Types ranged from the now obsolete rotary engine to the water-cooled twelve-cylinder V engine
EXTERNAL PIPES FED THE INLET VALVES on the cylinder heads of the 80 horse-power Le Rhone rotary engine. The mixture was taken by the pipes from a collector box on the rear of the crankcase. The engine developed 85 horsepower at 1,300 revolutions a minute. Oil was consumed at the rate of one gallon an hour and petrol consumption was 6-7 gallons an hour.
FOUR classes of aero engines were used during the war of 1914-18. There were rotary engines, radial engines, air-cooled stationary and water-cooled stationary engines.
The rotary engine has died out. Heavy centrifugal stresses confined it to a relatively low power range; in addition, it was uneconomical in consumption, especially of lubricating oil.
The reliability of rotary engines may be gauged from the instructions that were issued for their examination and overhaul. Partial stripping, or opening up and cleaning, and replacement or adjustment were ordered as under: Gnome engines after fourteen hours’ running; Clerget and Monosoupape engines after twenty hours’ running; Bentley engines after thirty hours’ running.
Complete dismantling and overhaul were required after the following hours of running: Bentley engines, ninety hours; Clerget and Monosoupape engines, sixty hours; Gnome, forty hours; Le Rhone, thirty hours.
The other three classes of engine used during the war have since been improved enormously in reliability and power-to-weight ratio; the increase in total power output has also been remarkable.
In this chapter, engine development during the war is considered by individual classes.
Rotary engines were most ingenious. In their day they offered a good power-to-weight ratio, were compact and ran at low revolutions. All were air-cooled. Their cooling was effected by the forward motion of the aeroplane through the air, by the rotation of the engine itself and by the feeding of the fuel through the crankcase.
The rotary engine was mounted in the aeroplane by two transverse bearer plates fitted in the fuselage; through holes in the bearer plates the rear end of the crankshaft was fitted, keyed and locked in position. The weight of the engine was thus usually overhung, but sometimes a spider was fitted to serve as a front mounting.
The crankcase, cylinders, pistons and connecting rods revolved round the crankpin of the stationary crankshaft. The rear end of the crankshaft was hollow; on most rotary engines it carried the carburettor, acted as the main induction pipe and conveyed oil to the engine. As the petrol and oil had a common feed in the crankcase, pure castor oil (which does not mix with petrol) was used for lubrication.
The airscrew, of the two-bladed type, was mounted on a hub which formed an extension of the front cover of the crankcase.
The pilot’s controls for most rotary engines comprised a fine adjustment valve which controlled the pressure and quantity of petrol delivered to the carburettor jet, and a throttle which simultaneously operated a tapered needle in the carburettor jet. Both controls were usually operated by levers that were placed side by side and moved in a quadrant on the side of the cockpit. The first of the rotary engines was the Gnome. The 50 horse-power Gnome had seven cylinders with a bore of 110 mm. and a stroke of 120 mm; its petrol consumption was 5 to 5½ gallons and its oil consumption three-quarters of a gallon an hour. It was used in a few of the earliest war aeroplanes.
The 80 horse-power Gnome was used in the Avro 179 (1914-15), the Avro 504 (1914-17), B.E.8 (1914-15), Bleriot (1914), Bristol Scout (1914-16), Caudron (1914-15), Henri Farman (1914) and Sopwith Tabloid (1914).
This engine had seven cylinders of 124 mm. bore and 140 mm. stroke; petrol consumption was about 6 to 7 gallons an hour and oil consumption about 1¼ to 1½ gallons an hour. The normal full r.p.m. in flight were 1,150, maximum 1,250; the weight of the engine was 209 lb. and weight per horse-power 2.59 lb.
A special feature of Gnome engines was the total absence of inlet pipes to cylinders, achieved by the placing of the inlet valves in the piston heads. The piston head inlet valves gave considerable trouble and were a frequent source of forced landings. The relatively light weight in relation to horse-power of this engine, however, impelled its use in a large number of aircraft types.
The 80 horse-power Le Rhone was used in the Bristol Scout (1914-16), Caudron (1914-15), Caudron Twin Day Bomber (1915-16), Morane Scout (1914-16), Morane Parasol (1916-17) and Sopwith Pup (1916-17).
This nine-cylinder rotary engine was fitted with an inlet and an exhaust valve in each cylinder head, with external pipes that ran to the inlet valves from a collector box on the rear of the crankcase. The bore was 105 mm. and the stroke 140 mm; power developed was 85 horse-power at 1,300 r.p.m. and the weight of the engine was 240 lb. Its petrol and oil consumptions were 6-7 gallons and 1 gallon an hour respectively.
The 80 horse-power Clerget was a seven-cylinder engine of 120 mm. bore and 155 mm. stroke, with inlet and exhaust valves in the cylinder head. It weighed 256 lb. and developed 85 horse-power. The normal running speed was 1,200 r.p.m; petrol and oil consumptions were respectively 6-8 and 1-1½ gallons an hour.
The 100 horse-power Monosoupape (“Single-Valve”) Gnome was used in the Avro 504 (1917-18), D.H.2 (1916-17), Vickers Fighter (1915-16) and F.E.8 (1916-17).
This nine-cylinder rotary engine had, as its name implies, only one valve to each cylinder; this was the mechanically operated exhaust valve in the cylinder head. Inlet to the combustion chamber was provided by a series of holes, drilled near the bottom of each cylinder, which were uncovered by the pistons on their downward stroke. The engine had no carburettor. The petrol required was fed into the crankcase through the hollow crankshaft under the control of a fine adjustment valve operated by the pilot. The exhaust valve remained open for the first two-thirds of the suction stroke and thus admitted air to the cylinder. At this point the valve closed and after a short period of suction the cylinder holes were uncovered to admit rich gas from the crankcase.
“Blip-Switches”
As the speed of the Mono engine (as the type was generally called) was controlled solely by the setting of the petrol fine adjustment valve, it could not be made to run slowly. An auxiliary press-button ignition switch was therefore fitted to the top of the control column. If this switch were intermittently pressed, the ignition was switched on and off to obtain slow running. This procedure was commonly called “blipping” the engine, probably because “blip-blip-blip” was a fair imitation of the sound made by the engine during the process. The switch was known as the “blip-switch”.
All rotary engines had “blip-switches”, but several of them, particularly the Le Rhone and Bentley, could be throttled down to really low speeds without blipping.
The bore and stroke of the Monosoupape engine were 110 mm. and 150 mm. respectively. The weight was 275 lb. and the r.p.m. were 1,200. Petrol and oil consumptions were 9-10 and 2 gallons an hour respectively.
The 110 horse-power Le Rhone was used in the Avro 504 K (1917-18), Bristol Monoplane (1917-18), D.H.5 (1917-18), Morane Scout (1914-16), Morane Parasol (1916-17), Nieuport Scout (1916-18), Sopwith Camel (1917-18) and Vickers Bullet (1916).
This nine-cylinder rotary engine was generally similar to the 80 horsepower Le Rhone, but there were detail points of difference in design. The bore and stroke were 112 mm. and 170 mm. respectively, and the weight was 245 lb. Normal full r.p.m. were 1,205; petrol and oil consumptions were 8 gallons and 1¼ gallons an hour respectively.
The 110 horse-power Clerget was used in the Nieuport two-seater (1916-17) and the Sopwith 1½-Strutter (1916-17).
This nine-cylinder rotary engine had two mechanically operated valves in each cylinder head. Its bore and stroke were 120 mm. and 160 mm. respectively; weight complete was 380 lb, compression ratio 4 to 1, normal horsepower 110, effective horse-power 115 and r.p.m. 1,180. Petrol consumption was 8½-10½ gallons and oil consumption 1½-2 gallons an hour.
AN EARLY GNOME ROTARY ENGINE from which the more powerful Monosoupape Gnome rotary engines were developed. On the early Gnome rotary engines the exhaust valve was in the cylinder head and the inlet valve in the piston head This position for the inlet valves made inlet pipes to the cylinders unnecessary, but the piston head valves gave considerable trouble and caused many forced landings.
The 130 horse-power Clerget was used in the Sopwith 1½-Strutter (1916-17), the Sopwith Triplane (1916-17) and the Sopwith Camel (1917-18).
This engine was similar to the 110 horse-power Clerget, having the same bore, stroke and compression, but the normal horse-power was 130 and effective horse-power 135. The r.p.m. were 1,250, weight was 381 lb. and petrol and oil consumptions were 9-12 gallons and 1½ gallons an hour respectively. The 150 horse-power Monosoupape Gnome was used in the Sopwith Camel (1917-18).
This was a fourteen-cylinder double-bank rotary engine comprising two banks of seven cylinders mounted one behind the other. The principle of valve operation was the same as in the nine-cylinder Monosoupape. The 150 horsepower engine was developed specifically for use at considerable heights and could not give full power at low altitudes. The means of control for altitude was through the ignition; at low heights cylinders fired and missed on alternate power strokes.
Quantity Production
The 150 horse-power Bentley B.R.1, used in the Sopwith Camel (1917-18), was a nine-cylinder rotary engine designed by W. R. Bentley. The bore and stroke were 120 mm. and 170 mm. respectively; the normal full horse-power was 154 at 1,250 r.p.m. and the maximum 156 at 1,300 r.p.m; the compression ratio was 5.9 to 1 and the weight was 416½ lb. The petrol and oil consumptions were 11 gallons and 1½ gallons. The 200 horse-power Bentley B.R.2 was used in the Sopwith Snipe (1918) and the Sopwith Salamander (1918).
This was a nine-cylinder rotary engine of 140 mm. bore and 180 mm. stroke; the normal full brake horse-power was 250 at 1,250 r.p.m. and the weight 475 lb. Petrol and oil consumptions were 20 gallons and 2 gallons an hour respectively.
Static radial engines were being developed in Great Britain in large numbers at the end of the war of 1914-18. During the war the British forces had used two types of static radial engines, both of French manufacture. Had the war continued until 1919, air-cooled radial engines of British design would have been used.
The 100 horse-power Anzani was used in the Caudron Twin Day Bomber (1915-16). It was a ten-cylinder engine built up in two banks of five cylinders. The bore and stroke were 105.1 mm. and 140.2 mm respectively, the r.p.m. 1,200 and the weight 290 lb. Petrol consumption was about 7 gallons and oil about 1¾ gallons an hour.
The 140 horse-power Salmson was used in the Henri Farman “All-Steel” (1915-16) and Voisin Bomber (1915-16).
This engine was a nine-cylinder water-cooled radial engine of French design and manufacture. The M.9 type, built in 1914-15, had a bore of 120 mm. and stroke of 140 mm. It developed 130-140 horse-power at 1,300 r.p.m. The P.9 type was a later development of this engine. More than 1,200 Salmson P.9 engines were built in 1915-16. The bore was increased to 125 mm. and the power developed was 150 horse-power at 1,300 r.p.m.
THE WATER-COOLED SALMSON RADIAL ENGINE was an unusual type. The nine cylinders were arranged horizontally, a right-angled reduction gearing taking the drive to the propeller. The M 9 type, built in 1914-15, developed 130-140 horse-power at 1,300 revolutions a minute. More than 1,200 Salmson P.9 engines, developed from the M9, were built in 1915-16.
Of the air-cooled stationary engines, the 70 horse-power Renault was used in the B.E.2 and B.E.2c (1914-15) and in the Maurice Farman (1914-17).
This eight-cylinder air-cooled engine had two banks of cylinders set at 90 degrees and staggered to allow two connecting rods to work on one crankpin. The bore and stroke were 96 mm. and 120 mm. respectively. Normal r.p.m. were 1,800 and maximum 2,000; the weight was 375 lb. Petrol and oil consumptions were 8 gallons and 4½ pints an hour respectively.
The 90 horse-power R.A.F.1a was used in the Armstrong-Whitworth (1916-17), B.E.2c (1915-17), B.E.2e (1916-17) and De Havilland 6 (1917-18).
Designed at the Royal Aircraft Factory at Farnborough, this eight-cylinder air-cooled engine had two banks of cylinders set at 90 degrees and staggered to allow two connecting rods to work on one crankpin. The bore and stroke were 100 mm. and 140 mm. respectively. Weight, complete with cowls and two magnetos, was 450 lb; weight per horsepower was 4-9 lb. Petrol consumption at 1,600 r.p.m. was 6½ to 7½ gallons an hour, and at 1,800 r.p.m. 9½ gallons an hour. The oil consumption was 5-6 pints an hour.
The 150 horse-power R.A.F.4a was used in the B.F/12 (1916-17), R.E.7 (1915-17) and R.E.8 (1916-18).
This twelve-cylinder air-cooled engine was designed at the Royal Aircraft Factory and was a development of the 90 horse-power R.A.F.1a. The normal horse-power was 160 at 1,800 r.p.m.
Of the water-cooled stationary engines the 90 horse-power Curtiss was used in the J.N.4 (1915-17).
This was an American eight-cylinder engine with the cylinders staggered in two banks of four cylinders set at 90 degrees. The bore and stroke were 101.6 mm. and 127 mm. respectively; the dry weight was 325 lb. with a single magneto, and the weight per horse-power was 3.61 lb. Normal r.p.m. were 1,250, and maximum 1,450. The petrol and oil consumptions were 6½ gallons and 4 pints an hour respectively.
The 120 horse-power Beardmore was used in the Armstrong-Whitworth (1917-18), D.H.1a (1915-17), F,E.2b (1915-17), Martinsyde (1916-17) and R.E.5 (1914-15).
This was a six-cylinder vertical engine with cylinders set in line. The bore and stroke were 130 mm. and 165 mm. Respectively; the weight was 609 lb., with dual magnetos and two carburettors, and the weight per horse-power was 5 lb. Petrol and oil consumptions were 10 gallons and 4½ pints an hour respectively; normal r.p.m. were 1,200, maximum in flight 1,400 This engine was developed by William Beardmore, Ltd., from the original Austro-Daimler design.
Continental Influence
The 150 horse-power Hispano-Suiza was used in the S.E.5 (1917-18) and the S.P.A.D. (1917-18).
This was an eight-cylinder engine, with two cylinder banks set at 90 degrees. The bore and stroke were 120 mm. and 130 mm. respectively. The weight (including airscrew, dual magnetos and dual carburettor, with separate supply to each cylinder bank) was 455 lb; normal horse-power was 150, maximum 170; normal r.p.m. were 1,500, maximum 1,700. Fuel consumption was 9½ gallons an hour and oil 5 pints an hour at normal revolutions.
The 160 horse-power Beardmore was used in the F.E.2b (1917-18), Martinsyde (1916-17) and R.E.7 (1915-17). It was an improved version of the 120 horse-power Beardmore engine. The bore and stroke were 142 mm. And 175 mm. respectively, the normal horse power was 166 at 1,250 r.p.m. and 192 at 1,450 r.p.m. Petrol and oil consumptions were 12 gallons and 5 pints an hour respectively at normal revolutions. The weight complete was 600 lb.
The 180 horse-power Hispano-Suiza was used in the B.E.12b (1918) and the Sopwith Dolphin (1918).
This engine had eight cylinders set in two monobloc banks at 90 degrees. The bore and stroke were 120 mm. and 130 mm. respectively; the normal horse-power was 180 at 1,700 r.p.m. Petrol and oil consumptions were 13½ gallons and 1¼ gallons an hour respectively; the dry weight was 485 lb.
The 200 horse-power Wolseley Adder W.4.B engine was used in the S.E.5a (1917-18).
This engine was developed from Hispano-Suiza designs and had Hispano-Suiza characteristics. The bore and stroke were 120 mm. and 130 mm. respectively; the normal speed was 2,000 r.p.m; petrol and oil consumptions were 15 gallons and 1¼-1½ gallons an hour respectively. The weight was about 570 lb., complete with reduction gear to the airscrew hub. This gear gave an airscrew speed of 1,186 r.p.m. at an engine speed of 2,000 r.p.m.
The 200 horse-power Sunbeam Arab was used in the Sopwith Cuckoo (1917-18) and the N.T.2b flying-boat (1918).
This was an eight-cylinder V engine with the cylinders set at 90 degrees and a reduction gear to the airscrew. The bore and stroke were 120 mm. and 130 mm. respectively; the normal horsepower was 217 at 2,000 r.p.m. and the maximum 224 at 2,100 r.p.m; the petrol and oil consumptions at normal speed were 13½ gallons and 7¾ pints an hour respectively. The dry weight was 550 lb.
The 200 horse-power R.A.F.3a was used in the D.H.4 (1917-18).
This was a twelve-cylinder V engine with the cylinder banks set at 60 degrees. It was designed at the Royal Aircraft Factory. The bore and stroke were 114.3 mm. and 140 mm. respectively; the maximum horse-power was 230 at 1,700 r.p.m; petrol and oil consumptions were 16 gallons and 4 pints per hour respectively; and the weight of the engine (including radiator and cooling water) was 897 lb.
The 240 horse-power B.H.P. was used in the D.H.9 (1918). The initials stood for Beardmore, Halford and Pullinger, the designers of the engine. It was built by the Arrol Johnston Co., Ltd.
This was a six-cylinder-in-line vertical engine. Its bore and stroke were 145 mm. and 190 mm. respectively; it developed 236 horse-power at 1,400 (normal) r.p.m. and 250 horse-power at
1,500 r.p.m. It was later developed into the Siddeley Puma engine, in which its design remained substantially unaltered. The dry weight (including airscrew boss, carburettors and magnetos) was 680 lb; petrol and oil consumptions were 16¼ gallons and 6½ pints an hour respectively at normal revolutions.
A TWELVE-CYLINDER V ENGINE, the Rolls-Royce Eagle VIII, was produced in 1917. This water-cooled engine was built on similar lines to the Rolls-Royce engines of 1938. The banks of cylinders were set at an angle of sixty degrees and a reduction gear was used to drive the airscrew. The normal horse-power was 352 at 1,800 revolutions.
The 250 horse-power Sunbeam Maori was used in the Fairey 3b float seaplane (1918).
This engine was a twelve-cylinder V type with two banks of cylinders set at 60 degrees and a reduction gear to the airscrew. The bore and stroke were 100 mm. and 134.8 mm. respectively; the normal horse-power was 265 at 2,100 r.p.m. and the maximum 280 at 2,200 r.p.m. The dry weight was 890 lb. and the petrol and oil consumptions were 18¾ gallons and 6¼ pints an hour respectively.
Famous British Type
The 250 horse-power Rolls-Royce was used in the Blackburn Kangaroo (1918), Bristol Fighter (1917-18), D.H.4 (1917-18), F.E.2d (1916-17), R.E.7 (1915-17) and Short Bomber (1916-17).
This engine was the Rolls-Royce Falcon III, a twelve-cylinder engine with two banks of cylinders set in a 60 degrees V, and a reduction gear to the airscrew. The bore and stroke were 101.6 mm. and 146 mm. respectively; the normal horse-power was 267 at 2,000 r.p.m. and the maximum 280 at 2,300 r.p.m. Petrol and oil consumptions were 20 gallons and 5 pints an hour respectively and the dry weight was 695 lb.
The 300 horse-power Hispano-Suiza was used in the Martinsyde Buzzard (1918).
This was a direct-drive eight-cylinder 90 degrees V engine, with each bank of cylinders in monobloc. The bore and stroke were 140 mm. and 150 mm. respectively; normal horse-power was 308 at 1,850 r.p.m. Petrol and oil consumptions were 24 5/8 gallons and 1 gallon per hour respectively; and the dry weight was 595 lb.
The 320 horse-power Sunbeam Cossack was used in Short and Fairey seaplanes.
This engine was a twelve-cylinder V with the cylinder banks set at 60 degrees and a reduction gear to the airscrew. The bore and stroke were 110 mm. and 160 mm. respectively; normal horse-power was 350 at 2,000 r.p.i., and the maximum 364 at 2,100 r.p.m. Petrol and oil consumptions were 24½ gallons and 1½ gallons an hour respectively; the dry weight was 1,118 lb.
The 360 horse-power Rolls-Royce Eagle VIII was used in the D.H.4 (1917-18), D.H.9a (1918), Fairey 3c float seaplane (1918), F.2a flying boat (1917-18), F.3 flying boat (1918), F.5 flying boat (1919), H.16 flying boat (1918) and Handley Page V 1,500 (1918).
The Eagle VIII was a twelve-cylinder engine with two banks of cylinders set at 60 degrees and with a reduction gear to the airscrew. The bore and stroke were 114-3 mm. and 165 mm. respectively; normal horse-power was 352 at 1,800 r.p.m; petrol and oil consumptions were 24 gallons and 6¼ pints an hour respectively; the dry weight was 916 lb.
The 400 horse-power Liberty was used in the D.H.9a (1918) and the D.H.10 (1918). The Liberty engine is illustrated on this page.
DESIGNED IN THE UNITED STATES, the 400 horse-power Liberty engine had twelve cylinders arranged in two banks of six at an angle of forty-five degrees. The maximum horsepower was 430 at 1,800 revolutions a minute; no gearing to the airscrew was used These engines were fitted to the D.H.9a and D.H.10 aeroplanes in 1918.
