S-49/R-6A/HOS-1/Hoverfly Mk II HELICOPTER

Sikorsky S-49/R-6A Army Serial No. 43-45379

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.

Nash-Kelvinator R-6 production line in Detroit Michigan

S-49/R-6 Development Timeline

April 30, 1943. Cost plus fixed fee contract for six XR-6 helicopters signed. October 15, 1943. First Flight of the XR-6 September 1943. Contract negotiated with Nash-Kelvinator to build R-6 helicopters. Sikorsky

contracted to provide engineering services and dynamic components. August 28, 1943. Production contract for Nash-Kelvinator to build 900 Sikorsky R-6A helicopters

under license signed. March 2, 1944. XR-6A set unofficial nonstop distance record of 397 miles in 4 hours 55 minutes.

September 1944 First XHOS-1 delivered to USN and transferred to USCG Air Station Floyd Bennett Field.

October 23, 1944. First Nash-Kelvinator R-6A helicopter accepted by USAAF.

First YR-6A Helicopter completed by Nash-Kelvinator in Detroit

January 1945. Last XR-6A accepted by USAAF. May 27, 1945. Three R-6A helicopters make first helicopter rescue in China. Three crewmen from a C-

46 crash in the Yuan Chiang Valley are rescued nearly 100 miles from the helicopter base in Kunming, China.

July 14, 1945. Army R-6A helicopter dispatched to the Paricutin Volcano in Michoacán, Mexico to gather scientific information by hovering over the volcano. The scientists benefited by studying the lightning-like discharges with thunder within the erupting material and the Army gained experience with high altitude (over 8,700 feet), turbulence, and high temperature operations similar to those encountered in the South Pacific. Over 60 flights were conducted. Igor Sikorsky, an amateur volcanologist, accompanied the expedition.

R-6A flies over Paricutin volcano in Mexico July, 1945

August 16, 1945. Nash-Kelvinator R-6A contact cancelled after 219 of 900 helicopters ordered were completed.

July 1, 1946. VX-3 (Helicopter Development Squadron Three), the U.S. Navy’s first helicopter Squadron is formed at NAS New York with 7 HOS-1 (R-6) and numerous HSN-1 (R-4) helicopters transferred from the U.S. Coast Guard.

July-October 1946. First four helicopter Detachment of VX-3 HOS-1 helicopters embarked on USS Saidor (CVE-117) and joined Operation Crossroads to collect data during Atomic Testing at Bikini Atoll in the Marshall Islands. The helicopters retrieved film from camera towers that were inaccessible using any other means. During the trip from the east coast to the west coast a VX-3 HOS-1 became the first helicopter to fly nonstop from the Atlantic to the Pacific ocean along the Panama Canal

September 20, 1946. A U.S. Coast Guard HOS-1G from CGAS Floyd Bennett is disassembled, loaded in a C-54, and reassembled in Gander, Newfoundland to assist in rescuing 16 survivors of a SABENA airlines DC-4.

December 1947. Captain Clayton Marcy, the CO of VX-3, completes the first transcontinental helicopter trip from Lakehurst, NJ to San Diego, California in a HOS-1 helicopter.

May 1949. Last USCG HOS-1G is retired from service. August 1951. Last RAF Hoverfly Mk II is retired from service.

VX-3 Sikorsky HOS-1 takes off from a Seaplane Tender

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.

R-6A Main Components

Main Rotor AssemblyA 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.

S-49 (R-6) Main Rotor Assembly

Main Gear BoxThe 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.

A cutaway of the S-49 (R-6A) Planetary Main Gear Box

EngineA 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 BladesThe main rotor blades were constructed with tubular steel spars, plywood ribs and leading edge, canvas covered pockets, and a NACA 0012 airfoil.

Tail RotorAn articulated tail rotor with 3 blades was installed. Blades were constructed of laminated wood with a fabric cover.

General Arrangement Drawing

S-9 (R-6A) 3-view 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.

XR-6A on floats

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.

USCG S-49 (HOS-1) over Kill Devil Hills, NC with Igor Sikorsky as a passenger December 17, 1947

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.

XR-6A Army Serial No. 43-28240 with litters installed

General Characteristics and Performance S-49 (R-6)

PERFORMANCE Standard Day, Sea LevelMaximum speed (Vne) 115 mph / 100 kts

185.2km/hr.

Range (Maximum Demonstrated) 400 miles 643.7 kmService ceiling 13,200 ft. 4,023.4mRate of Climb 780 ft./min 3.96 m/sAbsolute hover ceiling 3,000 ft. 914.4 m

WEIGHTS

Maximum takeoff gross weightR-6A 2,590 lbs. 1,174.8 kgR-6A Alternate gross weight Rescue 2,620 lbs. 1,188.4 kgR-6A Alternate gross weight - Six 100 lb. Bombs 4,985 lbs.1,409.8 kgR-6A Alternate gross weight – Two 250 lb. Bombs 2,952 lbs. 1,339.0 kgR-6A Alternate gross weight – Two 325 lb.Depth Charges 3,138 lbs. 1,423.4 kgWeight empty 2,016 lbs. 914.4 kgMaximum fuel load 75 gal 283.9 ltr

GENERAL DATA

Crew seating capacity Pilot and Copilot/Observer 2

POWERPLANT RATINGSStandard 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 mTail rotor diameter (blade tip circle) 8’ 2.5”" 2.44 mFuselage length 33’11" 10.06 mLength over-all (including rotors) 48’0” 14.63mHeight over-all 11’ 7” 3.35 mMain 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).

RAF Hoverfly Mk. II Rescue Helicopter 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.

Prepared by Vinny DevineOctober 2012