My engine ( a plain old 912) has 720 hrs on it now and at last check showed
virtually
no sign of use. I also run it at 4ooo rpm for economy cruise. I see less
than 10 liters per hour of fuel flow (in cold air). I could not think of any
reason why the engine would wear prematurely if run at such speeds (or does idle
kill engines ?). Every millimeter the throttle can be pulled back will improve
fuel flow. Only a tick more and she uses 14 liters with only a 2 knot gain
in speed.
I am looking forward to building those glider wings and partially wet them. With
onboard fuel (and only a slight disregard of gross weight) the endurance could
be pushed to over 30 hours. Where would you rather be than in the air ?
happy skies,
<Thomas, N81EU>
----- Original Message -----
From: "Duncan McFadyean" <ami@mcfadyean.freeserve.co.uk>
Subject: Re: Europa-List: Rotax 914 question?
Date: Tue, 30 Aug 2005 00:07:58 +0100
>
> <ami@mcfadyean.freeserve.co.uk>
>
> OK, I'll bite!
> I cruise at about 4,000rpm. And have done for over 200 hours of use,
> excepting climb-out at 4,800 and the odd spurt to see how fast it will go.
> The plugs are squeaky-clean. The piston crowns are quite clean. There is no
> loss of compression or performance that suggests that the piston rings are
> coked. The engine uses virtually no oil between changes and the oil
> discolouration is mid brown colour at 100 hours.
> Our local Rotax dealer commented flippantly that at these speeds the engine
> would 'last forever'!
>
> Now for the science bit: Engine wear will be a function of loading (all
> other things being equal (for example adequate thermal control, proper
> lubrication and sliding velocities less than 20m/s)). The more load the more
> wear. Gas loads reach a maximum at 4800 rpm. Mechanical loads increase with
> the square of the crank rotational speed. So, these inertial loads will be
> 56% greater at 5,000 rpm than at 4,000 rpm.
>
> However, there is a point where gas loads will be at an optimum and will
> balance some of the inertial loads. That speed is said to be at around 3300
> rpm on a Lycoming. I don't know where it is on a Rotax; someone care to work
> out the maths using a function of BMEP and piston/rod inertias? Or let me
> know what a Rotax piston and rod weighs, plus the length of a rod between
> centres, and I'll do it.
>
>
> Duncan Mcf.
> ----- Original Message -----
> From: "Jim Brown" <acrojim@cfl.rr.com>
> To: <europa-list@matronics.com>
> Subject: Re: Europa-List: Rotax 914 question?
>
>
> >
> > Hi Jim;
> >
> > I wonder if he will post having a bad miss in the engine when the plugs
> > foul
> > during "economy cruise"????
> >
> > Jim Brown
> >
> > Jim Thursby wrote:
> >
> >>
> >> I won't argue with you. You run yours at "economy cruise" rpm's and see
> >> what happens. I never did and never will.
> >>
> >> Jim T
> >>
> >> -----Original Message-----
> >> From: owner-europa-list-server@matronics.com
> >> [mailto:owner-europa-list-server@matronics.com] On Behalf Of Gilles Thesee
> >> To: europa-list@matronics.com
> >> Subject: Re: Europa-List: Rotax 914 question?
> >>
> >> --> <Gilles.Thesee@ac-grenoble.fr>
> >>
> >> Hi Jim,
> >>
> >> Understand your speed point, though running at 80% instead of 75% gives you
> >> only a 2% speed gain. That's hardly an extra 2 knots.
> >> Now, if speed is the main goal and longevity not a problem, why reduce
> >> boost
> >> in descent ? As for the carbon issue, no Rotax 9xx I know of have suffered
> >> of significant deposits.
> >> Now saving fuel is indeed an honourable goal ;-)
> >>
> >> Regards,
> >>
> >> Gilles Thesee
> >> Grenoble, France
> >>
> >> >--> <jthursby@tampabay.rr.com>
> >> >
> >> >Speed. And the 912/914 series longevity is based on 5,000 plus cruise
> >> >rpm's It does NOTHING but save a little fuel running them lower. And
> >> >carbon them up quicker.
> >> >
> >> >
> >> >
> >>
> >> >--> <Gilles.Thesee@ac-grenoble.fr>
> >> >
> >> >
> >> >Those numbers correspond to rather high settings. While the engine may
> >> >run at 100 % continuous, what is the point for a cruise above 75 % ?
> >> >
> >> >
> >> >
> >>
> >
> >
> >
>
>
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