The kid I watched fly one looked to me as if the VPP is just on a seperate servo like the flap or gear swtch as mentioned above. Now picture this, he would fly straight down to the ground & just as you thought he was gonna plant it, he flpped the switch & shot straight back up 3 ft backwards flipped the switch again & proceeded to fly forward doing Harrier type torque rolls. The kid was awesome by the way. but think about this, switching with throtlle as suggested above is more like a transmition going from drive thru neutral to reverse. Planes drops like a rock. He has to keep the throttle on & the pitch change on a seperate switch to make the prop change pitch allmost instantaneoulsy in order for it to keep flying or like I said it will just drop like a rock. I watched him do this several times from as close to 3 to 6 inches of the deck. The prop speed cannot change, just the pitch of the prop to reverse the thrust fast enough for it to keep flying.