Sikorsky Product History
Sikorsky S-49 / VS-316B
Background
The Sikorsky S-49/R-6/HOS-1 model was a follow-on to the successful R-4 helicopter with the first flight on October 15, 1943. It was designed as a streamlined R-4 with an all metal fuselage, a larger engine, and a planetary gear main gear box. The XR-6 helicopters featured the R-4B 38 foot 3 bladed fully articulated main rotor and a 3 bladed tail rotor powered by a 225 hp Lycoming O435-7 six cylinder horizontally opposed engine. The Lycoming engine was replaced by a 235 hp Franklin O-405-9 engine in the XR-6A and all subsequent R-6 models. The S-49 had 2 place side by side seating in the cockpit. One Experimental XR-6 and five XR-6A/XHOS-1 helicopters were initially built by Sikorsky Aircraft.
On March 2, 1944 a Sikorsky XR-6A helicopter flew non-stop from Washington, D.C. to Patterson Field in Dayton Ohio a distance of 387 miles in 4 hours 55 minutes with a ground speed of 80 mph. The flight crossed the Allegheny Mountains at an altitude of 5,000 feet. The pilot was Colonel Frank Gregory and the passenger was Ralph Alex, the Sikorsky project engineer. World records for speed, distance and endurance by a helicopter were eclipsed by this flight.
Since Sikorsky Aircraft was at maximum production capacity with the R-4 and R-5 models, the USAAF, Production Division at Wright Field directed that the S-49/R-6 production be License built by Nash-Kelvinator. Nash-Kelvinator was selected since they were already producing Hamilton Standard Propellers and Pratt and Whitney Double Wasp R-2800 engines under Licenses from United Aircraft Corporation. Sikorsky Aircraft was very reluctant to release control over helicopter production and showed little interest in accepting a contract to furnish the engineering and design data while another manufacturer did the fabrication. Sikorsky eventually complied with the government decision.
Nash-Kelvinator was awarded a contract for 26 YR-6A developmental helicopters followed by a production contract for 900 R-6A helicopters. Since the Kenosha and Milwaukee Wisconsin areas (Nash-Kelvinator’s home) had labor shortages, the War Production Board directed Nash-Kelvinator to build the R-6 helicopters elsewhere. Nash-Kelvinator built cabins in Grand Rapids, Michigan and performed final assembly in Detroit Michigan. Other components came from suppliers across the country including Sikorsky Aircraft providing Rotors, gearboxes, blades, and most drivetrain components. Production was slow in coming mainly because Sikorsky made countless changes to the original design which delayed the delivery of drawings for long periods of time. The XR-6A prototypes were still in Testing and Sikorsky wanted the helicopter to be as perfect as possible before releasing the production drawings. As a result Nash-Kelvinator did not test its first production model until mid-September 1944 with the first delivery on October 23, 1944. Nash-Kelvinator had 4 assembly lines producing 16 helicopters at a time. At peak production Nash-Kelvinator was producing 50 helicopters per month. Production was halted in 1945 with Nash-Kelvinator producing 219 R-6 helicopters.
S-49 / R-6 Development Timeline
Configuration Features
The Sikorsky S-49 fuselage was built in 5 major sections: 1. Cabin Section – a non-structural frame formed of plastic and a resin impregnated glass fibre cloth externally covered by dural cap strips, transparent plastic windows, and side by side seating for two; 2. Lower Beam Assembly – an aluminum structure that provided the cockpit floor which supported the entire nose section of the helicopter; 3. Center Section – a tubular steel frame; 4. Fairing Assembly – provided a covering for the center section made as plastic laminate panels, and 5. Tail Cone – a dural aluminum frame with magnesium skins and a semi monocoque design.
Main Rotor Assembly
A 3 blade fully articulated main rotor head was installed on the R-6 helicopter. The rotor diameter was 38 feet. This was the same rotor as the R-4B helicopter.
Main Gear Box
The main gear box with a magnesium housing stood vertically between the engine and main rotor. It conveyed power to the main rotor at reduced speed ratio of 12.96 to 1 and to the tail rotor at a reduced speed ratio of 1.309 to 1. It also included a freewheeling unit to allow autorotation in case of engine failure. A hydraulic rotor brake was located at the rear of the main gear box. The S-49 main gear box contained a planetary system gear reduction system. This was the first use of this method for speed reduction in Sikorsky helicopters and various planetary configurations were used in most subsequent Sikorsky helicopters.
Engine
A Franklin 235 hp O-405-9 six cylinder horizontally opposed engine was installed vertically under the center section of the helicopter with a cooling fan/flywheel above. A centrifugal clutch connected the engine to the main gear box.
Main Rotor Blades
The main rotor blades were constructed with tubular steel spars, plywood ribs and leading edge, canvas covered pockets, and a NACA 0012 airfoil.
Tail Rotor
An articulated tail rotor with 3 blades was installed. Blades were constructed of laminated wood with a fabric cover.
General Arrangement Drawing
Mission Systems
The tactical mission of the S-49 helicopter was for liaison, observation and medical evacuation. The fuselage was equipped with attach points for “Hot Dog” floats and provisions for tubes to support dual litters or bomb racks.
U.S. Coast Guard S-49 (HOS-1) helicopters were equipped with rescue hoists, emergency flotation gear, and bubbles on the fuselage to accommodate a stretcher horizontally across the cabin.
Provisions for carrying 2 enclosed litters were provided for the R-6A. The original design also included bomb racks to carry bombs and depth charges, but in late 1944 the Bomb Racks were deleted from the requirements.
General Characteristics and Performance
Performance Standard Day at Sea Level | |
|---|---|
Maximum Speed (Vne) | 115 mph / 100 kts / 185.2 km/hr |
Range (Maximum Demonstrated) | 400 miles / 643.7 km |
Service Ceiling | 13,200 ft / 4,023.4 m |
Rate of Climb | 780 ft/min / 3.96 m/s |
Absolute Hover Ceiling | 3,000 ft / 914.4 m |
Weights | |
|---|---|
R-6A Maximum Takeoff Gross Weight | 2,590 lbs / 1,174.8 kg |
R-6A Alternate Gross Weight Rescue | 2,620 lbs / 1,188.4 kg |
R-6A Alternate Gross Weight – Six 100 lb Bombs | 4,985 lbs / 1,409.8 kg |
R-6A Alternate Gross Weight – Two 250 lb Bombs | 2,952 lbs / 1,339.0 kg |
R-6A Alternate Gross Weight – Two 325 lb Depth Charges | 3,138 lbs / 1,423.4 kg |
Weight Empty | 2,016 lbs / 914.4 kg |
Maximum Fuel Load | 75 gal / 283.9 ltr |
General Data | |
|---|---|
Crew Seating Capacity, Pilot and Co-Pilot/Observer | 2 |
Powerplant Ratings Standard Day at Sea Level | |
|---|---|
Franklin O-405-9 Horizontally Opposed 6 Cylinders | 235 hp / 172.8 kw |
Aircraft Dimensions | |
|---|---|
Main Rotor Diameter (Blade Tip Circle) | 38’ 0” / 14.63 m |
Tail rotor diameter (blade tip circle) | 8’ 2.5″ / 2.44 m |
Fuselage Length | 33’ 11″ / 10.06 m |
Length Overall (Including Rotors) | 48’ 0” / 14.63 m |
Height Overall | 11’ 7” / 3.35 m |
Main Landing Gear Tread | 9′ 0″ / 2.74 m |
Production History
S-49 (R-6) production consisted of 225 helicopters:
- 1 XR-6 model manufactured 1943 Sikorsky Aircraft
- 5 XR-6A models manufactured by Sikorsky Aircraft 1943. Three were purchased from the USAAF by the U. S. Navy as XHOS-1 helicopters.
- 26 YR-6A models manufactured under license by Nash-Kelvinator 1944
- 193 R-6A models manufactured under license by Nash-Kelvinator for the USAAF. The USAAF sold 36 helicopters to the US Navy (HOS-1) and 27 under Lend-Lease to the Royal Air Force (Hoverfly Mk II).
Additional Information:
The S-49 (R-6) was replaced by the more capable S-51 helicopter which addressed many of the lessons learned from the S-49 program.
- by Vinny Devine
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