FT SIMPLE CUB

[LeonD]

Hi Guys
This is my first post.
Just a quick question, my son and I have just built a Ft Simple Cub, both planes built together and everything is
almost identical except for the motors, he's motor is a bit stronger!
The problem is, when we went to maiden them, my one flew beautifully whereas my sons one was totally
uncontrollable, it would take off and climb, then go into a steep climb, stall and nose straight into the ground. C of G is the
same on each aircraft.
Any ideas of what could be wrong?
Appreciate any ideas!
Thanks

 

[Hai-Lee]

You did not give much info on the difference but I will try to give you a few pointers as to what to look for.

The design has a weakness in the rear of the wing centre section trailing edge and the rubber bands holding the wing can cause this to collapse and thereby severely alter the main wing incidence. Check and ensure that the wing sits flat on top of the fuselage.

The simple cub can be very susceptible to "P" factor issues especially if the throttle is applied coarsely. apart from that I would check build quality. Simply swap the wings over and see if the behavior follows the wings or the fuselages. If the behavior follows the wings I would check the wings for warps and similar problems. If the problem stays with the fuselage then revise the side and down thrust angles.

Just one more thing to consider is the setup of control surface deflections and the amount of Expo in the transmitters.

A little more info on setup might help solve the issue.

Have fun!

 

[Forster]

You might also throw some engine thrust angle offset at the problem. I'm using the stock B kit with a 9x4.7 prop and use a few degrees of down and right (mount tapers 4mm from upper left to lower right corners). I built the pod (less the engine mount) and sanded it to shape, then added the pod.