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>
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:
>
>> <jthursby@tampabay.rr.com>
>>
>> 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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