Displacement during snap rolls (was Why is it so quiet?)

[Bob Richards]

>>>I do have a question though.  How can an aircraft be “semi-stalled?”  Either the aircraft is stalled or it isn’t.<<<
 
Rarely is the entire wing stalled. A true snap roll or spin will have one wing panel stalled more than the other. The lateral difference in lift causes the rotation.
 
>>>It progresses over a range of angles of attack, and the autorotative tendency of the plane  both comes and goes as the plane increases angle of attack. Stalled does not mean zero lift! The center of gravity will and must wobble some in a snap. Because the plane does not go from flying to stalled  instantaneously, there will be a displacement of the CG both to the top of the plane, and to the side being snapped, assuming a positive snap.<<<
 
Dean, excellent description!!! I've heard a lot of people talk about "stalls" as a loss of lift, when in fact the lift will be the highest possible just as the stall begins. A portion of the wing may be stalled, but the unstalled portion may still be increasing in lift with an increase in angle-of-attack. 
 
In most general-aviation aircraft, you will find stall strips on the leading edge, almost always towards the inboard portion of the wing, that will force the stall to occur on a small portion of the wing long before it happes elsewhere. If the stall starts inboard, you will still have aileron effectiveness and can still fly the airplane.
 
>>>It is one of those maneuvers that is very commonly scored a 9, 9 ½, and a 0.<<<
 
Possibly because there is a fine line between a clean break and none at all. I think the best snaps are probably the one with the least amount of control deflection that still gives an obvious break. I also think that the sequence of control deflection can make a difference as well. If you could always stall the plane with elevator first, then deflect the rudder to start the rotation, it would score higher. It might also be possible to release the elevator before the rudder, and actually apply opposite rudder and elevator to stop the rotation and reduce the lateral offset of the snap. Problem is, my brain ain't that fast, and neither are my thumbs!!!
 
You will notice a rule somewhere that no automatic timers or sequencers are allowed in the radios. The original Futaba 8ch 512 pcm radio had a snap switch that would engage the elevator and rudders for predetermined amount of time that could be adjusted by pots. I have an 8ch radio, and the pots are not there -- most likely because of that rule change. Can you imagine, flipping the switch only starts the snap roll, the timers determine when the snap stops regarless of when you let go of the switch.
 
I experimented once with flap deflection during snaps, and determined it would be possible (most likely with inboard flaps) to deflect the flaps up, along with lots of up elevator, to force a stalled condition with very little deflection in the flight path. The only planes I had at the time either had full span or barn door ailerons, and I never had the opportunity to try it with inboard flaps. I had limited success with full-span flaperons.
 
I remember scribing during the FAI finals at the '93 Nats. One of the manuevers was a 1/2 cuban eight with 1.5 snaps down. Chip Hyde did it better than anyone else, IMHO. One thing he did that was very subtle (most people did not notice it) was that on the downline before the snap, he applied a small amount of rudder opposite the direction of the snap. It was hard to see since at that point you were only seing the edge of the plane. The heading on exit from the snap was right on track. Instead of correcting the flight path on exit, he was compensating some before the snap, at a point where it was hard to see.
 
Bob Richards
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