A Fighter for All Speeds

Part of the hoopla last week at the General Dynamics plant in Fort Worth may have been political, and the roll out date of the TFX fighter may indeed have been advanced a bit to have an effect on the presidential campaign. But the TFX (or F-111, as it is now called) is nonetheless a phenomenal airplane.

Said General Bernard Schriever, head of the Air Force Systems Command: "The F-111 represents a quantum step forward in the development of tactical air weapon systems." Despite all the claims that Defense Secretary Robert McNamara made an expensive mistake when he insisted on a single basic plane for both Air Force and Navy, the General Dynamics-Grumman partnership that was chosen for the job has managed to match both versions of their fighter to an astonishing degree. The F-111 construction pro gram is not only meeting a tight schedule that was set when the contract was signed two years ago, it is also running below its estimated cost.

Variable Sweep. The trouble with conventional supersonic jet fighters is that they must sacrifice too much to gain high speed. They cannot carry much load, cruise any great distance, or land slowly on small or rough runways. The F-111 avoids these failings by using variable sweep wings, a difficult design concept that has been tried experimentally but never used in an operational airplane. When the wings are fully extended, they have hardly any sweepback, and the airplane looks oddly oldfashioned. In this condition it will fly with old-fashioned slowness. Then, as speed increases, the wings are swept backward, reducing lift and drag, and permitting speed to increase still more.

At top speed, the wings will angle back ward at 72.5DEG, turning the airplane into a sharp, pointed arrowhead. The problem of moving the wings quickly and surely under the enormous air pressures of high speed was not easy, but it seems to have been licked.

The F-111's actual speed and range were not released, partly because they are legitimate military secrets, partly because the airplane has flown so far only in wind tunnels, and its true performance can only be estimated. But the Government claims it will be faster (about Mach 2.5, or 1,650 m.p.h.) than any operational plane. It will fly twice the distance and carry twice the payload of the best current U.S. fighter. By cruising at moderate speed with wings extended, it will have "transoceanic range without refueling"; if permitted to refuel, it can fly to any part of the earth in one day. It can land much more slowly than other jet fighters, which will permit it to operate from small, poorly surfaced fields. Its Navy version, the F-111 B, which is being built by Grumman, should encounter no trouble in landing and taking-off from present-day carriers.

For power, the F-111 uses two radical TF-30 engines built by Pratt & Whitney Aircraft. At slow cruising speeds, they are turbofans similar to the engines on up-to-date jetliners, very sparing of fuel. At Mach 1 and above, the fan action is cut down or eliminated. When full power is called for, the engine uses an afterburner. Aerodynamicists credit the versatile engines as well as the wings for the varied talents of the F-111.

Out with the Cockpit. Unlike most jet fighters, the F-111 will have a crew of two sitting side by side in a lifesaving cockpit that is something of an aircraft in itself. If anything goes wrong and a bail-out is called for at high speed, the crewmen will not risk getting clawed to shreds by racing air. Ejected by powerful rockets, the whole cockpit will separate from the ship. It has fins that will keep it from tumbling, and when its speed has slowed enough, a parachute will open to waft it down to a landing on water or solid ground. If it hits water, it will float indefinitely. If the whole plane should dive under the surface, the cockpit will detach itself and bob to the surface.

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