David Luff: Here is an update to the engine model. It now takes

David Luff:  Here is an update to the engine model.  It now takes
the actual air pressure and temperature from the LaRCSim model
instead of assuming that it is at sea level as before.  This has
reduced the ceiling from over 60000 ft to about 9000 ft.  This is a bit
low (should be around 13 - 14000 ft I think) but I still have some
stuff to do with the engine power correlation and its ignoring the
temperature at the moment so I'm not panicking yet :-)

I've also changed the mixture-power correlation to one from a
published paper since the curve from the IO360 manual seemed to
be a load of rubbish, and didn't have any numbers on the mixture
axis anyway.

I've also knocked the full rich mixture down a touch in line with
Riley Rainey's recommendation, and cleaned up the code a bit.