Here's a quick mock-up of the basic idea (not to scale): http://i.imgur.com/bNL4y.png
When vertical, the UAV operates essentially as a quadrotor, with the CG as low as possible to maximise stability.
When in horizontal flight, I think that differential thrust will be sufficient for controlling yaw, but not sure about pitch stability. On conventional aircraft, the CP (Centre of Pressure or Centre of Lift) is positioned behind the CG, with a stabiliser at the rear of the fuselage causing a downward force to balance out the weight at the front, like a see-saw.
However, I am hoping to not need any conventional flight control surfaces (in order to reduce mechanical complexity, weight and drag). So should I make the CG and CP coincident, thus creating a longitudinal equilibrium using differential thrust for minor pitch adjustments?
Replies
if the wing creates lift, it will pitch... the problem with using the motors for pitch control is that modulating power can adversely affect pitch... takes a good system to keep power (Speed) and pitch independant... and in the case of a power failure... no controlling the glide...
I suspect roll control will be very weak as you will need to rely on motor toque to achieve it....
Elevons with a positive pitching moment airfoil are the likely solution....
imho