I don’t understand how MSFS is calculating the dynamic pressure. As a result,
it is difficult to match sim values of lift and drag. As you know, dynamic
pressure is simply 1/2ρVtrue2. For Imperial units, ρ would be in slugs/ft3 and
Vtrue in ft/sec. As you can see from the following screenshot, both SimVar
watcher and the dev speed debug window in MSFS show that for an airspeed of
154 KCAS at 3000 ft AMSL, the true airspeed is 160.87 kts (271.523 ft/sec) and
the ambient density is 0.002175 slugs/ft3. Plugging these values into the
above equation, dynamic pressure = 80.2 lb/ft2. However, for this condition
MSFS shows a dynamic pressure (as shown in SimVar watcher and the speed debug
window) of 81.4 lb/ft2. Where is this difference coming from (that is, how is
MSFS calculating the dynamic pressure)? Thanks,
Don
Hello @donstim The formula we use to compute the dynamic pressure is the one
you described. The discrepancy you’re seeing comes from the fact the dynamic
pressure is computed on multiple positions on the aircraft and the one we
output in the simvar and debug panel is the one at the center of the aircraft,
where the pitot usually is. As the air speed is changing the lot across the
aircraft surfaces (propwash, turbulences, etc…), the dynamic pressure
changes a lot too. We will add a second measure of the dynamic pressure on the
left wing tip in the debug view. And we will also consider adding parameters
to configure the position of static and dynamic pressure probes. Edit: In
addition, try to avoid making your measure while the game is paused as it can
invalidate some of the debug data. Regards, Sylvain