Code One Magazine: F-16 Refresher Course

A good share of the current crop of F-16 pilots was flying diapers when Phil Oestricher throttled YF-16 No. 1 into the skies over the Mojave Desert that January day in 1974. Yes, the F-16 hits the ripe old age of twenty-five this year. And it’s proven to be much more than twenty-five years ahead of its time. A silver anniversary, though, provides a great excuse for looking back at the history of the F-16 and explaining why it remains the most potent fighter around.

Before the F-16, fighters had historically cost more than twice their immediate production predecessors. The F-16 changed that history by becoming the first fighter in nearly forty years to cost less than its predecessors. In fact, the F-16 began life as a reaction to that growing cost and accompanying weight and complexity of fighter aircraft. In the mid-1960s, an informal and underground group labeled the Lightweight Fighter Mafia began promoting a new fighter concept within the Air Force. These mafiosi advocated small, austere, and highly maneuverable fighters. By the 1970s, their concept gained more proponents in the Air Force and then in the Congress. This concept eventually mushroomed to the 4,000-plus F-16s ordered to date.

Everest Riccioni, a core member of the Fighter Mafia assigned to the Tactical Fighter Requirements Division of Air Force Headquarters, managed to fund a study in early 1971 for the preliminary design and analysis of several configurations for a lightweight fighter. Entitled, "Study to Validate Expanded Energy-Maneuverability Through Trade-Off Analysis," this ambiguously titled work was conducted by General Dynamics and Northrop. Fueled by the study’s funding (about $150,000 total) and the good tradeoff data it produced, the lightweight fighter concept was ready to move from paper to metal. The transition was accelerated by the Packard Commission’s resurrection of prototyping to validate new aircraft and other military programs before they go into production.

The lightweight fighter concept offered other incentives for building a prototype as well: the Air Force needed a lower-cost alternative in case the F-15 development program faced major problems; the service also needed a low-cost fighter to augment the F-15 in modernizing and expanding its fighter force (what became the successful "high/low" mix acquisition strategy); and the United States needed an inexpensive export fighter to replace a large number of aging aircraft for NATO member countries.

Early work on the lightweight fighter involved analyzing the relationships of wing loading and thrust loading; the Fighter Mafia wanted a clear understanding of the relationship between these two variables. They wanted low wing loading and high thrust loading. But they knew that low wing loading (larger wings) meant more weight and more drag and that high thrust loading (more powerful engines) meant higher fuel consumption. They also knew that airplanes with high thrust-to-weight ratios were normally equated with short range. As a result, the group started looking at fuel fractions (the ratio of fuel capacity to aircraft weight) to tie all these variables together and to get a better feel for the boundaries involved. They wanted to determine trends how quickly changes in one variable affected other variables.

The original purpose of the lightweight fighter competition was to demonstrate useful technologies for next-generation fighter aircraft. As such, the Air Force was under no obligation to proceed to a production program when the competition ended. Like the fighter it requested, the proposal effort itself was also lightweight. The request for proposal, issued by the Air Force to nine aerospace companies in December 1971, weighed in at twenty-one pages. And it limited responses to a mere fifty pages, to include wind tunnel data and an actual wind tunnel model of the proposed aircraft so that the Air Force could verify the data. Five companies responded Boeing, General Dynamics, Lockheed, Northrop, and Ling-Temco-Vought. General Dynamics and Northrop were picked as finalists for the competition in April 1972. Each company received about $40 million for the subsequent prototype effort.

General Dynamics and Northrop each built two prototypes. The General Dynamics design, called Model 401, rolled out in December 1973 in Fort Worth and was transported to Edwards AFB, California, on 8 January 1974. The YF-16 flew for the first time less than two weeks later. The Northrop design, designated P-600, rolled out in April 1974 at Hawthorne, California. The YF-17 took off on its first flight at Edwards in June. The YF-16s flew 330 missions and logged 417 hours of flight time during the competition, which ended in December 1974. The YF-17s flew 268 flights and logged 324 hours. On 13 January 1975, Secretary of the Air Force John McLucas declared the YF-16 the winner of the competition.

Secretary of Defense James Schlesinger cheered the selection, "It is a happy circumstance that the airplane with the best performance is also the lowest cost." Besides meeting the low-cost goal, the YF-16 met or exceeded all other USAF-established goals including those met by the YF-17. The YF-16 had a mission radius advantage over the YF-17 of 200 nautical miles; a sustained turn rate advantage of 0.5 degrees/second at Mach 1.2 at 30,000 feet; a fifteen second advantage accelerating from Mach 0.9 to Mach 1.6 at 30,000 feet; and a ferry range advantage of 350 nautical miles. Air Force Deputy Chief of Staff for Research and Development, Lt. Gen. William Evans, noted the differences, "The YF-16 outperformed the YF-17 from the beginning of the flight test program. The YF-16’s maneuver energy, dash speed, turning rates, and handling qualities were all superior."

The F-16 prototype design team did not incorporate technologies for the sake of incorporating technologies. Only technologies that significantly increased the combat performance of the aircraft were pursued. The electronic flight control system is often identified as the single-most important technology incorporated in the YF-16. This system reduced the lag times associated with heavier and more complex hydromechanical flight control systems found in every production jet fighter preceding the F-16.

These fly-by-wire flight controls, as they are called, allowed much more precise control of the aircraft. They also greatly improved flying qualities. They also increased safety by imposing g limits to keep the pilot from overstressing the airframe and angle-of-attack limits to prevent the aircraft from stalling and departing. The system also automatically compensated for forces associated with gun firing. The F-16 became the first production aircraft to feature a fly-by-wire flight control system with no mechanical backup.

The fly-by-wire flight control system enabled the F-16 to be designed with relaxed static stability. Conventional, statically stable aircraft are designed to return to a preset trim condition. Conventional aircraft require constant downward loads on the horizontal tail to maintain level flight. Maneuvering flight requires substantial control surface deflections. The drag associated with these stabilizing deflections can become quite high during hard maneuvers and supersonic flight. A design with relaxed static stability, on the other hand, is always attempting to change its direction. Constant control inputs are required to keep such designs from departing from controlled flight. High-speed computers stabilize the aircraft at any desired cruise or maneuver condition by making quick, small adjustments to the control surfaces.

In the YF-16, relaxed static stability decreased the trim drag at high load factors and at supersonic speeds by as much as fifty percent. The F-16’s combination of a fly-by-wire flight control system and relaxed static stability produced a fighter that could respond to control inputs twice as fast as any previous fighter.

The blended wing-fuselage design of the YF-16, another innovation, provided additional lift with increasing angles of attack. The blending also improved the volumetric efficiency of the fuselage and increased the structural depth of the wing where the loads are the highest. A conventional wing-fuselage design would have required a fuselage more than five feet longer to carry the same volume. Blended wing-fuselage designs reduce transonic drag as well.

The blending of wing and fuselage, however, presented a major problem in latter design stages of the YF-16. At higher angles of attack, the tapered outer edges in front of the wing generated vortices that lowered directional stability. After several unsuccessful attempts at subduing the effects of these vortices, the designers took an opposite approach they intensified the vortices and controlled them to generate more lift over the wing. The sharp-edged strake at the forward root edge of the wing does just that. The strake was probably one of the most highly analyzed and iterated parts of the YF-16, as indicated by the designation of the final strake wind tunnel model design Z119.

The effects of the strake-generated vortices were further enhanced by automatic variable camber wings. The leading edge flaps effectively vary the camber of the wing by automatically deflecting to an optimum position based on the angle of attack, pitch rate, and speed. The combination of the strake and leading edge flaps improved directional stability of the aircraft by as much as 400 percent at high angles of attack and reduced buffet intensity to a mild level throughout a nine-g maneuver.

The F-16 inlet is an example of a low-tech approach to a complex problem. Before settling on a final design and location for the inlet, the YF-16 design team investigated many options: twin inlets, variable-geometry inlets, and a three-dimensional flow inlet, called a Ferri inlet.

The inlet of the YF-16 was located below the fuselage to benefit from the high air pressure and the relatively uniform air flow in that region, especially during maneuvers at high angles of attack. The relatively flat lower surface of the fuselage acts as a shield and straightens out the air flow as it enters the inlet. The face of the inlet was located at the peak of the canopy for aerodynamic reasons (in technical terms, to counter the bump in the area curve caused by the canopy). The splitter plate between the fuselage and the inlet prevents low-energy boundary layer air from entering the inlet (ingesting such air lowers engine performance).

The YF-16 cockpit allowed pilots to take advantage of the raw performance of a nine-g fighter design. The cockpit was the first to combine a number of features that enhanced pilot situational awareness and g tolerance. Side-mounted stick and throttle controllers created more space for critical displays in the center of the instrument panel. Side-mounted controllers also provided more precise aircraft control under high-g maneuvers. A thirty-degree seat back angle and six-inch heel elevation reduced the effective distance between the brain and the heart and increased g tolerance by about two g’s. The seat angle also improved the pilot’s ability to track targets visually under high-g loads. A frameless bubble canopy produced a full 360-degree view at eye level and above. The canopy provided maximum downward view angles of fifteen degrees over the nose and forty degrees to either side. The F-16’s head-up display, combined with ergonomically located switches on the stick and throttle controllers, allowed the pilot to concentrate on combat instead of searching for cockpit switches or display screens.

Increasing thrust is one way to create a higher thrust-to-weight ratio. Thrust, however, was a fixed quantity in the lightweight fighter program since the aircraft had to use an existing engine—the Pratt & Whitney F100-PW-100 afterburning turbofan developed for the F-15 program. Instead, the designers concentrated on the weight and size of the aircraft to improve the thrust-to-weight ratio. The result was impressive. The F-16 was the first US fighter that could take off and immediately accelerate in a straight vertical climb with full internal fuel. Engine commonality with the F-15 also reduced development costs significantly.

Company test pilot Phil Oestricher flew the YF-16 for its unanticipated maiden flight on 20 January 1974. The test mission was scheduled to include taxi tests at various speeds, but no leaving the ground. During a high-speed taxi test, the YF-16 lifted off the ground and the left wing dropped rapidly. Oestricher reacted with a right roll command and the aircraft began oscillating at a high frequency (ten cycles in about fourteen seconds). The roll oscillation stopped, but only after the airplane bounced on its landing gear several times and after the right horizontal tail tip and the outboard fin of the left AIM-9 scraped the runway. These oscillations were caused by a mismatch in the electronic control system gains between the roll and pitch channels. The bouncing caused the aircraft to veer off the runway, at which point Oestricher elected to apply power and get in the air. He flew around the pattern at about 600 feet above the ground and landed safely a few minutes later. Flight 00 had concluded. The gains on the flight controls were changed to correct the problems associated with the unofficial first flight. Oestricher then piloted the first official flight on 2 February. This ninety-minute mission included wind-up turns to three g’s, max speed to 350 knots, and altitude of 30,000 feet.

Part of the lightweight fighter competition consisted of a 1974 mandate by Secretary of Defense Schlesinger and the US Congress that the Navy adapt the winner of the Air Force’s lightweight fighter competition to carrier operations. Subsequently, General Dynamics teamed with Vought and Northrop teamed with McDonnell Douglas to design navalized versions of their competing aircraft (by then called air combat fighters). Several YF-16 Navy variants were pursued. All of them looked much like an F-16, each one having beefed-up landing gear, tail hook, elevated seat and canopy to improve forward visibility for carrier landings, slightly shorter fuselage, and a more powerful radar to accommodate the Navy’s required beyond-visual-range radar-guided missiles. The Navy pursued a navalized version of the YF-17, which became the F/A-18.

General Dynamics later proposed the F-16/79 (an F-16 with a J79-GE-119 engine) to the Navy for low-cost adversary training in the fall of 1980. This proposal, however, was not accepted. Eventually, the Navy bought twenty-six Block 30 F-16s to use in a highly successful adversary training that began in the late 1980s. These aircraft, designated F-16Ns, were subsequently retired from Navy service in 1994.

Since its relatively small beginning with an initial USAF plan of 650 aircraft, the F-16 has become one of the largest and most successful military production programs in the history of aviation. A few months after the Air Force selected the F-16 as its air combat fighter in 1975, Belgium, Denmark, the Netherlands, and Norway announced plans to buy F-16s, bringing the initial program to 998 aircraft. Before the first decade of production ended, seventeen air forces in sixteen nations had ordered more than 3,000 F-16s. Currently, more than 4,000 aircraft are on order for nineteen countries, including follow-on purchases by most countries. In addition, several countries have acquired F-16s from USAF inventory and more orders are pending.

In air-to-air combat, F-16s have compiled a 70-to-0 air-to-air exchange ratio with guns and infrared and radar missiles. Fighting Falcons were combat tested in the early 1980s, very soon after becoming operational, by destroying several high-value strategic targets and mobile surface-to-air missile sites without a loss. F-16s also achieved the first three combat kills with the radar-guided AIM-120 air-to-air missile.

In the early 1990s, the F-16 was deemed the workhorse of Operation Desert Storm, flying 13,500 sorties with 250 aircraft. During the Gulf War, F-16s provided more than forty percent of USAF bomb dropping sorties and delivered 20,000 tons of bombs. To maximize sortie rates andpayloads, F-16s operated from austere, forward-operating locations. The fighters performed a variety of air-to-ground missions, including scud hunting and killer scout (fast forward air controller or fast FAC), and produced the highest mission-capable and sortie rates of any aircraft in theater.

Since the Gulf War, F-16 squadrons from several nations have served in the United Nations peacekeeping operations by enforcing no-fly zones over Iraq and Bosnia. In these operations, the F-16 has served successfully in a variety of roles, including combat air patrol, close air support, day/night precision strike, defense suppression, reconnaissance, and fast FAC.

Summary

The F-16 program began as a secretive and revolutionary approach to fighter design. The aircraft reversed trends toward bigger, heavier, more complex, and more expensive aircraft. The result is a fighter with exceptional capability that has exceeded the expectations of its strongest advocates. And a fighter that is affordable to procure and operate in large numbers.

Good luck on the final exam.

Article by Eric Hehs

Special thanks to Mike Nipper for information on F-16 improvements since the Gulf War.