(OT...slightly) The Concorde's Sonic Boomlet

It's not strictly space, but I have a column at TCS today on the
Concorde and the possible future of supersonic flight.

http://www.techcentralstation.com/102403B.html

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

"Rand Simberg" wrote in message
...
It's not strictly space, but I have a column at TCS today on the
Concorde and the possible future of supersonic flight.

http://www.techcentralstation.com/102403B.html

Indeed, I have this feeling that Gulfstream Aerospace might know about this
research. There was an article published in Popular Science some time ago
about Gulfstream doing very serious studies on a supersonic business jet:

http://tinyurl.com/sbm7

One thing Gulfstream has done extensively in its research is to very
carefully shape the plane so you drastically reduce the pressure wave
buildup that causes the sonic boom in the first place. Also, with today's
engine technology, we are within reach of building jet engines that meet
today's strict noise and exhaust emission rules and still operate
efficiently at Mach 1.8 to 2.0 needed for a supersonic business jet.

When you have a company like Warren Buffett's NetJets expressing strong
interest in such a plane, Gulfstream may be very close to a decision to
build such a revolutionary machine.

--
Raymond Chuang
Sacramento, CA USA

On Sat, 25 Oct 2003 15:23:27 GMT, in a place far, far away, "Raymond
Chuang" made the phosphor on my
monitor glow in such a way as to indicate that:

"Rand Simberg" wrote in message
.. .
It's not strictly space, but I have a column at TCS today on the
Concorde and the possible future of supersonic flight.

http://www.techcentralstation.com/102403B.html

Indeed, I have this feeling that Gulfstream Aerospace might know about this
research.

They are aware of it, but AFAIK, studiously ignoring it.

There was an article published in Popular Science some time ago
about Gulfstream doing very serious studies on a supersonic business jet:

http://tinyurl.com/sbm7

One thing Gulfstream has done extensively in its research is to very
carefully shape the plane so you drastically reduce the pressure wave
buildup that causes the sonic boom in the first place.

Shaping can mitigate the problem somewhat, but not enough to make
their design practical.

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

"Rand Simberg" wrote in message
...
It's not strictly space, but I have a column at TCS today on
the Concorde and the possible future of supersonic flight.

http://www.techcentralstation.com/102403B.html

Conventional wisdom is that shock waves are an inevitable
consequence of supersonic flight, but there is actually no
law of nature that requires them. In fact, shock-free
supersonic bullets have been designed for use by military
snipers (for the purpose of keeping misses quiet -- much
of the noise of a conventional bullet whizzing past the
ear is a small sonic boom).


Rand:

Do you have any references to support the claim of a "shock-free supersonic
bullet"? I am extremely skeptical of such claims (not to mention shock-free
supersonic flight).

I am aware of a great deal of good academic work being done on the sonic
boom problem, but most of it is on modifying the acoustic signature of the
boom in order to lower the "annoyance factor." There is also much more
speculative work being done on eliminating shock waves via weakly ionized
gas, etc., but I don't believe this is what your article was referring to.
--
Andrew J. Higgins Mechanical Engineering Dept.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://www.mcgill.ca/mecheng/staff/academic/higgins/

On Sat, 25 Oct 2003 17:56:21 GMT, in a place far, far away, "Andrew
Higgins" made the phosphor on my monitor
glow in such a way as to indicate that:

Do you have any references to support the claim of a "shock-free supersonic
bullet"?

Not off hand--it was related to me verbally, but I'll see if I can dig
one up.

I am extremely skeptical of such claims (not to mention shock-free
supersonic flight).

Because you don't think it possible, or because you don't think it
worth doing? Certainly isentropic supersonic flow is possible.

I am aware of a great deal of good academic work being done on the sonic
boom problem, but most of it is on modifying the acoustic signature of the
boom in order to lower the "annoyance factor." There is also much more
speculative work being done on eliminating shock waves via weakly ionized
gas, etc., but I don't believe this is what your article was referring to.

No, it's not, and I don't think that those are fruitful areas of
research. The ionized gas solution almost certainly requires more
energy than just generating shocks.

There was an extensive discussion on this in the newsgroup a few years
ago.

Try these threads:

http://groups.google.com/groups?q=si...&sa=N&filter=0

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

In article ,
Andrew Higgins wrote:
Do you have any references to support the claim of a "shock-free supersonic
bullet"? I am extremely skeptical of such claims (not to mention shock-free
supersonic flight).

To quote from a posting of mine a few years ago:

In Shapiro ("The dynamics and thermodynamics of compressible fluid flow",
2 vols, 1954), see pages 451-2 for theory of shock cancellation and
wind-tunnel photos of it (in a simpler system), and pages 688-690 for
theory of a centerbody-plus-ring shape which could fly -- at zero angle of
attack -- without a radiated shock and with quite low wave drag.

See also http://naca.larc.nasa.gov/reports/1946/naca-report-841/, and
the discussion of the "Busemann biplane" in section 7.7 of Pope's
"Aerodynamics of Supersonic Flow", 2nd ed (1958).

This stuff is not so much new, as old and largely forgotten. The reason
why it was forgotten was that it seemed to be impossible to generate lift
with a shock-free shape.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

"Rand Simberg" wrote in message
...
On Sat, 25 Oct 2003 17:56:21 GMT, in a place far, far away, "Andrew
Higgins" made the phosphor on my monitor
glow in such a way as to indicate that:

I am extremely skeptical of such claims (not to mention shock-free
supersonic flight).

Because you don't think it possible, or because you don't think it
worth doing?


Because it is not possible.


Certainly isentropic supersonic flow is possible.


Isentropic flow is only possible when you can use a combination of
aerodynamic surfaces to cancel out shock waves with carefully matched
expansion waves. Even then, this is extremely sensitive to Mach number and
does not work at "off-design" cases (the classic example being the Busemann
biplane). Further, for a simple, axisymmetric shape like a bullet, I do not
see how this is possible at all.

For example, you can design a bullet with a needle-sharp nose that gradually
tapers out to the diameter of a normal bullet, and there will be no shock
wave emanating directly from the bullet; the flow over the projectile
surface will be isentropic. In the "far field" (i.e., a long distance from
the bullet), the isentropic compression waves will coalesce into a shock
that is almost identical to shock that emanates from a regular bullet. This
is a fundamental, inescapable feature of nonlinear waves.

In fact, regardless of the shape of the supersonic body (bullet, aircraft,
etc.), in the far field, you always get the classic N-shaped double shock
structure. The amplitude of this wave (which is what you hear on the ground
as a sonic boom) is, to the first approximation, related to the absolute
aerodynamic drag on the vehicle. Now, it may be possible to modify the
shock profile, or direct more of it up (away from the ground--although I
can't see how to do this with an axisymmetric bullet), but it will always be
there.

If you have access to Milton van Dyke's classic "An Album of Fluid Motion"
http://www.amazon.com/exec/obidos/tg...l/-/0915760029, shock wave
coalescence in an initially isentropic flow is beautifully illustrated in
pictures on pages 137 and 160.
--
Andrew J. Higgins Mechanical Engineering Dept.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://www.mcgill.ca/mecheng/staff/academic/higgins/

On Sat, 25 Oct 2003 21:54:32 GMT, in a place far, far away, "Andrew
Higgins" made the phosphor on my monitor
glow in such a way as to indicate that:


"Rand Simberg" wrote in message
.. .
On Sat, 25 Oct 2003 17:56:21 GMT, in a place far, far away, "Andrew
Higgins" made the phosphor on my monitor
glow in such a way as to indicate that:

I am extremely skeptical of such claims (not to mention shock-free
supersonic flight).

Because you don't think it possible, or because you don't think it
worth doing?


Because it is not possible.


Certainly isentropic supersonic flow is possible.


Isentropic flow is only possible when you can use a combination of
aerodynamic surfaces to cancel out shock waves with carefully matched
expansion waves. Even then, this is extremely sensitive to Mach number and
does not work at "off-design" cases (the classic example being the Busemann
biplane).

Right, but an airliner can operate in an on-design condition during
cruise, which is all that really matters. And of course, the Busemann
biplane didn't generate any lift--otherwise it was a great idea...

Further, for a simple, axisymmetric shape like a bullet, I do not
see how this is possible at all.

For example, you can design a bullet with a needle-sharp nose that gradually
tapers out to the diameter of a normal bullet, and there will be no shock
wave emanating directly from the bullet; the flow over the projectile
surface will be isentropic. In the "far field" (i.e., a long distance from
the bullet), the isentropic compression waves will coalesce into a shock
that is almost identical to shock that emanates from a regular bullet. This
is a fundamental, inescapable feature of nonlinear waves.

You design it as a converging/diverging nozzle. As long as you shape
and size it so it doesn't choke, you can maintain isentropic flow.

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

In article ,
Andrew Higgins wrote:
...Even then, this is extremely sensitive to Mach number and
does not work at "off-design" cases (the classic example being the Busemann
biplane). Further, for a simple, axisymmetric shape like a bullet, I do not
see how this is possible at all.

A bullet doesn't necessarily have to have a traditional bullet shape.
Clip a length out of the top wing of a Busemann biplane, and bend its ends
down and inward until they meet at the bottom, so you've got sort of a
Busemann cylinder rather than a Busemann biplane. (Three-dimensional flow
will probably require adjusting the "airfoil" shape slightly, but that's a
detail.) You now have a simple axisymmetric shape, albeit with a hole
through the middle, and the shock cancellation still works.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

On Sat, 25 Oct 2003 20:51:58 GMT, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

In article ,
Andrew Higgins wrote:
Do you have any references to support the claim of a "shock-free supersonic
bullet"? I am extremely skeptical of such claims (not to mention shock-free
supersonic flight).

To quote from a posting of mine a few years ago:

In Shapiro ("The dynamics and thermodynamics of compressible fluid flow",
2 vols, 1954), see pages 451-2 for theory of shock cancellation and
wind-tunnel photos of it (in a simpler system), and pages 688-690 for
theory of a centerbody-plus-ring shape which could fly -- at zero angle of
attack -- without a radiated shock and with quite low wave drag.

See also http://naca.larc.nasa.gov/reports/1946/naca-report-841/, and
the discussion of the "Busemann biplane" in section 7.7 of Pope's
"Aerodynamics of Supersonic Flow", 2nd ed (1958).

This stuff is not so much new, as old and largely forgotten. The reason
why it was forgotten was that it seemed to be impossible to generate lift
with a shock-free shape.

What he said... ;-)

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers: