#2
Post
by Mait » 16 Nov 2002, 20:02
PS! I found a short article in internet about that:
"Versuchsgleitboot" - The World's First Hovercraft
by Erwin Franz Ferdinand Bilzer (+) and Erwin F. Sieche, Vienna
The practical development of the idea of reducing the hydrodynamic resistance of a vessel by blowing air under the hull dates back to the first years of the century.
Lieutenant-Commander ("Linienschiffsleutnant") Dagobert Müller von Thomamuehl, of the Austro-Hungarian Navy first made intensive studies of this problem when he was commander of the torpedo-boat 60 T (ex-Schwalbe). His idea was to reduce both resistance and displacement by lifting the hull out of the water on a cushion of pressurised air. He made model-towing tests, on his own initiative, using the torpedo-boat he commanded, and his knowledge of the science of testing scaled-down models was so great that all his figures and diagrams show an astonishing engineering brillance. On 26 March 1915 he submitted to the Austrian Technical Committee (Marinetechnisches Komitee, MTK) a paper entitled 'Study of the construction of a high-speed gliding boat'. The accompanying drawing showed a rectangular boat with hull dimensions of 16.3 x 6.6 x 0.75m (53.3 x 20.9 x 1.8ft) and a displacement of 12.25 tonnes (12.05 tons). This was a true hovercraft employing two (or three, depending on the engines available) Austrodaimler aircraft engines of 120hp each for surface propulsion, and one 65hp Austrodaimler engine, driving an aircompressor giving 450m^3 of air per minute (15.734 cu ft per min) for hovering. The vessel was designed for a speed of 32kts an endurance of 550nm and an armament of 4x450mm torpedoes in outboard containers.
When looking at this first design, one notes some very important features of hovercraft design. The fan was situated in the forward section of the rectangular hull and produced an air cushion over the full length of the bottom, allowing the boat to rise nearly 10in. Skirts at both sides prevented the air from escaping but there were no skirts at stem and stern. For the machinery Müller faced a problem in the only suitable engines with the required high power/weigth ratio were aircraft engines. Since 1909 the Östereichische Daimler Motoren Gesellschaft at Wiener Neustadt had produced the Austrodaimler engines, designed by Ferdinand Porsche - later become famous as the constructor of the Volkswagen. These very reliable engines had now been developed to a point where they had reached 300hp and Müller, therefore, proposed to borrow obsolete 120hp engines from the Pola Naval Air Station (Seeflugstation Pola).
The MTK Appraisal
The MTK judged Müllers tests as follows: "...the injection of air under the hull has a very positive influence on the resistance and, therefore, on the necessary amount of (propulsive) power which rises (initially) to maximum but decreases at higher speeds ... The measured towing forces show that the resistance of the proposed hull form is so great that this vessel could only make 12kts ... Stability is insufficient to enable operations even in light sea states... Tests should be carried out to ascertain if it would be better to situate the propellors deeper under the bottom or free from the stern".
The MTK ordered the construction of an experimental hovercraft, now called Versuchsgleitboot, to modified design, with dimensions of 13.0 x 4.0 x 0.36m (42.64 x 13.12 x 1.18ft), and a displacement of 7.8 tonnes (7.6 tons) and propelled by four 120hp 6cyl. Austrodaimlers to drive the propellers and one 56hp Austrodaimler for hovering. Comparison with the pre-project design shows some important differences:
1. A more streamlined hull profile.
2. Only the after section of the hull was to be lifted by the air cushion; the forward section would simply glide on the water surface.
3. A more powerful surface propulsion plant
4. Torpedoes situated inboard, placed in open chutes for sternward ejection.
Hull
The MTK design had a rectangular hull of spindle-shaped profile, with the bottom divided, by a vertical step, into gliding and hover sections. To ensure eddyless air-injection a swallowtail-shaped duct was situated at this vertical step. The hull was built completely of wood but the torpedo chutes were lined with sheet metal. A forward rudder was positioned under the driver's cockpit and an after rudder near the stern, both on the centreline. As all standard formulas for the calculation of rudders and propellers (eg Hope's Formula, first published in Engineering in 1915) were not applicable, various rudder shapes and propellers from different suppliers (each differing in radius and inclination) were tested.
Machinery
Each pair of 120hp surface propulsion engines drove through a common gearbox to a single propeller shaft. Thery were placed in tandem and all exhaust gases wre injected into the hover section, under the hull, to assist the 65hp hover engine.
Armament
A single 8mm Schwarzlose machine gun Mk (19)07/12 was mounted on the hull forward. The torpedo armament consisted originally of two 45cm weapons, each in an open chute arranged for launching over the stern by means of compressed air. Later a depth-charge thrower, for three small 6kg (13.23lb) bombs, was placed on the stern slope. Unfortunately, I have been able to locate neither plans nor photographs of this device.
Construction
The Versuchsgleitboot was built at Pola Navy Yard to the following schedule:
17. 6. 1915: Start of preparatory work
1. 7. 1915: Keel laid
16. 9. 1915: All fittings on board
2. 9. 1915: Launched
3. 9. 1915: First trials
Test Results
As might be expected, since this was an experimental vessel some minor problems were encountered but they are not discussed here as they do not directly concern the success or failure of the basic concept. These difficulties were with such items as the ignition, the gearbox and son on. Tests with the originally planned 45cm torpedoes showed poor results, so it was decided to switch to the more reliable 35cm torpedoes. (The technical and tactical problems of firing a torpedo from a high-speed vessel are discussed in the next section).
More interesting are the results of the world's first hovering trials (Table 1). When hovering, without forward movement, the area abaft the bottom step was completely filled wih air, the hull rising out of the water by 15cm, giving an apparent displacement reduction of 6.3 to 3 tonnes. The air flowing out sternwards also produced a 3kts forward speed. The tests showed that the greatest improvement of speed lay between 16 and 24kts, the true speed increase being about 4-5kts. At higher speeds the improvement provided by hovering decreased to between 2.4 and 2.7kts. Owing to the hull form, the boat came out of the water at speeds above 20kts, even when hovering was not employed. As we will see later, the MTK had to decide if the additional speed of about 2kts was worth the extra weight involved in the provision of a fifth engine, a fan and the additional fuel. When judging the maximum speed, it must be kept in mind that the fastest potential opponent of the Versuchsgleitboot were the Italian Motoscafi anti sommergibili (MAS, or motor anti submarine boat) capable of only 24kts, or, in the case of a torpedo-carrying hovercraft attacking a convoy. Allied escorts were capable of 28-30kts. However, in the case of the Italian MAS, it is clear that what was really needed was a fast, armoured, motor gun boat and not a hovercraft.
At first sight a small high-speed boat appears to be an ideal torpedo-carrying vessel, but on closer examination we find that the release of the torpedo becomes a problem when the speed of the launching vessel approaches that of the torpedo itself (the contemporary Austrian 45cm torpedo was capable of 38-40kts). In principle there are four different methods of launching torpedoes, regardless of the equipment used (torpedo tubes, launching frames, chutes and other devices):
1. Over the bow. Here the vessel has to slow down to let the torpedo run on ahead.
2. Over the stern. Here the vessel has to do a half-turn at the height of its attack, showing her full broadside to the target. Unless she slows down, this turn has, necessarily, to be of large tactical diameter. In addition, the Austrian tests showed that a fast-running boat leaves a wake of disturbed water which was liable to upset the accurate run of a standard torpedo.
3. Over the side, parallel to the hull. This could be achieved by dropping the weapon from clamps (as in the Italian MAS) or outboard containers (as in Müllers pre-projected design). Using this method, attack was possible at both high and low speeds.
4. Launch in forward direction, form fixed or trainable inboard torpedo tubes. Not suitable for a small 40ft vessel.
The Final Judgement
On the 20 October 1916 the board of the MTK met for a final judgement on Müller's idea, the boat and the results. For this naval constructor Dipl Ing Max Szombathy prepared a paper entitled Schiffbauliche Bemerkungen which ist quoted below as it is much clearer and more professional the final 'official' document.
"The basic idea proved practical and, from this point of view, the experimental vessel was successful. Military use of the boat is not recommended due to the following disadvantages:
1. The boat is not seaworthy. The broad snub bow would require speed reduction in heavy seas and might lead to hull stress.
2. The boat ist open, so rain and sea spray might disturb both electric ignition and the carburettors.
3. The boat has no bulkheads and a single leak could cause the total loss of the vessel.
4. The engines are not silenced which could lead to premature detection in night attacks.
5. The engines have no self-starters and it is a rather involved process to start them by crank. However, if the engines are kept in neutral when the vessel is stopped, to avoid the need for re-starting, they become over-oiled.
6. Torpedo launching over the stern ist unsatisfactory, as the boats turning radius at high speed is to great.
7. The torpedo suffers from wide deviation when ejected at high speed due to propeller turbulence. It cannot stabilise itself and jumps out of the water or dives to great depth.
8. The throwing of depth-charges is satisfactory but the minimum burst distance should be checked."
Synopsis
"The vessel has been built to run basic trials. For military use a number of modifications would be necessary. This would mean a complete rebuilding which would not however alter the boat's bad seaworthiness. In addition the crew should undergo special training. At present and in the existing form the boat cannot be recommended for military use."
Based on this document, and the subsequent discussion thereof, the board judged that:
1. The boat was insufficient in terms of shipbuilding technolgy, was not seaworthy, and was difficult to handle.
2. The boat was unarmoured, open and without bulkheads.
3. The noise of the unsilenced engines would warn an enemy of its approach.
4. The speed, in full load condition was to slow(!).
5. The torpedo ejection over the stern was inefficient and the turning circle at high speed was so great that it would cost vital time in operational use.
6. The boat accelerated and stopped badly.
7. The boat could not carry out exact depth-charging, as visibility over the stern was not good enough at high speed.
8. The action radius was to small (120nm).
9. The boat was no substitute for a seaworthy, armoured, motorboat. '... But vessels of this or a similar type may be of value for the Navy if they can achieve a reliable speed of 40kts, at a sufficient action radius, and can carry a 1200kg (2645.54lb) warload ... '
Some of the comments of the board are rather surprising or, at least, in contradiction with earlier comments. For example, earlier reports spoke of good handling capabilities and commented that istwas not necessary to install reversing gear as the manoeuverability was sufficient. Considering the details of enemy high-speed craft, the argument about insufficient speed seems not to have been throughly discussed. Nevertheless, the basic intrinsic value of the hovercraft has not changed during the last 53 years. A modern hovercraft is, like ist remote predecessor, a vulnerable weapon carrier, suitable only for special missions, and needs very special maintenance and care.
The story if the Versuchsgleitboot ends prosaically: the engines were sent back to the Aviation Arsenal in Vienna and the hull was probably cannibalised during the following years. The last remnants of the world's first hovercraft may well have ended as firewood in the stoves of Pola.
