quadrotor but with gas engine?

[anchange]

Why hasn't anyone built a quadrotor (http://en.wikipedia.org/wiki/Quadrotor) using a gas engine?

Couldn't you control the yaw and maneuver with 4 independent collective pitch controls, one for each rotor? As one rotor pitch increases the opposing rotor decrease in pitch. The RPMs remain the same, one engine drives all 4 rotors from some central location.

I'm assuming that I'm missing something here but where is my logic going wrong?

Thanks for any help you can give. Quadrotors seem so interesting I'm surprised that they don't have a big following.

Brad

P.S. if the collective pitch control is adjusted does that automatically change the engines RPMs for some reason?
P.S.S. Why don’t quadrotor’s have to deal with coning/flapping, leading/lagging?