Sikorsky R-4



The Sikorsky R-4 was a two-place helicopter 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 to enter service with the United States Army Air Forces, Navy, and Coast Guard, as well as for the United Kingdom's Royal Air Force and Royal Navy.

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 made its initial flight on 13 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 761-mile (1,225 km) cross country flight from Connecticut to Wright Field, Ohio, set a service ceiling of 12,000 feet (3,700 m), 100 flight hours without a major incident, and an airspeed approaching 90 mph (140 km/h).

The British Admiralty, having learned of the VS-300, made a ship available that had been intended to show the USN their work with autogyros and ship operations. The Empire Mersey was fitted with a landing platform. After her loss in 1942 to a U-boat, she was replaced by the SS Daghestan. The British would receive two of the first eight helicopters built.

On 5 January 1943, the United States Army Air Forces ordered 29 prototypes. The first three prototypes were designated as the YR-4A and used for evaluation testing. The YR-4A benefited from a larger, 180 hp (130 kW) Warner Super Scarab (R-550-1) engine, compared to the 165 hp (123 kW) R-500-3 engine in the prototype, and a rotor diameter increased by one foot (30 cm). Evaluation of the YR-4A demonstrated a need for further improvements, including moving the tailwheel further towards the rear of the tailboom, venting the exhaust to the side instead of downward, and increasing the fuel capacity by five gallons (19 liters). These and other design changes led to the designation of later prototypes as YR-4B, which were used for service testing and flight training.

Operational history
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 (3,000 m) tall, to reach a weather station located at an elevation of 4,700 feet (1,400 m). The higher than normal altitude required a downhill run of 20 ft (6.1 m) 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.

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 of the RAF Hoverfly 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.

Variants


Some R-4s had the tail wheel located at the extreme aft end of the boom near the tail rotor while others had it positioned at the midpoint of the boom. Additionally, some had short "stub" exhaust pipes from the engine while others had a much longer one which extended vertically and then aft above the main landing gear struts.


 * XR-4
 * One prototype Model VS-316A with a crew of two and dual controls, 165 hp R-500-3 engine, became XR-4C


 * YR-4A
 * Version with larger rotor diameter and a 180 hp R-550-1 engine; three built.


 * YR-4B
 * Version with detailed changes; 27 built for development testing followed by a further batch of 14, seven to US Navy as HNS-1s.


 * R-4B
 * Production version with 200 hp R-550-3 engine; 100 built including 20 for the US Navy and 45 for the Royal Air Force.


 * XR-4C
 * Prototype XR-4 re-engined with 180 hp R-550-1 engine with the larger YR-4A type rotor.


 * HNS-1
 * Three YR-4Bs and 22 R-4Bs transferred to the US Navy; two diverted to the United States Coast Guard.


 * Hoverfly I
 * UK military designation of the R-4 for the Royal Air Force and Royal Navy; 52 delivered and one later transferred to the Royal Canadian Air Force.


 * Sikorsky S-54
 * An R-4B modified with an observers seat aft of the main rotor gearbox for trials.

Operators

 * Royal Canadian Air Force
 * Royal Canadian Air Force


 * Royal Air Force - Helicopter Training Flight 43 OTU, Transport Command Development Unit, Kings Flight (mail flights between RAF Dyce and Balmoral)
 * Fleet Air Arm - 705 NAS
 * 🇺🇸 United States
 * United States Army Air Forces
 * United States Navy
 * United States Coast Guard
 * United States Coast Guard

Aircraft on display

 * XR-4C prototype, the Smithsonian Museum's Steven F. Udvar-Hazy Center
 * R-4B (s/n 43-46506) is on display at the National Museum of the United States Air Force at Wright-Patterson AFB near Dayton, Ohio. It was donated by the University of Illinois in 1967.
 * Hoverfly Mk.1, KL110/KL995, at the Royal Air Force Museum London. Supplied under lend-lease, it arrived in Britain in February 1945. It flew with the RAF, later the Royal Navy, until 1951. It was used by the College of Aeronautics, Cranfield until it was presented to the RAF museum in 1966.
 * R4-B, serial number 43-46503, is on display at the New England Air Museum, located next to Bradley International Airport, Windsor Locks, CT.
 * R-4B in the Storage Hangar of the Canada Aviation and Space Museum in Ottawa, Ontario
 * National Museum of Naval Aviation in Pensacola, Florida. Exhibit is an HNS-1 Hoverfly (Bureau Number 39047) - On indoor static display in US Coast Guard markings.
 * Army Aviation Museum at Fort Rucker, Alabama. U.S. Army R-4B Hoverfly (Serial Number 43-46592) and R-6A Hoverfly II (Serial Number 43-45473) on indoor static display.
 * Yanks Air Museum in Chino, California has an R-4B (Serial Number 43-46534) in their restoration hangar.