I was wondering if anyone had experience with a VTOL quad system where the center of lift for the quads was different than the center of gravity for the plane. I’ve noticed every single VTOL plane’s quads are always at the center of gravity (for understandable reasons). However, I was wondering if the pixhawk can work on a VTOL system without the center of lift for the quads being 2-10 inches from the CG?
A couple of cm/inches usually is no problem, but the offset from the CG to the center of the quad frame shouldn’t be bigger than let’s say 10% of the quad frame diameter. So 10 inches sounds a lot to me, except if your frame is quite large. You can also try with more than 10% offset, but you’ll lose efficiency and at some point probably also controllability when some motors are close to saturation.
It is thus also a bit depended on how much large your lift to weight ratio is: When you already need 70% to just hover then I would make sure to have CG properly placed, if you’re at 40% then you have quite some margin.
I had one that was about 3.5" from the fixed wing CG and it overworked the aft ESCs and motors at hover and flipped it over. The ESCs essentially burned up making the motors just go full throttle. It’s probably doable but you’ll need to experiment on the correct asymmetrical motor, prop and ESC combination to compensate for it.
It’s sounding more and more like it’s just easier to have the quad center of lift centered at the CG.
The plane does have a 5 foot wingspan but my capstone teacher decided to put the quads on the tips of the wings instead of about 1/4 half span like most VTOL systems.
In my opinion, that’s a big mistake. My Ranger EX had the booms about 300mm or almost a foot from the fuselage centerline. Watch about 1:03 how the torque of the pusher motor and quad motors’ attempt to keep her straight and level during the FW transition. I can’t imagine how much twisting it would’ve done if they were on the wing tips.