I have an Impulse which is a 40 size pattern type model made by phoenix models. The problem IÆm having is if I push hard on inverted flight, to go vertical or do a tight inside loop, without any other control input it does a near perfect half right snap roll. Upright flight, it behaves fine. I only need slight down elevator for inverted flight. I have a small weight on the left wingtip to obtain lateral balance for the engine / silencer offset. IÆve also checked for elevator differential movement, and as far as I can see there is no warp in the wing. What could be the cause?

What you are expierencing is what is known as an accellerated stall. By sharply feeding full down elevator you cause the wing to exceed the "Critical Angle of Attack". Remeber that a stall has absolutely nothing to do with airspeed, only angle of attack. The reason it snaps after the stall can be caused by a number of things. Possibly engine torque (think about a power on stall, the plane is more adept to break the way that the engine torque is pulling it. A slightly warped wing (caused the crash of my Global Raven...slightly warped wing....a little too much elevator on approach.....BAM!!!). some airplanes just have a tendancy to fall one way or the other in a stall (as opposed to just the nose falling straight forward). Thats about the extent of my aerodynamics knowledge....maybe my cousin will read this and prove me wrong....(Aerospace Engineer, Embry Riddle).

Hope I made sense (Yeah right!!! )

Micah (SloFlight)

Thanks for that SloFlight. It does make sense.

Another thing which I forgot to mention, is that if I back off the airspeed and initiate a stall, both on level flight and inverted, it just drops the nose without dropping a wing. I also have about 3deg right thrust.

Cheers Warren

Too much throw?.... Or just pushing the stick too far?... Might need that throw for some maneuvers.

But yes, since it snaps both ways similarly... its excessive elevator travel for the airspeed and load conditions.

Possiblly... check that the CG is correct. If the CG is too far forward, the snap tendancy will be more noticeable.


www.nsrca.org ahs a page on how to verify what trim effect is doing what to your aircraft in flight. Helps with making sure you haven't cross-corrected rudder and aileron and that the CG is DEAD-ON.

Oftentimes the plane only need be lightened to end the snaps.