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Re: [OM] Jim's Sonic Booms

Subject: Re: [OM] Jim's Sonic Booms
From: Jim Nichols <jhnichols@xxxxxxxxxxxxx>
Date: Fri, 16 Dec 2016 11:12:19 -0600
Thanks, Chris. But, next time, I will eat breakfast first! It is amazing how fast time passes when you get involved in something interesting.

Jim Nichols
Tullahoma, TN USA

On 12/16/2016 11:05 AM, ChrisB wrote:
Lovely stuff, Jim

That diverted me through the Whitcomb page, the F101, F102, F106, F89 and Genie 
pages :-)

Among several wastes of weight, space and money on the Tornado was the intake 
ramp of each engine.  It was required for use above M1.4, but we were never 
going to go that fast at low level, which was the intended flight regime.  
Another waste of the same was the swing-wing design, which should have gone out 
with the F111.

Chris
On 16 Dec 2016, at 16:09, Jim Nichols <jhnichols@xxxxxxxxxxxxx> wrote:

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 
<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 
<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.

--
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