Sikorsky S-75

S-75 ACAP

Sikorsky S-75 ACAP all-composite test aircraft
Role	Experimental helicopter
Manufacturer	Sikorsky Aircraft
First flight	July 1984
Primary user	United States Army
Number built	2
Developed from	Sikorsky S-76

The Sikorsky S-75 was a proof of concept all-composite helicopter. Sikorsky Aircraft used all composite materials to replace metal to provide greater strength, lighter weight, lower manufacturing costs, and reduce maintenance costs.

Design and development

The Sikorsky S-75 was developed under the US Army's Advanced Composite Airframe Program (ACAP), the goal of which was the development of an all-composite helicopter fuselage considerably lighter and less costly to build than predominantly metal airframes in support of the Light Helicopter Experimental (LHX) program.^[1]^[2] In February 1981, contracts were awarded to Sikorsky and Bell Helicopter, with Bell submitting its Model D292. The S-75 flew for the first time in July 1984.

The S-75 mated an entirely new composite airframe with the twin turboshaft engines, transmission, and main and tail rotors of Sikorsky's S-76A civil transport helicopter.^[1] The S-75's floors, roof and most exterior surfaces were of more ballistically-resistant Kevlar, while most of the aircraft's basic load-bearing structure was built of graphite or a graphite/epoxy blend. The machine was equipped with specially designed impact-resistant crew and passenger seats and high-strength pneumatic shock absorbers on its fixed tricycle landing gear, in keeping with the Army's requirement that the ACAP aircraft meet or exceed all existing military crashworthiness standards. The aircraft was flown by two pilots, and could carry up to six passengers in the 100-cubic-foot (2.8 m³) rear cabin.

Operational history

The S-75 underwent a 50-hour evaluation by the Army, and was found to have exceeded the weight- and cost-saving criteria set in the original ACAP specification.^[1] Sikorsky gained a wealth of data on the fabrication and use of composite airframes through building the S-75, and Sikorsky's later designs incorporated many of its features. Testing of the machine continued through April 1985, after which it was withdrawn from service and placed in long-term storage.

Specifications (S-75)

Data from U.S. Army Aircraft Since 1947,^[1]

General characteristics

Crew: 2
Capacity: up to 6 passengers
Length: 43 ft 8 in (13.31 m)
Rotor diameter: 44 ft 0 in (13.41 m)
Height: 13 ft 2 in (4.01 m)
Empty weight: 6,421 lb (2,895 kg)
Useful load: lb (kg)
Loaded weight: lb (kg)
Max. takeoff weight: 8,470 lb (3,820 kg)
Powerplant: 2 × Allison 250-C30S turboshafts, 650 hp (485 kW) each
Propellers: 1 rotor

Performance

Never exceed speed: knots (mph, km/h)
Maximum speed: knots (184 mph, 296 km/h)
Cruise speed: knots (159 mph, 256 km/h)
Stall speed: knots (mph, km/h)
Range: nm (398 mi, 640 km)
Service ceiling: 13,500 ft (6090 m)

References

1 2 3 4 Harding, Stephen (1997). U.S. Army Aircraft Since 1947. Atglen, PA, USA: Schiffer Publishing Ltd. p. 251. LCCN 96-69996.
↑ Historic US Army Helicopters

External links

Wikimedia Commons has media related to Sikorsky helicopters.

Sikorsky aircraft

Fixed-wing aircraft (company designations)	S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12 S-13 S-14 S-15 S-16 S-17 S-18 S-19 S-20 S-21 S-22 S-23 S-24 S-25 S-26 S-27 S-28 S-29-A S-30 S-31 S-32 S-33 S-34 S-35 S-36 S-37 S-38 S-39 S-40 S-41 S-42 S-43 VS-44 S-45

Fixed-wing aircraft (military designations)	C-6 C-28 JRS JR2S PS RS XBLR-3 XPBS XSS XV-2

Helicopters (company designations)	VS-300 (S-46) S-47 S-48 S-49 S-51 S-52 S-53 S-54 S-55 S-56 S-57 S-58 S-59 S-60 S-61 S-61L/N S-61R S-62 S-63 S-64 S-65 S-66 S-67 S-68 S-69 S-70 S-71 S-72 S-73 S-74 S-75 S-76 S-80 S-92/H-92 S-97 S-300 S-333 S-434

Helicopters (military designations)	SH-3 HH-3E/F R-4 H-5 H-6 H-18 H-19 H-34 CH-37 XH-39 HH-52A CH-53 CH-53E CH-53K CH-54 HH-60G HH-60J MH-60R/S SH-60B/F SH-60J/K UH-60 VH-60 RAH-66 CH-124 CH-148

Experimental aircraft	Cypher Cypher II Firefly X2 XBLR-3 XV-2

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