Sikorsky R-4


The Sikorsky R-4 is a two-seat light helicopter that was designed by Igor Sikorsky with a single, three-bladed main rotor and powered by a radial engine. The R-4 was the world's first large-scale mass-produced helicopter and the first helicopter used by the United States Army Air Forces, the United States Navy, the United States Coast Guard and the United Kingdom's Royal Air Force and Royal Navy. In U.S. Navy and U.S. Coast Guard service, the helicopter was known as the Sikorsky HNS-1. In British service it was known as the Hoverfly.

Development

The VS-316 was developed from the famous experimental VS-300 helicopter, invented by Igor Sikorsky and publicly demonstrated in 1940. The VS-316 was designated the XR-4, under the United States Army Air Forces' series for "Rotorcraft". The XR-4 first flew on 14 January 1942 and was accepted by the Army on 30 May 1942. The XR-4 exceeded all the previous helicopter endurance altitude and airspeed records that had been set before it. The XR-4 completed a cross-country flight from Bridgeport, Connecticut, to Wright Field, Ohio, set a helicopter peak altitude record of, while achieving 100 flight hours without a major incident and top airspeed approaching
The British Admiralty, having learned of the VS-300, made a ship available, Empire Mersey, fitted with an landing platform, intended to show the USN their work with ship-borne autogyros. After her loss in 1942 to a U-boat, she was replaced by SS Daghestan. The first deck-landing trials aboard Daghestan were carried out in 1944. The British received two of the first eight helicopters built.
On 5 January 1943, the United States Army Air Forces ordered 29 prototypes. The first three were designated YR-4A and used for evaluation testing. The YR-4A benefited from a Warner R-550-1 Super Scarab engine, compared to the Warner R-500-3 in the prototype, and a rotor diameter increased by. Evaluation of the YR-4A demonstrated a need for further improvements, including moving the tailwheel further aft on the tailboom, venting the exhaust to the side instead of downward, and increasing the fuel capacity by. These and other design changes led to the designation of later prototypes as YR-4B, which were used for service testing and flight training.
United Aircraft announced on 5 November 1944 that the one hundredth helicopter had been completed, and that the production rate had reached five every six days.

Operational history

Following the explosion and sinking in January 1944 of USS Turner, U.S. Coast Guard Commander Frank Erickson flew the first U.S. helicopter rescue in a Sikorsky R-4 carrying life saving blood plasma for the casualties from New York City.
On 22–23 April 1944, U.S. Army Lieutenant Carter Harman of the 1st Air Commando Group conducted the first combat rescue by helicopter using a YR-4B in the China-Burma-India theater. Despite the high altitude, humidity, and capacity for only a single passenger, Harman rescued a downed liaison aircraft pilot and his three British soldier passengers, two at a time. On 22–23 January 1945, another rescue by the R-4 involved several legs for refueling and navigating through passes between mountains nearly 10,000 feet tall, to reach a weather station located at an elevation of 4,700 feet. The higher-than-normal altitude required a downhill run of 20 ft to get airborne.
While the R-4 was being used for rescues in Burma and China, it was also being used to ferry parts between floating Aviation Repair Units in the South Pacific. On 23 May 1944, six ships set sail with two R-4s on board each vessel. The ships had been configured as floating repair depots for damaged Army Air Forces aircraft in the South Pacific. When the helicopters were not being used to fly the parts from one location to another, they were enlisted for medical evacuation and other mercy missions. Helicopter pilot 2LT Louis Carle was assigned to the Brigadier General Clinton W. Russell, the Fifth Aircraft Repair Unit. From June 15 to July 29, 1945, Carle and five other pilots evacuated 75 to 80 wounded soldiers, one or two at a time, from the highlands northeast of Manila. They were the second group of helicopter pilots after Lieutenant Carter Harman to evacuate wounded via helicopter during World War II. Unlike Harman, they were targeted by Japanese soldiers who tried to shoot them down with machine guns. Their six-week effort constitutes the largest combat helicopter operation before the Korean War.
On June 15, 1945, the Fifth Air Force received a request from the 38th Infantry Division to evacuate two soldiers with head injuries from a spot east of Manila. Carle flew one of his ship's Sikorsky R-4 helicopters and landed near the front lines, much to the amazement of the soldiers, who had never seen a helicopter. The helicopter was not configured to handle stretchers, and they removed a seat and placed the wounded man on the aircraft floor. Carle flew the soldier to the 311th General Field Hospital near Manila. Once word got out of their availability, they were called on again and again. Carle flew seven hours and made six evacuations on the same day.
In Royal Air Force service, the R-4 was called the Hoverfly. The Helicopter Training School, formed January 1945 at RAF Andover, was the first British military unit to be equipped with the helicopter. Many RAF Hoverfly Mark Is were transferred to the Royal Navy for training and one was used in 1945–46 by Fairey Aviation to develop rotor systems for their Gyrodyne helicopter.

Piloting difficulty

The helicopter was difficult to fly. The aircraft's blades were made of wood ribs around a steel spar and covered with doped fabric. The blades were difficult to keep rotating in the same plane and vibrated excessively. The cyclic made continuous small orbits, vibrating continuously. There was no governor to control rotor speed, and the pilot had to correlate the throttle continuously with collective pitch inputs. The Chicago Tribune reported on Carle's efforts to transport the wounded. They wrote that the "control stick shakes like a jackhammer, and the pilot must hold it tightly at all times. Should he relax for even a minute the plane falls out of control. Pilots of regular planes say it's easy to identify a helicopter pilothe has a permanent case of the shakes."

Variants

;XR-4
;YR-4A
;YR-4B
;R-4B
;XR-4C
;HNS-1
;Hoverfly I
;Sikorsky S-54

Operators

;Canada
;United Kingdom
Image:Sikorsky R-4B U.S. Army Aviation Museum.jpg|thumb|R-4B Hoverfly, US Army Aviation Museum
;United States