The Sikorsky S-67 Blackhawk was a private-venture, prototype attack helicopter built in 1970 with Sikorsky Aircraft research and development (R&D) funds. A tandem, two-seat aircraft designed around the dynamic drive and rotor systems of the Sikorsky S-61, it was designed to serve as an attack helicopter or to transport up to eight troops into combat.

Design and development

AAFSS and S-66 bid

The United States Army issued a request for proposals (RFP) for its Advanced Aerial Fire Support System (AAFSS) program on 1 August 1964. Lockheed offered its CL-840 design, a rigid-rotor compound helicopter. Sikorsky submitted the S-66, which featured a "Rotorprop" serving as a tail rotor but as speeds increased would rotate 90° to act as pusher prop. The S-66 had short, fixed wings and was powered by a Lycoming T55 turboshaft engine. The design was to have a speed of with the ability for for brief periods.

The U.S. Army awarded Lockheed and Sikorsky contracts for further study on 19 February 1965.

thumb|S-67 Blackhawk in head on view

The S-67 featured a five-bladed main rotor and tail rotor. The main rotor was taken from the S-61, but was modified to have a hub fairing, swept main rotor blade tips and a special "alpha-1" linkage which was added to the main rotor controls to increase collective pitch sensitivity and so extend the collective pitch range. The 20° swept main rotor blade tips help to overcome a phenomenon called sub-multiple oscillating track (SMOT) that causes variations in tip track at high Mach numbers. These allowed the S-67 to achieve and maintain high cruise speeds. To reduce drag at high speed, the main wheels retracted fully into the stub wing sponsons. It had speed brakes on the wing trailing edges that could be used to decrease speed or increase maneuverability. Neither aircraft was selected to replace the AH-56 Cheyenne. Instead, the Army chose to create the new Advanced Attack Helicopter program, which would lead to the AH-64 Apache several years later.

The S-67 performed a series of aerobatic maneuvers during its various marketing tours, including rolls, split-S, and loops. The S-67 was reputed to be very smooth and responsive, in spite of its size and speed.

Piloted by Sikorsky Test Pilots Kurt Cannon and Byron Graham, the S-67 established two E-1 class world speed records on 14 December 1970 by flying at over a course, and on course on 19 December 1970. These records stood for eight years.

As part of internal Sikorsky R&D efforts, in 1974, the S-67 had a ducted fan fitted instead of its original conventional tail rotor. In this configuration it reached a speed of in a test dive. Development work on the S-67 ceased after the accident.

The U.S. Army later assigned the name Black Hawk to the Sikorsky UH-60 Black Hawk helicopter.

Specifications (S-67 Blackhawk)

thumb|S-67 3-view

See also

References

Notes

Bibliography

  • Derived from text at Historic U.S. Army Helicopters - Modern era helicopters
  • Apostolo, Giorgio. The Illustrated Encyclopedia of Helicopters. New York: Bonanza Books. 1984. .
  • Donald, David. "Sikorsky S-67, S-69 and S-72".The Complete Encyclopedia of World Aircraft. New York: Barnes & Noble Books, 1998. .
  • Great Britain. Sikorsky S-67 Blackhawk N671SA: Report on the Accident at Farnborough, Hampshire, England on 1 September 1974. Aircraft accident report, 1/76. London: H.M.S.O., 1976. .
  • Landis, Tony and Dennis R. Jenkins. Lockheed AH-56A Cheyenne. Warbird tech series, v. 27. North Branch, MN: Specialty Press Publishers and Wholesalers, 2000. .
  • Yamakawa, George M., Albert L. Winn, Raymon B. Smith, Roy J. Anderson, Jr., and Warren E. Griffith, II. Attack Helicopter Evaluation, Blackhawk S-67 Helicopter. Ft. Belvoir: Defense Technical Information Center, July 1972. Retrieved on 22 December 2010.
  • Sikorsky S-67, First Blackhawk on helis.com