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The shockwave-less supersonic body

In Slovanian, by Mary Orban:

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:
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
Page 163 & 174 Example 8.5

May 2012

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