I crave people's indulgence with this one.
Last weekend I experienced a very slight vibration that lasted for a few
minutes whilst flying. It was just audible and just noticeable through the
control column. The frequency at 4800 rpm was about 2 or 3 beats per second
and was very reminiscent of "interference" or "sympathetic" vibration that
might occur if part of the 'plane was vibrating in sync. with the engine.
I reduced the throttle to see if it would disappear, but the frequency just
reduced with the reduced engine revs. I then opened up the throttle and
experienced what I can only describe as something akin to going over "rumble
strips" on a road in a car, after which the initial vibration disappeared.
I have thought about this a lot and cannot come to any conclusion about what
this could be. Has anyone else come across this, and if so could you share
it with me? I really would like to avoid the "silent front end".
My only, very amateur, thought, apart from the electrics going 'belly-up' or
water in the fuel, is - with the under cowl temperature being uneven from
side to side, is it possible for one carb only to get some slight icing
which could produce the vibration which could then clear with opening up the
throttle, with the ice being drawn into the cylinders, thereby producing the
"rumble" effect due to misfiring?
I have on two other occasions experienced this "rumble strip" effect and
tended to put it down to air pockets or some such thing (ignorant idiot, I
hear people say) but with the advent of an ANR headset :-) I was able to be
more aware of the change in 'plane feel prior to the rumble on this occasion
Any thoughts would be most gratefully received.
Regards,
Peter
PS - 80hp 912 'classic' with cold air plenum
mailto:peterdavis@ntlworld.com
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