By the end of World War II, Igor Sikorsky had established himself as a leading innovator in helicopter design. The XR-5 came about as a direct result of lessons learned from Sikorsky's development of the R-4, America's first production helicopter. The XR-5 represents another major step in the maturation of the helicopter into a truly capable and reliable category of aircraft. While the R-4, and its developmental cousin, the R-6, saw operational service in World War II, they were underpowered, difficult to fly, and required excessive maintenance, which led to a limited service life. The production R-5s and their civilian counterpart, the S-51, overcame these difficulties and played an important role in establishing the helicopter as an indispensable aircraft for military and civilian operators.
The development of the XR-5 officially began when the British Air Commission placed an order for two "large" (compared to the diminutive XR-4) prototype Vought-Sikorsky helicopters on April 29, 1942. The British had been surprised by the good performance of the XR-4 helicopter. At this time, German U-boat wolfpacks remained a considerable threat to the lifeline of trans-Atlantic convoys that sustained Great Britain. The convoys were particularly vulnerable in mid-Atlantic, beyond the range of shore-based anti-submarine patrol aircraft. There were also very few aircraft carriers available to sail with the convoys and provide air cover. A helicopter that could carry bombs or depth charges and operate from the decks of escort vessels or even merchant ships appeared to offer an ideal solution to the U-boat problem.
The U. S. Army Air Forces (AAF) caught on to the possibilities of an upgraded XR-4 and quickly submitted a request on May 8, 1942, for an upgraded design, a "workhorse" helicopter with a useful load of over 495 kg (1,100 lb). The request stated, "it is urgently desired to develop a helicopter with greater useful load, endurance, speed, service ceiling, which would have greater utility than the XR-4." Any increase in any aspect of the XR-4's performance would be greeted with fanfare because the helicopter had almost no useful load once the pilot was on board. On May 27, the Air Material Command issued Technical Instruction 1124. This order released funds for the construction of four helicopters of the "workhorse" type, designated XR-5. The requirements of the AAF and the British were similar enough that a single design could probably fulfill both needs. Two of the four machines described in TI 1124 were earmarked for Britain to be paid for using Lend-Lease funds.
The design process for the XR-5 was already well under way by the time TI 1124 was issued. More than six months earlier, Igor Sikorsky had anticipated a military request for a purpose-built observation helicopter. The Platt-LePage XR-1 had already won the AAF contract for development of an observation helicopter, but Sikorsky knew it would never become a practical service machine. Well ahead of actual events, he launched a program to develop a more practical design called the VS-327 (V for Vought and S for Sikorsky. Vought, like Sikorsky, was one of several companies owned by the holding company United Aircraft). Development began on September 26, 1941, and William E. Hunt was named project manager. When the Technical Instruction for the XR-5 was issued, the VS-327 handily met the requirements.
Work on the design progressed quickly, but when construction began on the first prototype, the pace slowed. As chief designer, Igor Sikorsky had a pivotal role to play but the demands of other projects distracted him. There was also considerable difficulty obtaining certain strategic materials such as aluminum to build the helicopter. The AAF considered helicopters interesting and promising, but gave conventional warplanes a higher priority. Sikorsky had to build certain sections of the helicopter, such as the tailcone and fuselage panels, from non-strategic materials, such as wood. This increased the aircraft's weight, reduced structural integrity, and delayed the project. Aluminum versions replaced these wooden components when the predicted shortages failed to materialize. The Pratt & Whitney R-985 engine chosen for the XR-5 was also a source of trouble. At that time, this power plant was used in Vought's OS2U Kingfisher naval floatplane. To speed construction, Sikorsky retained the Kingfisher engine mount arrangement in the XR-5 but during ground runs, the helicopter overheated badly. A fan was needed to force more cooling air through the engine compartment, but there was not enough space to install it within the Kingfisher engine mount. Revising the mount and adding the fan further delayed the program.
Sikorsky was aware that the box-top fuselage of the XR-4 obstructed airflow from the main rotor and reduced the rotor's lifting capacity. He also knew that visibility out of this earlier design could be much improved and these two design goals drove the overall layout of the XR-5. The fuselage was more streamlined and slimmer in profile, and nearly the entire nose of the helicopter was covered in Plexiglas windows. The observer occupied the front seat of this "fishbowl," while the pilot occupied the seat directly behind him. The XR-4 used a tricycle undercarriage supplemented by a strut and wheel extending attached beneath the rear fuselage to prevent the tail rotor from striking the ground during flight-testing. Sikorsky dispensed with this wheel and strut on the production models.
Each of the three rotor blades resembled the fixed-wing of a conventional airplane. A laminated wooden spar supported wooden ribs and the whole assembly was covered with fabric. These blades were difficult to build, hard to balance, and easily damaged by rain. Sikorsky replaced the wooden spars with steel tubes in production versions of the XR-5 and this resulted in safer, more durable blades. However, he had to retain the fabric covering. It was not yet possible to build a rotor blade skinned with metal that was also flexible enough to flap and flex in flight.
Company chief test pilot Les Morris carried out the first flight of the XR-5 (s/n 43-28236) on August 18, 1943. Following adjustments to blade tracking and lead-lag dampers, flights soon exceeded 30 minutes. On September 13, the XR-5 lifted a pilot, observer, and eight passengers perched on the landing gear strut fairings, and exceeded the military useful load requirement by 270 kg (600 lb). Testing progressed well until October 12. With Sikorsky's nephew, Jimmy Viner, at the controls, the tail rotor failed at an altitude of 23 m (75 ft). Viner crash-landed and neither he, nor his observer were injured, but the aircraft suffered significant damage. Production on the next XR-5 (s/n 43-28237) was quickly stepped up and test flying resumed the last week of November 1943.
AAF leaders authorized series production of the XR-5 on March 24, 1943, to commence whenever the final development phase of the XR-5 was complete. This contract specified a production run of 250 aircraft, 100 of them earmarked for Great Britain. The contract soon increased by 150 helicopters for the AAF, and the Navy ordered 50 more. The development process had continued at a steady but relatively slow pace, as much of Sikorsky's effort was focused on series production of the R-4 and R-6. These helicopters had met their contract requirements while the XR-5 was still struggling through the test program. Great Britain cancelled two XR-5s on March 25, 1944, because aircraft carriers and long-range patrol aircraft had filled the antisubmarine role originally envisioned for the R-5. The AAF quickly moved to take over this order, as Lt. Col. Frank Gregory, head of the AAF helicopter program, remained enthusiastic about XR-5. He considered it more advanced than any other American helicopter developed up to that time. Flight tests began on the fifth and final XR-5 at the Sikorsky plant in Bridgeport, CT, on January 17, 1944. The AAF accepted this aircraft and transferred it to Wright Field for further development on September 30, 1944.
That this dawn of a new technological era remained perilous for both man and machine is graphically illustrated by the fate of the XR-5s. The third (s/n 43-28238) was destroyed on November 4, 1944. The fabric covering one of the rotor blades tore loose and in the ensuing crash, the helicopter rolled over. The second XR-5 suffered a fatal crash at Gainesville, Florida, on December 2, 1944, when welds in one of the steel collars holding the blades to the rotor mast failed. As a result, a different welding technique was adopted on the assembly line. The first XR-5 suffered an engine failure while flying to a war bond rally in Nebraska. The pilot crash-landed but the airframe was too damaged to repair it was scavenged for spare parts. The AAF continued to test the last XR-5 (s/n 43-47954) until 1946, when the service handed the helicopter over to the National Air Museum (later the Smithsonian National Air and Space Museum).
By March 29, 1945, the AAF declared the XR-5 development program complete and service planners cleared the R-5A for series production. The AAF designated the first 26 aircraft off the line as YR-5A service test aircraft, but these helicopters did not otherwise differ from production R-5As. Trouble returned to the program after the R-5A began flying. Poor aerodynamic analysis by the National Advisory Committee for Aeronautics (NACA) caused Sikorsky to turn out unbalanced rotor blades, and the company was forced to correct the flaw with makeshift repairs that hurt performance of the production aircraft. When World War II ended, the AAF cancelled or reduced a number of aircraft contracts, including the R-5A, and Sikorsky completed 60 YR-5A and R-5A aircraft, of which, only nine were delivered before V-E Day. Ironically, the cancellation allowed the designer to further refine the aircraft, and to develop it for the civil market. This work produced the R-5F and its civilian counterpart, the S-51. In these models, the rear-seat cockpit was converted into seating for three and the observer seat became the pilot's position.
Although the AAF accepted R-5A helicopters before the end of World War II, these never reached operational units and service interest in the aircraft appeared to be waning. Sikorsky believed that without military customers, the civilian S-51 held the key to continued growth of the helicopter market and he promoted it vigorously. On November 29, 1945, an S-51 dramatically rescued two seamen from a foundering barge off the coast at Bridgeport during severe weather. This event renewed military interest and a number of R-5 variants served until after the Korean War. Before the arrival of Bell's famed H-13 (Model 47) into the Korean combat zone in 1951, military pilots flying the H-5 (H for helicopter replaced R for rotorcraft) conducted most of the thousands of medical evacuation (medevac) missions flown during that war. The H-5 and the H-13 reduced the fatality rate among wounded soldiers during the Korean War by more than 50 percent, however, the narrow center of gravity range on the H-5 soon made it obsolete compared to newer helicopters. Sikorsky attempted to extend the longevity of this classic design by offering the U. S. Navy a new five-seat version, the XHJS-1, but the helicopter lost out to Piasecki's tandem-rotor HUP-1. As the H-5 disappeared from the U.S. military inventories, Westland Aircraft Limited of England continued to build the aircraft, under license, as the HR.1 Dragonfly. These aircraft served with the Royal Air Force and Royal Navy throughout most of the 1950s.
Helicopter Air Transport (HAT), based in New Jersey, became one of the first commercial helicopter operators when it took delivery of several S-51s in 1946. The operating cost of these aircraft proved too high for HAT's primary business, flight training, and the company went bankrupt. A number of airlines and other companies experimented in the late 1940s and early 1950s with the S-51 for passenger, freight, and mail service but again, the costs of operating and maintaining the helicopter were simply too high for any of these enterprises too succeed. The S-51 failed to develop into a commercially viable aircraft but it proved that civilian helicopters could perform useful jobs, and it paved the way for more advanced designs. However, no helicopter airline has survived without massive government subsidies. Sikorsky Aircraft Corporation continues to produce helicopters that trace their lineage back to the XR-5.
Rotor Diameter: 14.6 m (48 ft)
Length: 13.7 m (44 ft 11.5 in)
Height: 3.9 m (13 ft)
Weights: Empty, 1,656 kg (3,650 lb)
Gross, 2,223 kg (4,900 lb)
Engine: Pratt and Whitney air-cooled radial, R-985-AN-5, 450 horsepower
References and Further Reading:
Gregory, H. Franklin. "Anything A Horse Can Do." New York: Reynal and Hitchcock,
1944.
Hunt, William E. "'Heelicopter': Pioneering with Igor Sikorsky." Shrewsbury, England:
Airlife Publishing, Ltd., 1998.
Spencer, Jay P. "Whirlybirds: A History of the U.S. Helicopter Pioneers." Seattle:
University of Washington Press, 1998.
XR-5 curatorial file, Aeronautics Division, National Air and Space Museum
Roger Connor, Russell Lee, 8-9-01
