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

A Tale including Four EPP Foamies, Two of Which Flopped


The cross over to where NeuMotors 1100 series beats the rest of them in a slower aerobatic airplane is about the Gemini or Acromaster size airframe (about twice the size of these three covered here) with a geared motor.  The three conventional foam airframes covered here are rough surface,  kind of slow,  just fly them for the joy of it,  airframes,  for which large diameter,  low pitch propellers are optimal.  


For that slick surfaced,  speed is everything,  pylon plane,  use a smaller diameter higher pitch prop at ten times the rpm,  contact Steve and Jeff at NewMotors.


I didn’t need 50 flights to make up my mind about affordable,  or 2S LiPo verses 3S LiPo systems in this type of airplane


The Mosquito Wiesbaden Waldacker  Summer 2013  After the going out of business little hobby shop on the edge of town (where a parking place was always easy to find) because they couldn’t make it into the Internet in time,  and I decided that ten months is long enough to wait for replacement Multiplex wings for a Twin Star II,  I took a new (25) gram Robbe motor in trade.  Like Sureflite,  they just lost out to a poor economy and the changing way business is done.  I’m going to miss them both.


As specified by the manufacturer,  and right in there with the recommendation of the manufacturer of the airframe,  on 2S size 350 and 500 mAh LiPos with an 8X3.8 APC prop,  well,  flights with the Mosquito matched the descriptions I’d read about.  ho hum (zu Deutsch so so la la)  Yes,  I could cut the weight,  streamline it with a more suitable receiver and even put a more effective propulsion in it.  See the following;  Just buy a whole system from Hacker (or DW Models) and enjoy it.  


Give the Mosquito to somebody else was my evaluation.   Or maybe try it as a glider for release from the top of a Twin Star II…


A Tau of Poo event,  at least now I know it wasn’t worth doing,  this year 2013 original article for The Silent Electric Fliers of San Diego might point out the fallacy of believing everything you read without seeing first.  And maybe the newer stuff is so much better then even just a few years ago that…  I’m not one to give up easy,  the second time around I did.  Follow along as I try to get things to fly well.


The cheap,  or even inexpensive,  stuff isn’t
Although my Gemini,  Fun Cub and Acromaster all can accept the same motor carrier by just a few screw turns,  so swapping entire propulsion systems is easy,  and I often use any of the three to evaluate equipment,  I still get surprises.  I had run the following combinations in the Fun Cub,  Acro Master and Mini Mags,  both were just ok,  I actually liked the Robbe set up better in the Fun Cub and Mini Mag,  neither the Robbe or this “small” Hacker setup satisfied in an Acromaster.  

From experience with Robbe and Graupner 28mm size outrunners,  when run at reasonable rpm (below 2000) you may expect about (75) flights out of them before the bearings wear out.  It must be possible to wear out Hackers and Scorpions,  has anybody done it yet?  On direct drive with propellers in the seven to ten inch range,  pitch about half the diameter,  with standard fixed timing motor controllers on 3S a Robbe or Graupner combination is about half the initial investment for a Hacker with a dedicated motor controler.  4S LiPo controllers, often with settable timing,  are becoming readily available.


An oddity of current production Hackers in this approximately (28)mm size,  they come with 3.0mm shafts (two replacement shafts included),  for which fitting them with modern 6mm hinge folding propellers is a problem,  as everything else has gone to 3,17mm (1/8th inch) shafts.  The package from Hacker includes a really good propeller collet,  lesser ones are often a source of vibration and other problems.  I use Aero-Naut collets,  when they fit.


Using a Robbe (62) gram motor on 4S (goes for Euro32/$44- locally),  with a Aero-Naut 3 bladed prop carrier and three Aero-Naut 10X4 blades that drew (10) amps at (14) volts on a 4S 1100 mAh battery I demonstrated to a new pilot that not everything is listed that flies.  If you have been following my series,  why would you believe an article where they tried only one combination,   and then only or a few flights,   and were satisfied with it,  as being the truth,  the whole truth and nothing but the truth?  With an 8 to 11 inch diameter two blade folding propeller that Robbe motor on 3S or 4S LiPos can be great,  affordable fun in a Mini Mag (he just bought one with a bad motor,  the bearings shaving creamed out) with flights going on for up to forty five minutes here where must land on farm fields.  The Robbe combinations flew the Fun Cub well too,  at least with it the Gemini was interesting,  it was kind of like an underpowered Park Master.  


The next day I then put a (55) gram Hacker in with two Graupner 9X5 folding blades that made a killer combination.  On the bench with a 4S 1100 mAh LiPo it drew (12) amps at (14) volts.  Even with the fixed timing (probably 5%,  better would be more like 20%) motor controller climb went from;  With the Robbe,  that’s nice for flitzing around,  but at (60) feet of altitude gain it’s either put the nose down or hammer head stall it back down,  to,  with the Hacker (goes locally for Euro65/$87-),  unlimited vertical up.  Flights with the heavier 4S 2200 mAh LiPo went better as with the lighter 1100 the balance was too far rearward.   Just blast around for a couple of minutes (vertical knife edge loops using the rudder are fun,  even if the fifty foot diameter is limited as compared to more powerful combinations),  glide to enjoy it all,  fly  on and on and on (fifty foot horizontal loops for as long as you have the concentration) for something like twenty five minutes (take a pause to glide now and then) a flight.  


No,  for pure aerobatics a (50) gram Hacker is not as effective as the (105) Gram Sport Plettenburg or Scorpion (loops in any diameter you want,  in any direction you feel like,  for as long as you want,  visibility sets the limit) I usually fly a Gemini with,  but that (55) gram Hacker on 4S is a shockingly good,  fun to fly combination.  I’ve has a dozen propulsion combinations in Geminis,  this was unexpected…


Next up,  a genuine Hacker (30) amp motor controler along with the interface to I can set the parameters (timing,  brake etc.) on the laptop.  We need it for,  among other things,  the search for a really effective Hacker combination for the Horizon Hobbies Speed XS,  since all of the NeuMotors inliners I have (which I would rather use) the shaft sticks out the wrong end.  So far,   although the (55) gram 10 pole Hacker is limited to (220) watts-in for fifteen seconds,  and an (80) gram NeuMotors 1105 can go to (450) watts-in,  at a little better efficiency,  it looks like we can’t take advantage of any more power in the rough surface foam Speed XS anyway.  I can’t set it to words,  but that little Hacker pylon racer motor in the Speed XS (use a smaller then recommended battery in the 3S 1800 mAh to 1100 mAh size to get the weight down,  be sure you use servos able to sustain the loads) is just bliss.


I’m going to put two of these 924 kV Hackers in my newest Twin Star II (revamped the inside of the fuselage for more room for the batteries and controllers),  on 5S LiPos with cheap motor controllers (which have settable timing,  if we ever figure out the instructions,  since Hackers are currently limited to 2S and 3S) just to see how it goes,  stay tuned.  Back in San Diego I’d contact DW Models for a Scorpion brand motors and controllers.  We are really pleased with the Scorpion stuff we get here in Germany.


May I quote or own manufacturer of NeuMotors,  “You get what you pay for”.  The cheap stuff is junk,  even the inexpensive stuff just doesn’t come up to comparison as watts-out is what flies the airplane,  not watts-in.


Do you really want to design RC airplanes?
If a manufacturer can provide a complete system that flies better then what I can assemble myself,  I buy it and use it.  The middle of 2012 Hacker made a series of similar to the Mosquito and Borjet sized EPP airplanes available at a reasonable price with great 3S LiPo propulsion using motors in the (30) gram size.  I had been trying to get the Mosquito to fly on mediocre 2S LiPo combinations,  which just weren’t doing it.  For a while the smaller physical size of 2S was the in thing,  but now that 3S works so much better,  and after seeing what the Depron airframes can do,  and watching a hundred flights of a friends Park Master,  my expectations have changed…  


If I wanted to get that first rate 3S LiPo Hacker combination for use in the Mosquito the most direct route would be to just buy a whole airplane kit from Hacker,  effectively they threw in the airframe for not much more. My two Hacker EPP airframes have the best cut EPP I have ever had,  they fly wonderfully,  something you can’t see in a picture or really establish from a You Tube video.  Odd,  they cost about a quarter more then average too,  but not in proportion to the improvement in performance.  Sport Hacker motors and controllers are the best you can buy for the required prop size for these two and a half foot wing span size RC airplanes.  


If there is any improvement possible for this two and a half foot wingspan size it might be a NeuMotors Proton geared down.  At least then you can use a standard fixed lead motor controler.


The promise of EPP
is being able to take a hit,  and be easy to build with,  provided it’s cut right by the supplier.  At the expense of sloppy handling as the whole thing flexes in flight,  and a limited,  kind of low speed range as the surface roughness limits things.  Even Multiplexes airframes (not EPP,  Elapor,  but similar and at least as durable) have select reinforcement and enough bulk that flexibility isn’t usually a problem.  I can still remember EPP first coming on the scene about 1995,  we slope soarers at Estancia in Costa Mesa CA were ecstatic.  But,  maybe that brutal flying/landing and the way we used the EPP flying wings is the only real need for EPP.  The thermal pilots tried it,  for anything other then first trainers they gave it up.  It seems to be at a net disadvantage for dynamic aerobatics,  and too heavy compared to Depron.  The flying/landing on water stuff makes good use of it although what Mission Bay’s salt water does to equipment…


My Depron/fiberglass Sturmoviks perform well and they don’t break under the conditions I fly here in Western Germany.  But slightly reinforced Multiplex Elapor RC airplanes fly so much better I atticed my self built Depron/fiberglass stuff.


A Tau of Poo event,  at least now I know it wasn’t worth doing.  This year 2013 original article for The Silent Electric Fliers of San Diego might point out the fallacy of believing everything you read without seeing first.  And maybe the newer stuff is so much better then even just a few years ago that…  I’m not one to give up easy,  although the second time around I did.  


If I wanted to get that Hacker first rate
3S LiPo combination for use in the Mosquito the most direct route would be to just buy a whole airplane kit from Hacker,  effectively at Euro109/143- they threw in the airframe for not much more.  My two other Hacker EPP airframes have the best cut EPP I have ever had,  they fly wonderfully,  the propulsion is astounding,  something you can’t see in a picture or establish from a You Tube video.  Odd,  they cost about a quarter to half again more then average too,  however,  the cost less in proportion to the improvement in performance.  Sport Hacker motors and controllers are the best you can buy for the required prop size for these two and a half foot wing span size RC airplanes.  They are close enough to the theoretical maximum efficiency possible for outrunners that there isn’t any reason for competition motors at this level.


Hanging out
at the end of summer 2012 at a near by flying club above the Rhine River,  I watched one of newest Hackers combinations,  an sort of scale (like the profile fuselage we used to use for control line) Me 109,  fly.  The owner,  knowing that I like stuff like that,  asked me to check his airplane.  Somehow getting the control horns symmetrical had evaded him.  Even if they don’t cost much,  as I have noted in so many articles on foam framed airplanes,  a few hours more spent on initial assembly (more then what you read about) pay off in better performance over the whole life of the airframe.  Which,  being EPP and electric,  is in the hundreds of flights.  The servos throws were off too,  a result of inexpensive servos that didn’t match.  I did what I could using the trim of his non computer radio and adjusted the control rods.  If it was my airplane I might go to a higher performance propeller then what was in the package,  I’d spend the money for better servos and use a computer radio,  but all in all,  the one I tweaked and flew was assembled close enough to right to fly well.  While I was at I taped his leading edges with Tessa 4124 packing tape.


Just one aspect though,  to keep it flyable for inexperienced pilots,  for me it would be a slightly dull airplane.  Think the original EPP sloper from back in 1995,  the Carnisouris,  with a motor to substitute for a slope,  but with better inverted flight.  As usual when fitted with matched Hacker propulsion the effectiveness is outstanding.  At the owners request,  since the group always wonders,  is it the pilot or the airplane,  I out flew the owner.  At least now he has a goal at improving his skills.  Fortunately,  I prefer “soft” control surface throws,  which the owner can use until he gains enough experience to decide for himself.


I do complete reporting
the good and the bad both.  Sad,  but the two following little EPP RC airplanes,  the Borjet and Mosquito,  just didn’t work out no matter what I did with,  what was three years ago,  typical low investment equipment.


The Mosquito


For the Spring RC Swap Meet in Lampertheim Germany,  on the 25th of February 2012,  two of us drove south on what was the first nice day in two months.  Unlike my slow little camper van,  his car does a hundred and ten miles an hour,  between other slower cars.  There is a famous section here,  straight,  nearly level,  still with no speed limit,  eighteen miles long.  This being direct along the flat portion of the Rhine River Valley,  although gray,  cool and damp,  no snow or ice,  which is just a few miles to either side.  At least we now have ten hours a day of light.


Outside the main hall,  there it sat on the ground,  an EPP kit for a small RC airplane.  About the same size as the Borjet airframe (80cm wingspan),  EPP fuselage and wing,  Depron tail,  with a new Euro11/$15- HiTek HS-55 servo glued into the wing,  for Euro15/$20-.  I went for it,  just had to try it again.  If it doesn’t work out,  I still have the servo.  It figured in that I have a killer Hacker (17) gram motor and controler that match the previous attempt’s manufacturer’s recommendations,  and since it came matched to a flying wing of just about the same area ought to work.  A I just bought a used Graupner motor wound for four cell NiCads  which ought to work on 2S LiPos which,  although heavier and not near as efficient as the Hacker,  ought to fit,  and five 2S LiPo batteries in what should be about the right size(s).  


That Hacker motor/controller in a Hacker EPP flying wing with just about the same area provides great performance on 2S LiPos.  Outstanding actually,  even in my heavier then necessary one.  That simple wing had the best cut EPP I ever laid hands on and flew,  by the standards of a small flying wing,  wonderfully.  It’s only money that held me back from buying another one and using better servos and a lighter receiver to really let it rip.  The Hacker is agile,  even loaded well above the manufacturer’s recommendation,  flights on 2S LiPos last at least fifteen minutes,  they can go on for half an hour.  But,  after (52) flying wings,  with no slope anywhere nearby,  I’m bored with flying wings for flat land aerobatics,  no matter how well they fly.


31 March 2011 (Fr.)  As part of a general review of my flying things,  and motivated by an article in the (German) magazine Foamie,  the Borjet thing was taken out again and reexamined.   The covered in the magazine EPP airplane,  the Epptasy 3D was almost like both the Mosquito and Borjet with the foam parts coming in at (80) grams,  or even less for the profile fuselage instead of the rounded one with lightening holes.  It should be buildable at weights as low as 185 grams although the authors airplane came in at 210 grams.  That required three (5) gram servos,  a (25) gram motor and (30) to (50) gram battery.


On checking the Internet, the Mosquito kit,  currently available from a German foam cutter advancing into kit offerings,  was much less expensive at Euro25/$33- plus shipping,  the all EPP Borjet runs Euro75/$100-.  I looked at an Internet video of one of these flying,  but couldn’t establish much.  Evidently the plywood motor mount and elevator control horns were missing.  Even if the picture of the kit didn’t show the already installed spar in the wing,  the assembly instructions (which wouldn’t download)  a single sheet included with the purchase,  gave all the details needed.


The Borjet airframe (bare,  no equipment) is listed by the manufacturer as weighing (130) grams.  The recommended Nano Red motor for the Borjet turns out to be one optimized for 2S LiPo operation,  it weighs (23) grams,  maxes out at (9) amps and has a kV of 1700 for use with 7 or 8 inch propellers.  It would normally be hung off the front of the EPP fuselage by boring a hole in the front for the tube like mount.  The recommended battery size is a 2S 450 mAh LiPo.  The recommended servos for the Borjet are in the (8) gram (HS-55 like) size,  they recommend a three servo setup with one servo for both ailerons instead of the four servo setup I used.  An estimate of the all up weight would then put the airplane,  ready to fly at in the (280) to under (300) grams range.  I had been flying my Borjet at (440) grams on 3S LiPos and even heavier on 2S.  No wonder it was never entertaining to fly!


To be fair,  in the Borjet kit the tail parts were EPP,  not the Depron tail of the Epptasy.  Irritatingly,  evidently both airframes are shipped without the cores from which the wing is cut.  EPP is floppy stuff,  I can visually spot a warped tail and coax it into being flat again,  warped wings,  without the foam cores they were cut from,  are a lot harder to deal with.


Specifications for the Mosquito:
Weight         80 grams    just the airframe parts
Wingspan        800 mm
All up weight     300 grams,  as recommended by the manufacturer


The Germans use an odd measurement for RC wing loading,  grams/decimeter squared,  it’s the only use I know of that measurement.  We Americans use ounce/square foot.  The intended wing loading for the Borget was in the 23gram/dm² (8 oz/ft.²) range,  I had been forcing the Borjet it fly at 36 gram /dm² (12 oz/ft.²).  Flying a wing at 60% over it’s intended weight completely changes the whole character of an airplane.


Hum,  a recommended weight for the Mosquito right in there with the otherwise nearly identical Borjet and Eppstacy.  The tail surfaces are about half the size of the Borget,  in Depron and not EPP.  Unlike the Epptasy covered in the magazine article,  no lightening holes in the fuselage.  Schulze (the manufacturer of the Mosquito) recommends a smallish 28 mm diameter motor (no weight given) on a 2S 1500 mAh LiPo swinging an 8X5 prop,  a (20) amp ESC,  and three mini servos in the (8) gram size.  Balance is given at 56mm behind the leading edge.


Since (8) gram servos function fine in far larger airplanes,  they are oversized for here,  but I have them already.


Although the instructions show no equipment location (a nice exploded CAD drawing though),  and the rudder isn’t cut out of the vertical stabilizator,  the text recommends one wing servo.  If I had them (4) gram servos could function fine,  it depends on how much hinge resistance the servo has to overcome.  The EPP of the Mosquito is decently cut.  As installed the single servo has no adjustments for control rod lengths,  and they aren’t balanced.  The problem being that the first owner glued the servo in with it at it’s basic neutral,  which wound up being angled to the wing.  The result is severely asymmetrical throw at the ailerons.  There wasn’t any way to make it right,  that may have figured into the original owners decision to “just sell the thing”,  the single wing servo was removed.


I never did like just one wing servo,  one hinge was so stiff (even after manually flexing it a hundred times) that even if actuated at the inside edge,  the outside edge hardly moved.  The EPP is well cut (better then average and way better then the price would suspect),  just the typical tolerances in effect.  The control arm of the original servo was mounted at an angle,  there were no provisions for aligning the ailerons which were attached to glued on control horns.  So,  the single servo was removed,  the hinge beveled with sandpaper wrapped around a credit card and two (8) gram (each) servos plus (3) grams for linkage and control horn were mounted in the wing.


Then the little airplane was fitted with a self made plywood mount fixed to the EPP fuselage,  and two different motor plates that screw to it.  Since I was fiberglassing anyway,  a trace amount was used to help the CA.


Had I been confident in the airplane (being entertaining),  and,  able to afford it,  I’d have used (5) gram HiTek precision servos.  Because I had them,  I used slightly heavy rods and control arms with Multiplex like adjustable connections.  Use of the better stuff would have saved about ten grams.  Fly it first and see is sometimes my attitude,  the servos are glued in,  but at least I can change the control rods later.


The Wing was already fitted with an aluminum tube wing spar,  firmly glued in,  so the gap was filled with Depron and sanded flat.  I prefer carbon fiber,  and would likely have used a pair of 0,5mmX3mm CFK strips,  glued into opposite sides of the wing in knife cut slots saving a few grams and an improvement in stiffness.  One of the down sides of scrounging,  you have to take what you can find.


As for mounting the wing,  I only paid Euro15/$18- for this thing,  new but not built up,  at a swap meet,  including what should be a Euro11- servo,  this is suppose to be a simple easy airplane,  glue it to the fuselage was the decision.  Even if that meant the only available Spektrum receiver (six grams sticks out the top receiver,  two grams in line servos would have been better) went between the wing and fuselage.  A better choice then the sticks out the front receiver would one where the servos go out the end (both at six grams) or better yet,  a park flier receiver,  but I didn’t have one,  yet.


The Depron tail was lightly sanded,  clear tape was used to form the elevator hinge,  it was glued on.  Depron is Fragile stuff for my flying conditions,  but,  let’s see how it goes first…  If thing proves to be worthwhile,  the Depron will be treated to a layer of fiberglass held with hardwood flooring paint.


After the (17) gram Hacker outrunner and it’s matching (5) amp motor controller was front mounted intending to use the rubber band held GWS 4,3X4 propeller was mounted,  it was determined that the minimum size battery that would achieve balance was 2S 1000 mAh @ (60) grams.  Even then the battery had to be mounted (provisionally) with Velcro almost even with the nose of the fuselage.  Recommended was 2S 500 mAh LiPo.  I have 2S LiPos in the (350),  (500) and (1000) mAh sizes,  but this thing,  even with the (8) gram motor mount won’t make balance with a lighter battery.


So an (8) gram servo right under the wing with (5) grams of linkage and control horn were mounted to actuate the elevator.  It could have gone further forward,  but I eventually want to cut a slot to carry the battery,  that would have put the servo in the way.


The all up weight was then (250) grams,  well past the target,  and well below what the manufacturer recommends.  Even without reinforcing the Depron.  Had one wing servo been enough,  the motor mounted direct to a single layer of plywood ect.  there might have been a savings of (20) grams,  and it still wouldn’t only have just made the target of (230) grams.  The recommended (25) gram motor and heavier controler would have made it even worse with the same battery.  From the experience with a similar EPP airplane (Das Borjet) I didn’t even want to try my (45) gram motors (yet) plus their controllers,  too heavy and so too fast would be the likely result.  Maybe the fuselage back half could still be hollowed out to allow the use of a lighter battery,  for now I want to fly this thing first.


The rubber band mounted prop,  which worked well enough in pusher configuration,  would not stay on in tractor configuration.  From forty attempts,  only twice did it hold.  An hours worth of disappointment,  and one flew away in the basement to ruin a GWS prop.  Glad I bought two spares a while back.


So,  the motor was reversed,  the nose hollowed out and a little bitty Graupner 5,1X3.5 on 2mm hinges folding prop mounted to replace the 4.3X4 fixed GWS propeller.  It draws a little too much power on the bench this way,  with that blunt nose it only slightly folds (long soft grass to land on right now),  and cooling is going to be a lot less,  but now it can be used.  It’s a good thing I checked with an amp meter,  I have a small hinge 6X3,  which Hacker lists,  in fixed,  as being suitable.  It drew (7) amps,  way over max.  So back went on the 5.1X3.5.  That little folding prop is still in the catalog,  it’s intended to go on a speed 280 with three times the weight and one third the watts-out.  Ok for a few flights though.


Ever notice the magazine authors don’t mention things like having to turn your shop inside out to find a folding prop that will fit on a (2)mm shaft that you thought you would never use.  Or that you first spend forty five minutes digging through your fixed prop accumulation only to confirm you had nothing that would work since this is only your second use of such a small motor.  The included with the motor two shafts,  two fiberglass Indoor Depron motor mounts and propeller collet won’t work with APC propellers,  not that any I had were small enough.  Or half an hour sweeping the floor to find a dropped screw.  Total time to get to the first flight,  five hours in the shop,  not including the hunting for parts.  


Cash out of pocket,  only the original Euro(11).  The used servos run Euro5/$7- each (new),  another Euro2- for the linkage.  The servos are both slow and not all that good a resolution,  as it turns out,  for the first flights that didn’t matter at all.  That great Hacker motor (spare shaft,  two for Depron motor mounts,  two O rings included) and controler run Euro61/$78-,  plus the prop.


Flight 1  Next to the Airport in Bingen  30 June 2012 (Sa.)  clear sunny sky  zero wind  a grassy field near the man carrying airport.


It’s not like I fly here often at thirty miles from home (I was scrounging used bicycle parts),  it was too muggy (zu Deutsch schwulwarm) to take the bicycle off the van’s rack and go cruise the Naha river as planed and I felt like flying on this long summer day.


First try,  the complete prop flew off.  Back at the camper with the nose cone removed,  one of the two little pins that hold the folding prop blades in fell out into the grass.  A ten minute cut the grass short with my pocket knife and drag the magnet of my hide a key resulted in the recovery.   Tightened the screws until they almost stripped.  


A gentle push,  and it flew right off.  Not a click of trim required. Really neutral stability,  not even a trace of nervousness.  Worried about overheating the motor,  most of the three minutes of the first flight were at part amps,  and below 20 feet.  This thing is slow.  It did a couple of loops,  ok,  but small diameter due to the low speed.  Came out of one half loop inverted,  just a trace of having down elevator required demonstrating that the C.G. on the spar is right.  Not enough lift to try a roll.  On recharging the 1000 mAh battery it only took on (200) mAh.


It’s slow and dull,  I’m disappointed.  That same Hacker motor and controler and battery were just a joy in a Hacker flying wing.  They ar