John, Isn't this a case of designing in failsafe mode? Getting the boost set
in max isn't the end of the world as long as you know about it, since
throttling back should make everything manageable. If you had the wastegate
failure mode giving zero boost then you could be in serious stuck if it
failed on you when you were high up in inhospitable mountain country, or
trying to climb out of somewhere hot, high and heavy. I appreciate that
getting either a surge in power or a drop in power could be pretty
distracting when you are in a circuit situation, but I think I might go for
the surge personally!
Regards, David Joyce G-XSDJ 914 XS
----- Original Message -----
From: "Graham Higgins" <ghiggins@norex.com.au>
Subject: Europa-List: Re:Wastegate sticking on 914
>
> After my prang which I believe was due to overboost from wastegate
sticking, I
> have been at a loss to understand Rotax thinking. The turbo charger
wastegate
> default position is closed - ie turbo operating fully unless otherwise
> commanded by the electronic control system. If any part of that system
fails,
> there is risk of overboost, and major engine damage.They advocate warning
> lights to show turbo surge, and if overboost is likely, simply recommend
> "reduce power to acceptable limits, limit operations (land), and fix the
> cause"
> My question is why not have some more positive option for the pilot in
this
> situation than simply warning light(s).
> Has anyone considered having a manual over-ride to open the wastegate
when
> the warning lights indicate overboost is likely? I would have had plenty
of
> power to fly clear of trouble on 80 hp. and avoided the severe damage to
the
> aircraft and myself,if I could have simply disabled the turbo, and used
the
> normally aspirated function of the engine.
> It should not be too difficult a task to devise a cable attached to the
> servomotor cable outer, so that the wastegate can be forced open if
> necessary. I do not know what forces would be required, but it would need
to
> be greater than the servo motor to be of any benefit.
> Has anyone else had similar thoughts, or done any research, or know the
force
> generated by the servo motor on the wastegate arm??
> I would like to have more options to do something about it when overboost
is
> threatening.
> Graham Higgins in Oz.
> 914, Mono, Airmaster, 98 hrs to prang, rebuilding, but wanting something
> better before I fly again.
> > Subject: Re: Europa-List: 914 Waste Gate Sticking
> >
> >
> > > Upon departure, at about 1800' agl, the waste gate stuck
> >
> > > closed, the engine over boosted and snapped the crank.
> >
> > > John Lawton
>
>
> ________________________________________________________________________
> Doctors.net.uk e-mail protects you from viruses and unsolicited messages
>
> Free education for all doctors.
> The simple, fast way to prove you are keeping up to date.
http://www.doctors.net.uk/education
> _______________________________________________________________________
>
>
|