Dave,
The Factory BMW indeed did not have two of everything, except that it did
have two independent power supplies (battery and alternator) and two fuel
pumps.
The failure rate of a single ECU (once past the "burn-in" period) is not
dissimilar to the failure rate of TWO magnetos together (the old type with
miles of frantically spinning wire).but it would be difficult to argue that
efi is significantly more reliable than carbs.
Fuel efficiency of efi (in the automotive world) is reckoned to be about 15%
better than carbs., but the use of efi on cars is driven more by meeting
emission targets than by economy or power.
However, the primary requirement of an aero engine is reliability (ahead of
economy, power, lightness etc).
Different props would make no difference as most efi systems operate on the
alpha-n principle, which effectively measures engine load.
The technology already exists for providing automatic detection and
adjustment for different fuels and most efi ECUs have spare capacity for
additional maps; it would be a 'simple' matter to include this.
As regards the efi offering for the Rotax, my view is that the injection
would work reasonably well. But I don't think I'd want to be trying it on a
914, which is already "boosted" in terms of power and has probably too many
additional variables for the simple EFI control system shown.
It's a pity that the offered system misses an opportunity to sort out the
poor distribution characteristics of the stock inlet manifolds. The use of
the stock manifolds is firstly likely to wrong-foot the batch-fired EFI
injectors into providing uneven fuelling (or in other words a compromise
mixture set-up that will have to be richer than it could have been, and
therefore give away some of the likely efficiency gains) and secondly there
is power to be had in shorter lengths of independent manifolding all meeting
together in a common plenum located centrally on the top of the engine (see
Honda Goldwing, from which the 912 design probably borrowed heavily),
although the 'tame' valve timing on the 912 does not make the engine
'pipe-sensitive'.
Note also that the earlier 912s had alternate drilled and tapped bolt holes
at the cylinder head inlet manifold face that would allow such an
orientation of inlet manifold.
By the way, it was the same "starting problem" as experienced on some 912S's
that was the principal reason for the demise of the BMW project!
Rgds.,
Duncan McF.
----- Original Message -----
From: "david MILNER" <dave@wmilner.fsnet.co.uk>
Subject: Re: Europa-List: Fuel Injected Rotaxs
> <dave@wmilner.fsnet.co.uk>
>
> Terry & Karl
> I seem to recall that the factory were developing a BMW fuel injected
> engine
> conversion for the Europa, I doubt if it had the luxury of
> 2 of everything (ecu, injectors etc), but had it proved succesful I am
> sure
> many would be flying today.
> It seems the fear of the unknown is part of the objection or scepticism of
> fuel& ignition control by an ECU
> 1) Reliability, Millions of cars operate without redundancy of the system
> just as your Rotax does
> 2) Efficiency, Variable ignition timing, fuel supply, altitude
> compensation
> & temperature compensation according to prevailing conditions.
> 3) Problems, Different maps for the ECU would be required for different
> fuels and I suspect different props
>
> It's certain that fuel efficiency would improve as would starting as there
> is a seperate map for starting and warm-up, altitude compensation would be
> no problem as the MAP sensor can handle from absolute vacuum to plus 2 or
> 3
> bar.
> Even using a compromise map in the ECU would show considerable improvement
> over " carbs and fixed ignition"
>
> I am not saying the company you are talking about is the one with all the
> answers just that ECU controlled ignition and fuelling is the way to go
> for
> efficiency and
> reliability.
> Regards
> Dave Milner
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