Aircraft engine EFI

[Jeremy Harris]

Don, Paul, Bernd, Bruce, Dave, Alvaro, Bill,

Many thanks for the input, all much appreciated.

Bernd, the glide ratio is pretty good, this is a very light a/c, 450kg MAUW.
It is to be flown on a Permit to Fly here in the UK as a homebuilt, which
means no aerobatics or inverted flight.  Also I can't (due to the terrain
and airspace limitations here) go much over 4000 to 5000ft, hence my lack of
concern about altitude compensation.  There are a lot of people fluying
around here with slide type carbs that have no altitude compensation and
they work fine.

Dave, I accept that the weight difference over twin carbs is probably not
that much of an issue, but C of G is.  Ideally I would like to shift some
weight rearwards, if thats the EFI pump and ECU then that would help.

I had pondered about redundancy, but I know that this engine does not
deliver enough power to sustain flight if one carb fails (a friend flys an
Avid Speedwing fitted with a BMW engine and he had one carb ice up just
after take off).

I had wondered about fitting two injectors to a single throttle body feeding
both cylinders, with two really simple ECU's and injector drives and an
arbitration system (or manual change over switch) to select which
ECU/injector to use.  Looking at the MTBF of injection systems and their
components, I'm not convinced yet that the redundancy argument really stacks
up (although I do have dual independently Hall effect triggered ignition
systems, because the "rules" here say I have to).

Bruce, thanks for the advice about icing, I hadn't realised that it could
affect EFI systems as well as carbs.  I can easily couple the throttle
body/intake runners to the oil sump on the BMW engine, so could arrange
enough heat transfer to relieve this potential problem I think.

Alvaro,  Thanks for the heads up on the Haltech F9/F9A, I'll take a look at
it.

Bill,  I think that your thinking is aligned more with mine.  The limited
range of operating conditions is exactly what started me thinking about a
simple EFI system.  I was actaully stripping and rebuilding the Bing CV
carbs and looking at all the relatively complex bits on them that I didn't
need.  It just started me thinking about ways to make a really simple
fuelling system, and being of an electronic ilk, EFI sort of floated to the
surface as an option to look at.

Thanks again everyone, I'll post some details of my first experiments with
the "minimum EFI" system (s)!

Jeremy


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