QUAD X Motor Tailsitter without control surfaces (H-Wing)

Hello. I have been following this project from the very beginning. I liked your drawings very much. You shared it before but the link is broken. I couldn’t download it at all. Is it possible to share it again?

Thank you very much. I will reply back.

Finally something I can read up on!! Been trying hard to solve the issue I have with my buildup (although it’s on EDFs vs props)

That said, is there any way that thrust vectoring codes can be put in? I’ve been trying very hard to see how can i couple it in.

Wanted to see if I could get any opinions:

I have built up a quad tailsitter without control surfaces running a 6S. The quad basically looks like this: https://www.youtube.com/watch?v=9pEqyr_uT-k, with a small symmetric cruciform tail at the rear. It has been well tuned in QStabilize, and transitions and de-transitions to FBWA seamlessly. It flies well between around 35-60 m/s, but past 60 m/s it begins to develop a buildup of slow period yaw oscillations that only damp when throttle is cut. The highest average throttle I’ve hit is only about 45% when I pushed to 80 m/s, at which point the yaw oscillations pulled about 10 Gs during its lateral oscillation. Given the vehicle is axisymmetric, I see no reason that there should be an instability in the forward stance yaw-frame, when the vehicle’s quad-frame pitch and roll gains are identical, and I have verified that the tailsitter code correctly applies the rotation to the Q gains in FBWA. I would really like to be able to take full advantage of this vehicle’s performance in FBWA and some quick CFD & motor testing suggests that I should be able to hit about 100 m/s with sufficient control bandwidth left for maneuvering.

One current theory I have is that this may be the result of an improperly configured Q_M_THST_EXPO or Q_THROTTLE_EXPO reducing gains at higher throttles. I am planning on stepping these down and flying later today. Another thought I have had is that the propeller thrust may be dropping as a result of the advance ratio at high airspeeds, but I’m not sure why this wouldn’t reflect in complete reduction of control, as opposed to only a yaw instability. Furthermore, I’m already using very high pitch props, so I would expect it to be ok at the airspeeds I’m flying.

Any thoughts or input would be highly appreciated, not sure if this is a problem anyone else has encountered.

Copter tailsitters are inherently unstable in fast forward flight as the motors lose the ability to stabilize as the props unload in the airstream…must be flown at speeds where there is still a lot of dynamic torque available from each motor…

this is very true. With the h-wing i had the same problem. At 100 throttle he motors saturated enough that it was doing uncontrollable rolling. once i brought down the throttle down to 85 or 70 percent it was doing way better. but i would recommend adding control surfaces if they wont react well