ENGINES FOR BOMBERS.

Waikato Times, Volume 121, Issue 20254, 24 July 1937, Page 25 (Supplement)

ENGINES FOR BOMBERS.

LIQUID-COOLED POWER-PLANT. FOR ROYAL AIR FORCE. (From a Correspondent.) ivONDON, June 8. First performance details are released for publication of the Merlin liquid-cooled 12-cylinder fully supercharged engine, which has been ordered in large numbers for Installation In high-performance bomber and fighter aeroplanes now being built for the Royal Air Force. This latest Rolls-Royoe engine to go into big production follows the lines of its forerunners in delivering enormous power from relatively small cylindrical dimensions and in its oompaotness and low head resistance. It is the most powerful engine yet in course of supply to the Royal Air Force. Statistics released by the Air Ministry reveal that the international power rating of the Merlin is 990 h.p. (1.004 c.v.) at 12,000 feet, and its maximum output 1050 h.p. Net dry weight of the engine is 1 31 and Its weight power radio, therefore, Is only 1.251 b /h.p. at normal maximum output—an extremely low figure for a liquid-cooled engine designed for the long service and trouble-free running that are characteristic of Rrltlsh aero engines. Its total cylindrical capacity Is* 27 litres, which means that the engine at full power turns out nearly 40h,p. per litre. It is cooled by ethylene-glycol, a mixture which enables engines to run at temperatures considerably higher than that of boiling water, and thereby to perform more efficiently. Further, a smalled quantity of the mixture is required for effective cooling than in the eriuivalenfc water-cooled engine, with consequent saving in head resistance and weight. Merlin engines in the new warplanes are designed to work with “ducted” radiators, the British invention that has markedly lessened the head resistance of )owerful engines. Tlie Merlin is planned to operate with variable-pitoh airscrews, both •with the two-position screws now in general use and with the new’ British “constant speed” airscrews that provide nearly ideal running conditions for the engine. Provision Is made for tapping the lubricating oil system to provide hydraulic power needed to turn the airscrew blades. “Five Miles a Minute” Warplanes. Among the aircraft powered by the Merlin are the Hawker Hurricane and Supermirlne Spitfire single-seat fighters, two “300 m.p.h. plus” aircraft ordered in great numbers for air defence. Both are low-wing monoplanes of exceptionally clean lines with retractile undercarriage and all-en-closed cockpit. A Merlin engine is also installed in the Fairey Battle medium bomber and in the new Fairey and Hawker light bombers. The Battle, which reaches a maximum level speed of between 250 and 300 miles an hour, has been the subject of substantial orders and is being built in a State "shadow" factory as well as by the Fairey company. It has recently been ordered by the Belgian

Government. I Immediate forerunner of the Merlin was the Kestrel, a 12-cylinder engine which has been supplied to the Royal Air Force, to three Dominions and to seventeen foreign countries. More than four thousand Kestrel engines are in use all over the world. First

engine of the type, styled the F.X., was an ungeare‘d and unsupercharged engine in the design of which every effort was made to reduce frontal area and thereby to keep head resistance as low as possible. It completed its first oflloial type-test in 1927. Before it was put into production in 11)28 a reduction gearing to link engine with airscrew in the plaoe of direct drive was added. In subsequent years, as the demands of aircraft constructors and the needs of military and naval aviation for more Eower at heights far above sea-level ecame more insistent, low and high level superchargers were added, and different reduction gear ratios made available, till at present the basic

Kestrel engine is produced In twelve varieties. Concurrently, power output has enormously Increased. The P.X. unit gave 480 h.p. at sea-level; the Kestrel XVI gives 745 h.p. at a height of 14,500 feet, but Is not one oublo centimetre more In cylindrical capacity than the first engine. The Rolls-Royce company has been engaged In the production of aero engine* continuously since 1915. Its first produotlon-type unit was the Eagle, which provided poxver in hundreds of war-time bombers and after the war became world-famous through successful accomplishment of the

first direct transatlantic flight, the first flights to Australia and South Africa and across the North Pole, and the first flight across the South Atlantic. An idea of the Immense strides mhde in aero engine design and construction since those early days may be got from comparison of the Eaglo I with the current unauperoharged Kestrel X engine. Power output per unit of cylindrical capacity has increased by 120 per cent., specific weight has been reduced by 52 per cent., and fuel consumption by 33 per oent., yet the normal running life between overhauls of the Kestrel is 500 hours as against the 60 hours obtainable with the Eagle I. If the comparison were made with the modern supercharged Kestrel the figures would show even more overwhelmingly in favour of the presentday unit. Engine Flight Experiment*. Research and development are never allowed to slacken In pace. Recently. in addition to intensive engine

development, Rolls-Royce engineers have concentrated on the planning of liquid-cooled engine Installations which combine the compactness accessibility of component parts, low bead resistance, and minimum weight consistent with trustworthiness. To this end the engine mounting lias been changed to permit carrying the radiator closer to the crankcase, while mounting the “header” fuel tank round the noso of the reduction gear has much reduced the amount of piping in tile system. A great deal of work has been done on exhaust systems. and the company has now produced a system which makes for quiet running and effectively damps exhaust flames, but Is light In weight and ofTers little head resistance. A special experimental flight section investigates difficulties met in planning (Continued In next column.)

the lay-out of engines and their installation In the aircraft. Flight problems raised by the use of vari- j able-pitch airscrews have occupied i much of Hit* time of this section in j recent month*. '