> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:flightgear-devel-
> [EMAIL PROTECTED] On Behalf Of Arnt Karlsen
> Sent: 23 April 2005 22:02
> To: FlightGear developers discussions
> Subject: Re: [Flightgear-devel] YASim turbo/supercharger issues
> On Sat, 23 Apr 2005 20:02:48 +0100, Vivian wrote in message
> <[EMAIL PROTECTED]>:
> > Arnt Karlsen wrote:
> > >
> > > > Andy Ross wrote
> > > >
> > > > >
> > > > > Drew wrote:
> > > > > > IMHO, it's best to use interpolation tables rather than
> > > > > > equations if you're trying to curve fit empirical data.
> > > > >
> > > > > Not in this context. The data here isn't being used to model a
> > > > > specific engine, but to provide sane parameters for all
> > > > > (super/turbochared) engines. The performance and code size
> > > > > advantages of an equation here are significant.
> > > >
> > > > At the moment we are looking at gear driven centrifugal
> > > > compressors. Although I haven't researched it in any detail, the
> > > > output of turbo-driven centrifugal compressors do not have a
> > > > direct relationship with rpm (turbo lag), and the situation is
> > > > complicated by the wastegate which operates on the turbo rather
> > > > than the compressor. I suspect that this is another black art!
> > > > Gear driven is easy in comparison. When someone comes up with a
> > > > turbo we may have to have separate models.
> > >
> > > ..if your supercharger code takes shaft input (shaft speed, torque
> > > or power), then it can be re-used in the turbocharger's compressor
> > > code.
> > It doesn't because a gear driven compressor has a fixed relationship
> > to engine rpm, and I deal with 2 speed superchargers separately, but
> > you are right: a centrifugal compressor neither knows nor cares if it
> > is gear- or turbo-driven.
> > > ..the turbocharger's compressor or turbo-compound engine's
> > > crankshaft then only needs a turbine derivering shaft outnput (shaft
> > > speed, torque or power) to the compressor or gear box.
> > >
> > Now, if we knew what the turbo rpm was for a given engine rpm,
> .._not_ gonna happen. Turbo rpm will always, always, always be a
> function of the exhaust gas pressures piped in and out, and, the
> turbines own shaft loads, temperature, mass, and time.
> ..just think of any water wheel, or power turbine, to do the power
> turbine code part of the turbo. Then you can saw the gear box off the
> supercharger shaft and weld that stub onto the power turbine to make
> a turbocharger. ;o)
> > and I think we need throttle opening ... any guidance welcome.
> ..just like in the supercharger code. Now, keep in mind, the power
> turbine _only_ sees exhaust gas pressures and temperatures piped
> in and out and its own mass and inertia, time and the shaft and
> bearing and lube film loads.
> ..the compressor on the _other_ end of that turbo shaft, will see the
> _same_ as the supercharger, except for the power turbine replacing
> the gear box.
> ..exhaust gas pressures and temperatures vary, think pulses, spikes,
> waste gates and even exhaust throttles, if you wanna model a new
> fancy way of blowing up a model engine in that spectacular way
> I read about in some model magazine some 20 years back. ;o)
Or TFD - I'll think about it later (much later :-).
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