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Old Oct 17, 2004, 10:28 PM
Been There! Done That!
boomerace's Avatar
Eugene, Oregon, United States
Joined Sep 2001
19,187 Posts
Converting .25 Fuel J3 Cub to Electric.

Sent my Astro 020 into Astro for gearbox shaft replacement after the Miss 2 folded wing incident last week and began looking for a suitable plane for the power plant. Really like a bigger cub but all the electric versions are too light for the 36oz 200W of power so begin looking for something in fuel suitable for conversion. Ran on to an E-Zone thread where the ModelTech J3 Cub had been converted with a Astro 020 but with the non planetary GB. Report said it flew great so ordered one for conversion from Hobby People. I am well along with assembly but trying to figure out how and where to install the iRate 2200 3S1P Gen 2 Pack was a nightmare. I was determined to make it removable. Being I didn't have the motor back I weighted the motor mount with a dummy motor weight and checked where the pack would have to go. Where else but with the front of the pack into the motor compartment! So great now how do I get it in and out??? Finally came up with a solution by cutting the bottom out of the cowl which really isn't noticeable except from below and made a slide in battery box for the pack with a velcro retaining strap. I also didn't like the spoke wheels they sent so came up with a cub like hub cap made from a painted Ping Pong ball! Also painted the LG cub yellow. Will post more as I get motor installed and am further along. One thing funny the aileron,elevator and rudder install talked about epoxying in the preinstalled hinges in one side of the hinge and went on about greasing or oiling the hinge pin area so it wouldn't glue shut and when I went to install found CA Hinges instead! Must of changed in mid stream! Since ARF Kit is made in China it probably lost something in translation. I will say however this is one of the best kits I have ever seen. Covering is tight and well done, All parts so far have fit perfect without alteration and I am amazed at the quality! Last pic is a pic of the finished cub from the Hobby People website.
boomer
www.boomerseflight.com
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Old Oct 17, 2004, 11:05 PM
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Eclipse_7's Avatar
United States, TX, Houston
Joined Nov 2003
1,486 Posts
Quote:
Originally Posted by boomerace
Miss 2 folded wing incident
LOL me too
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Old Oct 19, 2004, 05:45 PM
Been There! Done That!
boomerace's Avatar
Eugene, Oregon, United States
Joined Sep 2001
19,187 Posts
OK it's complete wired and waiting on the Astro 020 Planetary and NC Numbers. Astro says repair should be done this week. We'll see! One thing I love about the Astro setup is no adjustment needs to be done mounting the motor. If you mount it in the same position as the Fuel motor it lines up perfectly.
boomer
www.boomerseflight.com
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Old Oct 19, 2004, 05:50 PM
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Eclipse_7's Avatar
United States, TX, Houston
Joined Nov 2003
1,486 Posts
looking good
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Old Apr 01, 2005, 10:41 PM
BLACK SHEEP 2
captglover's Avatar
Alexandria, VA
Joined May 2004
340 Posts
Boomer, I hope you are still around after the brush up you had with that moderator a while ago.

ey! I have the same plane! And have converted it to electric: An Axi 2808/24 and TP 3S 2100 w/ CC 25A BL ESC. HS -81 servos for the tail feathers and a standard for the ailerons. A APC 10x5E prop. Oh, I also got some smaller low bounce wheels so It might look more scale.

Mine is all balanced up and ready for maiden. I sawed off the engine mounts off the firewall and mad a wood base for the Axi to mount to, and be long enough. I then just put in a plank for the battery under the instrument panel area in the front of the fuselage and it Balanced there! Must be the extra weight in the cowl (I also used a large Al. spinner).

Any tips for me before I fly it? It balances right where the instructions say: 1 7/8" behind the LE of the wing at the fuselage. The Axit is rated for planes up to 52 oz. and mine is 48oz. The combo puts out 190 watts also.

Let me know how yours flew - and any tips. I plan to maiden it next week.

Cheers,

Michael

H
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Old Apr 02, 2005, 11:40 AM
Registered User
Herndon, VA
Joined Jan 2004
98 Posts
Michael,

I have been thinking about this conversion for several time. So , I am really interested in your results. My fist choice would have been a Axi 2820/10. Can you elaborate more on your choice?

Thanks,
Mark
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Old Apr 02, 2005, 12:31 PM
Tin
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Boca Raton, FL
Joined Nov 2004
7 Posts
where did you guys get this J3 cub? i am very interested in it.
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Old Apr 02, 2005, 12:53 PM
BLACK SHEEP 2
captglover's Avatar
Alexandria, VA
Joined May 2004
340 Posts
Tin, It's a Modeltech J-3 Cub .28 size. My LHS had one, you can get it one line, just look up modeltech cub. They run about $80 for the ARF.

Mark, The Axi specs say the 2808 is good for a model up to 52 oz. As the cub was 31 oz. w/o equipment, I thought I could do it (my AUW=48 oz.)

With the TP 3S 2100 and an APC 10x5E prop it gets 192 Watts at 21 Amps. The CC ESC is a 25A, the motor is rated to 22A - and that 21A will unload once in the air. The lipo battery is 10-12 C and can handle 21-25A normal and burst of 33A. So it all checks out.

The only thing left is waiting for good weather and a day off to maiden it. I didn't go with a bigger motor, for while the additional cost of the motor wouldn't be much, the upgrade in ESC/+BEC and larger lipo battery pack would be A LOT more!

It should have enough power, I had to wear a dust mask when bench testing the motor set-up, the wind coming off the prop made it hard to breath!

I'll keep you all posted as to how it flies and the power it has. I'm not going to try to do vertical ascent with it anyway, it is a cub...

Michael

p.s. Sorry about the size of my pics, I can't seem to figure that one out...
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Old Apr 03, 2005, 12:11 PM
Registered User
Herndon, VA
Joined Jan 2004
98 Posts
Michael,

Where do you fly? Is your hobby shop hobby hangar?

Mark
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Old Apr 03, 2005, 12:36 PM
BLACK SHEEP 2
captglover's Avatar
Alexandria, VA
Joined May 2004
340 Posts
Mark,

Yes, I shop mostly at Hobby Hanger in Chantilly. Tyler is an electric whiz and helped me with the final numbers on the set-up.

I belong to NVRC out by Dulles, where I intend to fly this cub. I live in Alexandria, and have a baseball field I fly my Tiger Moth at, but for this one, and some of the hotter warbird foamies, I need to fly at NVRC where there's room. Nice site and people. No glo-predudice against park flyers. Many of those guys have electrics too. Weekends are busy but I often fly during week.

I notice you are in VA, where at? I am new around here, so I don't know where Herndon is.

Cheers,

Michael
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Old Apr 03, 2005, 12:55 PM
Shine On !
AtomHeartMother's Avatar
Northern Ohio
Joined Feb 2003
1,013 Posts
I had the glow version of the lil' modeltech cub. It is a very well built arf.
Tips for flying. Check out your wings for washout... Mine had just very slight washout in one wingtip, but not the other. This can easily be fixed with a covering iron.
Keep the elevator throw at the recommended specs...maybe even just a touch less. She WILL tip stall on take off if you yank the elevator and try and horse it off the ground. You guys might be lighter than my glow version was, so that may help some.
Build up plenty of speed before rotating. Mine required a healthy dose of right rudder during take off as well. In the air it's a pussy cat, just watch the take offs and landings. This is really a clipped wing cub so don't get REAL slow when you come down from your flight.
I look forward to your test flights.
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Old Apr 03, 2005, 03:11 PM
BLACK SHEEP 2
captglover's Avatar
Alexandria, VA
Joined May 2004
340 Posts
Atom'

Thanks for advice!

This is my first monocoat-type covered plane, can you tell me what washout would look like on this wing? I have some wrinkled 'coat on my elevator surfaces, should that be ironed out before I fly her?

Also, I bought this plane at an auction, pre-built, so there is no instructions. I looked up the cg when in my LHS (1 7/8" from LE at fuselage), but I didn't get the throw recommendations. Do you still have your manual? Could you let me know the suggested throws for ailerons, elevator and rudder?

Thanks!

Michael
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Last edited by captglover; Apr 03, 2005 at 03:38 PM.
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Old Apr 03, 2005, 04:38 PM
Shine On !
AtomHeartMother's Avatar
Northern Ohio
Joined Feb 2003
1,013 Posts
I surprised myself even...I found the manual....LOL
Control surface throws...
Ail: 1/4 inch low rate 3/8ths inch high rate
Elevator: 3/8th inch low rate 1/2 inch high rate
Rudder: 3/4 inch low rate 1 inch high rate
Cg is recommended 1 and 7/8ths inch from the leading edge at the wing root. 1/4 inch deviation is allowable, but I would stick to 1-7/8ths.

Wash out is where one or both wing tips angle of attack is reduced. How to look for washout. Hold the wing straight out in front of you so you're looking at the trailing edge. Center the wing on your nose basically so you can see both halves of the wings equally. Now looking at the trailing edge of the wing, you may see the wing tips trailing edge sweep upwards just slightly..that's washout. It's designed to help prevent tip stalls at low speeds. I don't think the cub intentionally has any washout built into it... My wing was just slightly warped. If it does have washout in both wing tips and looks equal or very close...no problem. If it just has slight washout in one wingtip it can be trimmed out in flight with aileron trim. If it is too severe, then you'll want to hold the wing straight ...twisting the washout out of it(or twisting wash out IN the other wingtip) heat the covering with an iron or heat gun and let it cool before releasing the wing. The covering should hold the wing straight now. Sometimes this is easier with 2 people. You can also check washout on a flat surface if you carefully brace the wing up evenly(accounting for the dihedral) and then just measure the distance from each wingtips trailing edge to the table. Remember though the table or surface must be flat. This, or if you want to get fancy and put and incidence meter on it, will tell you more exactly how much washout you might have. Don't get really concerned about it though if it's really small.
Big things to reinforce.... watch the elevator throw... cg no further back than mentioned and plenty of groundspeed before you try rotate.
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Old Apr 04, 2005, 08:46 AM
BLACK SHEEP 2
captglover's Avatar
Alexandria, VA
Joined May 2004
340 Posts
Atom'

Thanks again for the info! I really appreciate it. See there is a reason to save those old manuals...

It appears my wing is OK on washout. I adjusted the throws on the ailerons and elevator this morning. Good thing too! My elevator was at DOUBLE the high rate distance. Rudder channel is not adjustable on my radio, but it is at the high rate now, I'll just go easy with it. I need to confirm battery placement/ CG one more time and I'm ready to go.

I may get out early Tuesday morning. If so, I'll report later that night.

Thanks for all the help!

Michael
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Old Apr 04, 2005, 01:36 PM
RCAPA #005
MGBGTRacer's Avatar
USA, VT, Springfield
Joined Jan 2004
3,858 Posts
I live about 3 miles from that club- and I have that same J3! Of course, mine isn't done yet because I'm not sure what to put in it. I was considering an Endoplasma with a gearbox.
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