by D-EKEW » Wed Nov 02, 2016 12:14 pm
Actually that is wrong.
q_bar is the dynamic pressure, which is used to calculate aerodynamic forces and moments from aerodynamic coefficients.
Impact pressure (q_c) is the pressure when you substract the static pressure from the total pressure. It is used for calculating the Indicated Airspeed.
If you assume that air is incompressable and isentropic (thus Bernoulli is correct), these would be the same. But as you fly faster, the difference gets larger and larger and cannot be neglected anymore.
Cheers,
Eric