We were testing a self made quad plane of 2.5m wing span. we did two flights in auto modes.
The first flight was quite unstable and was saved due to quad assist. We thought probably the control surfaces were too loose. In the second flight the Drone was going fine till it was in a straight line but went into a nose dive as soon as the turn started. What could be reason for this? I am attaching both the log file for reference.
Log files
The following is just my guess.
Due to the low rigidity of the main wings, a larger roll angle (>25deg) caused torsion in the main wings, resulting in aileron reversal.
In the flight on September 29, aileron reversal occurred during the first turn after transition (DesRoll = -30deg) and almost caused the plane to crash, but the wing torsion was recovered suddenly and the crash was avoided.
On the next turn (DesRoll=-25deg), a roll oscillation occurred, probably due to the repeated twisting and recovery of the wing.
In the September 29 flight, the wing twisting occurred in opposite directions on the left and right sides, but in the October 13 flight, both wings probably twisted in the direction of decreasing angle of attack. The aircraft completely lost lift and dived to the ground.
I would suggest that you check the rigidity of the wings.
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Thanks for the reply.
We have a 3 part wing assembly ( Left and right side wing and a center wing), The Center wing is fixed with the fuse and also have the VTOL arms, while the side wings(with ailerons) are connected to the center wing with tubes and latch locks. Should we look into the main wing ( VTOL motors might be causing the twist ) or the side wings? Can some fluttering in side wings at high speed also lead this?
Also, I recently found out that gaps with the wing and aileron can lead to decrease in aileron efficiency. which was also the case.
If aileron reversal is the cause of this problem, the side wings to which the ailerons are attached are the source of the twisting. It is also possible that the twist in the side wings propagates to the center wing.
Aileron reversal is more likely to occur the larger the deflection angle of the aileron surface, but it is not clear whether the gap between the wing and aileron surface affects aileron reversal.
From the logs, it seems that high-frequency fluttering does not occur.