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F-14 Tomcat

Design

The Grumman F-14, the world's premier air defense fighter, was designed to replace the F-4 Phantom II fighter (phased out in 1986). F-14s provided air cover for the joint strike on Libyan terrorist targets in 1986. The F-14A was introduced in the mid-1970s. The upgraded F-14A+ version, with new General Electric F-110 engines, widespread throughout the fleet, was more than a match for enemy fighters in close-in, air combat. Even at the time the F-4 was developed, it was recognized that considerably improved performance could be gained through three technical advances which were incorporated in the F-14. The first of these is the replacement of more aluminum with titanium, (and, to a lesser extent, boron composites), which reduces structural weight and improves high maneuver "G" limits. The reduced deadweight improves just about every performance parameter, including range, payload, acceleration, characteristics of climb, etc. Only about 9% of the F-4's structural weight was titanium. The F-14's percentage was greater, being some 25%. The F-4 Phantom II made effective, if limited, use of titanium primarily in the main structural keel member between the engines and for inner liners for the pressurized engine compartments. Altogether about 900 lbs. of titanium were used in each of the early Phantom II's. Later models increased that use by a factor of two. The F-14 made far more substantial use of titanium to gain optimum strength-to-weight ratios. It was anticipated that its structural strength and high thrust-to-weigh ratio, particularly with the "B" engine, will enable the F-14 to have speeds substantially in excess of Mach 2, with great agility in close-in air-to-air combat. The second technical improvement of the F-14 over the F-4 was the use of new gas turbine turbofan power plants, which shaved something on the order of twice the thrust-to-weight ratio and half the specific fuel consumption of the engines originally employed on the F-4. These new engines on the F-14 provided even wider cruising radii for the same total fuel consumption. The "B" engine gave the F-14 an aircraft thrust-to-weight ratio greater than 1, assuring tremendous acceleration, high speed, and even the ability to climb vertically, if required. The variable-sweep wing was the third -- and most important -- major technical advance of the F-14 over the F-4. It was particularly valuable in a multi-mission plane -- permitting lower landing speeds, higher top speeds, longer loiter time, and a wider cruising radius, corresponding to the variable wing loadings permitted by the various wing settings.

The AWG-9 is a pulse-Doppler, multi-mode radar with a designed capability to track 24 targets at the same time while simultaneously devising and executing fire control solutions for 6 targets. Designed in the 1960's and one of the oldest air-to-air radar systems, the AWG-9 is still the most powerful and new software will increase its capabilities for the 21st century.

The cockpit is fitted with a Kaiser AN/AVG-12 Head-Up Display (HUD) co-located with an AN/AVA-12 vertical situation display and a horizontal situation display. A Northrop AN/AXX-1 Television Camera Set (TCS) is used for visual target identification at long ranges. Mounted on a chin pod, the TCS is a high resolution closed circuit television system with two cockpit selectable Fields Of View (FOV), wide and narrow. The selected FOV is displayed in the cockpit and can be recorded by the Cockpit Television System. A new TCS, in development, will be installed in all three series aircraft. Electronic Support Measures (ESM) equipment include the Litton AN/ALR-45 radar warning and control system, the Magnavox AN/ALR-50 radar warning receiver, Tracor AN/ALE-29/-39 chaff/flare dispensers (fitted in the rear fuselage between the fins), and Sanders AN/ALQ-100 deception jamming pod.

The Tomcat has an internal 20-mm Vulcan Gatling-type gun fitted on the left side, and can carry Phoenix, Sparrow, and Sidewinder AAMs. Up to 6 Phoenix missiles can be carried on 4 fuselage stations between the engines and on 2 pylons fitted on the fixed portion of the wing; 2 Sidewinder AAM can be carried on the wing pylons above the Phoenix mount. Although the F-14 was tested with conventional "iron" bombs on its external hardpoints in the 1960s, the BRU-10 ejection racks were not strong enough to provide a clean separation. Tests in 1988-1990 showed that BRU-32 racks could drop Mk 80-series bombs safely. Later tests would qualify the AGM-88 HARM and the AGM-84 Harpoon.

The design of the F-14B allows for incredible pitch authority as well as good roll control to produce an extremely agile fighter. Rolling maneuvers are accomplished through the use of differential horizontal stabilator and 8 spoilers located on top of the wings. Its general arrangement consists of a long nacelle containing the large nose radar and 2 crew positions extending well forward and above the widely spaced engines. The engines are parallel to a central structure that flattens towards the tail; butterfly-shaped airbrakes are located between the fins on the upper and lower surfaces. Altogether, the fuselage forms more than half of the total aerodynamic lifting surface. With the wings in the 20 degree position most of the lifting force comes from the wings, in the 68 degree position over 60% of the lift is generated from the fuselage itself.

The wing carry-through is one-piece electron beam-welded structure of TI-6A1-4V titanium alloy with 6.71m span. Fuselage has machined frames, titanium main longerons and light alloy stressed skin; centre-fuselage is fuel-carrying box; radome hinges upwards for access to radar; fuel dump pipe at extreme tail; fins and rudders of light alloy honeycomb sandwich; tailplanes have multiple spars, honeycomb trailing-edges and boron/epoxy composites skins.

The wings are shoulder-mounted and are programmed for automatic sweep during flight, with a manual override provided. It's adjustable wing design provides amazing versatility between blazing speed and turn performance. The wings can be adjusted automatically by an onboard computer or manually by the pilot for optimum performance at all altitudes and airspeeds. The twin, swept fin-and-rudder vertical surfaces are mounted on the engine housings and canted outward. The wing pivot carry- through structure crosses the central structure; the carry through is 22 ft (6.7 m) long and constructed from 33 electron welded parts machined from titanium; the pivots are located outboard of the engines. Normal sweep range is 20 to 68 deg with a 75-deg "oversweep" position provided for shipboard hangar stowage; sweep speed is 7.5 deg per second. The fixed glove has dihedral to minimise cross-sectional area and reduce wave drag. Small canards on F-14A known as glove vanes extend forward progressively to 15 from inboard leading-edge to balance supersonic trim change and unload tail surfaces. Aerodynamically, the F-14 was markedly superior to the F-4: it was faster, more maneuverable, has greater acceleration, and longer range. These advantages were gained through three principal technical advances: greater use of titanium, providing improved structural strength-to-weight ratios; new gas turbine turbofan power plants, offering significantly higher thrust-to-weight ratios and lower cruise fuel consumption; and the variable geometry wing, augmented by automatic sweep programming, maneuvering slats and flaps, and glove vanes. Technical advances such as these account for the need for -- and the increased cost of -- the development of successive generations of fighter aircraft.

Grumman's experience with the XF-10F -- the first swing-wing aircraft built in the U.S. -- and the F-111B provided the background of technical experience needed to design several major advantages into the F-14 variable-sweep wing which either did not exist or existed only in minor form in competitive fighters.

The F-14 has three such unusually effective and unique features associated with its variable-sweep wing:

  1. Automatic sweep programming;
  2. Maneuvering slats and flaps; and
  3. Glove vanes.

These three features provide optimum lift-to-drag ratios throughout the entire dog-fight speed zone. It is generally acknowledged that most dog-fights occur below Mach 0.9; however, there is some feeling that this figure should be raised to Mach 1.2. This upper limit is determined by the pilot's ability to see the enemy fighter after an opposite direction pass (head on) and subsequent 180 degree turn. At higher speeds, the radius of turn is so great that the operating aircraft lose each other visually after the initial pass.

At the low end of the Mach spectrum (below 0.8), the F-14 maneuver slats and flaps offer a significant increase in lift by decreasing the effective wing loading from 85.6 PSF (pounds per square foot) to 50.6 PSF. This increase in lift is at its maximum with the wing at 22 , the full forward position. The F-14 advantage which cannot be realized in aircraft without variable-sweep wings, is that the 5% chord thickness of the fully swept wing (at 68) becomes a 9% chord with the wing in the full forward (22) position. This "fat" wing, with the associated increased span at full wing extension, gives an excellent coefficient of lift, not available to a competitive fighter without variable sweep, and adequate room for the mechanical installation of the maneuver slats and flaps themselves.

Automatic sweep programming is a dramatic advantage not available to any other known fighter. Going from the maximum F-14 sweep (68) to the full forward (22 position, the auto sweep programming modulates the wing to "ride the envelope" or capitalize on the span loading payoff :,f variable sweep. This advantage is available from Mach 1 to Mach .7, which is where most dog-fights would begin. All pilots agree that this is a feature which definitely would be used and which would materially add to dog-fight superiority.

The F-14 glove vanes are controlled both manually and automatically. Their real value is at supersonic speeds, and their principal advantage is that they reduce the tail load (drag) and hence increase the power (thrust) available. There are several aircraft throughout the world that use canards for the same purposes as the glove vane. But, as far as is known, they are not as effective in allowing the aircraft to achieve maximum lift-over-drag (L/D) at high altitudes; a very real advantage where tight turns at high altitudes and supersonic speeds are required.

There are important differences in the wing geometry of the F-14 and F-111. In terms of the wing semispan in the low sweep position, the pivot of the F- 14A is 10 to 12 percent farther outboard than that of the F-111. The more outboard pivot location results in a much reduced rearward movement of the center of lift with increasing sweep angle. As a consequence, trim drag is reduced and available pitch-control power is increased. The favorable effect of locating the pivot in the proper outboard position is, of course, in accordance with NASA basic research.

Lateral control is achieved by long-span spoilers, ahead of flaps, and tailerons. Automatic leading-edge slats assist maneuvering, and strakes emerge from the wing glove leading-edge at high airspeeds. The automatic wing sweep has manual override, with automatic scheduling of control with airspeed and autostabilisation and angle of attack protection provided by the autopilot and automatic carrier landing system (ALCS). Airbrake panels are located above and below tail, between the twin fins and rudders. For roll control below 57 deg, the F-14 uses spoilers located along the upper wing near the trailing edge in conjunction with its all-moving, swept tailplanes, which are operated differentially; above 57-deg sweep, the tailplanes operate alone. For unswept, low-speed combat maneuvering, the outer 2 sections of trailing edge flaps can be deployed at 10 deg and the nearly full-span leading-edge slats are drooped to 8.5 deg. At speeds above Mach 1.0, the glove vanes in the leading edge of the fixed portion of the wing extend to move the aerodynamic center forward and reduce loads on the tailplane.

The sharply raked, 2-dimensional 4-shock engine intakes have 2 variable-angle ramps, a bypass door in the intake roof, and a fixed ramp forward; exhaust nozzles are mechanically variable. Viewed from ahead, the top of the intakes are tilted toward the aircraft centerline; from above, the engines are canted outward slightly to reduce interference between intake airflow and the fuselage boundary layer. The engines exhaust through mechanically variable, convergent-divergent nozzles.

The landing gear is of the retractable tricycle type. Twin-wheel nose unit and single-wheel main units retract forward, main units inward into bottom of engine air intake trunks. Arrester hook under rear fuselage, housed in small ventral fairing.

The tail control surfaces on F-14s are known as "rolling tails", in that the aircraft does not have ailerons on the wings to control roll. Roll control is instead provided at low speeds by wing-mounted spoilers and at high speeds by differential horizontal stabilizer deflection. This configuration also produces side force, or yaw, which contributed to the inadvertent spin entries. This large tail configuration is to aid in takeoff from aircraft carriers, by providing more pitch moment.

The F-14's fuel system is one of the very first things technicians check when the Tomcat pulls in for scheduled maintenance. Any leak in the fuel system can be critical, even one that isn't visible to the human eye. Finding the smaller leaks can be extremely difficult. Current maintenance practice involves a low-tech approach to finding larger leaks - having technicians run their bare hands along the accessible areas of the fuel line. However, this hands-on approach can miss small leaks completely, or when small leaks are felt by technicians, the precise location may not be readily apparent if the leak is covered by a flange or coupling.



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