Shock waves around supersonic airplanes, rockets,
canonballs or boats are a problem. Here are two ideas to avoid
hem. The basic principle is that the shock waves are held
inside the traveling body. These ideas have not been tested out and I'm
not convinced they will produce positive results.
Reflective plates around the body.
The plates around the body are thin and do virtualy not generate shock
waves by their own. But they make the heavy shock wave originated by
the front of the body go back to it's rear. At the rear, the shock wave
is absorbed, anihilated.
Theoretically, no shock wave leaves the body to polute the outside
world.
This shape, with the plates around the body, has two main drawbacks:
It is only effective at one given speed, for wich the plates and
the body have been designed. At other speeds, the reflected shock wave
will arrive before or afther the tail. The shock wave will then not be
anihilated, it will bounce back and continue it's way towards the
outside world. And the shock wave of the back will be originated,
poluting the outside world too. You may think about moveable plates,
that would allow the body to adapt itself to different speeds, but thay
may be difficult to manufacture, or heavy.
It would probably be easier to make the tail
move so it can put itself at the right place to
receive the shock wave.
If this shape is not brought into quick rotation around it's
axis, and controled by an effective electronic system and actuators, I
fear it will tumble around into the air and do everything except a
straight steady flight. Maybe
a stable shape and weight repartition can be
computed.
An application could be for boats. Imagine a
sort of polynesian pirog with the external floaters
replaced by vertical plates plunging into the
water. The water wave created
at the front would be redirected by the plates
towards the back of the boat and push it.
Water waves created by boats form a
triangle with a constant angle whatever the speed of
the boat, thus such a boat perhaps could travel at
any speed with no need to adjust the position of the plates.
It would be a sort of zip that opens the
water in front of it and closes it back behind.
Another way to do it would be to construct channels with a precise
width, or put fixed vertical plates in the
water, and build ships with the appropriate length.
The ships would then glide inside such channels an
use less energy.
The rocket motor shaped body
If the body is a hollow short tube, the shape of the hollow being that
of the convergent and divergent of a rocket motor, the pressure of the
shock waves in the convergent will be transformed into a pushing force
into the divergent. It is a rocket motor using air under pressure as
fuel.
As a first approximation, the force in the divergent will equilibrate
the pressure at the front.
This shape too does virtually not generate shock waves in the outside
world. The shock waves originated inside the front of the tube are used
to generate a pushing force in the back. You have no shock waves at the
back, just a straight flow of air.
This shape will require less accuracy for the speed than previous
shape. The air traveling
trough the body may even become subsonic, provided
the subsonic zone does not inflate up to the front
op the body and generate a shock wave in the outside world.
Maybe best application would be for a long range canon
shell. It will have no stability problems because it
is a heavy torus rotating at high speed. The gyroscopic effect will
make it remain straight. Yet a
little precession will be necessary to make the shell's
axis rotate slowly along the trajectory path in order
not to make the shell deviate aerodynamically constantly in one
direction.
Another application may be for boats (see picture below).
While traveling just under the water surface such a shape will
generate virtually no water shock waves around it. The
water will enter the U shape, rise along the inner part of the body
then
come back down at the tail.
J. Mann mailed the following remarks about
technological possibilities: "The plates have to be accurately shaped
for them to work, it would only be able to maintain one set speed for
them
to work... UNLESS you can manipulate the shape of the plates.... do a
honeycombing of cells underneath and inflate/deflate as needed.
With the right engineering, you could maybe get the
air pressure at the front to force the plates to conform to the best
shape." "The engineering abilities with silicon has got to the point
where they can create tiny cogs and motors, so you can create say
a car that works perfectly but is about 2cm long."
Simcha Chamberg send in this reference: Fluid Dynamics
Schaum Outline Series
Hughes & Brighton
1967
Page 163 & 174 Example 8.5
