|Jul 22, 2010, 12:57 PM|
Speedy 400 Project
Some time back, I purchased a Speedy 400 from Hobby Lobby Intnl. The plane was essentially a pylon racer trainer, powered by a brushed Graupner Speed 400 motor, pulled by a 6x4 folding prop, and fueled via an 8 cell AA NIMH 1100 battery pack. The first flight clearly indicated I was having a problem flying the plane, it was constantly "late" on aileron input. No rudder on this plane, just barn door ailerons and elevator. I was up and down (Speedy was very sensitive to elevator movement!) and all over the place in trying to maintain level flight.
The problem was the central mounted servo/bowden cable arrangement for the ailerons. I went up on RCGroups and asked for help. A fellow in Switzerland replied, advising I install individual servos for the ailerons, as the stock system allows for non-centering of the ailerons due to friction of the bowden cable within the plastic tubing that located the cable within the wing. Wow! What a difference. I used Hitec HS-55's, used a Y-cable arrangement, and the problem was solved.
After flying the Speedy 400 on it's stock motor arrangement, I decided to go brushless. Wish I knew then what I know now. I grossly over "motored" the Speedy by installing a Mega 16/15/3 brushless inrunner. Talk about high prop rpm's and eating amps. The NiMH 1100 packs would barely hold voltage, got so hot the plastic wrap melted! Then I discovered Lipos. A 2-cell 2100 Thunder Power 12C pack would provide more sustained voltage than the previous 1100 NiMH's, but "oomph" wasn't quite so mind-blowing as one might suspect. Also, managed to puff a pack or two, and risked eating the 25A Castle Creation Phoenix ESC.
One day I accidently slipped a 3S 2100 pack into the Speedy. Yikes! I could not force my self to go to WOT, for fear the motor would tear loose from the plane. So, it was back to a 2-cell Lipo, a Flightmax Zippy 2200, but 40C this time around. Voltage held much better, the pack was only slightly warm after an 8 minute flight, and I could fly WOT when I got the hots to do so.
Glad I modified the wing hold down arrangement. Much stronger, but it will cause the wing to be destroyed should I cartwheel the plane. I just don't want the wing separating from the plane when pulling some major G's in tight turns.
Two more Speedy 400's (some scratch & dent specials from Hobby Lobby) are on the shelf, awaiting assembly. The next "Speedy" will have the Mega 16-15-4 or equivalent in-runner, allowing more reasonable throttle control when running a 3-Cell Lipo. Also, I plan on installing a carbon fiber main spar reinforcement in the wing.
Unfortunately, to the best of my knowledge, the Speedy 400 is out of production. WIPA Model of the Czech Republic built the model. One might find a Speedy or two floating around in Cyber Space. Best of luck in finding one, and NO, I am not selling my spare units! Sorry about that.
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