Sea Otter Spirals Out Of The Sky

[dengar256]

I maiden my Sea Otter this weekend and have a question. The first flight went ok, felt a little tail heavy. As I was slowing down to land to fix the CG it suddenly spiraled out of the sky. Not knowing what was going on a cut the throttle and tried to get the nose up as best I could. At first I thought an aileron got stuck but when I got to the plane all control surfaces were working and there was no damage from the crash. I moved the battery and chucked it in the air. This time it flew perfect. I took it up higher to see if I could recreate the issue. I throttled back and it started the death spiral. The only way to get control was to dive and build up air speed. So my question is this normal stall behavior for a sea otter or is there something wrong with my build? Or is this not a stall but something else. Like I said at speed it flew great.

 

[Tench745]

This is what's known as a stall-spin. When the airplane stalls and one wingtip drops first (not an unusual thing, usually the left wing) the plane enters a spin. At this point both wings are stalled or nearly stalled. The solution is to dive or add power to build airspeed and un-stall the wings while applying rudder opposite the direction of spin to stop it.
This is not an unusual thing, just something else to be aware of. Many modern day full scale and RC trainers have been designed to be "unspinnable" to improve safety. Obviously, not all planes are.

 

[raybeau528]

I have an FT Sea Otter and didn't notice any tendency to stall like that. It has undercambered wing tips which I think is supposed to help with that. Do make sure the CG is close to stated location. Even a plane that's not prone to stalls as you describe can snap roll if it's too tail heavy. Also check that your throws aren't too high. Try lower rates and see if you get the same problem.

Ray

 

[Tench745]

I have an FT Sea Otter and didn't notice any tendency to stall like that. It has undercambered wing tips which I think is supposed to help with that. Do make sure the CG is close to stated location. Even a plane that's not prone to stalls as you describe can snap roll if it's too tail heavy. Also check that your throws aren't too high. Try lower rates and see if you get the same problem.

Ray

Undercambered tips help prevent the tip from stalling, but doesn't stop it entirely. The ability/tendency to spin is, I believe, more a function of when the wingtips stall, and how that interacts with the aerodynamics of the rest of the aircraft.

Lower rates would help prevent accelerated stalls, but not prevent power-off stalls. Personally, I like to know I have the throw available for slow speed manuvering so long as it doesn't seem excessive.

Tail heaviness is/was the real culprit here. Nose heaviness helps prevent stall-spins among other things, which is another reason the FT guys recommend trimming nose heavy.

It sounds to me like a little more basic trimming and you'll have a good little plane. I would not try to trim out the spin tendency specifically, just be aware of it and see how any other flight-trimming you do affects it.

 

[dengar256]

Thanks for the tips. It did spin to the left. The throws were set according to the plans and the plane was not too twitchy. It has been crazy windy here lately. As soon as we get a nice day I will give it another try. I am a little nerves because I don't think the plane can take another hard hit on the nose.