Sikorsky S-75
{{Infobox aircraft
|name= S-75 ACAP
|image= Lhxs75.jpg
|caption= Sikorsky S-75 ACAP all-composite test aircraft
|type= Experimental helicopter
|manufacturer=Sikorsky Aircraft
|designer=
|first_flight= 27 July 1984
|introduction=
|retired=
|status=
|primary_user= United States Army
|more_users=
|produced=
|number_built= 2
|unit cost=
|developed_from = Sikorsky S-76
|variants =
}}
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, lighter and less costly to build than predominantly metal airframes in support of the Light Helicopter Experimental (LHX) program.{{cite book |last= Harding|first= Stephen |title= U.S. Army Aircraft Since 1947 |url= https://archive.org/details/usarmyaircraftsi0000hard_c0o7|url-access= registration|year= 1997 |publisher= Schiffer Publishing Ltd. |location= Atglen, PA, USA |lccn= 96-69996 |page = [https://archive.org/details/usarmyaircraftsi0000hard_c0o7/page/n254 251]|isbn= 9780764301902 }}[http://tri.army.mil/LC/CS/csa/aahist3.htm#LHX Historic US Army Helicopters] {{webarchive|url=https://web.archive.org/web/20090627075327/http://tri.army.mil/LC/cs/Csa/aahist3.htm |date=2009-06-27 }} 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 27 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. 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 {{convert|100|cuft|m3|adj=on}} 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. 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)
{{Aircraft specs
|ref=U.S. Army Aircraft Since 1947,
|prime units?=kts
|crew=2
|capacity= up to 6 passengers
|length ft=43
|length in=8
|length note=
|width ft=
|width in=
|width note=
|height ft=13
|height in=2
|height note=
|empty weight lb=6421
|empty weight note=
|gross weight lb=
|gross weight note=
|max takeoff weight lb=8470
|max takeoff weight note=
|fuel capacity=
|more general=
|eng1 number=2
|eng1 name=Allison Model 250-C30S
|eng1 type=turboshaft engines
|eng1 shp=650
|eng1 note=for take-off
|rot number=1
|rot dia ft=44
|rot dia in=
|rot area sqft=
|rot area note=
- Blade section: - root: SC1012R8/SC1095R8 ; tip: Sikorsky SC1095{{cite web |last1=Lednicer |first1=David |title=The Incomplete Guide to Airfoil Usage |url=https://m-selig.ae.illinois.edu/ads/aircraft.html |website=m-selig.ae.illinois.edu |accessdate=16 April 2019}}
|max speed kts=160
|max speed note=
|cruise speed kts=138
|cruise speed note=
|never exceed speed kts=
|never exceed speed note=
|range nmi=346
|range note=
|ferry range nmi=
|ferry range note=
|endurance=
|ceiling ft=13500
|ceiling note=
|climb rate ftmin=
|climb rate note=
|time to altitude=
|disk loading lb/sqft=
|disk loading note=
|fuel consumption lb/mi=
|power/mass=
|more performance=
|avionics=
}}
See also
{{Portal|Aviation}}
{{aircontent
|see also=
|related=
|similar aircraft=
|lists=
}}
References
{{reflist}}
External links
{{commons category|Sikorsky S-75}}
- [https://books.google.com/books?id=eE-trX3XZawC&q=%22S-75%22&pg=PA119 The Sikorsky Legacy S-75 Advanced Composite Airframe Program]
- [http://www.globalsecurity.org/military/systems/aircraft/lhx.htm LHX program on globalsecurity.org]
{{Sikorsky Aircraft}}
Category:1980s United States helicopters
Category:1980s United States experimental aircraft