Originally Posted by
Sailvi767
I assume you are a non pilot. When you ask a generator to produce electricity it requires power to do so. 500 HP can produce a lot more power than 5 HP. A gas turbine loses about half it’s available power from sea level to 20,000 feet. At some point in a climb the available power usually becomes less than the rated output of the generator. You must reduces electrical output at that point or the gas turbine will either overtemp or be unable to maintain the required RPM resulting in the generator frequency output falling below limits.
You may assume what you want to...
I'm also well aware of the behaviour of gas turbines.
But maybe you missed my point.
If the APU runs on constant RPM it simply means the gas turbine has enough power for the generator.
Yep, at some point the turbine may give up, but the generator doesn't "lose power with altitude" it will trip off.
Look at the #2 graph of Smythe. 90kVA all the way....