Desired Pitch ignored - crashing at launch

ArduPlane Plane 4.5
1

Hello all!

I try to maiden a fixed wing, atomrc swordfish but have crashed badly two times already.
Now getting prepared for the third time but I feel pretty worried it will end up crashing again.

Can you spot what I do wrong?

The Swordfish flight controller AtomRC F405 comes loaded with Inav but I am familiar with Arduplane and flashed 4.5.1 stable. I set it up like I have done with many planes before and checked all is good.

Flight one - goal is to launch in FBW mode and soon enter Autotune.

Hand launch in to the wind and starts fine but then refuse to gain altitude despite giving full pitch up and full throttle. Crashed in some seconds.

Changes after crash 1 -

  1. The center of gravity was too far to the nose. Moved it to the marks on the wings.
  2. Pitch settings checked - range and sensitivity. I doubled the P term on pitch and saw good response in fbwa mode.
  3. Wings angle of attack - it was flat and I changed it to some 10 degrees so in horizontal flight there is lift.

Flight two - goal same as first flight. Hand launch in to the wind but same result again and crashed in some more seconds.

I do not understand why :thinking:

Changes after crash 2 - so far…

  1. I recalibrated the Accelerometers completely since maybe they were off.
  2. Added even more angel of attack to 20 degrees
  3. Moved the physical travel of the pitch of V-Rudders to max travel.
    4. … what else to change?

First and second flight logs attached
2024-05-02 SwordFish Maiden crash.bin (444 KB)
2024-05-08 SwordFish Maiden crash.bin (580 KB)

2

If the CG is correct, I suspect some sort of trim issue.

When you say “Wings angle of attack - it was flat and I changed it to some 10 degrees so in horizontal flight there is lift.” and “Added even more angle of attack to 20 degrees” – How did you adjust this angle? Are you describing adjusting the physical wing, or is this the max pitch limit (PTCH_LIM_MAX_DEG)?

3

Thank you for reply Neil,

Yes, am in to similar thinking its simply not enough pitch.
For angle of attack, I just use the 3rd button on Mission planner accelerometer screen.
Maybe not the best way? but has worked on other fixed wings for me.

Screenshot 2024-05-16 at 10.15.08
Screenshot 2024-05-16 at 10.15.081344Ă—734 55.7 KB

I have now changed the default 0.5 setting of the Vtail MIXING_GAIN parameter to 0.85 that results in considerable more pitch travel.

4

yup, that fixed the problem.

Thanks a lot
karl

5

Glad things are fixed.

I would recommend calibrating the vehicle on a level surface, rather than inclined. The purpose of calibration is to teach the IMU its orientation, not set AoA. Level calibration will ensure maximum IMU accuracy. Then you should use PTCH_TRIM_DEG to set AoA in degrees above level. Most airfoils will stall at 20deg alpha, you probably want to start in the region of 2-5deg.

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