[GZG] Breaking the sound-barrier (Was: Gzg-l Digest, Vol 35, Issue 9)

This old chestnut is always being trotted out when someone wants to
hand-wave some inconvenient piece of physics, especially to justify
reactionless propulsion or FTL travel. I've never seen a quotation from
any actual professional aero-engineer, or physicist working in the
field, from the pre-supersonic flight era stating that supersonic travel
was physically impossible. A difficult engineering challenge, yes;
physically impossible, no.

Supersonic airflows around bullets had been under study from at least
the 1880s (Ernst Mach et al), when heavier-than-air flight was strictly
for the birds. Prandtl and Meyer first published on the mathematics of
shock-waves in supersonic flows in 1908, only a few years after the
Wright brothers' first flight. Practical compressibility problems first
reared their ugly heads during the First World War when the propeller
tip-speeds of diving aircraft started to push into the trans-sonic zone,
and mathematical studies of the problem were published by the Royal
Aeronautical Establishment in 1918 and 1919. When compressibility
problems *really* began to bite aircraft designers (and test-pilots even
more so), in the 1930s, the theoretical background was already quite
strong. By the 1940s, when supersonic ballistic missiles were falling on
London, the impossibility of travel faster than sound would have been
difficult to sustain in professional circles.

So next time you want to throw away thermodynamics, conservation of
momentum, relativity etc., choose another analogy, m'kay?

RNB.

On 08/07/2010, at 05:39 , Indy wrote:

> And people used to say there was no physical way possible to fly
faster than the speed of sound. Proved that wrong, didn't we?
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