IN 1940.

Southland Times, Issue 21073, 3 May 1930, Page 17

IN 1940.

USE OF THE AEROPLANE DIESEL. ADVANTAGES OF THIS POWER UNIT. It is a far cry from the cumbersome stationary Diesel engines of the past, deep rooted in massive foundations and wrought in cast iron, to the perfection of the present day aeroplane engine says Roswell H. Ward in the Scientific American. However, it has been this technical gulf, this wilderness of abstruse metal-lurgy, combustion phenomena, and stress analysis which the Diesel engineer has had to bridge in essaying the development of a practical aviation Diesel engine. How successful these experiments have been 'is evidenced by the remarkable evolutioh of light weight, high-speed Diesels in recent years. In the 11 years since the .World War, the weight of the lightest Di-

esel engine has. been reduced from about 65 pounds per horsepower’ to less than three pounds per horsepower, and the speed, which in the past was supposed to be definitely limited in the Diesel engine, has been increased from about 750 revolutions per minute to well over 2500! Any aeroplane—whether large or ■ small —is subjected to a daily inspection, a careful grooming and scrutiny. Skilled mechanics go over the engine, riggers examine the wings and control surfaces, keen-eyed inspectors check their reports and repair work with great care, and finally, the operations executive carefully scrutinizes the reports of both ground engineers and pilots. A race horse of a fine motor car gets-no more attention on the eve of a great contest than ddes a transport aeroplane in the course of everyday service. ' Let us follow the inspection of a 1940 Diesel “motorship of the air” such as we forsee, and determine wherein it differs from the present petrol-driven airliners. As the cowling is removed from one of the sixcylinder “in-line” air-cooled Diesels, (a cowling which leaves the upper part of the cylinders exposed and directs the air stream along the cooling fins), our attention is drawn to its extreme simplicity. There is no carburetter or intake manifold; there is no electrical ignition, no magneto or spark plugs; there is only a small pipe to the head of each cylinder, and there is only one valve in each cylinder head, from which a small “exhaust deflector” projects. The ground engineer does not have to adjust the carburetter; he does not have to worry about the intricacies of electric ignition or fouled spark plugs; when there are valves to be ground, there is just one, which takes care of both the air intake and . exhaust in each cylinder. With a compression about twice that of the ordinary' aviation petrol engine, this Diesel draws in the outside air through the single valve in the head, compresses this air to a temperature sufficient to ignite the charge of fueloil sprayed in from a little nozzle in the top of the cylinder, and when the power stroke is complete, exhausts the spent charge through the same valve in the cylinder head. Our mechanic now has to remove and inspect the fuel nozzles in each cylinder head and, while the engine is running, he will also have to assure himself that the fuel pump which supplies a minute quantity of oil to each cylinder is functioning properly in its split-second work of metering and pumping. This fuel pump is one of the points often criticized by those who question the reliability of the Diesel. It is the perfect embodiment of precision workmanship, is ground and honed so that its plungers fit to extremely close limits. This, in theory, is a difficult production problem. However, in actual practice, certain well-de-signed types of fuel pumps have shown themselves to be almost fool-proof. Most' American difficulties with experimental fuel pumps have, to speak bluntly, been due to poor design, or to poor production engineering. As the demand for this type of equipment increases, this problem will be overcome, as many other intricate problems have been solved. The writer feels quite safe in saying that the Diesel Aeroplane Engine will assume a position of ever-increasing importance in those services where long range reliability, weight carrying capacity, mechanical simplicity, and safety are desired.