The Sikorsky R-4 Hoverfly was an early utility helicopter that was used by the United States during World War II.
The R-4 had a single Warner R-550 piston-engine that was capable of propelling it at speeds of up to 120 kilometers per hour. However, it was later discovered in the field that this was slightly underpowered, which could cause some problems in the field, especially in the critical time it took to recover lost personnel. The R-4 required only a single pilot to operate, though could carry another passenger. The operational range of the craft was around 370 kilometers and a service ceiling of 2,340 meters.
The total weight of the R-4 was around 952 kilograms with a total length of 14.7 meters. Rotor diameter meanwhile was 11.6 meters. The reliability of the R-4 was good enough for operational service, though the craft did experience some troubles in the CBI theater where it initially served, particularly the humidity caused by the jungle conditions, which made the Warner engine struggle.
The first variant of the YR-4 or later designated R-4 was the R-4B model, now equipped with a more powerful Warner R-550-3 engine providing more thrust. A total of 100 examples of this type were built, more than any other type of "Hoverfly". The Hoverfly Mk I was merely a redesignation of the original R-4. The 22 R-4Bs in US Navy service were designated HNS-1.
The R-4 Hoverfly was developed as the VS-316A in 1941 by Igor Sikorsky, following previous developments into rotorcraft technology. It first flew in early 1942, being accepted for service only a few months later. This prototype was designated the XR-4. Most notably, it had outperformed every other attempt at a helicopter before it. At around the same time, seven examples of the R-4 were sent to Great Britain. The first production models finally left the prototype phase in 1943. It wasn't until mid 1944 that the R-4 finally saw its first combat operation. This took place in the CBI theater in which an R-4B was used to rescue several lost airmen. Afterwards, the R-4 was used in various other operations, notably serving as repair vehicles, ferrying parts between ships in the South Pacific. The first R-4s finally entered the Western Front with Britain in 1945. In total, around 131 examples had been produced during World War II.
- Gunston, Bill. Illustrated Guide to Military Helicopters. Salamander Books Ltd. 1981. ISBN 0 86101 110 4 Page 106