From: John D. <js...@av...> - 2008-12-14 19:56:57
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On 12/13/2008 06:16 PM, Jon S. Berndt wrote: > The manual should allow some fairly thorough testing. OK, good. I reckon thorough testing would be helpful. As several others have mentioned, before delving too deeply into the Cessna-specific details, it might be worthwhile to vet the engine and prop models. Here are some specific hints about where to look: 1) Under standard sea-level conditions, I observe the c172p model (from rc2) developing 120% of its rated power at _zero_ kias. That is peculiar, to say the least. Usually the static power is significantly less than the rated power ... not more. 2a) I observe the engine putting out 90% of its rated power at 60 kias at 10,000 feet. Based on my experience, that seems "optimistic" to say the least. http://www.av8n.com/fly/fgfs/engine-power.png It is also "optimistic" for the engine to put out more than 100% of its rated RPM at 10,000 feet at modest airspeeds. 2b) Also I observe a trend: At 10,000 feet, as the airspeed goes down, the engine rotation rate goes down (as expected) but the shaft power output goes _up_. http://www.av8n.com/fly/fgfs/engine-power.png This power trend is not only unexpected based on experience, it defies the laws of physics as I understand them. How can the engine produce more power at less RPM and constant manifold pressure? I suspect these engine anomalies are /masking/ various anomalies in the aircraft FDM. So, ironically, fixing the engine will make some things look worse in the short run. Sometimes exposing a bug is the best way to start fixing it. |