MFE Beliver Crash

I test flew my MFE Believer a few days ago and it crashed. I would like some help with figuring out what may have gone wrong.

I had had the aircraft set to auto takeoff mode and armed it. I threw the plane and it flew smoothly while gaining a little bit of altitude. Then at around 40 ft downrange and at an altitude of maybe around 6-8 feet, the plane banked sharply to the left. This caused it to lose altitude resulting in the left wing striking the ground and causing the plane to cartwheel once. The nose got broken off into several pieces, one of the v tail mounts broke off (at the glued joint) and there are some scratches on the wings but remarkably, the airframe is mostly intact. I’ve glued the nose back together and sanded it back into the correct shape. Now is the issue, I had my smartphone camera propped up to record the takeoff and a microsd card to record telemetry. However, by the time I took off, the phone battery died and post crash, I discovered the logging failed. The only data I have is what I saw and what I recovered.

hardware setup:

airframe: mfe believer 1960mm survey drone
motors: T-motor navigator series 3110 700 kv
esc: hobbywing x rotor 40A
propeller: apc 11x5.5e
servos: emax 3054
flight controller: matex f405 wte
receiver: radiomaster elrs rp2
gps: matek gps
battery: turnigy 6s 10000mah lipo
transmitter: radiomaster tx16s
NOTE: I was unable to get counter clockwise screw adapters for one of the motors so i locktited down both cone spinners. After the crash, I didn’t notice either being loose but in a previous ground test, the propeller did loosen one of the spinners. looking at the plane head on, the prop in the left ins spinning counterclockwise and the right is spinning clockwise. The plane veered left, so i suppose the left propeller(in the frontal orientation, right) could have been the cause if there was some kind of loss of thrust.

Radio setup:
radio setup: Standard elrs setup with yapuu. I got all the correct sensors with updating values but yapuu kept on not being able to read anything. I think this is just a version error and will be updating the script later. I also had a rare error where the plane would randomly give full bank to the ailerons. I think this only happened when messing with the packet ratio and wasn’t an issue(no way to know since no logging).

packet ratio: 1/8
transmitter module: elrs internal
scripts: yapuu(not functional)m yapuu maps(also not functional)

Parameters: The parameters are what I think most likely killed the plane. I have never tried auto takeoff as all my previou ardupilot planes were vtol.

If I had to take a stab at guessing what the issue is, it’s either something wrong with the parameters, the left prop nut coming loose causing lose of thrust, or
the radio sending strange readings causing full left ailerons.
mfe.param (19.1 KB)

Did you ever fly it again? A log file would be useful to try to figure out what happened

Before the auto take off, had you flown it successfully in FBWA mode?

This error sounds like the plane may be moving the control surfaces correctly when commanded with the radio, but not when doing self stabilization.

The way to check for this is to do the “high five” test from the flight test guys in manual mode. When giving right aileron, the right aileron should come up, when commanding left aileron, the left aileron should come up. When commanding up elevator, the elevator should come up and when commanding left rudder, the rudder should go left; etc.

The second part of the test is what I’ve seen some people not do correctly, and that is to put the plane in FBWA mode, and then holding the plane in your hands, bank the plane to the left, left wing down, right wing up. What you should see is the control surfaces move to bring the plane back to level. That is, the right elevator should come up and the left one go down. This would bring the plane back to level flight. Do the same with the elevator.

Even looking at the logs, I can’t see what your servos do, but this is most likely the cause of what you describe. Good luck, do a video of this test that I describe, both in manual and FBWA modes, a video of a flight and a log file so I and others can provide better inputs.

By the way, in my post of the setup (link below), I put a link to pictures and videos. There is a video of the launch, the one that is 32 seconds long. Take a look at the beginning of the video, when I’m holding the airplane and just about to start talking, I tilted the plane to the left, right wing is up, aileron is up. That is what you should see with yours. Best of luck!

Thanks for the reply. I was able to fix the issue a while ago. Turns out it was a loose propeller nut and also a few small things with the climb angle. Plane works great now.


Oh, ok, well a lose propeller on takeoff sounds a likely cause of your issue, glad you figured it out.

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