Hello. A friend of mine built a VTOL aircraft with an MTOW of 25 kg. Unfortunately, he isn’t familiar with ArduPilot or Mission Planner, so I handled the basic VTOL setup. We conducted the flight tests as follows:
We usually hover in QHOVER and then switch to QLOITER. If the aircraft hovers stably, we attempt the first fixed-wing flight in FBWA. In our case, hovering was perfectly fine.
For the initial fixed-wing flight, we performed a vertical takeoff in QLOITER, switched to FBWA for the transition, and flew several circuits.
After that, we switched from FBWA back to QLOITER for the reverse transition and then landed in QLOITER.
The problem is that immediately after switching from FBWA to QLOITER (reverse transition), the aircraft shows severe pitch oscillations and quickly loses stability. (Please see the video and logs at the link below.) I understand the initial pitch-up right after reverse transition—it’s essentially a hard braking action—but I can’t make sense of the subsequent loss of stability.
After discussing with friends, we came up with the following possible causes:
Parameter settings may be incorrect.
The aircraft may be too lightly loaded for the motor/propulsion output. (Although the system was selected for 25 kg MTOW, the actual weight—while not yet measured—is estimated to be around 10 kg.)
Some friends even suggest that the flight controller might be “saving” or enforcing an incorrect flight mode/behavior, which sounds odd to me. If anyone has insight into this, I’d appreciate your advice. I also need to clear up a growing misunderstanding that I misconfigured the setup. Thank you.
First of all, I’m really sorry for the late reply. I wanted to test a FBWA → QHOVER transition before responding, but—as you saw in the video—the airframe was damaged more severely than expected. It will take time to repair, so I don’t have a near-term flight plan.
Separately, may I ask a setup question?
I’m using a Futaba T16IZ transmitter with a CubePilot OrangeCube FC (the receiver is wired to the FC). All flight-mode configuration is done on the FC side. My transmitter lets me choose a fixed-wing (airplane) model type or a multicopter model type.
For a VTOL airframe, should I set the transmitter’s model type to Airplane or Multicopter?
Or does the FC’s flight-mode logic take precedence so the transmitter’s model type is effectively ignored, as long as I’m just sending standard channels?
I know these threads are quite old, but I recently found a solution to my problem. If you are experiencing similar issues and arrived here through a search, please follow the link below to see the details of what was causing it in my case and how I solved it:
Of course, I hope you are not facing exactly the same problem I did—but if you are seeing similar symptoms, I hope the information there helps you fix it more quickly and avoid the crashes and frustration I went through.
Planes with flight controllers have inputs closer to what multicopters use than regular planes. (4 wide channels + sometimes flaps on planes + maybe gimbal control + a lot of aux functions).
Thanks for your comment. I’m sorry for the late reply—between frequent fatigue and business trips, I haven’t had a chance to respond sooner.
If I understand you correctly, for a VTOL using a flight controller, it’s generally more convenient to set the transmitter up in a multicopter-style configuration (depending on the radio, of course).
When I was first learning ArduPilot, a senior colleague told me—without much explanation—that “VTOL should be set to multicopter mode,” so I’ve always wondered why that was the case.
Changing the transmitter mode wasn’t the root issue in my situation, but your explanation makes a lot of sense. I’ll keep your advice in mind and set up my VTOL radios in a multicopter-style configuration going forward. Thanks again!
Apologies for the late reply, alberto.munizagaAMV, and thanks for the great advice!
In my case, it actually turned out that I was using the wrong ESCs. I had installed ESCs meant for fixed-wing aircraft instead of multicopters. Someone suggested that I could fix it by re-flashing the firmware, but I didn’t have the skills to do that, so I just ended up buying new ESCs. The problem is solved now.
I definitely relate to the struggle with ESC calibration. When I first started, my English wasn’t good enough to understand the manuals, so I often went out hoping to fly, only to spend the whole time calibrating ESCs before going home.
