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

Henry Spencer wrote:

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.

Another way to think of this is as a supersonic inlet and nozzle hooked
together. The incoming gas is compressed and decelerated shocklessly
in the inlet, then reaccelerated (also ideally shocklessly) in the nozzle.

Paul

(Henry Spencer) wrote in message ...
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 Busemannbiplane). 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.


Yes, I've fired hollow, cylindrical projectiles similar to that (see:
Sasoh A., Higgins A.J., Knowlen C., Bruckner A.P., "Hollow Projectile
Operation in the Ram Accelerator," Journal of Propulsion and Power,
Vol. 12, pp. 1183-1186, 1996).

My question was in regards to "shock-free supersonic bullets...for use
by military snipers." I do not believe such a thing exists (or
supersonic aircraft that do not generate shock waves, for that
matter).
--
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/

h (Rand Simberg) wrote in message . ..
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:

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.


....and this is how the sniper's bullet works?
--
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 25 Oct 2003 22:47:09 -0700, in a place far, far away,
(Andrew Higgins) made the phosphor on my
monitor glow in such a way as to indicate that:

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.

...and this is how the sniper's bullet works?

That's my understanding.

--
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.
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On 25 Oct 2003 22:34:42 -0700, in a place far, far away,
(Andrew Higgins) made the phosphor on my
monitor glow in such a way as to indicate that:

My question was in regards to "shock-free supersonic bullets...for use
by military snipers." I do not believe such a thing exists

I don't know whether or not they currently exist, but I was informed
that they've been designed and tested.

(or supersonic aircraft that do not generate shock waves, for that
matter).

Well, those obviously don't exist. The issue is whether or not they
*can*.

--
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:

Henry Spencer wrote:
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:
snip
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.

Implying that it might be good for ballistic trajectories.
Do any of these structures generate lift when operated at non-zero AOA?
So, you'd takeoff ballistically, and transition to wing-assist when
over oceans.

I assume the drag doesn't magically drop due to the absence of a
shock wave.

Ian Stirling wrote:
I assume the drag doesn't magically drop due to the absence of a
shock wave.

No; there are always at least two components to drag;
shock and skin friction. Skin friction is essentially
a function of surface area and velocity. That won't
go anywhere even if you zero out the shockwaves in
the system... in fact, it will increase, because the
hollow tube projectiles have roughly triple the surface
area of a similar mass conventional bullet, if my models
are correct...


-george william herbert

George William Herbert wrote:

That won't
go anywhere even if you zero out the shockwaves in
the system... in fact, it will increase, because the
hollow tube projectiles have roughly triple the surface
area of a similar mass conventional bullet, if my models
are correct...

Ah, but the next step is to make some of the inner part
of the bullet combustible, so the compressed air is heated
to add thrust. A ramjet!

Paul

In article ,
Rand Simberg wrote:
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.

I seem to recall Ben Bova claiming in a story that if you take
an airfoil and curl it into a closed circle, you don't get a sonic boom.
Or lift, so the SST has to be LTA as well. Since air resistance is going
to be a problem, I think it pretty much needs a high-powered nuclear
engine as well, maybe the nuclear ramjet that was going to be used on
the SLAMs.

--
It's amazing how the waterdrops form: a ball of water with an air bubble
inside it and inside of that one more bubble of water. It looks so beautiful
[...]. I realized something: the world is interesting for the man who can
be surprised. -Valentin Lebedev-

(Henry Spencer) wrote in message ...
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.


Yes, this is the Busemann biplane. It is essentially shock
cancellation of in *internal* flow: basically the vehicle ingests a
flow equal to the *entire* projected cross-sectional area of the
vehicle.

Rand's article regarded solid bodies such as a bullet or jetliner. It
is not possible to eliminate shocks in the far field for a body like
this.


This stuff is not so much new, as old and largely forgotten.


Not really: a number of hypersonic inlet designs are fancy,
axisymmetric or three-dimensional variations on the classic Busemann
biplane. The funny "cow-catcher" shapes you see on the intakes of
some hypersonic airbreathing missile designs are a type of Busemann
inlet.
--
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/