The McDonnell HRH, company designation Model 78, was a 1950s transport helicopter proposal for the

United States Marine Corps The United States Marine Corps (USMC), also referred to as the United States Marines, is the maritime land force service branch of the United States Armed Forces responsible for conducting expeditionary and amphibious operations through combi ...

(USMC) by McDonnell Aircraft, designed to operate from ''Commencement Bay''-class

escort carrier The escort carrier or escort aircraft carrier (U.S. hull classification symbol CVE), also called a "jeep carrier" or "baby flattop" in the United States Navy (USN) or "Woolworth Carrier" by the Royal Navy, was a small and slow type of aircraft ...

Development

McDonnell Aircraft was awarded a contract for the aircraft in March 1951 after responding to a 1950 USMC requirement for an assault transport helicopter to carry 30 fully-equipped marines and two pilots from an

. The HRH emerged as a compound helicopter with a three-bladed rotor driven by McDonnell-designed tip jets fed by auxiliary compressors driven by the main engines, which were also equipped with three-bladed propellers that would provide forward thrust once the stall speed of the aircraft's stub wings was exceeded. The aircraft would be equipped with a hydraulic loading ramp under the cockpit, and could alternately carry two smaller vehicles or 24 stretchers instead of 30 troops. The rotors, stub wings, and tail would fold to allow the large aircraft to use the small deck elevators on ''Commencement Bay''-class escort carriers. A full-scale

mockup In manufacturing and design, a mockup, or mock-up, is a scale or full-size model of a design or device, used for teaching, demonstration, design evaluation, promotion, and other purposes. A mockup may be a ''prototype'' if it provides at leas ...

was inspected and approved by the U.S. Navy in October 1952 and construction of three prototypes ( bureau numbers ''133736'' to ''133738'') was authorized; however, officials were concerned about potential developmental problems, and the end of the

Korean War , date = {{Ubl, 25 June 1950 – 27 July 1953 (''de facto'')({{Age in years, months, weeks and days, month1=6, day1=25, year1=1950, month2=7, day2=27, year2=1953), 25 June 1950 – present (''de jure'')({{Age in years, months, weeks a ...

led to substantial US military budget cuts. Although the Bureau of Aeronautics had expected the XHRH-1 to fly in December 1955, the design was cancelled in 1953 in favor in of the Sikorsky HR2S, the first prototype remaining uncompleted. All work on the aircraft was terminated in April 1954.

Specifications (Model 78 / XHRH-1 estimated)

References

{{Authority control United States military helicopters 1950s United States military transport aircraft 1950s United States helicopters

HRH Royal Highness is a style used to address or refer to some members of royal families, usually princes or princesses. Monarchs and their consorts are usually styled ''Majesty''. When used as a direct form of address, spoken or written, it takes ...

Tipjet-powered helicopters