Rotax 912: Irregular engine tone

[Guest Easeback1]

Rotax 912F / Diamond Katana DA20 A1

 

 

 

Engine performing 100% normally during run-up.

 

During flight, engine tone periodically increases in pitch for a few seconds before returning to normal. No change in manifold pressure or RPM during this time.

 

 

 

This rarely occurs in straight and level flight, but usually immediately after adding power, initiating a turn or lowering the nose i.e. an increased load on the airframe. Something to do with the engine mounting? My experience is limited, so grateful for any advice.

 

 

[Ultralights]

Try looking at the exhaust sytem, there might be a spring or three missing, or a crack opening up and closing again.