Can also be a worn propshaft bearing(s), where the shaft is rotating in the
bearing
(as normal) and simultaneously orbiting around the centre of that rotation
(allowed by radial play).
Duncan McF.
> On 19 June 2020 at 14:58 clivesutton <clive.maf@googlemail.com> wrote:
>
>
>
> Hi Jonathan, what you describe is 'Heterodyning' or 'Beat-frequency' created
by the difference between two noise or vibration frequencies very close
together.
>
> Do you have a recording on e.g. a mobile phone that i could listen to - along
with the engine speeds in play at the time? And what about:-
>
> 1) How the frequency of 'wow-wow' change if you speed up or slow down the
> engine
a bit?
> 2) How does the 'wow-wow' effect change with Airspeed?
> 3) the CS mode idea is viable too - does it occur when that is turned off/the
prop is not trying to hunt for optimum speed vs pitch?
>
> It's impossible to say from just the description given, but assuming the above
items make a significant difference, my initial suspicions would be one prop
blade with a slightly different prop pitch to the others and/or blade tip
tracking
differences between blades. Both of those parameters should be quite easy
to check on the ground (no engine running needed) and reporting any variation
you find?
>
> Clive
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>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=496930#496930
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