Engine development and evolution is often only mentioned an afterthought in the rapid development of aircraft between 1919 and 1939.
The list below is by no means a complete list of aircraft engines used in seaplanes.
It is simply a list of engines used in United States Navy two-engine flying boats that saw service or whose design had an impact on the future. The flying boat the engine was used in is in parentheses.
Rolls Royce, Hispano Suiza, BMW, and Armstrong-Siddely, just to name a few, were all water-cooled and radial engines made during the 1920's and beyond
for commercial and foreign flying boats.
- 1919
- 360-hp Liberty 12-cylinder water-cooled engine [Felixstowe F.5L]
- 1920
- 300-hp Wright-Hispano H-3 8-cylinder water-cooled engine [Naval Aircraft Factory TF]
- 1924
- 480-hp Packard 1A-2500 V-12 water-cooled engine [NAF PN-7]
- 525-hp Wright T-2 12-cylinder water-cooled engine [NAF PN-7]
- 575-hp Wright T-3 Tornado V-12 water-cooled engine [NAF PN-8]
- 1926
- 525-hp Wright R-1750 Cyclone 9-cylinder radial engine [NAF PN-7,Martin PM-1]
- 1927
- 225-hp Wright J-4 9-cylinder radial engine [Sikorsky S-36]
- 525-hp Wright R-1750D Cyclone 9-cylinder radial [NAF PN-8, 9, 10, 11, 12]
- 1928
- 525-hp Pratt-Whitney R-1690-32 Hornet 9-cylinder radial engine [Martin PM-3]
- 1930
- 450-hp Pratt-Whitney R-1340-96 Wasp 9-cylinder radial engines [XPY-1 Ranger]
- 1932
- 575-hp Wright R-1820E Hornet 9-cylinder radial engine [P2Y-1 Ranger]
- 1933
- 750-hp Wright R-1820-90 Cyclone 9-cylinder radial engine[P2Y-3 Ranger]
- 825-hp Pratt-Whitney R-1830-54 Twin Wasp twin-row radial engine [PBY-1 Catalina]
- 1935
- 900-hp Pratt-Whitney R-1830-64 Twin Wasp twin-row radial engine [PBY-3 Catalina]
- 1936
- 1,000-hp Wright R-1820-53 Cyclone 9-cylinder radial engines [PB2Y Coronado]
- 1937
- 1,200-hp Pratt-Whitney R-1830-88 Twin Wasp 14-cylinder radial engine [PB2Y Coronado]
- 1939
- 1,600-hp Wright R-2600 Cyclone 14, two-row, 14-cylinder radial engine [Boeing 314A]
Engine development and aircraft design went hand-in-hand, and this is particularly true of seaplane design during this period. The British Felixstowe F.5 had two engines that developed only 345 hp each, meaning it could only attain a maximum speed of 88 mph and an endurance of approximately 7 hours. Seven years later, little had changed as far as performance, though the engine had become more reliable. Flying boats still average a maximum speed of approximately 120 mph and were generally considered underpowered. Engine reliability was also a problem. In 1925, the Naval Aircraft Factory had to replace the Wright T2 radial engines with Packard 1A-2500 V-12 water-cooled engines on the PN-7 because of reliability issues. Pratt and Whitney responded with the R-1340 radial engine. It had 1,340 cubic inches of displacement, and the engine featured a new design of crankshaft and master rod, which had been shown to be a weak area in a number of other designs of the era. The is one example of the competition that went on to develop more powerful and reliable engines.
By 1927, the Pratt-Whitney, and the Wright radial engines, began to squeeze out the water-cooled engine competitors. Despite having more air resistance, the radial engines were easier to maintain in a marine environment and had become more reliable than the water-cooled engines. The Naval Aircraft Factory (NAF) continued to experiment with both types of engines. Because problems kept cropping up in water-cooled engines, in 1927, the Bureau of Aeronautics specified only air-cooled engines should be used by the Navy. Despite this, in 1932, the Navy experimented with one Hall XP2H-1 flying boat which used four Curtiss V-1570-54 Conqueror V-12 water-cooled piston engines. It was lost in 1933 due to a landing accident, and though it had extremely long range no others were built.
The 1930’s saw a dramatic increase in power from the radial engines, so it is no surprise there was a dramatic increase in size, and performance of the aircraft as well (See charts below). The final P2Y-3 had a maximum speed of 128 mph and a range of 2,650 miles. In 1938, when the PBY-3 came out with the 1,000-hp Wright R-1820-66 Cyclone 9-cylinder radial engines the aircraft had a speed of 191 mph and a range of 2,550 miles. More importantly, its power/mass ratio had increased from the P2Y-3’s 0.059 hp/lbs. to 0.067hp/lbs., meaning now the Consolidated PBY could now carry torpedoes. The Martin PBM Mariner, which entered service in 1939, had two supercharged Wright Cyclone 14 GR2600A2, two-row, 14-cylinder radial engines, which drove the flying boat at a cruising speed of 147 mph. Compared to the P2y-3’s gross weight of 25,266 pounds, the Boeing 314 had a gross weight of 60,000 lbs.
The 1930's and World War II saw the apogee of the radial engine design, and also its demise as the jet engine came into use. It would also see the end of military flying boats as the range of land-based patrol aircraft increased and landing fields became more ubiquitous.
