... My understanding of the aerodynamic principles of quads says there's no difference between
motor speed adjustments of fixed pitch rotors versus pitch adjustments of fixed speed motors.
So, YES you can drive the props with a gas engine and no you do NOT need any clutches.
YOU DO need to adhere to the opposing motor spins criteria though, as that is required as a function of
anti-torque correction to maintain yaw stability. Pitch and roll reactions are self evident, but yaw operates
entirely differently and is less intuitive in nature.
Motor pairs with identical spin directions when given more speed (or prop pitch) overcome the otherwise existing
counter rotational torque balance and allow the quad to spin in the opposite direction of the selected motor pair.
In other words, increasing the "prop bite" of (only) the clockwise props will cause counter clockwise yaw movement.
Now, having established the control scheme as viable, I'd offer a suggestion that would be a "nice touch" :
As a passenger carrying craft, you don't want the occupants being tilted forward looking at the ground in
forward flight. The quad (and hence the passenger compartment) can easily stay perfectly level in forward
flight if the arms the front and rear motors are mounted upon are able to pivot. This has already been done
with several quad models and there's Youtube videos showing them in operation.
