Ernest Kniepkamp joined the Heereswaffenamt (H.W.A.) in 1926, and was concerned with the development of German A.F.V.'s since that date. More recently he was in charge of the section responsible for the design and development of tracked and three-quarter tracked vehicles. His duty was to discuss with the General Staff their requirements with regard to A.F.V.'s, then to interpret these requirements into suitable designs and finally to submit his proposals to the General Staff. He explained that his policy was to prepare three, and if possible more, alternative designs, all of which he submitted to the General Staff, who then would select what they regarded as a suitable solution.
The firms which would ultimately be responsible for the development and construction of prototypes were supervised by Kniepkamp to ensure that the original requirements were fulfilled. If there were any difficulties with the firm in regard to carrying out the specified requirements, either by their inability to do so, or by their desire to foster their own designs or proposals, then an outside authority on the subject concerned would be brought in by Kniepkamp, with a view to controlling and/or helping the firm in providing designs in accordance with the originally specified requirements. Such experts were normally recruited from suitable research establishments, or were engineers or scientist eminent in the particular field concerned.
In Kniepkamp's opinion, the main task of an A.F.V. is to bring the highest firing power up to the enemy at the highest possible speed, and with the best possible protection, the importance of the different factors being in the order stated. Other aspects of A.F.V. design are of secondary importance, therefore so far as the crew is concerned it is of no interest whether the vehicle is driven by a diesel or a petrol engine, as long as it is driven at all, for a broken down tank of superior design is of very little use if attacked by five enemy tanks of inferior design, capable of bringing their firing power to bear against the broken down vehicle.
In Kniepkamp's opinion, his main responsibility as far as the engine was concerned was to determine which type of engine could be used to the best advantage. The most important consideration was that of space required. Therefore in his view, that engine will be the best which, together with its auxiliaries and fuel tanks, would require the least space in terms of vehicle miles or operating hours.
The German General Staff requirements were that enough fuel should be carried in an A.F.V. to enable its engine to operate under full power conditions for no less than five hours. On the basis of this five hour full load requirement, the best engine is the petrol engine, for the total space required to accommodate the engine, its auxiliaries, cooling plant and fuel, is less than that required by an equivalent diesel
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engine, on the basis of present day development. If, however, the minimum time of which the engine should be capable of operating under full load conditions be increased to 10 hours, then the diesel engine would be of greater advantage, as the volume of engine, etc., and fuel to be carried would be less than that of a petrol engine.
Whilst the H.W.A.'s aim was to provide sufficient fuel to meet the five hour requirements, this was not often possible, but the E type of A.F.V. was to have sufficient tankage to ensure a five hour run at full load.
Kniepkamp himself had no preference for the diesel or petrol engine on technical grounds. In his view the best engine the Germans had was the Maybach type H.L.234 unit, which had a piston displacement of 23 litres, and was capable of developing 900 P.S. unsupercharged and 1200 H.P. supercharged, whilst as a diesel engine the same unit was capable of developing 650 and 900 P.S. respectively. Compared with this the Kloeckner-Humbold-Deutz 8 cylinder 23 litre diesel engine would be capable of developing 700-800 P.S. at 2000 r.p.m.
There was a strong tendency to change over from petrol to diesel engines, particularly by the non-technical members of the General Staff, who very often tried to bring the controversy into the open by way of newspaper and journal reports, so as to influence public opinion, and so in turn influence the responsible technicians. In addition, Hitler preferred diesel engines, and was of the opinion that the diesel engine should be fostered because it was of German origin. (This statement is not very convincing in view of the fact that the "Otto" engine is also of "German origin').
In Kniepkamp's opinion it is far easier to develop a 1000 H.P. petrol engine, than an equivalent diesel engine, and he found from past experience that a suitable diesel engine was usually available some two or three years after a suitable petrol engine had been submitted. He cited the Maybach H.L.234 engine as the best and most advanced example of German engine development designed for m.e.p. of 12 kg/cm² and suitable for installation in the engine compartment of Tiger II originally accommodating the H.L.230 engine.
With regard to fire risks, in his opinion this was about equal for petrol and diesel engined vehicles, but whilst diesel fuel would burn, petrol would ultimately explode. The crews preferred diesel engines but irrespective of engine type wanted a complete partitioning off of the fuel tanks from the fighting compartment. Whilst they lost a number of vehicles through fires in the engine compartment, firing trials did show that it did not make the slightest difference whether the vehicles were petrol or diesel engined.
For extreme climatic conditions, the petrol engine would be preferred to the diesel. Tests had been carried out in a temperature of -45C and
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+50C, and in each case it was found that the petrol engine gave less trouble than the diesel. It is admitted that a petrol engined vehicle will require a 30% bigger radiator area.
To ensure efficient cooling with the least possible power expenditure, the latest fan drive schemes envisaged shaft driven fans with an hydraulic coupling incorporated in the hub of the fan. This coupling would be of the scoop control variety, the amount of oil in the coupling and consequently the slip being controlled by a thermostat, the setting of which was determined by the coolant temperature.
In Kniepkamp's opinion, the choice of the engine type was not determined by transmission conditions. He considers that the hydraulic transmission is the transmission of the future and with it the shape of the engine torque curve will not be of such importance as is the case with transmission of gear type. Here again he would prefer to use a petrol engine which it would be possible to boost by about 10% of required, which, he thought could not be done with diesel engine. The general understanding in Germany was that it was very much easier to produce petrol fuel than diesel fuel. About half way through the war, there were indications that the fuel supply situations would favour the diesel engine, but then it was too late to change.
Kniepkamp stated that, provided a diesel engine could be developed which could produce the same power in the same space as a petrol unit, he would prefer the diesel engine, mainly on account of the reduced fuel consumption.
With regard to the general engine size, he would, in principle, prefer a small supercharged engine, running at high speeds, to a large, slow running, unsupercharged unit, provided the reliability of the small unit would be satisfactory. He considers that the mean piston velocity should be limited to about 15 metres per second, and therefore would prefer to use engines with big bores, small stroke, very big valve diameters, and very strong valve springs. The latter requirement led to the use of Belville washers as valve springs for the Maybach H.L.234 engine. Such springs were very powerful and did reduce the opening time of the valve and ensured high rates of valve acceleration.
With regard to air cooled versus water cooled engines, Kniepkamp considers that at present, air cooled engines are less suitable for A.F.V.'s on the score of more difficult and expensive productions (in terms of man hours.) This is particularly so because the cylinder fins had to be machined. Whilst it is possible to use cylinders with cast, unmachined fins, the output per cylinder would be reduced because of the reduced rate of heat dissipation. A number of air cooled engines have been developed and partially tested in the form of
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single cylinder experimental units, but they have never been completed to a stage where they could be considered as suitable for installation in heavy A.F.V.'s.
Here again, it was the desire of Hitler that air cooled engines should be given preference, whilst Kniepkamp considered personally that he would never, under any circumstances, decide in preference of one or the other engine type. In his view at least two firms should be always asked to develop alternative engines, diesel, petrol, water or air cooled, in order to foster a competitive spirit, and thus obtain the best results in the least possible time. However, if given only one choice, and a time limit of say 10 years to develop an A.F.V., engine of 1000 H.P., he would choose a water cooled two-stroke diesel.
With regard to Allied engines, the best A.F.V. engine in his view was the 500 H.P. Ford V.8, which he regards as a very practical development, particularly from the productions and maintenance point of view.
With regard to German engines, he considers the Maybach H.L.234 unit as a great achievement. This unit has been developed from the Maybach H.L.230 engine, the main alterations being in details such as the introduction of water cooled sparking plugs, alterations to the pump and pump location, and improved form of intake manifold, which would ensure better air distribution, and an improved exhaust manifold. These alterations between them were responsible for improving the power output of unsupercharged petrol injection engine from about 700 to 900 P.S. The engine supercharger was to be driven by a 1 litre 2 cylinder four-stroke supercharged engine, capable of developing 70 H.P. This engine would be mounted in the «V» of the main engine, and would be set to run at a constant speed. One of the H.L.234 engines was installed in a Tiger tank, but the control arrangement was not finalised at the time. The fuel consumptions was about 235 gm/PS/hr at 1000 r.p.m., 225 gm/PS/hr at 2000 r.p.m., and 235 gm/PS/hr at 3000 r.p.m. A 12 litre in line engine, the design of which was similar to the 23 litre unit, was also developed by Maybach. This unit weights 600 kg. and develops 500 P.S. and 700 P.S. at 3800 r.p.m. unsupercharged and supercharged respectively.
All Maybach engines were of the water-cooled variety as Dr.Maybach refused to have anything to do with air cooled engines, having stated that "he was born water cooled and wanted to die water cooled".
Certain troubles have been experienced with the H.L.234 engine. These troubles were mainly due to the rubber seals and copper gaskets, but the adoption of designs found in the Merlin engine, have cured these troubles. Roller bearings were to be preferred to friction bearings, because they would permit smaller engine sizes. In addition, tests had shown that the use of friction bearings would increase friction losses three-fold.
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With reference to the M.A.N. type V.6.T.11.5/16 12 cylinder 2-stroke supercharged V engine, Kniepkamp stated that this was supposed to be ready in 1941, but was not ready even in 1943. This 400 H.P. unit would have been suitable in the early days of the war, but was of no further interest in 1943, on account of its size.
A 30 litre 12 cylinder petrol engine with rotary valves was under development by the Auto Union. This was designed to develop 900 H.P. A single cylinder experimental engine forming the development basis for this unit was developed at the Adler Works of the Auto Union. This 2 1/2 litre unit developed 87.5 P.S. at 3000 r.p.m., so that the complete 12 cylinder unit would develop 1050 P.S. The complete engine was to be ready in July 1945, but in Kniepkamp's opinion it will take another 3 years to finalise the development.
No 2-stroke diesel engine was available for A.F.V.'s. An aircraft diesel engine, developed by Dr.Flatz of Humbold-Kloeckner-Deutz had taken some 8 years to develop at an expense of about 10,000,000 marks.
With regard to gas turbines, Kniepkamp stated that these were of no interest to him, mainly on account of the high fuel consumption, which he understood was in the region of 450 gm/PS/hr for a turbine capable of developing about 1000 H.P. He understood that the possibility of using gas turbines in A.F.V.'s was investigated by the S.S. Tank School, nr.Vienna, but he did nor want to have anything to do with this development, which has taken place in a somewhat underhand manner. He was not impressed by the torque characteristic of the gas turbine, for the sprocket torque characteristic required by an A.F.V. would be provided by the hydraulic transmission, the use of which he envisaged in future A.F.V.'s.