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Wright R-760 Whirlwind-225 / J-6-7
Fábrica Nacional de Motores FNM R-760

 

  Wright-R760
Wright R-760

 

Wright introduced the J-6 Whirlwind family in 1928 to replace the nine-cylinder R-790 series. The J-6 family included varieties with five, seven, and nine cylinders. The seven-cylinder version was originally known as the J-6 Whirlwind Seven, or J-6-7 for short. The U.S. government designated it as the R-760; Wright later adopted this and dropped the J-6 nomenclature. Model designations included Whirlwind 235, 250, 285, and 320.
 
The R-760 cylinders are of a steel barrel over which an aluminium alloy head is screwed and shrunk. Intake ports are at the rear with exhaust ports on the forward side of cylinder.
 
The crankcase assembly is composed of four major castings of aluminium alloy. The cam follower housing carrying the tappet guides is cast integral with the main section of the crankcase.
 
Two-piece single-throw crankshaft with one-piece master rod and “H” section articulated rods.
 
Aluminium alloy pistons, cross ribbed on under side of head, and fitted with full floating hollow pins held in place by expanding spring wire locks.
 
Tulip shaped valves, solid stem inlet valves and hollow stem exhaust valves.
 
Rotary induction system of Wright design, with “pre-heating” device on carburettor. Provision is made for obtaining, at all times, a clean supply of air to the carburettor.
 
Lubrication system is designed to eliminate all external oil pipes to the engine.
 
Equipment supplied was air cleaner and heater, nose cowling, complete exhaust manifold, priming pump, ignition switch, tool kit, external oil filter, and instruction book.
 
Accessories available at extra cost were Ecllipse hand inertia starter, Eclipse generator, Eclipse generator control box, standard steel propeller hub, fuel pump, Eclipse combination hand and electric inertia starter, Eclipse hand starter with booster magneto, Eclipse electric inertia starter, propeller hub for wooden propeller, metal propeller, and hubs for two or three blade props.
 
Wright-R760-02

 

Like all the members of the J-6 Whirlwind family, the R-760 had larger cylinders than the R-790. The piston stroke of 5.5 in (14.0 cm) was unchanged, but the cylinder bore was expanded to 5.0 in (12.7 cm) from the R-790's bore of 4.5 in (11.4 cm). While the R-790 was naturally aspirated, the R-760, like the other J-6 engines, had a gear-driven supercharger to boost its power output.
Over time, Wright refined the R-760, using suffix letters to indicate successive versions. The original R-760 (or J-6-7) was rated for 225 hp (168 kW), while the R-760E of 1931 could do 250 hp (186 kW) thanks to an improved cylinder head design. Wright later added another suffix to show different power levels. The R-760E-1, introduced the same year as the R-760E, had a takeoff power rating of 300 hp (224 kW) thanks to higher-compression pistons and a greater RPM limit. The even more powerful R-760E-2 of 1935 could reach 350 hp (261 kW) for takeoff due to increased supercharging and an even higher RPM limit. On the other hand, the R-760E-T, designed for trainer aircraft, had the R-760E-1's high-compression pistons, but the supercharger was removed, thus giving just 235 hp (175 kW).
 
The R-760 was a direct replacement for the R-790, with similar displacement and power. The U.S. Navy used it as the powerplant for several biplane primary trainers, including the Consolidated NY, the Curtiss N2C Fledgling, and the Naval Aircraft Factory N3N Canary. The last of these was produced in large numbers, with most of the engines built under license by the Naval Aircraft Factory. Trainers usually had the unsupercharged R-760E-T engine.
 
A variety of civil utility aircraft also used the R-760, including models built by Beechcraft, Cessna, Curtiss-Wright, Howard DGA-8, Stearman, Stinson, and Waco. These aircraft generally used the various supercharged versions of the R-760.
 

Production of the R-760 continued until 1945, with about 1400 examples being built by Wright, and more under licence by foraign anufacturers such as Fábrica Nacional de Motores in Brazil. 


Applications:
Beechcraft Staggerwing
Cessna DC-6B Scout
Consolidated NY-3
Curtiss N2C-2 Fledgling
Fairchild Model 45
Howard DGA-8
Naval Aircraft Factory N3N Canary
St. Louis YPT-15
Stearman C3R Business Speedster
Stinson Junior
Stinson Reliant
Waco CSO and CTO
Waco CJC, CJC-S, DJC, DJC-S, and DJS
Waco CUC, DQC-6, EQC-6, DGC-7 & 8, EGC-7 & 8
Waco CRG

 

Specifications:

 

Type: 7 cylinder air cooled fixed radial
Military Rating: 225 hp at 2000 rpm
Commercial Rating: 225 hp at 2000 rpm
Displacement: 756 cu.in
Compression ratio: 5.1-1
Bore: 5 in
Stroke: 5 1/2 in
Length: 40 23/32 in
Diameter: 45 in
Weight: 445 lb
Fuel consumption: not more than .55 lb/hp/hr
Oil consumption: not more than .035 lb/hp/hr
Lubrication: Pressure pumps
Ignition: Scintilla dual
Carburation: Stomberg, single barrel
Spark plugs: 2 per cylinder
Price: $3900

 

J-6-7 (R-760)
225 hp (168 kW) at 2,000 RPM.

 

R-760E
Power, continuous: 250 hp (186 kW) at 2,000 RPM
Compression ratio: 5.1:1
Supercharger gear ratio: 7.05:1
Octane rating: 73
Dry weight: 530 lb (240 kg)
Higher power from improved cylinder head.

 

R-760E-1
Power, continuous: 285 hp (213 kW) at 2,100 RPM
Power, takeoff: 300 hp (224 kW) at 2,250 RPM
Compression ratio: 6.1:1
Supercharger gear ratio: 7.05:1
Octane rating: 73
Dry weight: 565 lb (256 kg)
Higher compression ratio.

 

R-760E-2
Type: 7-cylinder supercharged air-cooled radial piston engine
Bore: 5.0 in (127 mm)
Stroke: 5.5 in (140 mm)
Displacement: 756 in³ (12.4 L)
Length: 42.44 in (107.8 cm)
Diameter: 45.0 in (114.3 cm)
Dry weight: 570 lb (259 kg)
Valvetrain: 2 valves per cylinder, pushrod-actuated
Supercharger: gear-driven, 9.17:1 impeller gear ratio
Fuel type: 80 octane
Reduction gear: Direct drive
Power, continuous: 320 hp (239 kW) at 2,200 RPM at sea level
Power, takeoff: 350 hp (261 kW) at 2,400 RPM
Specific power: 0.42 hp/cu-in (19.3 kW/L)
Compression ratio: 6.3:1
Power-to-weight ratio: 0.56 hp/lb (0.92 kW/kg)

 

R-760E-T
Power, continuous: 235 hp (175 kW) at 2,000 RPM
Compression ratio: 6.1:1
Supercharger gear ratio: none
Octane rating: 73
Dry weight: 540 lb (245 kg)
Unsupercharged version of R-760E-1 for trainer aircraft.

 

R-760-2, -4, -8
235 hp (175 kW) at 2,000 RPM.
U.S. Navy versions of R-760E-T.

 

 


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