No, Tricopter flys great with props above or below each other. I hope the link to video comes over. If it doesn't go to MultiWiiCopter and watch his videos. He has a good example.
With all motors in a single plane, you want to find the average thrust line. But this is not what you're asking. Any thrust line above the wing will tend to push the nose down. Any thrust line below the wing will tend to push the nose up. Torque tends to move the nose up, and to the left.
In a biplane or triplane the CG is figured out by estimating the "combined" front to back length of a single abstract wing. It seems that you need a way to estimate the "combined" leverage of the 2 motors on the same plane, versus the 1 on the higher plane. Imagine the 2 motors on the same plane BELOW the wing, and the other motor an equal distance above the wing. Then the 2 motors on the same plane would exert twice the force to rotate the plane up as the third motor does to rotate the plane down. But if you put the 2 motors (on the same plane) right on the wing center line, they will have no rotational force on the aircraft (ignoring wind resistance...). Then the third motor up above will be the only rotational force, and uncompensated.
What do you other guys think?
(You could increase the tail surface area by 50-100%, and use it to trim the unbalanced thrust.)
Replies
No, Tricopter flys great with props above or below each other. I hope the link to video comes over. If it doesn't go to MultiWiiCopter and watch his videos. He has a good example.
https://www.youtube.com/watch?feature=player_detailpage&v=lkzHKw...
With all motors in a single plane, you want to find the average thrust line. But this is not what you're asking. Any thrust line above the wing will tend to push the nose down. Any thrust line below the wing will tend to push the nose up. Torque tends to move the nose up, and to the left.
In a biplane or triplane the CG is figured out by estimating the "combined" front to back length of a single abstract wing. It seems that you need a way to estimate the "combined" leverage of the 2 motors on the same plane, versus the 1 on the higher plane. Imagine the 2 motors on the same plane BELOW the wing, and the other motor an equal distance above the wing. Then the 2 motors on the same plane would exert twice the force to rotate the plane up as the third motor does to rotate the plane down. But if you put the 2 motors (on the same plane) right on the wing center line, they will have no rotational force on the aircraft (ignoring wind resistance...). Then the third motor up above will be the only rotational force, and uncompensated.
What do you other guys think?
(You could increase the tail surface area by 50-100%, and use it to trim the unbalanced thrust.)
Someone must have a quick answer for this...