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Pratt & Whitney R-1860 Hornet B

Pratt & Whitney R-1860 Hornet B


The Pratt & Whitney R-1860 Hornet B was a relatively uncommon aircraft engine, first run in 1929. It was a development of Pratt & Whitney's earlier R-1690 Hornet and was basically similar, but enlarged in capacity from 1,690 to 1,860 cubic inches (30.5 L). Bore was increased by 1/8" and the stroke by 3/8". Both engines were air-cooled radial engines, with a single row of nine cylinders.
The master connecting rod has a solid instead of detachable cap big end for higher crank speeds. The single throw two-pice crahkshaft is divided into a forward and rear section. The crankpin is integral with the forward section which transmits power to the propeller hub carried by it. The rear section telescopes into the crankpin and is carried completely through it. The two sections are united by a through bolt and kept in the proper angular relation by splines.
The main crankcase of forged aluminium is divided into two similar sections in the plane of the cylinder and united by nine through bolts between the cylinders as well as by the cylinder flanges.
The cylinder and valve design was with two large valves driven by pushrods. All valve operating parts are enclosed. The rocker arms are supported by ball bearings and are mounted in the rocker housings which are part of the cylinder head. The push rods are enclosed by telescopic covers held in place by springs.
Every Pratt & Whitney engine is provided with a General Electric rotary induction fan used to provide proper mixture distribution. With suitable gear ratio it is possible for certain specialised purposes to provide a reasonable amount of supercharging without additional weight or complication.
All the accessories are grouped at the rear of the engine protected by the cowling.
On geared engines a 3:1 propeller speed reduction is provided by a geared unit of patented Pratt & whiney design, weighing 885 lb.
The enlarged engine was designed by George Willgoos and was first available in 1929.
The fourteen-cylinder Twin Wasp was more complex and costly than the nine-cylinder, single-row Hornet B. The Twin Wasp was by far the more powerful engine though, even in its early versions it produced 800 hp to the Hornet B's 575 bhp. A further advantage was the reduced diameter of the Wasp: 48 inches compared to 57. This reduced drag, and the very large diameter of the Hornet would also have been a serious drawback for visibility if used in a small single-engined aircraft.
Although a technically competent design, the enlarged Hornet B engine was not a commercial success. Customers preferred to buy the R-1830 Twin Wasp instead, which in time became the most numerous aircraft engine ever produced.


Bellanca C-27 Airbus
Boeing Monomail
Boeing YB-9
Consolidated Commodore
Consolidated Fleetster
Fokker F-32
Keystone B-4A
Keystone LB-8 (prototype only)
Keystone XLB-12 (engine evaluation testbed only)
Martin XT6M (prototype only)
Sikorsky S-40
Sikorsky S-41



Type: Nine-cylinder single-row supercharged air-cooled radial engine
Rating - direct: 575 hp / 429 kW at 1950 rpm
Rating - geared: 550 hp at 1950 rpm
Displacement: 1860 (30.54 L)
Compression ratio: 5-1
Bore: 6.25 in (158.8 mm)
Stroke: 6.75 in (171.4 mm)
Length: 44 9/16 in / 113.7 cm
Diameter: 56 3/4 in / 144.6 cm
Weight: 810 lb
Dry weight: 376.4 kg (830 lb)
Fuel consumption: not more than .55 lb/hp/hr
Oil consumption: not more than .035 lb/hp/hr
Lubrication: Pressue (gear pump) 75-100 lb
Ignition: Scintilla dual
Carburation: Stromberg, 2 bbls
Supercharger: Single-speed centrifugal type supercharger
Valvetrain: Pushrod-actuated, two valves per cylinder
Starter: Eclipse
Spark plugs: B.G.
Price Series B: $8500
Price Series B G: $9500








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