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Pratt & Whitney R-1690 Hornet A
Fiat A.59
BMW Hornet


Pratt & Whitney R-1690 Hornet


First run in June 1926, the Pratt & Whitney R-1690 Hornet was a widely used aircraft engine. It was a single-row, 9-cylinder air-cooled radial design. Displacement was 1,690 cubic inches (27.7 L).
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.
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 2:1 propeller speed reduction is provided by a geared unit of patented Pratt & whiney design, weighing 840 lb.
It first flew in 1927. Developed by Pratt & Whitney, 2,944 were produced from 1926 through 1942.
It was built under licence in Italy as the Fiat A.59. In Germany, the BMW 132 was a developed version of this engine.
The R-1860 Hornet B was an enlarged version produced from 1929.


525 hp (392 kW), 625 hp (466 kW)
525 hp (392 kW)
575 hp (429 kW)
600 hp (450 kW), 775 hp (578 kW)
700 hp (522 kW)
750 hp (559 kW)
750 hp (559 kW)
850 hp (634 kW)
1,050 hp (780 kW)
Fiat A.59 R.
Licence built in Italy with reduction gearing.
Fiat A.59 R.C.
Licence built in Italy with reduction gearing and supercharger.
BMW Hornet
Licence production of the Hornet in Germany, independently developed as the BMW 132.


Bach Air Yacht
Bellanca 31-40
Boeing 80
Boeing Model 95
Boeing 221
Boeing Model 299
Burnelli UB-14
Douglas O-38
Fokker F.32
Junkers Ju-52
Junkers Ju 86
Junkers W 34
Keystone B-3
Lockheed Model 14 Super Electra (L-14H)
Lockheed Lodestar (C-56A, C-56B, C-56C, C-56D, C-56E, C-59/Mk 1a)
Martin XB-14
Vought O2U Corsair
Sikorsky S-42
Sikorsky S-43
Wedell-Williams Model 44




Hornet A-1
Type: 9 cylinder fixed radial, air cooled
Military Rating: 525 hp at 1900 rpm
Commercial Rating direct: 525 hp at 1900 rpm
Commercial Rating geared: 500 hp at 1900 rpm
Displacement: 1690
Compression ratio: 5-1
Bore: 6.125 in
Stroke: 6.375 in
Length: 44 7/8 in
Diameter: 55 7/16 in
Weight: 775 lb
Fuel consumption: not more than .55 lb/hp/hr
Oil consumption: not more than .035 lb/hp/hr
Lubrication: Pressure (gear pump) 75-100 lb
Ignition: Scintilla, dual
Carburation: Stromberg, 2 bbls.
Starter: Eclipse
Spark plugs: Eclipse
Price Series A: $8500
Price Series A.G: $9500


R-1690 SIE-G
Type: Nine-cylinder single-row supercharged air-cooled radial engine
Bore: 6 1⁄8 in (155.6 mm)
Stroke: 6 3⁄8 in (161.9 mm)
Displacement: 1,690.5 in³ (27.7 l)
Length: 50.98 in (1,295 mm)
Diameter: 54.41 in (1,382 mm)
Dry weight: 1,014 lb (460 kg)
Valvetrain: Pushrod-actuated
Supercharger: Single-speed centrifugal type supercharger, 12.0:1 gear ratio
Fuel system: Two-barrel Stromberg carburetor
Fuel type: 87 octane rating gasoline
Cooling system: Air-cooled
Reduction gear: Epicyclic gearing, 2:3
Power output:
789 hp (589 kW) at 2,300 rpm for takeoff
740 hp (552 kW) at 2,250 rpm at 7,000 ft (2,135 m)
Specific power: 0.47 hp/in³ (21.26 kW/l)
Compression ratio: 6.0:1
Specific fuel consumption: 0.6 lb/(hp•h) (362 g/(kW/h))
Oil consumption: 0.42 oz/(hp•h) (16 g/(kW/h))
Power-to-weight ratio: 0.78 hp/lb (1.28 kW/kg)



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