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Sikorsky S-72 (X-Wing)

Experimental Compound Helicopter Prototype

Sikorsky S-72 (X-Wing)

Experimental Compound Helicopter Prototype


The Sikorsky S-72 experimental helicopter of the late-Cold War period was used to test a compound helicopter design - two flyable prototypes were completed before the end.
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ORIGIN: United States
YEAR: 1976
STATUS: Cancelled
MANUFACTURER(S): Sikorsky Aircraft / Lockheed / NASA - USA
OPERATORS: United States (cancelled)

Unless otherwise noted the presented statistics below pertain to the Sikorsky S-72 (X-Wing) model. Common measurements, and their respective conversions, are shown when possible.
LENGTH: 70.54 feet (21.5 meters)
WIDTH: 62.01 feet (18.9 meters)
HEIGHT: 14.50 feet (4.42 meters)
WEIGHT (EMPTY): 20,944 pounds (9,500 kilograms)
WEIGHT (MTOW): 26,048 pounds (11,815 kilograms)
ENGINE: 2 x General Electric T58-GE-5 turboshaft engines driving a four-bladed main rotor with four-bladed tail rotor; 2 x General Electric TF34-GE-404A turbofan engines.
SPEED (MAX): 230 miles-per-hour (370 kilometers-per-hour; 200 knots)



Series Model Variants
• S-72 - Base Series Designation; two examples completed.
• S-72 "X-Wing" - Revised S-72 prototype with rigid main rotor which could be paused in flight after achieving vertical take-off; turbofan engines then handled forward thrust.


Detailing the development and operational history of the Sikorsky S-72 (X-Wing) Experimental Compound Helicopter Prototype.  Entry last updated on 8/7/2018. Authored by Staff Writer. Content ©
First flown on October 12th, 1976 the "S-72" was an experimental, high-speed compound helicopter design by Sikorsky Aircraft. The design, born through the Rotor Systems Research Aircraft (RSRA) project, stemmed from a U.S. Army / NASA venture (with work handled by Sikorsky) seeking to collect high-speed data on helicopter rotor characteristics by way of a combination powerplant arrangement. The end-product involved the Sikorsky S-67 helicopter framework coupled with the Sikorsky S-61 main rotor. Beyond the turboshaft engines used to drive the rotor assemblies, additional power was to be had from a pair of General Electric TF34 turbofans situated along the fuselage sides. A low-set, straight monoplane was fitted under the aircraft while the tail rotor (facing portside) was retained. Just two of the aircraft were completed for testing.

The S-72 carried a crew of two or three and had a length of 70.6 feet with a wingspan of 62 feet and a height of 14.5 feet. Empty weight was 21,700lb and the Maximum Take-Off Weight (MTOW) reached 26,050lb. The rotors were powered by a pair of General Electric T58-GE-5 turboshaft engines of 1,400 horsepower each and the turbofan installations were 2 x General Electric TF34-GE-400A engines of 9,400lb thrust. Performance specs included a maximum speed of 230 miles per hour with a cruise speed of 160 miles per hour.

The original S-72 form could be flown with or without the main rotor unit and, due to the uniqueness of the S-72's design, an equally-unique crew ejection system was developed for the compound helicopter to increase survivability of the test pilots. The process involved complete jettison of the main rotor blades via controlled explosives and rockets ejected the crew positions out and away from the fuselage. After a first-flight in 1976 and testing thereafter, NASA received one of the aircraft in February of 1979. Beyond data collection, this model did not progress beyond its experimental design.

An offshoot of the S-72 became the so-called "X-Wing" aircraft which used a rigid main rotor unit (shaped as an "X" over the fuselage) which could be paused by the operator during flight. The aircraft could therefore take-off vertically like a traditional helicopter and then engage forward, high-speed travel with the available turbofan engines, combining the best elements of both aircraft types. Lockheed handled the concept work under DARPA and attention then turned to Sikorsky to modify one of the existing RSRA prototypes for the tests. This product appeared in completed form during 1986 but was not flown for the program was given up for good in 1988.


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Relative Maximum Speed Rating
Hi: 300mph
Lo: 150mph
    This entry's maximum listed speed (230mph).

    Graph average of 225 miles-per-hour.
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Unit Production Comparison
Comm. Market HI*: 44,000 units
Military Market HI**: 36,183 units

  * Commercial Market High belongs to Cessna 172.

  ** Military Market High belongs to Ilyushin Il-2.

Supported Roles
Ground Attack
Aerial Tanker
A2A=Air-to-Air; UAV=Unmanned; CAS=Close Support; ASW=Anti-Submarine; AEW=Airborne Early Warning; MEDEVAC=Medical Evac; EW=Electronic Warfare; SAR=Search-Rescue