Well, you are right about the boost gauge, it doesn't go near max normally. There is an easy way to tell if you are getting maximum throttle. If you engage War Emergency Power (WEP) and it works, you have full throttle. WEP will only engage (on planes that have it, most fighters do) if the throttle is full open. If you can hit the P key at full throttle and see your boost and hear your engine increase with WEP, you are getting full throttle.
RPM is the speed of the propeller. Aces High has somewhat of a simplified engine and propeller management system, so the RPM gets automatically adjusted with the throttle setting. You can adjust engine RPM separately by using your keypad + and - keys. Normally you don't need to muck with setting RPM manually at all. If you are trying to milk the maximum fuel economy from your engine, you may want to decrease RPM's as well as throttle. Honestly though, that seems to make little difference, and I get just as good a result by simply decreasing throttle to save gas.
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Sean "Lephturn" Conrad - Aces High Chief Trainer
A proud member of the mighty Flying Pigs
http://www.flyingpigs.comCheck out
Lephturn's Aerodrome for AH articles and training info!