Tilt-rotor VTOL sudden dive into ground after about 10 seconds of transition

ArduPlane VTOL Plane
, , , ,
1

Hello. Please refer to below Information, Flight Video, Flight log, time table :

(1) Aircraft Model : Freeman 2100 VTOL(MakeFlyEasy)

(2) What I have done with this aircraft:
Built VTOL and tested with Quadcopter mode, set up parameters as maker suggested, extended airspeed sensor for preventing airflow on tilt prop to affect airspeed sensor(It worked), Checked fixed wing servo neutral position and direction(Including tilting aircraft on QStabilize mode and watch it react to tilting), Checked Weight balance, battery is tightly installed inside frame

(3) Problem : as described on the Post’s title.
It suddenly started to dive into the sea/ground whenever I fly it and I changed to QHover mode and manage to land safely everytime it dives.

(4) Video and flight log :

(5) Time Table of video :

02:56 Changed mode from QHover to FBWB
03:10 Sudden Decrease about 13m, at airspeed 19m/s, changed to QHover
03:11 GPS speed increased to 30m/s, meaning that it almost dived into sea

04:11 Changed mode from QHover to FBWB
04:20 Sudden Decrease about 10m, at airspeed 20m/s, changed to QHover
04:22 Airspeed increased to 31m/s, meaning that it almost dived into ground
05:12 landed with QStabilize mode

It seems that the aircraft is okay until GPS speed 19m/s, and after the speed it dives.
before, airspeed sensor was not good and that time it dived with airspeed 12m/s and GPS speed 19m/s

I’m not very sure, but I put my transmitter at neutral.(didn’t touch the throttle)

2

I experienced same thing with VTBird 4+1 VTOL before.

Am I doing something wrong?

3

in QStabilize, Manual, FBWB and FBWA mode,

[1] When I lift up the aircraft nose, the elevator control surface goes down
[2] When I down aircraft nose, the elevator control surface goes up
[3] When I down the elevator stick, the elevator control surface goes up
[4] When I lift up the elevator stick, the elevator control surface goes down

there seems to be nothing wrong.

4

I looked through the log and found “Desired Ptich” and “Pitch” value varies about 10~20 in very short time after reaching airspeed about 18m/s.

I’m looking through the center of gravity and elevator surface angle again.

I put elevator stick and if pitch(nose) down, the surface angle is about 20 degrees and if pitch(nose) up, the surface angle is about 10 degrees.

is it too small angle?

in freeman(aircraft name) webpage, they say rudder angle should be 30 degrees, but I’m not sure it is correct value and not meaning the aileron value.

now my vtail servo pwm range is 1100~1900

5

I adjusted Center of gravity because my previous measuring method could be inaccurate,

and I adjusted V-Tail PWM range from 1100~1900 to 800~2200.

but I’m not sure I can adjust V-Tail Servo PWM range.

Do I have to change PID value and tune again after changing servo range?

or is it independent of PID values?

6

It crashed into sea, and I suspect the front-tilt rotor hit the carbon rotor boom when it controls yaw.

After I changed the mode from FBWB to QHover, after few seconds, it sudeenly rolled and pitched very much. It became very unstable with quadcopter mode.

I experienced many RC helicopters and it was definitely aircraft’s problem.(It was like PID overshooting)
I have experience of this VTOL when the wind was very strong so with QHover mode and with full stick input it didn’t move. It was not control ability’s problem.

I called service boat for evacuating my aircraft in the sea, and one of the props was broken even though it very softly landed on sea(with QStabilize mode) and have no collisions.

It just float on the sea until it was evacuated, so there is nothing can break its rotor.
so I suspect rotor hit the main rotor pipes.

but my Q_TILT_YAW_ANGLE was just 10.

below is my flight log.