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FLY BY WIRE. From the outset, the YF-16 had no direct connection between the pilot's controls and the aircraft's control surfaces. Instead, the stick and rudder controls were connected to quadruple-redundant computers, which then told the elevators, ailerons, and rudder what to do. This had several large advantages over previous systems. It was quicker responding, automatically correcting for gusts and thermals with no effort from the pilot. It could be programmed to compensate for aerodynamic problems and fly like an ideal airplane. Most importantly, it enabled, with full safety, a highly efficient unstable design.
NEGATIVE STABILITY. All previous aircraft designs had been aerodynamically stable. That is, the center of gravity was well in front of the center of lift and the center of pressure (drag).
To illustrate the difference between stable and unstable designs, take a shirt cardboard and, holding it by the leading edge, pull it rapidly through the air. It will stretch out behind your hand in a stable manner. This is a stable design Now take it by the trailing edge push forward from there. It will immediately flip up or down uncontrollably. That is an unstable design.
The downside of aerodynamic stability is that the aircraft is nose-heavy and always trying to nose down. The elevator must therefore push the tail down to level the airplane. But in addition to rotating the airplane from nose-down to level, the elevator is exerting negative lift; that is, it is pushing the airplane down. In order to counteract this negative lift, the wing needs to be made larger to create more positive lift. This increases both weight and drag, decreasing aircraft performance. In pitch-up situations including hard turns which are the bread and butter of aerial combat, this negative effect is greatly magnified.
The YF-16 became the world's first aircraft to be aerodynamically unstable by design. With its rearward center of gravity, its natural tendency is to nose up rather than down. So level flight is created by the elevator pushing the tail up rather than down, and therefore pushing the entire aircraft up. With the elevator working with the wing rather than against it, wing area, weight, and drag are reduced. The airplane was constantly on the verge of flipping up or down totally out of control,. and this tendency was being constantly caught and corrected by the fly-by-wire control system so quickly that neither the pilot nor an outside observer could know anything was happening. If the control system were to fail, the aircraft would instantly disintegrate; however, this has never happened.
HIGH G LOADS. Previous fighters were designed to take 7Gs, mainly because it was believed that the human pilot, even with a G-suit, could not handle more. The YF-16 seatback was reclined 30 degrees, rather than the usual 13 degrees. This was to increase the ability of the pilot to achieve 9Gs by reducing the vertical distance between head and heart. Additionally, the traditional center control stick was replaced by a stick on the right side, with an armrest to relieve the pilot of the need to support his arm when it weighed nine times normal.
PILOT VISION. In addition to allowing full-circle horizontal vision and unprecedented vision over the sides, the YF-16 canopy was designed without bows in the forward hemisphere.
GROWTH PREVENTION. Traditionally, room for growth has been considered an asset. Fighter aircraft have averaged weight gain of about one pound per day as new capabilities are added, cost increases, and performance declines. The F-15, for example, was designed with about 15 cubic feet of empty space to allow for future installation of additional equipment.. In a radical departure, the YF-16 was intentionally designed with very little empty space, (about two cubic feet)., with the explicit intention of preventing growth. One member of the House Armed Services Committee actually wrote to the Secretary of the Air Force asking that the F-16's empty space be filled with Styrofoam to insure that "gold-plated junk" was not added to the design.
COMBAT RADIUS AND PERSISTENCE. General Dynamics chose a single turbofan engine, essentially the same engine as one of the two that powered the F-15. Use of a single engine helped minimize weight and drag; use of a turbofan rather than a pure jet engine gave high fuel efficiency. Additionally, the YF-16 designers used a "blended body" design in which the wing gradually thickened at the root and blended into the body contours without the usual visible joint. The space thus created was filled with fuel. With such a high fuel fraction and a fuel-efficient engine, the YF-16 was able to break the presumption that small aircraft were necessarily short-ranged.
RADAR INTEGRATION. Because the YF-16 carried no radar-guided missiles, it could only fight within visual range. Moreover, the small weight and space available limited the range of its radar. Nevertheless, it was given a technologically advanced small radar, with excellent look-down capability. Most importantly, the radar was integrated with the visual combat mode. That is, the radar projected an image of the target aircraft onto the Head Up Display so that, by looking at that image, the pilot was looking exactly where the target would become visible as he approached it. |
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