We have encountered a strange behaviour with the Kodiak. Here are the steps and what happens:
- Load the plane close to its maximum permitted aft CG, which is 40%
- Hold the brakes
- Increase power to 100%
- Release brakes
- The plane will fall on its tail (screenshot)
We initially attributed this to prop wash and reduced it, but nothing changed. It also happens with full trim down and full elevator down, so the elevator has absolutely no effect on this and nor does propwash, it seems.
It only happens:
- at high throttle settings of more than 80-85% and
- brakes released and
- speed less than 20kts
- CG beyond 35% (maximum is 40% for this aircraft)
If the plane accelerates past 20kts, I can throttle up to 100% and all is working as it should.
After running some tests and monitoring "ROTATION VELOCITY BODY X" I noticed that at lower weights with brakes held, the plane's pitch will fluctuate at the 2nd decimal, which increases as you put more throttle to the plane.
As soon as you release the brakes, the plane shows a nose-up pitch rate which is negligible at lower weights/forward CGs. If your CG is way back (always within the limits), that pitch-up tendency very rapidly increases to 7 deg/sec resulting in a tailstrike, as the elevator doesn't work to negate it. It seems like the plane does the rear-tilt as an "opposite" to the forward tilt it does when braking.