Aero Chapter 02, High-Speed Flight
T-45 Aerodynamics Student Workbook
WING SWEEP
With greatest advantages in the transonic regime, sweepback will delay the onset of all compressibility
effects and delay the onset of Mcrit and the force divergence Mach number. The peak of drag rise will
occur later, and maneuverability in transonic flight is preserved. Swept wings reduce the aspect ratio,
frontal area, and parasite drag which allows higher speed flight. The low aspect ratio swept wing
increases induced drag.
A means of achieving thin wing characteristics while using a thicker section is with wing sweep. Figure 30
illustrates how wing sweep “fools” the air into thinking the wing is of a thin airfoil section. The airflow over
the swept wing “sees” a longer chord length than actual chord length or the chord of an equivalent straight
CD
P
STRAIGHT WING
SWEPT WING
V
STRAIGHT WING
SWEPT WING
Flow Over
Wing
Spanwise Flow
Flow Producing Lift
Figure 30: EFFECT OF WING SWEEP ON HIGH-SPEED AIRFLOW
wing and would have a reduced thickness-to-chord ratio. Figure 30 also illustrates the effect of vectoring
airflow. Only the component of the airflow acting perpendicular to the leading edge contributes to
compressibility effects. The
spanwise component does not.
Note that the perpendicular
0
SWEEP ANGLE, Λ
component of the airflow is of a
30
lower velocity than the free
DRAG
airstream component. Figure 31 is
45
COEFFICIENT
based on the “wing of infinite length”
60
CD
theory but adequately illustrates the
effect of wing sweep on reducing
the peak drag rise and delaying the
0
1.0
2.0
3.0
critical Mach number to a higher
MACH NUMBER, M
Mach number. The T-45 has 23.7
of wing sweep at 25% MAC and the
Figure 31: EFFECT OF WING SWEEP ON DRAG
stabilator has 30.1 of sweep.
(7-99) Original
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