Andy Ross wrote: > Vivian Meazza wrote: > > The attached diff models the output of a gear-driven > > supercharger. I've used a 3rd order polynomial which matches the few > > examples I have been able to find, giving near-linear output up to the > > max-power rpm of the engine, with a little tail-off below this point, > > and a larger one above. More importantly, it produces realistic > > results. > > Cool. Can you resend the patch as a "cvs diff -uw" output for > readability, and remove the unrelated changes? Are there any sources > for the curve you are fitting to? I'm not completely unwilling to > stick magic numbers into the source code where they produce acceptable > behavior; I just want to put a comment in explaining where the blame > lies. :) >

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Well, first I thought of using some real maths based on this lot: http://www.teknett.com/pwp/drmayf/turbocal.htm Then I found this: http://www.turbotechnics.com/supercharger/expo.htm The supercharger described is a smaller (much) version of that fitted to the Merlin, but it has the same arrangement of throttle ahead of the compressor. I'm very familiar with the engine - it is the same as the one in my track car (un-supercharged). The supercharger output described is pretty much linear up to the maximum rpm at 7000 rpm. It tails off a bit before that. I reasoned that the Rolls Royce engineers would have gone for pretty much the same output shape. I also wanted to take into account the surge boundary for later use when we model the so-called 'boost control cut-out' so I added a more rapid fall-off in output beyond the maximum power rpm. I did some curve matching, and came up with a suitable 3rd order polynomial. It's a very good fit up to max power; thereafter ... I'll look into that issue later in the context of the boost control cut-out. It probably doesn't matter too much. Not too much magic in the numbers. As to the throttle equation - it's a hack but it works - the P51d and the Hurricane are easier to land. This is pure voodoo except that 750-850 rpm seems to be the chosen idle speed for most piston engines. Big - slower, small - faster. I'd like to do better. It might be possible to put a lower limit on omega in PropEngine.cxx. Meanwhile, I attach a revised diff using -u - w. Hope this all makes sense Regards Vivian

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YASim.diff**

*Description:* Binary data

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