Re: [Jsbsim-devel] C-172 Performance

[David M. <dav...@gm...>]

On Tue, 12 Oct 2004 10:17:03 -0500, Jon S Berndt <js...@ha...> wrote:

> [ !!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.]

The 172r has had very little user testing in the last few years, while
the 172p is the default aircraft in FlightGear.  Also, relatively few
pilots have experience on the 172r, while the 172n and 172p are
pretty-much ubiquitious at flight schools and FBOs.  I have not tested
the 172p systematically around the edges of its envelope for a year or
two, but in normal flight regimes it performs very realistically -- I
just finished a partial-panel non-precision approach to minima using
it.

What parts of the 172p flight model are you uncomfortable with?

> 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)

You need to control a few other parameters to make this useful. 
First, you need to make sure that the temperature is ISA (which
FlightGear will give you by default).  Second, you need to make sure
the plane is loaded up to maximum gross weight.  Third, you need to
use proper short field takeoff technique.  I suspect that you used a
very light plane but didn't use short field technique, so the two
cancelled each-other out.


All the best,


David

-- 
http://www.megginson.com/