Actually, the starting problem should be reduced by approaching or exceeding
the prop inertia limits as more prop inertia means lower resonant frequency,
which is further displaced from cranking speed.
Maybe the small, low inertia Europa props are contributory and it's not just
our relatively high utilisation that seem to be favouring us being victims.
Another aspect is prop material, the high modulus/low hyteresis Warp Drive
being hard on gearboxes. But then William Mills runs an Arplast (but did
once run a Warp Drive).
Duncan McF.
----- Original Message -----
From: "M.J. Gregory" <m.j.gregory@talk21.com>
Subject: RE: Europa-List: Rotax starting - 912S
>
> Could these problems be exacerbated by exceeding the maximum propeller
> mass-inertia limit recommended by Rotax? In the case of the 912 this was
> 6000 kg-cm squared.
> Does anyone know what the current recommended limits are for the 912S and
> the 914, and how commonly-used propellers such as Warp Drive compare to
> them?
>
> Mike
> Europa Club Safety Officer
>
> -----Original Message-----
> From: owner-europa-list-server@matronics.com
> [mailto:owner-europa-list-server@matronics.com]On Behalf Of Ami McFadyean
> To: europa-list@matronics.com
> Subject: Re: Europa-List: Rotax starting - 912S
>
> <ami@mcfadyean.freeserve.co.uk>
>
> That being so, the 'shaking and banging' is likely caused by the low
> frequency primary resonance (torsional and/or blade-flap) that is
inevitably
> present below normal cranking speeds. In the absence of any damping, the
> forces produced by resonance will build-up towards infinity. The crank and
> gearbox get hit with similar forces too; its just that the sprag is the
weak
> link in the chain (and, if it's any consolation, cheaper than a new
crank!).
> However, damping of resonance is provided by the friction clutch in the
> gearbox; hence Rotax's insistence that this be maintained at the upper
> limit. Also anything that accelerates the cranking engine quickly through
> and clear of the resonant band should help (i.e. powerful battery, good
> contacts, high torque motor). We have to hope that it is the 'shaking and
> banging' ONLY that causes the problem, not the loads of normal starting.
>
> Last Summer, there was a certain 912S CT that was regularly shaking the
> carburettors out of the mounting sockets on start up, possibly exacerbated
> by the big floppy 2-blade prop it had.
>
> Duncan McF.
> ----- Original Message -----
> From: "P.A.D.Clarke" <paddyclarke@lineone.net>
> To: <europa-list@matronics.com>
> Subject: Re: Europa-List: Rotax starting - 912S
>
>
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