Engine surge

I have 7 hrs. on my RV 12 and I love the way it flies. I have one issue though. At or below 4900 rpm the engine runs smooth. Above 4900 there is a very
slight surging at a frequency of about 1 1/2 seconds. It is very slight and not noticeable on the tach.

Anybody have any ideas? Synch was OK, wot 4930, true at 7500 ft., 5450 rpm is 125 kts. No heavy wing!

Doug Dahl
RV 9A, RV 12

Really cannot think of anything. Are you hearing something in the headsets? Are they ANR?

Hey Doug - -

guessing just harmonics. With a gear reduction, the sound can fool you. If the tach is not changing, it is likely sound only.

John Bender

May be harmonics. Don't think I had turned on noise cancelling last time I flew. Will investigate. Thanks.

Doug

These are "thin skinned" little birds and do make a lot of noise!