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Aero Oil Ur(,!_lently

7th July 1933, Page 48
7th July 1933
Page 48
Page 49
Page 48, 7th July 1933 — Aero Oil Ur(,!_lently
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En ines Needed

IN the past few months The Commercial Motor has urged the concentration of aero engine makers on the production of compression-ignition oil engines. Commercial aviation is just at the turning point where it is commencing to become economically profitable, and it needs but the flip of one or two fresh advantageS to, carry it quickly forward to ' success.

• SearceIY anything t-h a t engineering science can at present offer to the aircraft producer is more promising than the oil engine, which of f e re . advantages that do not figure in connection with its use in road transport. Quite apart from the essential economy, which arises from an inherent superiority of thermo-dynamic efficiency, there is the question of safety from fire.

To remove the fire risk, the need for all those precautions that are indispensable on aircraft to-day, would have an immense effect on the popularity of air travel. What theme more sound for the advertisements of Imperial Airways or any other operating company than the fire immunity of new oilengined air liners?—a poster showing a fuel tank being filled and a passenger lighting his pipe close by!

The lower specific fuel consumption of the oil engine means that for a given quantity of fuel the aeroplane has a longer range, or for a given range it may carry more pay-load than one that is petrol driven. Again, the higher specific weight of the fuel saves anything up to 10 per cent, of its storage space. Not only does the compressionignition engine burn less fuel, but the fuel is cheaper than petrol, so that a big all-round fuel economy results.

A further point of comparison is that with a decreasing load the fuel consumption of the petrol engine is prone to rise rapidly, whereas that of the oil engine is at its best at something' below, below. full load, corresponding with the cruising speed of the normal aeroplane.

When the troubles of early development have been overcome, a higher degree of reliability can be hoped for in the oil engine, because electric-ignition devices and highly sensitive carburetters are replaced by simpler mechanical pumps and injectors. Obviously, the more the working process of the engine is controlled by mechanical means, the simpler and less sensitive will be the components.

Again, the efficient operation of the petrol engine is disturbed by aspiration irregulari-, ties that have nothing like the same effect on the oil engine ; carburation is sensitive to atmospheric conditions, power being greatly reduced at high altitudes. Warming up is necessary when starting from cold and starting itself is prone to give trouble, the constitution of the firing mixture not being positively controlled. Mixturedistribution to the cylinders calls for manifolds that are a compromise.

Atmospheric conditions affect the oil engine far less; for high-altitude flying the mixture of fuel and air can be positively varied within quite wide limits. Mechanical control of the fuel supply means that the oil engine is unaffected by changes of position when in flight, also that more fuel than normal van be temporarily supplied to give the extra power required when leaving the ground. Problems of variable-pitch airscrews may thus eliminate themselves.

Another important point in the oil engine's favour is that the electric interference of the ignition system of a petrol engine upon the wireless apparatus of an aircraft—so vital in fog or night flying—is absent, no additional equipment for screening the ignition system being necessary.

Some oil-engine developments are already taking place. The Royal Aircraft Establishment has converted a Rolls-Royce Condor engine to compression ignition. The total weight is 1,513 lb., compared with 1,895 lb. for the petrol type. The compression ratio is 1.2i to 1 and the rated power is 480 b.h.p. at 1,900 r.p.m. (giving 3.152 lb. per b.h.p.) and the take-off power is given as 500 b.h.p. The cruising fuel consumption is .423 lb. per b.h.p. This engine has passed its civil type test of 50 hours,

A specialist in radial air-cooled engines, the Bristol Aeroplane Co., Ltd., has produced an oil engine of this layout, called the Plnsnix. It is similar to the famous Jupiter petrol engine and its normal output is 8501 b.h.p. at 1,900 r.p.m., with a takeoff power of 380 b.h.p. at the same speed. The cruising fuel consumption is .4 lb. per b.h.p.-hour and the compression ratio 14 to 1. The Phcenix

engine weighs 980 lb. (giving 2.8 lb. per b.h.p.) and it has completed about 180 hours' running, including 15 hours' flying and operation at an altitude of 16,000 ft.

An important Continental oil engine

for aircraft is the Junkers two-strolse, opposed-piston, water-cooled unit made by the Junkers Motorenbau, Dessau, Germany, and described in this paper on May12.. The Jumo IV is a sixcylindered unit giving a normal output of 750 b.h.p. and weighing 1,654 lb. (or 2.205 lb. per b.h.p.), and it is claimed to have run without trouble at 22,000 ft. in a temperature of 35 degrees C. below zero. The two crankshafts are geared together, the airscrew drive being taken from one of the intermediate gearwheels. D. Napier and Sons, Ltd., has acquired the rights of manufacture in this country.

A smaller six-eylindered model, the Jumo V, has now been produced. This develops 540 b.h.p. at 2,100 crankshaft ' r.p.m. and weighs 1,089 lb. (2.02 lb. per b.h.p.). The fuel consumption of the two models ia equal at about .353 lb. per b.h.p.-hour, which is very low.

Another Continental development is that of the Daimler-Benz Co., tinterturkheim, Germany, vsrhich concern is likely to announce in the near future a 12-cylindered V-type water-cooled oil engine of 165 mm. bore and 210 ram. stroke, giving about 750 b.h.p. at 1,700 r.p.m., and weighing 2,000 lb., or 2.78 lb. per b.b.p. On tests a fuel consumption of .392 lb. per b.h.p.-hour has been reported. Injection, into a pre-combustion chamber, is by Bosch equipment

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Locations: Dessau

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