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S-67 BlackHawk

S-67When AH-56A production was cancelled in 1969, Sikorsky first offered an intermediate aircraft, consisting of an armed version of the S-61, then designed a simplified AAFSS using the maximum number of components from the S-61. The result was the S-67 BlackHawk which appeared in 1970. Note that this "BlackHawk" attack helicopter predates the current Sikorsky BlackHawk UH-60 transport/attack helicopter.

The S-67 was a two-place, twin-turbine, high-speed, armed helicopter. It incorporates five-bladed main and tail rotors and is powered by two T58-GE-5 turbine engines. The BlackHawk looked like a helicopter with conventional rotors (those of the S-61) and had the now typical lines and features of a combat helicopter: two stub wings with a 8.33m span and an all-moving tail plane. A wing provides additional lift and attachment points for external stores. The wing panels have speed brakes to control dive airspeed and increase deceleration capability. The main rotor blades feature swept tips designed to enhance high-speed capability.

A stability augmentation system (SAS) and a feel augmentation system (FAS) are incorporated to improve handling qualities. The main-wheels were retractable, while the tailwheel was not. One of the most interesting features of this aircraft was the presence of speed brakes on the wing trailing edges, which could be used both as airbrakes and to improve maneuverability. In addition the main rotor blade tips were modified and given a sweep-back of 20, to reduce vibration, stall speed and noise.

The S-67 Blackhawk prototype attack helicopter was designed and built by Sikorsky Aircraft Division (SAD) of United Aircraft Corporation under an in-house funded program independent of any military requirement. The design phase was initiated on 20 November 1969 and construction began 15 February 1970. The first flight of the S-67 was on 20 August 1970. The US Army Aviation Systems Test Activity (USAASTA) was tasked by US Army Aviation Systems Command (AVSCOM) test request to conduct an evaluation of the S-67 helicopter to support the Attack Helicopter Requirement Evaluation (AHRE) being performed for the US Army Combat Developments Command.

The Sikorsky S-67 was evaluated to determine aircraft performance, handling qualities, and maintenance characteristics. The tests were conducted at the Stratford, Connecticut plant of SAD from 25 May to 13 June 1972. During this flight program 25 test flights were conducted for a total of 26 productive hours. Handling qualities and vibrations were evaluated with respect to the applicable requirements of military specification MIL-H-8501A (ref. 2, app. A). Test configurations consisted of the following: clean (no external stores), external stores (two XM159 pods on each wing with thirteen 2.75-inch rockets in the outboard pods only), and TOW mission (two XM159 pods on each wing with nine, 2.75-inch rockets in each pod).

At take-off power, the standard day out-of-ground effect hover ceiling at a 20,270-pound gross weight was 2500 feet. At sea level, 95F day, the out-of-ground effect hover maximum gross weight was 18,630 pounds. The level flight airspeed in the clean configuration at normal rated power was 172 KTAS and the specific range at that airspeed was 0.107 nautical air miles per pound of fuel.

The vibration levels in forward flight were very low and enhanced the accomplishment of all tasks. During engagement of targets in diving flight, the speed brakes increased the available time on target. The gust response was heavily damped in all axes. This characterlstic aided the pilot in making precise attitude changes in turbulent conditions. The stable and consistently linear longitudinal trim control position gradient decreased pilot effort required while changing airspeed. There were 16 handling quality shortcomings noted. Long term longitudinal trim tasks were degraded by a noticeable delay in pitch response, excessive control system friction, weak control centering and essential2y neutral control position and force gradients.

The BlackHawk was put through a long series of tests from 1970 to 1974 but judged unsatisfactory. It nonetheless established an E-1 class world speed record on 14 December 1970 by flying at 348.971km/h over 3km, beating this on 19 December with a new record of 335.485km/h over a 15/25km circuit. The Sikorsky S-67 held the speed record for 8 years. In the final stages of testing, the S-67 was fitted with night vision systems, a TAT-140 turret with a 30mm cannon and an insulated and soundproof compartment for troop transport. The S-67 was also designed to carry an armament of 16 x TOW antitank guided missiles, 2.75 in Hydra-70mm rockets or Sidewinder air-to-air missiles.

The BlackHawk demonstrated excellent maneuverability, weapon carrying capacity and versatility. At the end of the test cycle, the U.S. Army asked for the aircraft to be modified by substituting a ducted fan for the tail unit, and in this configuration it reached a speed of 370km/hour in a test dive in 1974.



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