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<< Lancair Builders' Mail List >>
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Erik,
That point was well-taken, but clearly inapplicable to the case in
point.<<
Erik, really, it is *precisely* applicable to the case in point. Please
read on.
The data you presented are from your experiments, with "Case B" using
technology implemented, as I understand it, with a control loop closed on instantaneous
cylinder pressure, which requires some pretty sophisticated computer technology to implement.<<
Ah... no. Not at all. I apologize again for not being more clear. It was
not from any experiment.
This data (Case A and Case B) is from a real standard six cylinder
turbocharged aircraft engine operating with standard magnetos. PRISM not involved at all, other than I was using the cylinder pressure
transducers to measure what is really going on inside the engine. IF you are achieving the same BMEP (on the same
engine) with lower peak pressure, then no argument, the integral of the pressure curve is the same, and longevity will be better. <<
Yes!!! And in fact, that is exactly how you get a standard Lancair IV-P,
or my turbo Bonanza, to operate at 262.5 Hp continuously, in cruise, with
acceptable CHTs, and run for intervals that approach the OEM's wish list
for TBO.
However, the point which, I think, became obscured in the exchange is that
the technology you are marketing is advanced, and definitely not
commonplace. <<
Without PRISM, I do this every day, and so do well over a hundred Bonanzas
flying around with our turbo-normalizing systems.
For a lot of reasons, PRISM will make it much better, but we still
accomplish what I described in the example I posted, every day. In fact,
yesterday, I flew down to Vicksburg and back. Standard Bendix 1200
magnetos. I went down at 31.5" MP and 2500 RPM and 18.3 gph making right at
273 Hp. Came back at 31.5" x 2700 RPM and 20 gph, making right at 298 Hp.
Hottest CHT was 360F. Most assuredly, it was operating at Theta_P-P very
close to Case B, all the way. When that technology (to lower the peak and displace it further past TDC)
is implemented, either by computer magic, or by less complex means, then it certainly provides the opportunity for greater reliability at the same BMEP,
or the same reliability at higher BMEP, or some of both.<<
Yes. Exactly.
(BTW, did I miss your list of heavily-boosted, 175-BMEP, SI engines which
run 3000 hours before needing top end work??) Yes! You did. Re-read the message, it is there, with a short discussion of
the subject. (C-W 3350)
>>... 45" MAP on a crate motor ("no high-tech parts") with 9.0 to 1
calculated CR isn't likely to produce the kind of reliability that I'd fly behind. <<
Well, the proof will be in the test. And I agree, it will be a challenge.
<<<...However, in the context of the use of high powered piston engines for aircraft like the Lancair, a Malibu, or a Mirage, it is MY OPINION...that
the term is often used in an inappropriate and broader than warranted
manner...>>>
Well, thanks for making my point here. The 350-HP TSIO-550 used on the
Lancair and Malibu (not necessarily the same model) ran at about 187 BMEP
for takeoff (350 HP at 2700) and 158 BMEP at 75% cruise (262 HP at 2400 RPM). Now, I consider 158 to be a fairly conservative number, yet many have experienced less than laudable reliability from those engines, yes??<<
Yes... but primarily because of 1) lousy valve/valve guide/seat tolerances
by the OEM; and 2) horribly misguided operating recommendations by the OEM
and almost everyone else which caused the peak cylinder pressures and
associated Theta_P-P to be in the worst possible combination.
Regards, George
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