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Posted for "D.R. Smith" <timepilot@earthlink.net>:
Marvin Kaye wrote:
[When I first decided to use a 13B in my airplane I put together my "short"
list of priorities... #1 was reliability, #2 was power, #3 was reliability, #4
was economy, and #5 was reliability. Given the recurring theme, I decided
early in my turbo planning to limit boost to an extremely conservative number.
Since most of the turbo guys talk boost in PSI and after hearing numbers for
max boost that went anywhere from 7psi to 12psi and beyond, and since each psi
is about equal to 2"hg I figured on a standard SL day with the ambient
pressure around 30" that conservatively boosting to 2psi (or 34" MAP) would
preclude the possibility of overstressing the insides and fit well with my
reliability criteria. Even if I go to 15k ft and demand another 7.5psi of
boost to maintain my full power MAP of 34", that's all the MAP the engine will
be seeing and that's just fine with me.
I like the way you think about limiting your MAP by boosting as necessary to
maintain @ 4 " over sea level std. of 29.92 ... but perhaps you are being way too
conservative.
If you think of pressures in terms of atmospheres ... (1 atmosphere = 14.7 PSI =
30 in of Hg.) ... your 4" only works out to be a little more than one eighth of an
atmosphere.
The primary cause of turbo failure in the piston world ... & their bad
reliability reputation ... is their shedding exhaust valves into the turbo intake,
and the pieces lunching it out. We have no such worries. Rotaries are ideally
suited to turbocharging by virtue of their high energy exhaust that must be tamed
(muffled) somehow anyway, and their lack of valves (nothing to "swallow" when it
breaks).
Since we don't need to baby a weak part, half an atmosphere is nothing to these
engines. In my opinion, it would still be a very conservative boost. Maybe even
10 PSI for a take off power setting ... reduce to 7 once airborne, clean and
climbing.
I'm also a "belt and suspenders" kind of guy about reliability ... without it,
there is nothing else ... but why limit yourself needlessly?
Dale Smith
[I agree with your assessment about these engines' capabilities to withstand much higher levels of boost, but along with all that extra oomph also comes added heat load. I'll be starting out with the installation normally aspirated to prove out all the basic systems and to test the ability of my cooling system to shed the heat. If I discover that I have excess cooling capacity (yeah, right... who does that first time out of the gate? <g>) then I'll go ahead and add the turbo. If I'm still able to keep things cool, even at altitude where the cooling system is at a major disadvantage, then I probably would go ahead and, uh, boost my boost <g>. I'm as power hungry as the next guy, but I'd prefer to approach getting it in a reasonable fashion. Besides, the volume under a Lancair 360 cowl is pretty sparse, so getting the turbo inside there at all is going to be a trick... cooling might not be my only problem.
<Marv> ]
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