Considering converting the TT 82" J3 Cub to electric, your thoughts? - RC Groups
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May 27, 2005, 04:36 PM
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Zeroaltitude's Avatar

Considering converting the TT 82" J3 Cub to electric, your thoughts?

Hi guys!
As the title says, Im considering converting the 2,1m (82") Thunder Tiger Piper Cub ARF to electric.

This plane is supposed to wheigh 3-3,5kg (6,6-7,7lbs).
I want to use the Axi 2826-10 outrunner on 4s (14,8V 6600mAh) Lipos. This setup spinning a 13X6,5 APC-E prop is supposed to give me a static thrust of 2350gram (5,2lbs) and a pitchspeed of 76km/h (47mph).

Im considering occasionally using this plane for bannertow (I work parttime in a hobbystore, and it would be fun to do a bit of advertising for the store).

Ive done a couple of glow to E conversions, but nothing at this scale.
Does what I propose sound like a reasonable conversion? Has anyone done this conversion, or a similar one and if so what is your take on the idea?

Thanks in advance!
Anders O
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Jun 06, 2005, 02:08 AM
Pelanconi Flyer's Avatar
I had a similar cub and considered doing the same. I think it might be seriously tailheavy with that setup. Mine was tailheavy with a .50 engine, full tank(big) in the nose, and a good chunk of lead on the firewall. It will be a nice floater if you can balance it.
Jun 06, 2005, 06:44 AM
To be a great Astro Boy
edoc's Avatar
I just ordered #12, GP 3300s from for the same project, but planned to use an old Jeti 45-3 with 12-6 APC-E prop. ( NiMh instead of Li)

Per PCalc should get 81.9 Oz of thrust (2334.2 grams) and 51 MPH prop speed. Almost exactly the same as yours, but I bet you do it at alot less amps. Mine will pull about 39 amps.

I should be able to balance fine with the extra battery weight. I will custom build the pack(s) to get them to fit. May be with your Lipos all the way forward you will be close to balancing.... My 12 GP3300s will weigh about 27 oz.

I expect a nice slow flyer. hoping for 10-12 min putting along. This will be my first trip back to NiMh batteries since the big Lipo explosion. I Like those Lipos, but the charge time, cost and balance situation may make NiMh a better choice for this plane. I also like the idea of charging batteries in the plane.

I think our power will be great for a cub (they are flown grossly over powered with the recomended motors). My only concern is getting the Prop/Spinner to line up with the cowl. I don't want to build out the fire wall. Will see....

Jun 06, 2005, 07:11 AM
Name it, I've crashed it
Bill Germanson's Avatar
Originally Posted by edoc
... since the big Lipo explosion.
No pun intended???

How about a picture of your Cub

- Bill
Jun 06, 2005, 08:12 AM
To be a great Astro Boy
edoc's Avatar
Bill, I have puffed a couple of the early Kokams, but no fires or explosions!

Anders, Have you decided to do the conversion?

My batteries, Props and The TT J3 Cub were all ordered early this AM from 3 vendors. CBP/HL/and Tower. Now if they all converge here this week before my vacation ends I will get you a report.

Any experiance out there RE: mounting the Jeti 45-3 in a simular application.
Will I need to get much cooling to the GP3300s at 20-30 amp draw? (This is my first experiance with these batteries.) Where should I make the air outlet??

Jun 06, 2005, 10:22 AM
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Zeroaltitude's Avatar
Guys, the conversion is well under way. I dont know about balancing, but I believe with the 6600mAh 4s pack it should be possible without adding nosewheight. Well see.

Making pretty good process really. Wing is done (installed the servos on the coveringplates instead of in the pockets. Much easier to access and/or replace them that way), tailplane is on the fuselage. Landinggear is finished. Cut a hole in the firewall (beneath the enginemount) to let the pack stick out into the cowl. Replacing the pack will be done through the cowl (which will be split in an upper and a lower half).
Im working on the motorinstallation as we speak.
After that Ill be able to test the balancepoint, to make sure how far forward the pack will need to be, and build the structure for holding the pack.
After that, final installation of elevator/rudder servos, receiver, BEC and ESC, and then hopefully a testflight.

Man, assembling such a large plane is like juggling a 4m ladder. I dont know how many times Ive knocked the wingtips against walls, shelves and ceiling! Good test of the structural integrity though, seems to be holding together just fine!

Anders O
Jun 06, 2005, 12:27 PM
Visitor from Reality
Go search the scale forum. it's a pretty popular conversion. MUst have been dozens of these 80"+ plus BARFCubs electrocuted over on that forum

My 84.5" (real 1/5th scale) Sig Cub flew great on a 16 x GP3300, MaxCim 13Y and a 16 x 8 prop - I never got to measure the current, but doubt if it pulled over 25A flat out.

Just sold it, doubt if it flew more than a dozen times - too much of a PITA to haul around.

Jun 06, 2005, 12:58 PM
Real Men Fly Pink Planes...
kepople's Avatar
Look at the Adrian Page 80" super cub. Its a build, but an easy quick build, and its much lighter. Its flies very well and the price is right.

Jun 06, 2005, 02:16 PM
Registered User
Saw one done with Axi 4120/14 and 16 cells 13X6.5 prop......way more power than needed.
Jun 06, 2005, 03:33 PM
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Zeroaltitude's Avatar
Dereck, I searched and found several thread before posting this thread, but I was unable to find anyone doing it on the same powersystem, or a direcly comparable one. I posted a question in the "Power systems" forum, and after a bit of confusion we came to the conclusion that the Axi 28/26-10 should be enough for this plane on 4s Lipos.

Kirby, using an ARF for this conversion was mainly to get into the air quickly. Im considering building a 1/4 scale cub (or possibly an Auster) to electrify, but that wont be until fall at the very earliest.

Ron, thanks for that input. If I find that the 2826-10 lack in performance then the next step will be an Axi 41 series motor. I have great hopes that the motor Ive picked out will be quite enough though. It most certainly is "on paper".

Anders O
Jun 07, 2005, 02:27 AM
To be a great Astro Boy
edoc's Avatar
I went with the TT because it is lighter than the Sig. ARF, because I only get one short summer per year in Wisconsin. Probably not much longer than Ander's in Sweden.

My power will be inexpensive and relatively low Tech. No BEC or extra battery. Only 12 Cheap NiMh's. It will be easy to upgrade if not enough power. Luckily I have a full size van for that big wing.

Anders, I have flown the Sig on glow and found I was flying with 1/4 power most of the flight. I think you will have power to spare and flight times in excess of 20 minutes. What is your pack weight? I would love to see a Pic on how you do your cowl. I was thinking of something simular.

Jun 07, 2005, 03:08 PM
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Tim, the pack wheighs 595gram (21oz). Its a very long pack, around 30cm long (12").
I would have preferred if they would have configured it as a "brick" rather than as a "stick".

However, with the motor mounted, I found that the plane will balance quite easily, with only a small portion of the pack sticking out into the cowl. There is plenty of room for adjustment. Final adjustment, and building the batterytray wont be done until everything else is finished, but at least I know now that Ill have no problems getting the CG correct without adding nosewheight.

Ill post pics of the finished plane, and the mods Ive done to it once it is finished. I havent decided totally on how to do the cowl, but basically what Im planning to do is split the cowl in an upper and a lower half. The upper half will be mounted "permanently" by screws to the firewall and the front of the motormount, and Ill let the lower half swing on hinges (or possibly hingetape) on the left side, kept on to the right side by either magnets or some sort of latch.

Im doing good progress. The wing is finished (including linkage between servos and ailerons). I mounted the motormount today, and attached the motor to it (got about 3 degrees down and rightthrust). I also mounted the elevator and rudderservos, connected the pushrods and mounted the rx. Man, with an MZK Quatra rx, and two Bluebird BMS 380 Max servos in the fuselage, there is a LOT of space left in there! Im actually thinking of doing a semiscale cockpit complete with a pilot due to all the space available. That will have to wait until maiden has been done though, and so will building a scale engine and cutting the holes for it in the cowl.

All thats left now is:
- Soldering the electronics and mounting the ESC and BEC (they too will be placed within the cowl, theres plenty of space there too).
-Deciding on whether to use the supplied attachement points for the struts (held on by wood screws) or redo the struts with clevises for easy (and wear-free) field attachment. The struts dont seem to be a part of the loadbearing structure, so the wood screws would be fine I guess. Im just wondering how many times I can screw on and unscrew them before the holes in the attachmentpoints gets worn out? Clevises are better both from a structural viewpoint and for simple field use, but perhaps Ill fly it "stock" first and do that mod later on.

Anders O
Jun 08, 2005, 04:02 PM
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The Cub is basically ready for flight now. Ive cut the cowl in two parts, and the upper part is allready attached. The lower part is finished, but I havent attached it, and Im not 100% sure how I want to do it. There are several options, Im just not sure which one to choose.

Had a testrun of the motor today. With the 13X6,5APC-E prop Im drawing 53(!) Amps at static WOT. Too much really, since the motor is only recomended for 45A. I may get away with it though, since from the pull it seems I wont even need WOT for takeoff!
Ill experiment a bit with the props. I want to try a 12X6 and 12X8 APC-E prop along with the 13X6,5, which should lower the static Ampdraw somewhat.

Half throttle only pulls 20A, and the motor is still pulling hard. If I am correct that the plane will cruise somewhere between 1/3rd to 1/2 throttle, then Ill have more than 20 minutes duration with a bit of throttlemanagement, per pack (got two).

I havent started on the scale dummy engine, which meens that I havent cut out the openings in the upper cowl for it either. This in turn meens that Ill be doing the maiden with the lower cowl off, to allow a lot of cooling airflow over the motor and ESC.

With a bit of luck I might be able to squeese in a maiden flight tomorrow evening. If not, then itll be this weekend (weather permitting). Ill get back with a maiden flight report and some pics as soon as possible.

Im starting to get really excited about this "project"!

Anders O
Jun 08, 2005, 04:07 PM
Name it, I've crashed it
Bill Germanson's Avatar
If it's not a superstition thing - How about post a picture of the plane before the maiden, or at least take one and post it after...

Would really like to see what you have there.
Jun 08, 2005, 04:15 PM
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Zeroaltitude's Avatar
Bill, I would have posted pictures of the build allready, if it wasnt for one thing: Ive kept forgetting to bring my digital camera to the shop each and every day.

This time however, Ive allready put the camera in the pocket of my jacket, so unless I go to the shop only halfdressed tomorrow, there will be pictures tomorrow evening.

Ill most certainly be snapping a couple of pictures before the maiden. Not doing so is an almost guaranteed way to ensure a disaster on maiden (superstitious, ME?! ).

Anders O

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