Scribd
Upload
349 views43 pages

Reducing Wave Drag

This document discusses various techniques to reduce wave drag for aircraft flying at transonic and supersonic speeds, including: using thinner airfoils with sharp leading edges; applying area ruling to smooth cross-sectional changes; sweeping wing leading edges; and exploiting compression lift at high supersonic speeds above Mach 3. Key aircraft like the Bell X-1, F-104, and B-70 Valkyrie demonstrate the application of these techniques to achieve high speed flight. There are always tradeoffs to consider for any wave drag reduction method.

Uploaded by

JaredSagaga
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
349 views43 pages

Reducing Wave Drag

This document discusses various techniques to reduce wave drag for aircraft flying at transonic and supersonic speeds, including: using thinner airfoils with sharp leading edges; applying area ruling to smooth cross-sectional changes; sweeping wing leading edges; and exploiting compression lift at high supersonic speeds above Mach 3. Key aircraft like the Bell X-1, F-104, and B-70 Valkyrie demonstrate the application of these techniques to achieve high speed flight. There are always tradeoffs to consider for any wave drag reduction method.

Uploaded by

JaredSagaga
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 43

Techniques to Reduce Wave Drag

AE 164

Drag Divergence
Mcr = Critical Mach number.
The freestream Mach number
where sonic flow is first obtained
at some point on the surface of a
body.
MDD = Drag-divergence Mach
number. The freestream Mach
number where the drag
coefficient begins to rise
dramatically.

Critical Mach Number

Drag Divergence
Some people used to
believe the speed of sound
could not be exceeded
because it appeared that
drag would increase to
infinity at the speed of
sound, hence the term
sound barrier.
Airliners fly at the dragdivergence Mach number
for fuel economy reasons.

Low Mach Number Airfoil Shape

Supersonic Airfoil Shape


Biconvex airfoil

For supersonic flight, we want airfoils to have:


Sharp leading edge (weaker shocks)
Thin maximum thickness (weaker shocks)

Supersonic Airfoil Shape

http://www.dept.aoe.vt.edu/~devenpor/aoe3114/16%20-%20Airfoil%20Analysis.pdf

Thickness

Bell X-1
Wing airfoil thickness = 8%
Tail airfoil thickness = 6%
Tail airfoil delayed center of pressure shift due to shocks,
providing more control up to higher Mach numbers.

Fuselage modeled after a 0.50 caliber bullet

Supercritical Airfoil

Supercritical Airfoil
As far as I am aware, all
aircraft have a maximum
CD at Mach 1, and CD
decreases after Mach 1.

Area Rule
The area rule for Mach 1: The cross-sectional area distribution should be as
smooth as possible along the longitudinal axis of the body.

Area Rule

Sears-Hack Body
The Sears-Hack body has the ideal
area distribution for Mach 1

Area Rule

F-102

F-102A

Area Rule

X-3 Stiletto

X-3 Stiletto

X-3 Stiletto

Supersonic Area Rule


The area rule is different for
different Mach numbers.

The cross-sectional areas must be


cut at an angle equal to the Mach
angle ( = sin-1 (1/M) ). If the
Mach angle is NOT 90 degrees,
the area distribution will be
different at different roll angles of
the aircraft. This means the area
distribution must be calculated
over 360 degrees of roll and
averaged.

Forward Swept Wing (X-29)

Oblique Wing

Oblique Wing

Oblique Wing

F-104 (or how to go fast without using


wing sweep)

F-104

F-104 is outlier using


thin wing with little sweep

Swept Wing

Swept Wing

Mnormal = M cos LE

Swept Wing
LE

The wing cross section


(airfoil) perpendicular to
the leading edge of a
swept wing is what
matters for the
aerodynamics of the
wing, not the streamwise
cross section.

Swept Wing

Swept Wing

Swept Wing

Swept Wing

Compression Lift
Compression lift uses
the shocks produced
by the body to
enhance lift.

At high Mach numbers


(3+), the shocks are
close to the body. The
pressure is higher
behind the shocks, so
increasing the bottom
surface area
downstream of the
shocks increases lift.
This is the principle
behind waveriders.

B-70 Valkyrie

B-70 Wingtip Folding

B-70 Inlet

B-70 Nose

B-70 Inlet

B-70 Valkyrie

Summary
Can reduce wave drag by:

Thinner Airfoil
Sharp Leading Edge
Supercritical Airfoil (0.75 < M < 0.95)
Area Ruling Entire Airplane
Sweep Wing Leading Edge
Combinations of the above
Compression lift (if high Mach > 3)

There are major tradeoffs for each of these


choices

You might also like