Immersion Experiments

Immersion tests with design models of  9 mm diameter and  270 mm length were successfully executed with velocities of 300 - 500 m/s and flat angles between 10° and 1°. The figure shows a picture of an immerging model.
The model was flash lightend at two different points of time. So two stages of motion could be illustrated. The first stage shows the model short time after water entry (left side in figure). The second stage shows the model with long adjacent cavitation bubble in a later stadium (center of figure).

In order to receive pictures with high definition the duration of flash light had to be shortened to
1 microsecond.

Spinning Projectiles

Reichardt`s laws were also checked at higher velocities, larger caliber and with spinning projektiles.

Therefor a projectile caliber 40 mm, weight 1 kg with modified head was horizontally shot (Bofors gun) in a water filled concrete basin.
The head was shaped to produce a cavity larger than the projectile dimensions. The projectile run in straight line through the available basin length of 10 m and penetrated a high-strength steel plate of
13 mm thickness at the end of the basin (Lit.6).

Underwater Warhead Against Hovercraft

Because of their air cushion hovercrafts are less endangered by underwater explosions then normal vessels.

To guard the coast against landing crafts projectiles shot from the ground therefor should be a better possibility than conventional sea mines. To test the realizability of such a system a fast running supercavitating projectile (caliber: 38 mm, length: 350 mm, weight: 1.2 kg, cw: 0.013) was designed and tested.

The projectile was designed to run from depth of 10 - 30 m with a muzzle velocity of 250 m/s under angles of 0° - 40° against vertical line to the surface and penetrate a steel plate of 10 mm thickness.

In preliminary tests in the proving ground of Linz the launching facility and the projectile rendered the required properties concerning straight line running and penetrating of steel.
In final tests in the Baltic Sea shot from depth of 10 m the projectile penetrated a steel plate 2 m above the water surface.

Extended on larger scale a projectile of diameter 80 mm and length of 740 mm with a mass of 10 - 12 kg could transport an explosive mass of 5 - 3 kg.

With the tests conducted it was experimentally demonstrated, that supercavitating projectiles are adequate to fight hovercrafts (Lit.7).

On the basis of these results the company Diehl, Nürnberg, developed a coastal sea mine against landing crafts, which was planed to introduce in the German Federal Armed Forces. In the budget of the Armed Forces 2 billion DM were planed for buying the sea mine. Only the breakdown of the Eastern Bloc avoided the acquisition.

Underwater Rockets

In 1977 the first tests with underwater rockets were conducted on the proving ground in Linz. Therefor a cableway was constructed with one fixed-point outside the water, the other fixed-point on the ground of the lake through the 40m-basin. The cableway consisted of two steel wire ropes with a distance of
80 mm.

The test rocket consisted of a rocket motor with conical shaped head. It was confined by 4 eyes to the cableway. the rocket was ignited outside the water.

The rocket reached velocities under water of 130 m/s. So it was demonstrated that rockets are adequate to move projectiles under water.

In the following years a launching facility was developed to accelerate projectiles of caliber 120 mm on muzzle velocities up to 300 m/s.

For testing the launch facility the cableway was modified. Now one single cable reached central through the lauching facility into the water.

With this equipment rocket models with integrated rocket motor ( but without ignition of the motor) were tested with velocities up to 135 m/s (Lit.8).

The first tests with underwater rockets in free flight were conducted in 1980 with velocities of circa
140 m/s in the proving ground of the Armed Forces in Meldorf.

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