If you are still there and interested after all this time:
It doesn't seem like Flightgear is all resource hungry (on some graphics cards / drivers, there are apparently problems with shaders, etc. that can make it very slow). I would suggest checking first that you get good performance without your telnet interface and tuning Flightgear if not.
Secondly, IIRC, depending on what you want, you can use the actual airplane simulation code (for example, JSBSim) if you are only interested in flight dynamics, but not scenery, etc.
Third: if you are on Windows, you can check whether your old version of Microsoft Flight Simulator (for example, FS2004) meets your needs. If you have problems with FlightGear, I think that launching Microsoft FSX (the latest version) is out of the question.
-: , X-Plane , .