On Thu, 1 Apr 2004 08:47:15 +0100, Vivian wrote in message <[EMAIL PROTECTED]>:
> > > > Arnt Karlsen wrote > > > > > On Wed, 31 Mar 2004 13:32:39 -0800, Andy wrote in message > > <[EMAIL PROTECTED]>: > > > > > Vivian Meazza wrote: > > > > Thanks for all that: all looks good - the documentation has got > > > > a bit astern of station. Could you explain a bit more about the > > > > "turbo" attribute when used for a supercharger? > > > > > > Actually, the existing turbo-mul implementation is *more* like a > > > supercharger than a real turbo. YASim models the boost as a > > > simply multiplication factor on the input manifold pressure. If > > it's set to > > > 2.0, then the engine sees twice the static pressure, etc... Real > > > turbochargers don't have linear boost-vs-RPM curves, and tend to > > > lag > > > > ..you mean "lead"? On pouring gas, the first thing to happen > > is the extra fuel spins up _only_ the turbo, which then > > "promptly" feeds engine more air etc as soon as that turbo is > > spun up. > > I don't think so. Turbo-lag is well known. The throttle opens, more > fuel goes to the engine, which produces more exhaust gas which then > speeds up the turbo-charger which increases air flow to the engine, > hence the increase in inlet pressure lags the increase in engine rpm. ..for automobiles, I can agree, you "floor it", then it hops. For the geared supercharger, you need to move all the iron around first. ..another thing is the sizing "policy", in the air, you want good cruise performance and good altitude performance, and you don't wanna fry a dump valve if you can design it away. In an automobile, you need that dump valve and a giant turbine to turn that wee compressor, to get that marketing butt kick, and you get away with it because you cruise town at 5% between burnouts. (With stickshift, you don't.) ..for WWII combat planes, I can see compromises coming here. > > ..a geardriven supercharger is geared to the entire engine, > > and moves with the entire engine, and that too has to move > > around faster, before it can feed any more air. > > Whilst that is technically true, the increase in engine rpm brings an > instantaneous increase in supercharger rpm and an instantaneous > increase in output pressure. The only lag is caused in the ducting, > which is usually kept as short as possible. For a supercharger, any > lag can be ignored for practical purposes. ..this "lag" could easily be evaluated graphing rpm and manifold pressure etc against time. > > > (in time) engine power by a little bit. A gear-driven > > supercharger is > > > going to be closer to that ideal. > > > > Andy > > Regards > > Vivian Meazza -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) ...with a number of polar bear hunters in his ancestry... Scenarios always come in sets of three: best case, worst case, and just in case. _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
