What does 'Snap flap' mean?

[flystoolow]

What does this refer to?

[Phil Barnes]

When a model is programmed such that the flaps drop a bit when up elevator is applied this is called snap flap. I believe this is used on slope planes to make tighter turns since the increased camber allows for greater lift when up elevator is applied. I'm not sure if they also have the mix raise the flaps for down elevator.

People also use this term for thermal duration models although I don't personally like to use the snap flap term in that case. For a thermal duration model an elevator to camber mix is frequently used which means that when up elevator is applied, the entire trailing edge droops to increase the airfoils camber. Also for down elevator, the entire trailing edge raises to decrease camber. This mix involves raising and lowering both flaps and ailerons together and is done for the purpose of changing camber to match airspeed and not for making tighter turns.

I think snap flap is a term that fits for slope models doing tight, fast turns while the term elevator to camber mix is a better fit for thermal duration models.

[OVSS Boss]

It is a mix that allows a certain throw of your stab and then an instantaneous amount of flap is added for additional camber at a given point. I only use it for speed runs, when you you really want to come around really fast.

marc