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S-69

Sikorsky S-69/XH-59
Type Experimental helicopter
Manufacturer Sikorsky Aircraft
Maiden flight July 26, 1973
Primary users NASA
United States Army
United States Navy
Number built 2

The Sikorsky S-69 was an experimental compound co-axial helicopter developed by Sikorsky.

Contents

[edit] Development

[edit] Text 2

In late 1971 the Army Air Mobility Research and Development Laboratory awarded Sikorsky a contract for the development of a single engine research helicopter prototype designed specifically to flight test the company's Advancing Blade Concept (ABC) rotor system.[1] The resultant Model S-69, which was allotted the military designation XH-59A and the serial number 71-1472, made its first flight in July 1973.

The XH-59A's ABC system consisted of two three-bladed, coaxial, contra-rotating rigid rotors, both of which were driven by the craft's single 1,825shp PT6T 3 Turbo Twin Pac engine.[1] During high speed flight only the advancing blades of each rotor generated lift; this off-loaded the retreating blades and thereby eliminated the aerodynamic restrictions caused by blade-stall and the high mach number effect of the advancing blade tip. This, in turn, produced greater stability and maneuverability while eliminating the need for either a supplementary lift-generating wing or an anti-torque tail rotor_ The XH-59A's streamlined fuselage more closely resembled that of a conventional airplane than a helicopter, having a cantilever tail unit with twin endplate rudders, side-by-side seating for the two crewmen, and fully retractable tricycle landing gear.

The crash of the first XH-59A early in the flight test program led to the construction of a second prototype incorporating several significant control system modifications.[1] This second machine (73 21941) flew for the first time in 1975, and in 1977 was converted into a compound rotorcraft through the installation of two 3.000 lbst J60-P-3A turbojet engines. The modified machine was joint1% evaluated by the Army, Navy and NASA beginning in 1978, and was later able to reach and maintain speeds in excess of 320 mph in level flight. The first prototype was ultimately rebuilt as a compound rotorcraft under a NASA contract and subsequently test flown (with the new serial 73-29142) by mixed Army, Navy, USAF and NASA crews at NASA's Moffet Field, California, test facility. Both XH-59A aircraft were officially transferred to NASA following the 1981 end of joint Army/Navy participation in the tri-partite flight test program.

[edit] Design

[edit] Operational history

[edit] Variants

S-69
XH-59A 
YH-59A 
XH-59B 


[edit] Sikorsky S-69

[edit] Text 1

Also known by the military designation XH-59A, the S-69 was part of the Advancing Blade Concept (ABC) program.[2] This Advancing Blade Concept system consisted of two rigid, contra-rotating rotors which made use of the aerodynamic lift of the advancing blades. At high speeds, the retreating blades were offloaded, as most of the load was supported by the advancing blades of both rotors and the penalty due to stall of the retreating blade was thus eliminated. This system did not even require a wing to be fitted for high speeds and to improve maneuverability, and also eliminated the need for an anti-torque rotor at the tail.[1], Avia.Russian.ee Website[3]

[edit] Text 2

In late 1971 the Army Air Mobility Research and Development Laboratory awarded Sikorsky a contract for the development of a single engine research helicopter prototype designed specifically to flight test the company's Advancing Blade Concept (ABC) rotor system.[1] The resultant Model S-69, which was allotted the military designation XH-59A and the serial number 71-1472, made its first flight in July 1973.

The XH-59A's ABC system consisted of two three-bladed, coaxial, contra-rotating rigid rotors, both of which were driven by the craft's single 1,825shp PT6T 3 Turbo Twin Pac engine.[1] During high speed flight only the advancing blades of each rotor generated lift; this off-loaded the retreating blades and thereby eliminated the aerodynamic restrictions caused by blade-stall and the high mach number effect of the advancing blade tip. This, in turn, produced greater stability and maneuverability while eliminating the need for either a supplementary lift-generating wing or an anti-torque tail rotor_ The XH-59A's streamlined fuselage more closely resembled that of a conventional airplane than a helicopter, having a cantilever tail unit with twin endplate rudders, side-by-side seating for the two crewmen, and fully retractable tricycle landing gear.

The crash of the first XH-59A early in the flight test program led to the construction of a second prototype incorporating several significant control system modifications.[1] This second machine (73 21941) flew for the first time in 1975, and in 1977 was converted into a compound rotorcraft through the installation of two 3.000 lbst J60-P-3A turbojet engines. The modified machine was joint1% evaluated by the Army, Navy and NASA beginning in 1978, and was later able to reach and maintain speeds in excess of 320 mph in level flight. The first prototype was ultimately rebuilt as a compound rotorcraft under a NASA contract and subsequently test flown (with the new serial 73-29142) by mixed Army, Navy, USAF and NASA crews at NASA's Moffet Field, California, test facility. Both XH-59A aircraft were officially transferred to NASA following the 1981 end of joint Army/Navy participation in the tri-partite flight test program.

[edit] Text 3

In February 1972, Sikorsky announced the development of an experimental helicopter designated S-69, which was designed to study the Advancing Blade Concept (ABC). This new system consisted of two rigid, contra-rotating rotors which made use of the aerodynamic lift of the advancing blades. At high speeds, the retreating blades were offloaded, as most of the load was supported by the advancing blades of both rotors and the penalty due to stall of the retreating blade was thus eliminated. This system did not even require a wing to be fitted for high speeds and to improve manoeuvrability, and also eliminated the need for an anti-torque rotor at the tail.

The aim of the project was to evaluate the ABC with this helicopter, first using scale models for wind tunnel tests at the Ames NASA research center, and then the real aircraft, which flew on 26 July 1973. Unfortunately, however, this prototype was lost in an accident a month later. Following an inquiry, design modifications were requested, plus improvements to the control system. Tests were resumed in July 1975 with a second aircraft. When test flights as a pure helicopter were completed, a new experimental phase began with the addition of an auxiliary turbojet. In 1983 Sikorsky proposed further modifying the aircraft as the XH-59B, with a shortened fuselage and ducted fan providing forward thrust.

.[4]

.[4]

[edit] Text 4

NASA and DOD developed several rotary-wing-based aircraft that used powered lift technology. These included the XH-59A, advancing blade concept aircraft during the 1970s, the JVX or tilt-rotor aircraft, and the RSRA/X-wing aircraft. These aircraft had the common ability to take off and land vertically like a helicopter, but in flight, they used a variety of technologies to operate as conventional fixed-wing aircraft.

One way to eliminate the problem of stalling and reverse rotor blade flow that limits the forward speed of a helicopter is to use two counterrotating rotors. The Advancing Blade is that half of the rotor disc in which the rotation of the blade is moving in the same direction as the movement of the helicopter. If the helicopter is moving forward, the advancing blade will be the right half of the rotor disc; if moving backward, it will be in the left half; if moving sideward to the left, it will be in the forward half; and if moving sideward to the right, it will be in the rear half. Rotor blades flap to equalize lift between the advancing blade half and retreating blade half of the rotor disc. Dissymmetry is created by forward movement of the helicopter. When the helicopter is moving forward, the speed of the advancing blade is the sum of the indicated airspeed of the helicopter plus the rotational speed of the blade.

The Advancing Blade Concept (ABC) uses two rigid counterrotating rotors in a coaxial arrangement to provide advancing blades on both sides of the aircraft. This makes use of the high dynamic pressure on the advancing side of the rotors at high forward speed, virtually ignoring the low dynamic pressure on the retreating side, while still keeping the rotor system in roll trim. Theoretically, such a rotor system will maintain its lift potential as speed increases. The XH-59A was designed to investigate this theory.

This is the principle behind the XH-59A, built by Sikorsky Aircraft [S-69] in a jointly funded Army, NASA, and now, Navy program. The XH-59A program started in 1971; by 1973, two XH-59As were ready for flight-testing.

The XH-59A Advancing Blade Concept demonstrator was powered by the P&W-Canada PT6T-3 Turbo Twin-Pac and two P&W J60 turbojets. It had two stacked, contrarotating 36' rotors. As a pure helicopter, it achieved 184 mph level flight speed, 221 mph in a dive; with auxiliary propulsion, it achieved 274mph (>322mph) in level flight. However, one aircraft was lost during a hard landing.

Flight-testing of the XH-59A as a pure rotary-wing craft had been completed by 1977. The XH-59A’s extreme agility and maneuverability were even more than had been expected. This maneuverability comes about because of the very stiff rotor blades used on the XH-59A, making the ABC an ideal candidate for a combat aircraft. The stiffer blades are also more rugged and thus more likely to survive encounters with tree limbs and hits from small arms fire.

In 1978, the high-speed test program was started with the addition of two auxiliary 3000-pound thrust jet engines mounted on the fuselage. The YH-59A had two additional P&W J60-P-3As, and two aircraft were built. The first flew on 26 July 1973, but crashed on 24 August 1973. The second aircraft flew on 21 July 1975, and in March 1977 the two J60s were installed for forward flight.

The XH-59B with PT6T-3 and shrouded fan was proposed, but never built. It was to be converted with two T700-GE-700s, contrarotating rotors, and a tail-mounted pusher prop. This project, which was designated XH-59B, was not proceeded with.

Advancing Blade Concept was a contender for the RAH-66, but the transmission weight penalties were too high and so the trade study decided that the advantages were outweighed by the weight disadvantage.

[5]

[edit] Sikorsky X2

thumb|right|Computer concept of the Sikorsky X2 Demonstrator

Sikorsky will incorporate decades of company research and development into X2 Technology helicopters, including: the XH-59A Advancing Blade Concept Demonstrator which showed high speed was possible with a coaxial helicopter and auxiliary propulsion, the Cypher UAV which expanded company knowledge of the unique aspects of flight control laws in a fly-by-wire aircraft that employed coaxial rotors, and the RAH-66 Comanche, which developed expertise in composite rotors and advanced transmission design.[6]

[edit] Specifications (S-69)

Data from U.S. Army Aircraft Since 1947[1], Avia.Russian.ee Website[3]

General characteristics

Performance


[edit] References

  1. ^ a b c d e f g h Harding, Stephen (1997). U.S. Army Aircraft Since 1947. Atglen, PA, USA: Schiffer Publishing Ltd., 251. ISBN 96-69996. 
  2. ^ Michael J Taylor: The Illustrated Encyclopedia of Helicopters, page 20. Exeter Books, New York, NY USA, 1984. ISBN 0-671-07149-1
  3. ^ a b Sikorsky S-69 / XH-59. Retrieved on 2007-06-21.
  4. ^ a b Apostolo, Giorgio; Elfan ap Rees (1984). The Illustrated Encyclopedia of Helicopters. New York, NY, USA: Bonanza Books, 89. ISBN 0-517-439352. 
  5. ^ XH-59A Advancing Blade Concept (ABC)/S-69. Retrieved on 2007-06-22.
  6. ^ http://www.sikorsky.com/details/0,3036,CLI1_DIV69_ETI2088,00.html

[edit] External links

[edit] See also

v • d • e
Sikorsky Aircraft

Airplanes: S-29-A · S-38 · S-39 · S-40 · S-42 · S-43 · VS-44

Helicopters (Company designations): VS-300 · S-47 · S-48 · S-49 · S-51 · S-52 · S-53 · S-54 · S-55 · S-56 · S-58 · S-59 · S-60 · S-61 · S-61L/N · S-61R · S-62 · S-64 · S-65 · S-67 · S-69 · S-70 · S-72 · S-75 · S-76 · S-80 · S-92/H-92

Helicopters (Military designations): SH-3 · HH-3E/F · R-4 · H-5 · 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-60 · SH-60 · UH-60 · VH-60 · RAH-66 · CH-124 · CH-148

Experimental aircraft designations: X2 · Cypher · Cypher II


Related development

Comparable aircraft

Related lists

v • d • e
Lists relating to aviation
General
Military
Accidents/incidents
Records

Category:Military helicopters Category:VTOL aircraft Category:U.S. experimental aircraft 1970-1979