Re: 747 & 4cyls

[Garfield Willis <garwillis@msn.com>]

On Tue, 22 Aug 2000 13:29:48 -0400, "Bruce Plecan" <nacelp@bright.net>
wrote:

>There's a problem here.
>The TBI is gonna want to fire the injectors per the factories strategy and
>that is based on P+H injectors which can operate jus fine at about 1/2 the
>pulse width of a Sat one.
>So that is a big glitch.

I see; I'd forgotten that 747 was TBI only. I thot it had a TPI mode,
and that in TPI mode, you had one driver driving a gang of SATs; score
one more for altzheimer's I guess. At least I think there are SOME GM
ecms like that, ain't there?

>Other thing is MAP is going to be all important on this. (MAF is way too
>unreliable for aero use, IMO)

Oh yes, we're definitely going MAP, so no need to worry or factor in a
possible MAF into the equation; idn't gonna happen. Besides the
restriction and reliability issues, it's also a no-go if we wanted a
redundant pair of MAF sensors. Ick.

>Forgot to ask, DIS or Distributor?

DIS generally. The smallest engine in the family has a dizzy hole &
gear, and there's a retrofit to run an Escort dizzy (which would be
dual'd; pickups, modules & coils--for IGN redundancy) off one of the
OH cams, on the next engine up in size (which is what Andy's working
on), but for generality across the whole family, just assume we're
goin crank-fired.

>Haven't been ignoring thread just got hot irons everywhere, and been tip
>toeing around tryin not to get burnt...

Hey, no problem; when yer hot, yer hot. :)  And when yer busy, yer
usually buzzie, too. That's life in the GN fast lane, I guess. :)
How's black beauty doin, BTW. Are you finished with the main organ
transplants?

>Injector sizing may be an issue to.
>
>Have you taken a gm MAP sensor aloft and recorded the output with a 5v
>source / ground, might need to know rather early how this looks.

No need, they've been used in aircraft apps before. They be fine.
Geez, Bruce, we're not going into space with this stuff, just up to
12k ft. max (for VFR flight, anyway)!

>While a stock engine might idle at 40 K/Pa at sealevel, and reach 96 out of
>98 K/Pa at WOT, what is ambient K/Pa at altitude
>
>This is something where you might just want to get a full time baro input,
>and that would have to be with Johns 730 stuff.
>   The more I think about it the Baro is probably gonna be a mandatory item,
>or you'll be futzin with the AFR all the time.

Eat yer hearts out, you land-lubbers. This is one of the niceties of
the aircraft engine playground. Except for the VE errors caused by the
exhaust dumping into a different ambient than MSL, the MAP is good
enough for first-order alt. compensation inherently. At 10k ft. we're
used to making a max of 70% power at WOT. The OL fueling tables will
be close enough, AND your error is on the rich side also, so no
problemo. Since without an O2 sensor, we just about HAVE to have some
kind of manual mix control, and that with wide enough AFR authority to
cover cold-start enrichment levels too, those same manual controls are
more than able to be used to compensate for altitude effects, given
the inherent compensation from MAP-based fueling to begin with. This
is already/currently soup de jour in XA engines, sotaspeak.

Until unleaded Avgas comes to the fore, just assume we'll be using the
normal/everyday EGT and a manual tweak of AFR at cruise anyway. And
also no2worry re the "futzin"; remember an airplane's normal regime is
to climb to cruise altitude under 75-100% power (which assumes PE/OL),
level off, and then throttle back and tweak AFR for economy via EGT.
That's why I said "eat yer heart out"; with NO rapid or frequent
throttle excursions, the minimal "futzin" you mention is already a
normal part of a pilot's climb2cruise scenario, since the carb's in
use all have manual mix control anyway.

Point being it's already a demonstrated fact via carbs and other
custom manual-mix EFI systems out there, that OL in the ecm, along
with a manual AFR tweak, is perfectly workable and more than
acceptable to current pilots. But it's good to bring up all these
issues just in case we missed something on the way to the forum.

Gar


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