of sanded off blue/green and orange/green with the new (expletative deleted) yellow and red over the blue/green looks awful,  even by my low standards.  It looks kind of like the airplane is healing up from acne,  skin grafts after being burned all over,  and leprosy.  I couldn’t make the surface treatment any uglier if I tried.

But fly it some first is my method.  Usually that determines what really needs improvement rather then just trying to anticipate everything first.  I often build two of a type for that reason.

So a tried and true Multiplex Acromaster airframe well assembled with what could be considered best choice servos and a decent paint job.  The motor is on the cheap side, I don’t expect it to either perform all that well,  or for very long.  The controller,  downrated by the latest expectations as of 2012 of being able to advance the timing to correct for an outrunner,  is only ok quality,  but it will go directly to 6S and can reliably provide sufficient power to the servos.  As shipped the APC 13X4 propeller verses a better performing and stronger Graupner in the same size is a toss up.  Sometimes I’d rather the propeller break then the motor mount,  motor or nose.

From experiments with the Fun Cub,  which weighs just about the same as an Acromaster;  4S 2200 mAh and a Graupner fixed 9X6 provided more thrust for flights twice as long when compared to the APC 13X4 on 3S 2200 mAh,  both using the same controller and HiMax 1130 kV (135) gram motor.  That big flat pitch propeller,  specified back when 4S motor controllers were exotic and expensive,  provides great low speed controllability,  braking in the downward sections and in general a poor mans constant speed flight profile.  It also hangs up and breaks at every possible opportunity.  In the Fun Cub the controllability on 4S was even better,  the constant speed aspect will have to be explored with the Acromaster.  The slightly higher weight of the 4S 2200 mAh battery verses the 3S 2200 mAh was just buried by the higher thrust and duration.  Think going straight up to two or three times the height restrictions at San Diego’s Mission Bay at a count of ten and taking three minutes to glide back down.  On 3S that was more like a minute and a half.

This Acromaster’s nose  was slightly reshaped to accept a folding propeller.  The linkage for the ailerons needs a heim full 3S joint as otherwise it demands the control horns flex.

Just what is this for a Motor?

In every speed shop in the whole world there is a standard question;  Speed costs money,  how fast do you want to go?

It’s subjective,  I had no idea three years ago that foam airplanes,  even with the motor and prop in front,  could last hundreds of flights,  or use propulsion components so far off from what everybody else was using.  But all it takes is one time taking off with the computer radio set for a different airplane to trash the whole thing.  Even in my reinforced foamies the motor can get broken.

There wasn’t much info from the web site of the American manufacturer (importer really) brand Extreme,  about the motor that came used with my Acromaster,  the most important parameters are (35) amps max,  (105) grams and 3 or 4S LiPos at (900) kV with an allowable of (350-450) watts-in.

You have to be suspicious of that kV number.  If you are buying NewMotors,  or competition level ones like Hackers,  you may expect that to be accurate to two significant figures.  That means if Steve and Jeff report their world class racing motor as having a kV of (3100) it may be expected to be between (3150) and (3250).  Check with them personally as maybe they can hit even closer!  It takes top quality materials and manufacturing to be that accurate,  real measurements and a willingness as a company to be honest.  NeuMotors even offered a meter to verify kV for a while.  Anybody else’s motors,  figure more like one digit accuracy,  or off by (10) on up to (15)%,  maybe deliberately to con the customer into thinking they have more performance then they paid for.  Keep that in mind when your results don’t match P-Calk,  that any calculations or program’s accuracy is limited by the inputs.

If you ever wonder why my stuff puts out more power then yours,  some of it’s because I didn’t believe what the package the motor came with was marked as and fiddled with prop sizes using a watt meter and my fingers as a thermometer until the motor was running on it’s limit AND matched to the airframe.  The results are still sometimes a surprise.  That’s part of why I destain reports where all they tried was one combination.  Then too,  I like a “burst and glide” flight style reminiscent of slope soaring,  and holding my breath hunting lobster.  That may explain why my average flight times are about double what the magazines report.

So all I really may expect is that the kV of this motor is likely between (800) and (1000).  At this price level you must expect that individual motors of a series will not match.  There is insufficient information to model it on the P-Calk virtual dyno.  Luckily,  I have a watt meter,  like to fiddle and have been using motors in this size and kV for a while.  Test and tune will decide what works.

The 4mm shaft (interestingly with the brand name Axi etched on) was hack-sawed off shortened.  Turning it over in my hands the bearings feel smooth.  Weird,  the front bearing,  that can be seen,  is about average size for this weight of motor,  but the rear one,  inside the bell where it can’t be easily seen,  is very thin.  The inward rear bearing of an inrunner is usually one size smaller then the front one,  but this is way smaller,  like three sizes down.  That “mini” size bearing may have kept the initial price down.  Maybe it allowed larger coils for higher magnetic flux density,  getting an improvement in power.  It brings suspicions of poor durability as lately it is the bearings that give out ending the service life of brushless motors.  Something you won’t read about in reports made after just a few flights.  I own this thing,  I’m going to use it.

My similar Graupner (125) gram motor,  run at the much higher shaft RPM on 3S LiPos instead of the 2S LiPos Graupner rated if for,  held up for (75),  each and every one was a worthwhile life’s event,  flights.  I’d spend the twenty bucks for new bearings,  but the magnets came lose and I already have better…  One clue with bearings that small as the Extreme’s,  keep the RPM down.  In particular don’t screw up and over rev it with no load (the prop off) as you can wreck the bearings faster then you can pull the amp stick back.  Me,  I don’t ever run up an unknown combination without an amp meter connected.  Not even changing the prop diameter by half an inch or the pitch by half an inch.

The cheap motors,  I reran the measurements every twenty five flights or so as the increased drag from the bearings causes increased wattage draw burning them up.

Now days I just buy better motors in the first place. That,  was two years ago sixty dollar,  now eighty five dollars new,  (80) gram Typhoon motor puts out about (85)% of what the same size (70) gram NeuMotors one does for about (85)% of the duration,  at half the purchase price.  The Typhoon cogs between magnets,  you have to deliberately turn the NeuMotors,  the magnets and coils are that much better.  After a hundred flights (proped as near as possible to the manufacturers (350) watts-in rating,  the same size NeuMotors go to (400) watts-in,  although now obsolete,  the same size HiMax was rated at (300) watts-in) the bearings of the Typhoon are just starting to show some wear in the form of slightly higher current draw,  the Neumotor is still as perfect and smooth running as when it came out of the box and the dust shields wore in.

As for that almost