On 12/20/2008 10:39 PM, Ron Jensen wrote: > Here is a dynamometer test report of an engine intended for use in an > aircraft: > http://members.cox.net/alg3/Dynamometer%20test%20report.htm
Ah, good, that's useful data. > Please note especially the RPM v. Manifold Pressure chart at the end: > http://members.cox.net/alg3/Dynamometer%20test%20report_files/image005.jpg > The shape of this curve is the reverse of the curves you've postulated > in your figure 3. It also remains above 28 inHg to nearly 5000 RPM. > Your proposed model appears unable to duplicate this feat, as your full > throttle line is below 0.94 (28 inHg / 29.92 inHg) MAP by 0.07 RPM. Then you may like these MAP (and power) curves better: http://www.av8n.com/fly/engine.htm The MAP curves stay higher longer ... and they are even concave down over part of the range, which makes them look more like the curves at that "alg3" site. The analysis runs parallel to yesterday's analysis, except that I used a smarter model of the throttle, namely a nonlinear "orifice plate" model. This is more plausible physics and generates nicer-looking curves IMHO. > While we're at it, please consider this dyno picture > http://aagearinc.com/supercharged_na.gif > Yes, its a motorcycle engine not an aircraft engine, but both function > according to the same principles and studying one will lead to > understanding of both. > The red line is a normally aspirated engine. You can clearly see the > power peak and fall off. OTOH please note the power output at the "alg3" site. The power is a monotone increasing function of revs ... indeed a strongly increasing function of revs ... something that the physics model has been predicting would happen under *some* conditions ... but heretofore has been, ummm, unappreciated, to put it politely. > The blue line is the same engine with boost. It produces linear power > to the top of the RPM run because it can breathe. Let's not pick-and-choose the data. You can't point to the alg3 data and say "the" MAP must remain high and then point to the motorcycle data and say "the" engine can't breathe. Feel free to model one *or* the other. Feel free to switch from one model to the other, if you switch cleanly. But it doesn't make sense to ride both horses at the same time. ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
