[Jsbsim-devel] C-172 Performance

[Jon S B. <js...@ha...>]

Last night I did some performance analysis on the C-172 (using the 
C-172x config file, because I can do scripted testing with that one 
using the autopilot capability). There have been valid questions 
raised about the performance and dynamics of the C-172 model. Several 
people have noticed seemingly too high engine RPM, too fast flight, 
etc.

[ !!NOTE!! : the C-172x is essentially the C-172R aircraft with a test 
autopilot - the C-172P model features several differences which I have 
not yet figured out. I consider the C-172P model currently to be 
questionable.]

One thing that must be stressed, though, is to make sure that the same 
model aircraft with the same selected engine is being chosen when 
making comparisons. The JSBSim C-172R uses the Textron Lycoming 
IO-360-L2A engine, which produces 160 BHP at 2,400 RPM (directly from 
the Cessna web site).

One test that I ran was a takeoff performance test to see how little 
room is needed for takeoff. I set up a test with the throttle at full, 
and the mixture set to 85%. There were no winds, and the runway was at 
sea level. I got this:

Takeoff roll: 886 ft (270 meters)
Over 50' obstacle: 1664 ft. (507 meters)

The Cessna web site specifies this:

Takeoff roll: 945 ft (288 meters)
Over 50' obstacle: 1685 ft. (514 meters)

As you can see, the comparison seems pretty good - the takeoff roll 
over a 50 ft obstacle agrees to within 1.5%.

I'll do further testing this evening. Comments invited.

Jon