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 XR6A/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
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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.
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September 1944 First XHOS-1 delivered to USN and transferred to USCG Air Station Floyd Bennett
Field.
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October 23, 1944. First Nash-Kelvinator R-6A helicopter accepted by USAAF.
First YR-6A Helicopter completed by Nash-Kelvinator in Detroit
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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 C46 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
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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 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.
S-49 (R-6) Main Rotor Assembly
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.
A cutaway of the S-49 (R-6A) Planetary Main Gear Box
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
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 Level
Maximum speed (Vne)
115 mph / 100 kts
185.2km/hr.
Range (Maximum Demonstrated)
Service ceiling
Rate of Climb
Absolute hover ceiling
400 miles 643.7 km
13,200 ft. 4,023.4m
780 ft./min 3.96 m/s
3,000 ft.
914.4 m
WEIGHTS
Maximum takeoff gross weight
R-6A
R-6A Alternate gross weight Rescue
R-6A Alternate gross weight - Six 100 lb. Bombs
R-6A Alternate gross weight – Two 250 lb. Bombs
R-6A Alternate gross weight – Two 325 lb.Depth Charges
Weight empty
Maximum fuel load
2,590 lbs. 1,174.8 kg
2,620 lbs. 1,188.4 kg
4,985 lbs.1,409.8 kg
2,952 lbs. 1,339.0 kg
3,138 lbs. 1,423.4 kg
2,016 lbs. 914.4 kg
75 gal
283.9 ltr
GENERAL DATA
Crew seating capacity Pilot and Copilot/Observer
2
POWERPLANT RATINGS
Standard Day at Sea Level
Franklin O-405-9 Horizontally Opposed 6 Cylinders
235 hp
172.8 kw
38’ 0”
8’ 2.5”"
33’11"
48’0”
11’ 7”
9' 0"
14.63 m
2.44 m
10.06 m
14.63m
3.35 m
2.74 m
AIRCRAFT DIMENSIONS
Main rotor diameter (blade tip circle)
Tail rotor diameter (blade tip circle)
Fuselage length
Length over-all (including rotors)
Height over-all
Main landing gear tread
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 Devine
October 2012