Sikorsky S-67 Blackhawk

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. 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. The S-67 was fitted with a moving map display, a hands-on-collective radio tune control, and night vision systems. Its armament included a Tactical Armament Turret (TAT-140) with a three barrel cannon, and could carry 16 TOW missiles, rockets, or AIM-9 Sidewinder air-to-air missiles. The Blackhawk was powered by two General Electric T58-GE-5 engines. ==Operational history==

Evaluation and records The S-67 Blackhawk, along with the Bell 309 KingCobra, was put through a series of flight test evaluations in 1972 by the U.S. Army. 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)==