Ken,
The answers to your questions would constitute at least a one-semester
course when I was in college. I'll try to make it a "short course".
As an aircraft reaches the speed of sound, Mach 1.0, the resulting
shock, or compression wave, is nearly vertical, and the wave drag is
near its maximum. You've probably seen some of the popular photos of
aircraft with the front half encased in a condensation wave. As the
speed is increased further, the compression wave sweeps back in
accordance with the Mach angle relationship. I can't locate NACA Report
1135 right now, but here is an on-line reference to the relationships:
https://www.grc.nasa.gov/www/k-12/airplane/machang.html
A quick example shows that, while the Mach 1.0 shock is vertical, or 90
degrees, by the time a supersonic aircraft reaches Mach 2.2, the shock
angle has decreased to 27 degrees, and the wave drag is much less.
Wave drag IS sensitive to body shape, as you would imagine. NACA did a
lot of work in the 1940s to develop optimized shapes. Their famous
"Coke bottle" fuselage shape was an effort to smooth out the volume of
the aircraft from front to back, so the fuselage diameter was reduced in
the wing attachment area to compensate for the volume of the wing. Here
is a reference to Whitcomb's famous area rule:
https://en.wikipedia.org/wiki/Area_rule
Jet engine inlets are also sensitive to Mach angle, and must be designed
with a chosen Mach number in mind, or must include variable geometry to
control the shock position. The inlets of the F-111 and the XB-1 are
good examples of this.
I hope this answers at least some of your questions.
Jim Nichols
Tullahoma, TN USA
On 12/16/2016 9:05 AM, Ken Norton wrote:
Jim, Does the creation of a sonic boom contribute to an increase in
drag? Or is it a reduction? Or does it drag neutral?
Maybe "drag" is the wrong term.
According to the great and awesome Wikipedia, drag increases in the
transonic region, but I'm not sure if that's a result of incorrect
shape, object length (similar to a displacement hull in water where
speed is related to waterline length), or just compression of the air
in front of the airplane.
If the object is shaped optimally for transonic to supersonic speeds,
does it experience this increase in drag in the transonic region?
And if it is compression, once you pass the supersonic threshold, does
the drag decrease as the shockwave is penetrated? Or are you still
carting it along like a drogue parachute? And as the speed continues
to increase, does the drag continue to increase or does it stabilize?
Or is it increasing exponentially?
--
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