Posted by Peter Seddon on October 22, 2010 at 8:00am
This is a recent video of the IAI Panther UAV
that combines vertical take off with conventional fixed wing flight. This video is apparently of the miniPanther weighing 12kg and with 2hour endurance.
Joe is right. The aft rotor is tilted starboard to compensate for the yaw. All rotors seem to rotate CCW (its simpler) and the aft rotor has about 30 degress of tilt to produce the opposite yaw. In forward flight, the aft rotor shuts down and the yaw is probably compensated by rudders. Overall the design is not aerodynamically efficient and I wonder whether it actually does go to 65 km at that speed and altitude. See this video:
@Joe: Thanks! That makes a lot of sense. I know Jack Crossfire flies a tricopter but I don't know how he solves that problem. It has to be one of the solutions you mentioned, I think.
The two front props can rotate in the same direction but having one CW and one CCW reduces the yaw moment. With three props (or any odd number) you can never completely balance the moments and that has driven the popularity of quad, hex and octo copters. This is handled on a tri by tilting one or more of the rotors to counteract the yaw moment and this can be over or under driven to allow for CW or CCW rotation. Quads can do this by speeding up or slowing down a pair of motors to do the same thing. One more rotor or one tilting mechanism has been a fighting point between quads and tri rotors for a long time.
The two front props can both be going in the same direction. It's the task for the flight control system to vary the speeds, as needed, to insure that it flies straight and level. The same applies to the rear prop. All three can be balanced so that it flies straight and level, as required. Am I wrong about this? However, I can see that if all three props are rotating in the same direction, that there would be a yawing moment developed. How to tricopters handle that?
Because it is probably like a classic tricopter where the angle to the vertical of the third prop at the back can be varied and the two front props could easily be spinning in opposite directions.
Looks good. I can't tell for sure, but it appears that the rear motor is not used for conventional fixed wing flight. Is that true? I could see that if WERE used as a pusher, the motor would have to reverse its direction in order to go into hover mode.
Comments
Joe is right. The aft rotor is tilted starboard to compensate for the yaw. All rotors seem to rotate CCW (its simpler) and the aft rotor has about 30 degress of tilt to produce the opposite yaw. In forward flight, the aft rotor shuts down and the yaw is probably compensated by rudders. Overall the design is not aerodynamically efficient and I wonder whether it actually does go to 65 km at that speed and altitude. See this video:
https://www.youtube.com/watch?v=FJv-kQ2rN2c#t=47
Peter
I'm guessing the props spin opposite of each other?
If you could pivot the rear motor forward between the booms you could push with it as well.