droptine

Hopefully someone may have some idea as to why this happened.

I have a Space Scooter that I have flown just fine with the stock set up and an 8-cell CBP NiMh battery. Recently I switched out the stock motor for a Castle Creations Thunderbird 18 Brushless ESC and a BP 21 outrunner motor with an APCE 8x4 prop.

If the process of putting the new motor and ESC in I checked for balance according to the manual. With the new setup it balanced tail-heavy. I carved oiut some of the foam in the forward part of the battery compartment until the center of gravity was in the right place with the battery all the way forward.

To mount the motor, I traced the back plate of the stock gearbox on a piece of sturdy plastic and then cut it out. That way I could use the same cutouts for the back plate of the gearbox as the motor mount and I would only have to cut foam out so the bell of the motor would have enough clearance.

I tried to fly the new setup yesterday and had no success. I launched into the wind (~5mph) at full throttle. Immediately the plane started to climb and roll to the left. At about 50 feet or so, the roll had progressed such that the climb was now a dive. I attempted to control the plane, but no inputs seemed to do anything. I cut the throttle so the prop wouldn't break on impact and watched the plane nose into the ground and rip the nose up.

The controls were trimmed to neutral positions before the flight and the servos worked fined before and after the flight. One thing that I neglected to do before the flight was a glide test with the new center of gravity because it was where the manual said to put it. After the crash it still balanced at that same spot.

Any ideas as to what went wrong? Too much throttle at launch? Too nose heavy? Thrust angle wrong?

Thanks

AJ1202

Sounds like torgue roll got you, A lot of planes have this problem at launch and especially once you go brushless, for example the
P-51 will roll left and nose in every time unless you give it right and up trim at launch, using less throttle helps, I would suggest using some right trim and launch it at a lower throttle like 1/2 to 2/3, you may be seeing the power and torgue being stronger than your servo's, or the travel is not enough to compensate for it. You should be able to launch at lower power and get control of it and just adjust from there as needed. There is one other possibility and that would be your thrust angle could be off, did you factor that in when you installed the new motor

droptine

I did not try to adjust the thrust angle when I installed the new motor. I am going to redo the engine mount and give it a little down and to the right thrust. I also didn't think about the servos being overpowered. I will definitely be working it up to see where its limits are. Thanks.

Simi Mike

My Feedback: (2)

You may want to empty out the stock motor so just the can is left and glue ( or screw ) it to the mounting plate you made. This will ensure that the thrust line stays at mfgs. spec.