On Thu, 9 Apr 2009, Prentice Bisbal wrote:
I disagree with the sonic barrier wall analaogy. Is it that clearly
technical barrier the slowed down jet research, or did the nuisance of
sonic booms to people on the ground just make supersonic R&D less
convenient? I've heard that supersonic travel over land is restricted in
the US.
Actually, historically, it was absolutely the technical barrier, which
was profound. Pilots in WWII not infrequently went into a dive, and of
course diving one can approach the sound barrier quite easily.
They died. With very few exceptions, and they were lucky ones. One of
two things killed them. At near-supersonic speeds, the equations that
govern airflow and lift completely and nonlinearly change form. All of
a sudden, the pilots discovered that they were unable to actually move
the yoke of their aircraft against the enormous forces that locked them
in, and they discovered that the lift they were counting on to pull them
out of the dive (in particular the lift generated by the aircraft tail)
suddenly disappeared. A few clever pilots thought to put on their
airbrakes, slowed to subsonic speeds, and managed to pull out. The rest
didn't. The other problem that plagued the deliberate attempts to break
the sound barrier were harmonics that appeared and were nonlinearly
amplified as the aircraft approached the barrier. Those harmonics would
literally shake the ship to pieces, often with little warning or
opportunity to react. Lots of test pilots died as scientists worked out
the particular shapes that would permit supersonic flow without losing
control of lift and that wouldn't shake the plane to pieces as it passed
the actual barrier.
Sorry, information left over from books I read back when I was ten and
the sound barrier was still romantic (and when those ex-test-pilots were
American Heroes who were being shot up into space, still dying when
things went wrong). Actually a fascinating story, full of both real
heroism and scientific brilliance as well as a certain amount of willful
folly and stupidity.
Once the LEARNED to break the sound barrier, only THEN to the social
issues emerge, such as the fact that it is very wasteful of energy to
little actual benefit outside of war advantage, hard on glassware and
people's hearing, and so on. I have spent summers on the edge of lake
Huron with air force jets regularly popping the B just offshore, and it
is really amazingly, incredibly loud and vibratory. The boom can indeed
shatter things or knock glasses off of tables. And there is something
surreal about watching a jet flash by overhead and be miles out to sea
in front of you and THEN you hear it with the Boom like the roar of God
in your ear...
rgb
--
Prentice
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Robert G. Brown http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567 Fax: 919-660-2525 email:r...@phy.duke.edu
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