The shockwave-less supersonic body
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
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
- 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
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:
Schaum Outline Series
Hughes & Brighton
Page 163 & 174 Example 8.5
This article from the BBC deals with the concept:
I read about canon shells that contain a gas generator at their
back. It's like a solid propellant rocket motor, except that the
intention is not to get any propulsion. The role of the gas produced
is just to fill in the void behind the shell, in order to prevent
the rear shockwave and its drag. This allows the shell to fly
further. I wonder if something cannot be done also for the front
shockwave and that would be fit for a range of speed. For example
the front can be hollow like an intake and contain a kind of iron
wool or tiny rods. It would act like the silencer of a pistol,
generating many little shockwaves that will be contained inside the
intake, with the air getting subsonic at the end of the intake. The
air would then be ducted towards the back, where a gas generator
would add momentum to the air, possibly by adding fuel, and cancel
the hind shockwave too. Maybe well-designed rods don't even need to
be enclosed in an intake...
Eric Brasseur - March 30 1997 till
May 12 2012