@ChrisOlson wrote:
I'm experimenting with a TriPlane, which I call it a TriPlane instead of a TriCopter because it's kind of a hybrid. The small parawing airfoils produce about 50% of the lift to keep the aircraft airborne @ 9m/s, which enhances flight time.
A photo so you can understand what I'm flying
The thing flies more like an airplane in horizontal flight than a 'copter. But I'm using the Copter firmware to fly it, without tilting the wing motors. I just have the AoA of the airfoils set so it flies at 9 m/s and leaves enough load on the wing motors to effectively control roll. The aircraft is about 3 ft wingspan and weighs 1,716gr.
The problem is that it crabs into the wind like a conventional fixed-wing when flying waypoint miissions. I tried changing the wp_yaw_behavior param, and enabling and disabling compass_use with no effect. When it crosses a waypoint it tries to either point to the GPS course, or next waypoint, but then it crabs. If I manually hold the corrective amount of rudder then it will yaw to the desired heading and bank or "slip" into the crosswind. It's probably more power efficient for it to fly in a crab, but for some aerial survey work I need it to hold a yaw angle to the next waypoint.
I initially flew it with an APM2.8 and thought, well, maybe the APM is running out of CPU to try to constantly correct it. So I put a Pixhawk in it with Copter 3.4 and still got the same problem. And the logs don't show any significant deviation from desired yaw to actual. As it crosses a waypoint it momentarily points at the next waypoint, then the yaw drifts back into a crab to compensate for crosswind. Flying into the wind aloft, or downwind, it points perfectly. Only with crosswinds does the problem exist.
The wheelbase prop shaft to propshaft on the wing motors is 850mm. From either wing motor to the tail motor it is 900mm. The FC is not exactly at the CG of the aircraft - it's slightly forward - but I didn't think that should cause a problem. If I use a higher flight speed like 15m/s then it crabs less. I can set a ROI and it will point at and circle that perfectly. It's just on cross-country legs of a waypoint mission where it does this.
If any of the guru's have any ideas, as to whether this is completely normal behavior, or there is a problem, it would be fun to hear them.
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