Duncan,
If it has to resonate somewhere, I wish it would resonate off the
end of the wing and leave my engine alone ! However i note your comments.
The resonance only effects this very tight band and has no sign immediately
below or above. We have experienced of late starting problems which we have
put down to fuel, your comment on float bowls might have some bearing - as
before I'll keep the forum posted of any findings.
Tony
----- Original Message -----
From: "Duncan McFadyean" <ami@mcfadyean.freeserve.co.uk>
Subject: Re: Europa-List: 912S Resonance / Vibration
<ami@mcfadyean.freeserve.co.uk>
>
> It has to resonate somewhere!
> But it may not necessarily be the engine itself. The engine mount/engine
> will have a particular resonant frequency as will anything else hung off
it
> e.g. the exhaust system.
>
> However, your resonance is so tightly focussed around 3250 as to suggest
> that it could be a compounded effect eg a more general resonance that
causes
> a problem in one of the systems (eg carb vibration and shortlived
> overfilling of the float bowl).
>
> I have the same set-up on my Rotax as yours. There is a slight
> roughness/unhappiness between 4200 and 4500, which is only detectable when
> the prop and everything else is well balanced, but enough to want to avoid
> that speed range in cruise.I suspect this particular vibration is a
> propeller/gearbox interaction.
>
> Balancing the carbs throughout the speed range is impossible on many
> Rotaxes, due to a combination of tolerance differences including the
length
> and mounting of the throttle arms on the carbs. Best therefore to balance
at
> cruise engine speeds and not worry about other speeds.
>
> Duncan Mcf
> ----- Original Message -----
> From: "Tony Bale" <tony.bale@virgin.net>
> To: <europa-list@matronics.com>
> Subject: Europa-List: 912S Resonance / Vibration
>
>
> >
> > Folks,
> > We have just completed the first 2 1/2 hrs of ground
engine
> running (912S Warpdrive @ 21deg XS mono) apart from a couple of starting
> problems which we think are fuel related, the only issue which we are
> concerned about is a vibration / resonance at 3200 - 3300 RPM.
> > Could find nothing loose, re-torqued the blades and had a good poke and
> push around with all the bits and pieces, anyone any ideas / experience ?
We
> have spent considerable effort in reducing throttle cable drag and
balancing
> the carbs.
> > The rev band the resonance occurs at is very specific, and goes as
quickly
> as it starts, very consistent and repeatable, however the engine is smooth
> at all other speeds.
> >
> > I must say being a spam can pilot I was very impressed (not to mention
> releaved) at how controllable the aircraft was on the ground in some cross
> winds and up to high taxi speeds on grass
> >
> > Yours with blurrrrrred vision
> >
> >
> > Tony.
> >
> >
> > PS, I think CKT will be releasing an exhaust mod to prevent the manifold
> pipe (left rear) cracking some people have experienced. Also they were
> unaware of the tail pipe falling off some owners have experienced, they
are
> developing a better clamping device.
> >
> >
>
>
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