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L/D glide speed

T

tomerh

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118
Country
israel
Hi

I tried to fix default cessna 172 air (and cfg) files.
now I focus best glide speed: 68 KIAS.

I tried to glide from 1000ft in 80, 68, 60 KIAS, and the resaults I got is:

60 KIAS = 1.73 NM
68 KIAS = 1.78 NM
80 KIAS = 1.76 NM

so 68 KIAS is the best glide speed but the defferent between 68 and 80, 60 is not strong enough.

My question is how can I increase the different in glide range at speeds far from best glide speed without to harm other performance values.

the same question about VX and VY speeds

Thanks

Tomer
 
You need to make a drag polar that outputs the results you want. The drag polar is simply a plot combining all of the drag coefficients from induced drag, parasite drag, and compression drag vs CL. You will need to add a dimension for flap, gear, and windmilling drag; and anything else that causes drag on your gliding airplane.

Once you have done that, you can use dynamic pressure to find mach and drag for any condition you want.

You would then enter the data into the appropriate fields in the airfile and FS will output performance correctly in the sim.
 
examples of drag polars... These are done against CL. Yours can be against airspeed if you wish as long as the test conditions are limited to that same altitude and weather that you've plotted.

Also, remember drag increases with temperature, so your drag polar must be plotted at a given temperature, and the tests in the sim should be done at the same temperature.


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thanks!

can you please tell me which table in AIR file should I modify to make minimum drag at 68 KIAS ?
 
you have to set each drag separately.

CDp should include all types of drag that apply to your aircraft based on airspeed. This is set in the drag section labeled CDo.

Cdi should include all types of drag that apply to your aircraft based on lift. This is set by the CL lift table.

Cdg should include all landing gear drag. This is set in the drag section labeled CDg.

Windmilling drag for jets is set using the Airflow Factor table or thrust table.

I don't remember where to set drag for a windmilling prop. There is a field to do it but it's been years since I've worked on a prop file.



To find all the aforementioned tables and understand how to use them, do a Google search for "Flight Dynamics in MSFS By Yves Guillaume"


He provides a good outline and explanation of the tables.
 
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