Andy Ross wrote:
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:flightgear-devel-
> [EMAIL PROTECTED] On Behalf Of
> Sent: 22 April 2005 15:19
> To: FlightGear developers discussions
> Subject: Re: [Flightgear-devel] YASim turbo/supercharger issues
>
> Vivian Meazza wrote:
> > y = -0.25x3 + 0.15x2 + 1.11x
> >
> > Thinking about the over-speed situation overnight, the Merlin was
> > allowed to go to 3600 rpm for brief periods, and even then damage to
> > the engine was possible. This is a normalised value of 1.2. The K
> > Series will go to 9000 (don't try this on yours - it requires special
> > valve lifters and crankshaft) or 1.28 normalised. The curve shown
> > here:
>
> Yes, but remember that the "normalization" RPM isn't guaranteed to be
> a maximum speed. It might be for your merlin configuration, but I can
> guarantee you (seriously: 100% certainty) that if we include a model
> that goes wacky in some regime, someone will come up with a
> configuration to tickle the bug. This has happened again and again,
> often with your aircraft. :)
That's right, blame me for finding some bugs/features :-), but OK, good
point.
> How about this one instead:
>
> ln(rpm_norm - 1) * (1 / ln(2))
>
> It seems to qualitatively match the curve you posted (is there a
> primary source for that curve?) without the nasty dropoff.
Nope. I did a best fit to good data up to max power, and that was the
outcome. However, it seemed to me to encapsulate the idea of compressor
stall.
> You can
> see how it works, it just translates/scales a logarithm curve to pass
> through the origin and (1,1).
That got me going. Are you trying to calculate the natural log of a negative
number (rpm_norm - 1)? Isn't that a complex number? Did you mean:
ln(rpm_norm + 1) * (1 / ln(2))
^^^
And we can't do 0 rpm can we?
If you do mean this equation then I can certainly live with that. If not,
I'll need to put my thinking cap on ... I've updated the graphical
representation here:
http://myweb.tiscali.co.uk/vmeazza/FlightGear/supercharge.pdf
Let's go with that for now. Meanwhile, I've just done the boost control
cutout. Trivial, I'll let you have the diff once you've done this one.
Thanks again
Vivian
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