Sikorsky R-4

Summary

Description

The development of helicopters faced significant technical challenges that delayed their progress compared to airplanes. Igor Sikorsky, a Russian engineer who emigrated to the United States, became interested in helicopters but was unable to solve the problems related to vertical takeoff and landing, as well as hovering, before World War II. He therefore focused on designing airplanes, but eventually resumed his helicopter research in the late 1930s.

Sikorsky succeeded in designing a revolutionary prototype called the VS-300, which caught the attention of the US government. With its support, Sikorsky collaborated with Vought to develop the VS-316, which was later designated as the XR-4 by the US Army. Several versions of the XR-4 were produced, including the YR-4A with a more powerful engine and a larger rotor, as well as the YR-4B intended for the US Navy with an enlarged cabin. Despite their increased weight, these versions were successfully used for medical evacuations and pilot recovery operations.

The program continued to progress, and Sikorsky continued to improve the helicopter, which was renamed the R-4. Different versions of the R-4 were produced, including the XR-4C, which combined features from the XR-4 and YR-4A. A series of aircraft called the HNS-1 were delivered to the US Navy and US Coast Guards. The production of these helicopters was relatively short-lived as Sikorsky quickly turned to an improved model, the R-6.

The R-6, also known as the VS-316B, had a metal coating and a more powerful engine than the R-4. The production versions of the R-6 used by the US Navy were designated as HOS-1. The United States, the United Kingdom, and Canada were the main users of the R-4 and R-6, with a predominance of the US and the UK. The British helicopters were designated Hoverfly Mk I for the R-4B and Hoverfly Mk II for the R-6A. However, these models were quickly replaced after 1945 by more modern helicopters, such as the Sikorsky S-51.

Main versions:

• XR-4: a single prototype, developed for one pilot and one passenger, with dual controls.
• YR-4A: three units, equipped with an R-550-1 engine with 180hp and a larger rotor.
• YR-4B: an improved version of the YR-4A; forty-one units produced.
• R-4B: production version; one hundred units produced, with twenty-two for the US Coast Guards and US Navy, and forty-five for the Royal Navy.
• XR-4C: a single unit made from the XR-4 airframe, YR-4A rotor, and an R-550-1 engine with 180hp.
• HNS-1: a series of seven YR-4B and twenty-two R-4B delivered to the US Navy and US Coast Guards.

Technical specifications

Current operating countries

No country is operating the R-4 in 2024.

All operators

Canada • United Kingdom • United States

Photo of R-4