DV20 Spontaneous Rough Spurts

[johnichio]

Hello all, my first post here, be nice.

I'm a student flying DV20s out here in Switzerland. I've experienced the same kind of incident on two different aircraft and I'm trying to better understand what's going on under the hood.

The incident goes like this. Take-off and departure climb all fine, then cruising along at a medium power setting, when there is a brief vibratory jolt. It's fairly intense. I.e. it grabs the attention of even a seasoned instructor and is surprising. But it only lasts about a second.

Then it spontaneously happens every so often during the flight. This time around, through adjustments (up or down) also seemed to trigger it. I think I remember a prop adjustment also triggering it.

I've heard it described by different people as either a problem with the carburettor or with the gearbox, but nothing definitive is found.

Has anyone experienced something similar?

[johnichio]

Turned out to be a problem with the reduction gear.

[Rainair]

I know also some Rotax engines, that had this problem. Not sure, but I think there is at least a SB for the reduction gear on the Rotax which checks SN or so. If not, maintenance shall report it to the DAH.

[soarer20]

What was wrong with the reduction gear? What was the fix?