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YA9 vs YA-10...
The differences between the two aircraft started with their external shape. Where the Northrop design followed conventional fighter practice, with a shoulder wing, single fin and engines mounted close to the fuselage, the YA-10A resembled no previous combat aircraft apart from a few last-days-in-the-bunker German projects from 1945. The engines were mounted on the rear fuselage, airliner-style, there were twin fin and rudders and the main landing gear retracted into pods under the wing. The low-slung YA-9A was a design of elegant solidity, with its engines faired smoothly into the fuselage and the fin sweeping upwards from the aft body; its rival was a gangly beast, its long, skinny fuselage and broad wing improbably mated atop a stalky undercarriage.
Another material difference between the two aircraft was the choice of engine. Two high-bypass turbofans in the right thrust bracket were available in the USA. Fairchild selected the General Electric TF34, already under development for the US Navy's Lockheed S-3A antisubmarine warfare aircraft. Northrop chose a smaller engine, the Avco Lycoming ALF 502, which had been launched as a private venture in 1969. It received the military designation YF102LD-100. It delivered 15 per cent less thrust than the TF34, but was 23 percent lighter and only just over half as long, It was based on the world's first high bypass turbofan, the PLFI, which had run in late 1963. The main selling point of the F-102 was that it was derived from the T55 turboshaft, which had a long and distinguished record of peacetime and combat service in military helicopters. The YA-9A's cleaner shape largely made up for its lower installed thrust; the mission performance of the two aircraft was very similar, both meeting the specification, but the YA-10A would do so at slightly higher weights. Both contestants, though, were required to provide performance data with either engine.
Control Surfaces
Both A-X contenders featured combined aileron/speedbrake surfaces on their outer wings; these resembled conventional ailerons, but were split into upper and lower panels. When opened, they produced a powerful deceleration effect with virtually no trim change, unlike a fighter-type dorsal or ventral brake. The YA-9A went somewhat further than its rival, featuring a unique side-force control (SFC) system. This linked the speedbrakes and the very large rudder, and could be engaged or disengaged from the cockpit. If the pilot commanded a move to the left, the SFC system would deflect the rudder to the right, opposite to the usual direction. At the same time, the left speedbrake would open, preventing the aircraft from turning to the right. Instead, the thrust of the rudder would move the aircraft bodily to the left, without turning or banking. With SFC, the pilot could track a ground target without constantly worrying about the bank angle and fuselage direction changes that accompany a conventional turn; Northrop estimated that SFC could double the tracking accuracy of a typical attack.
more to come...
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