Transonic Compressibility Drag

This section deals with the effect of Mach number on drag from subsonic speeds through transonic speeds. We concentrate on some of the basic physics of compressible flow in order to estimate the incremental drag associated with Mach number.

The chapter is divided into the following sections:

Introduction
Predicting M_div and M_cc
3-D Effects and Sweep
Predicting C_Dc

Notation for this chapter:

C_L Airplane lift coefficient

DC_{D_c} Incremental drag coefficient due to compressibility

M_cc Crest critical Mach number, the flight Mach number at which the velocities at the crest of the wing in a direction normal to the isobars becomes sonic

M₀ The flight Mach number

b Prandtl-Glauert Factor (1-M₀)^1/2

t/c Average thickness to chord ratio, in the freestream direction, for the exposed part of the wing

V₀ The flight speed

DV Surface perturbation velocity

L_c/4 Wing quarter-chord sweepback angle, degrees

L_c Sweepback angle of isobars at wing crest, degrees

g Ratio of specific heats, 1.40 for air.

C_L	Airplane lift coefficient
DC_{D_c}	Incremental drag coefficient due to compressibility
M_cc	Crest critical Mach number, the flight Mach number at which the velocities at the crest of the wing in a direction normal to the isobars becomes sonic
M₀	The flight Mach number
b	Prandtl-Glauert Factor (1-M₀)^1/2
t/c	Average thickness to chord ratio, in the freestream direction, for the exposed part of the wing
V₀	The flight speed
DV	Surface perturbation velocity
L_c/4	Wing quarter-chord sweepback angle, degrees
L_c	Sweepback angle of isobars at wing crest, degrees
g	Ratio of specific heats, 1.40 for air.