I'm looking for some explanations regarding snap rolls

1. Why an outside (negative) snap roll requires cross control inputs while in an inside (positive) you require that the aileron is in the same direction as the rudder?
2. For a legitimate snap roll, are you required to first stall the airplane and only then roll it with aileron and rudder?

Thanks,

Yoav

Yoav,

It is similar to upright and inverted spins. If you understand the controls imputs in spins you will get the same conclusion for snaps.

Vicente "Vince" Bortone

In any inverted flight the rudder direction is reversed from upright flight. Therefore, for a negative snap the rudder direction must be reversed.
For a correct snap, the elevator input is started first to stall the wing before the aileron and rudder contols are input. The goal is to just see the nose break in the snap direction before rotation is started. The use of the elevator control first helps hold the airplane on its desired flight path. You will find that elevator input must be maintained during the snap. The amount of elevator can be reduced during the snap to assist in maintaining the original flight path.
John

John,

Does this mean that in a negative snap the plane must be inverted?
I thought that the down elevator is the only diference between inside and outside snap?

Thanks,

Yoav

No, Negative snaps can be on any line upright or inverted ,up line or down and 45 degree lines.
Rudder must be coordinated with the ailerons ie in the same direction.
Try this to understand it. Place your model on the floor upside down. now move the controls for a left snap. Note that that for the rudder to be coordinated with the ailerons you will have to use right rudder on the transmitter. Now try the same test with the model upright.
Another example is inverted flying, if you want to make a left turn while inverted you must use right rudder! Try it next time you go flying.
BTW the rudder is very important control for aerobatic flying.

Isn't the use of ailerons in a snap cheating?

Uhhh....no. [8D]

-Mike

Currently the judges in aerobatic competion expect to see use of ailerons to produce a rapid rate of rotation. Years ago I snap rolled without them.
John

The rudder isn't actually "reversed" when you're flying inverted. It still makes the plane yaw in the same direction as it would if you were upright. Put yourself in the cockpit and think about it. Forget about the ground reference for a minute. That being said, for negative snaps (i.e. DOWN elevator) you use opposite rudder and aileron inputs whereas for positive snaps you use the same rudder and aileron inputs. Aileron input helps with a Pattern plane - it actually affects the way the wing stalls so be careful. The airplane does not roll with rudder or aileron in a REAL snap roll. It rolls because one of the wings is stalled. This happens because you applied enough elevator to reach the critical angle of attack AND applied some rudder to start the autorotation. To stop a fully developed snap roll you should use the same inputs that you would to stop a spin: opposite rudder and neutral or opposite elevator (opposite compared to what you used to enter the snap roll or spin).

John Pavlick
Team Black Magic