On 12/21/2008 09:59 AM, Ron Jensen wrote:
> .... Given the data available in the configuration > file, how do we create values for K and a for all engines from the > smallest engines, like the Rotax582 in the Dragonfly to the Wasp R-5800s > in the DC6? This is newly discussed at http://www.av8n.com/fly/engine.htm I added a passage that says: The area a and the factor K enter only via the combination K a, so we don’t need to know a if we are willing to adjust K. In practice, we adjust K a to get a plausible MAP under known conditions. Real World data indicates that a ΔP of 1.5 inHg is reasonable, corresponding to a MAP of 28.4 inHg (at sea level, full throttle, max revs). Currently FGPiston uses several parameters, including rated power, rated revs, BSFC ... and it has been proposed to add a hard-to-guess Gagg-Farrar loss parameter "C". IMHO adding this easy-to-determine K (and thereby making "C" unnecessary) does not seem like an extravagant increase in complexity. ========= Perhaps I'll be ridiculed again for saying so, but I still think the shaft power is an increasing function of revs, throughout the revs band (*) right up to redline and presumably beyond. Perhaps I should mention that Lycoming thinks so too. I finally got some Lycoming factory data: http://www.av8n.com/fly/engine.htm#fig-o320-power and overlaid it on the model: http://www.av8n.com/fly/engine.htm#fig-x2x-5 Y'all can judge the goodness-of-fit for yourselves. I don't think the current FGPiston model would do a very good job of fitting this RW data. (*) Note I am still talking about a Real World Lycoming O-320 under standard sea-level full-throttle conditions. ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
