Aircraft

F-22 Design Evolution, Part I

By Eric Hehs Posted 15 May 1998

A significant portion of the history of the F-22 spent years encased in a collection of wooden boxes stacked in a small storage closet in the engineering building at Lockheed Martin Tactical Aircraft Systems. The containers conceal a variety of design study models dating back to the earliest phases of the Advanced Tactical Fighter-to what eventually became the F-22 Raptor.

The official beginning of the ATF program usually traces to 1981 when USAF Aeronautical Systems Division, or ASD, released a request for information for concepts for an advanced tactical fighter. (ASD is now the Aeronautical Systems Center at Wright-Patterson AFB, Ohio.) The term advanced tactical fighter and its abbreviation, ATF, however, appeared in a general operational requirements document issued to contractors by the Advanced Planning Branch of ASD almost ten years earlier in 1972. The requirements document pertained to a new air-to-ground fighter to complement the new F-15 air-superiority fighter. The ATF would replace an aging fleet of F-4 and F-111 aircraft.

ASD awarded concept exploration contracts for this ATF to General Dynamics and McDonnell Douglas. The requirements called for an air-to-ground fighter that could fly Mach 2.5 at high to medium altitudes and carry standoff weapons designed to destroy tanks and other ground targets. That aircraft never materialized. The F-16 Fighting Falcon, originally designed as an air-to-air day fighter, came in the back door to fill the air-to-ground role. ASD would have to wait ten years to embark on another new fighter program.

Studies for a new fighter subsequently shifted away from ASD to the USAF Flight Dynamics Lab, also located at Wright-Patterson (and now called the Air Vehicles Directorate of the Air Force Research Laboratory). While ASD supported new aircraft development programs, the lab pursued technologies related to military aircraft.

The Flight Dynamics Lab nurtured the advanced tactical fighter through the 1970s, sponsoring research and development contracts. General Dynamics and McDonnell Douglas performed a 1975 study titled, "Advanced Technology Ground Attack Fighter." After that, six companies participated in an "Air-to-Surface Technology Study." The lab sponsored two more studies in 1980: a "Tactical Fighter Technology Alternatives" for future air-to-ground fighters and a "1995 Fighter Technology Study" for future air-to-air fighters. Boeing and Grumman conducted the air-to-ground studies. General Dynamics and McDonnell Douglas conducted the air-to-air studies.

Lockheed was also involved in early studies, but for other government agencies. "Lockheed had done the first studies by the early 1970s for a 'superstealth' air-to-ground attack airplane for the US Navy," explains Bart Osborne, program manager for Lockheed's Tactical Systems in 1972. Osborne, now retired, was chief engineer during the demonstration/validation phase of the ATF program in the mid-1980s. Lockheed used superstealth to refer to a significant improvement in an aircraft's stealth characteristics.

"Lockheed's early work led to the company's proposal for the Navy's Advanced Tactical Aircraft program," Osborne continues. "It also led us to an air-to-ground USAF version, which was a superstealth design. We didn't know how we were going to do superstealth in those early days. We had some ideas, but nothing proven. The operational research in these early studies showed us just how powerful superstealth could be." Early ATF work at Lockheed, however, became dormant as the company focused its talents and energy on the early stages of the F-117 program.

Boeing studied a wide range of advanced air-to-ground fighters in the 1970s. "The aircraft ranged from relatively small single-engine airplanes to large twin engine airplanes," recalls Dick Hardy, who was in charge of a preliminary design group for Boeing at the time. Hardy would later become program manager for the F-22 at Boeing. "Our designs also ranged from supersonic to subsonic," he continues. "They varied from conventional non-low-observable airplanes to really low-observable airplanes and flying wings similar to the B-2 bomber."

General Dynamics studied a wide range of advanced fighter concepts and modifications to existing fighters. Advanced derivatives of the F-16, F-15, and F-111 competed with the new concepts for the same missions. The advanced concepts included a conventional aircraft called "Plain Jane," a supersonic stealth configuration, a small inexpensive fighter called "Bushwhacker," a large fighter called "Missileer" that could carry many long-range air-to-air missiles, and a highly stealthy all-wing fighter called "Sneaky Pete," which eventually evolved into the Navy's short-lived A-12 Avenger II.

These and other government-funded studies were interspersed with company-funded studies at Boeing, General Dynamics, Lockheed, and at all the other companies that would eventually vie for the formal ATF program.

The underlying motivation for all of these studies was to identify the most promising design concepts and enabling technologies for potential missions and roles of the next generation fighter. The development of a new generation of fighters in the Soviet Union intensified these efforts in the United States. In the early 1970s, the Soviets were working on what became the MiG-29 and the Su-27. The prototype for the MiG-29 first flew in October 1977. The Su-27 prototype (the second prototype, which more closely resembled the final design) first flew in April 1981. The Soviets were also rapidly advancing their surface-to-air and air-to-air missile technology. Projected exchange rates between US- and Soviet-built fighters were looking unacceptably even to USAF planners.

In performing these studies in the 1970s, the aerospace industry developed a broad range of aircraft concepts. Companies also created complex computer models for rapidly evaluating specific designs based on these concepts. General Dynamics, for example, had a highly refined process for evaluating designs. The process began with a design concept, which defined a general arrangement and a suite of aerodynamic, structural, avionics, armament, and propulsion technologies. Synthesis and sizing computer models then produced families of designs having a broad range of maneuver, speed, range, and other capabilities.

Families of these more specific designs were in turn fed into life-cycle cost models and into a set of effectiveness models that determined the susceptibility of each design to surface-to-air and air-to-air threats. Other models ascertained each fighter's lethality against its intended targets. The data from the effectiveness models were used in campaign models that accounted for force structures, mission allocations, basing concepts, threat distributions, strategies, and other details that define theater-level scenarios. The campaign models fought wars in which each conceptual design was only one element of the total air forces. Each design was placed in the campaign in numbers proportional to its cost.

This process allowed engineers to see how performance levels or design features affected the military usefulness of a new aircraft. Technologies and design features could then be recommended according to their contribution to the overall effectiveness of the combined air forces in the theater. The results also highlighted the performance requirements that each design concept needed to maximize its cost-effectiveness.

Stealth

Many of the analyses indicated stealth to be a highly desirable design feature. The final General Dynamics report in the "1995 Fighter Technology Study" (produced in 1980) identified stealth as the preeminent characteristic in achieving air superiority. "Fighters have almost always been camouflaged, and fighter pilots have always employed stealthy tactics," explains Bill Moran, then General Dynamics program manager for many of the analyses for the Flight Dynamics Lab. Moran is now a deputy director on the F-22 program in Fort Worth.

"The 'Red Baron Study,' a USAF real-time analysis of combat in Vietnam, showed that over half of the aircrews shot down and about eighty percent of those fired on in Vietnam were unaware of their attackers," Moran continues. "Available data shows that same experience to be true in World Wars I and II and in Korea. Biographies of fighter aces throughout history are full of references that credit their success to an ability to see their opponents before they were seen themselves, attacking from out of the sun, and attacking from their adversary's blind spot."

Stealth, in this sense, means being able to detect the other guy before he detects you. In a narrower sense, the term applies to the application of various materials and techniques that significantly lower the susceptibility of an aircraft to being detected.

As detection techniques evolved, so have techniques for avoiding detection. The development of effective radar networks in the early days of World War II, for example, led to stealth counters to radar. Radar-absorbing materials were initially used by Germany on submarine periscopes and air-breathing U-boat snorkels in the 1940s. Germany later incorporated radar-evading shapes and materials into designs for a jet-propelled flying wing fighter-bomber derived from the Horten Ho IX. Radar-evading techniques were simultaneously developed in the United States.

Soon, stealth was applied to drones and missiles. The Ryan Q-2 Firebee and Lockheed D-21 drones incorporated radar-absorbing materials. Boeing applied stealth technologies in the late 1960s to its design for the Short-Range Attack Missile, more commonly known as the SRAM and designated the AGM-69. The supersonic SRAM was used on B-52 and B-1 bombers until 1990. "The missile met a stringent radar cross section requirement," says Hardy, who worked on the program for Boeing.

General Dynamics was also a major player in the early days of stealth. The company built the prototype for the Air Force's first radar antenna target scattering facility (known as RatScat) in White Sands, New Mexico. The facility was used to measure accurately the radar cross section of aircraft. General Dynamics built RatScat and operated it for the Air Force through the 1970s. The company also operated its own radar measurement facility in Meridian, Texas, through the 1980s.

In the late 1950s, General Dynamics pursued a highly stealthy design concept to meet requirements set by the Central Intelligence Agency for a supersonic high-altitude reconnaissance aircraft to replace the Lockheed U-2. The design began as a B-58 parasite known as Super Hustler. It evolved into an independent aircraft optimized to cruise at 125,000 feet at a speed of Mach 6.25. This configuration, dubbed Kingfish, was to be built mostly of pyro-ceram (a heat-resistant and radar-attenuating ceramic material). Two Marquardt ramjets powered the aircraft in the cruise portion of its mission. Two retractable General Electric J85 turbojets provided power for takeoff and for acceleration to speeds at which the ramjets could be ignited.

The radical General Dynamics design, however, lost out to its competitor from Lockheed in August 1959. The resulting Lockheed airplane, the single-seat A-12, was the forerunner of the two-seat USAF aircraft more widely recognized as the SR-71 Blackbird. The A-12 capitalized on radar-evasive shaping and radar-absorbing structural materials. It is credited as the first operational aircraft to incorporate stealth to a high degree in its original design. Canted tails, sawtoothed structure, pie-shaped panels on leading and trailing edges, blended wings and chines, and radar-absorbing structure and paint combined to reduce the aircraft's radar cross section to a small fraction of more typical aircraft of the period.

Lockheed took stealth technology to an even higher level in the 1970s when it combined computer technology with some obscure mathematical formulas relating to the reflection of electromagnetic radiation. The resulting computer program, called Echo, could accurately predict the way a flat-surfaced object would appear on radar. The company applied the software in a Defense Advanced Research Projects Agency study to create the Have Blue aircraft. The small faceted aircraft, with tails canted inboard, was the predecessor of the F-117 Nighthawk. The development contract for the F-117 soon followed the DARPA project. The success of the F-117, significantly stealthier than any aircraft that preceded it, would greatly influence the ATF program.

Speed

The conceptual work generated for the Flight Dynamics Lab identified speed as another critical characteristic of an air-superiority fighter. Speed steals reaction time from the enemy and provides more freedom to engage and disengage as desired. The initiative often goes to the faster combatant.

Speed in these studies took the form of supercruise-supersonic flight without using an afterburner (a source of undesirable and unstealthy infrared energy). Optimizing an aircraft for supercruise leads to long, slender configurations with small highly swept wings and large high-temperature engines.

The ATF would not be the first military aircraft capable of supercruising. This title belongs to the B-58 Hustler. The B-58, however, had to employ its afterburners or dive steeply to accelerate through the transonic drag to get to the flight condition where it could supercruise. The F-16XL and newer-model F-16s are capable of supersonic flight without afterburner as well.

Maneuverability

Maneuverability was identified as another important characteristic of air-superiority fighters. Unlike stealth and supercruise, high maneuverability is more often used as a defensive tactic rather than an offensive one. "Despite the popular image conveyed in books and movies, like Top Gun," explains Moran, "outmaneuvering the other guy to shoot him down is usually not a good idea. Maneuvering engagements take too long and make you predictable to an opponent other than the one you're after.

"Down through history, successful air-to-air pilots have generally avoided maneuvering engagements whenever possible," Moran continues. "Sometimes they forgot, however. Manfred von Richthofen, the famous Red Baron, achieved a record-high eighty-three kills in World War I, only to be shot down himself while violating this precept. Fighter pilots usually choose to operate in parts of the flight envelope that favor maneuverability characteristics of their own aircraft and avoid areas where their opponents have an advantage. Having good maneuverability everywhere, however, eliminates that consideration and thus increases tactical flexibility."

Maneuverability was quantified in the 1960s by John Boyd in his energy-maneuverability theory [see "Tribute to John Boyd" in the July 1997 issue of Code One]. Boyd's ideas were used on the F-15, but the F-16 was the first airplane to be designed specifically to emphasize the principles established by this theory. The most common measures of merit for energy maneuverability are sustained g capability (the ability to turn hard without losing airspeed and altitude); instantaneous g (the ability to turn the nose of the aircraft without regard to the effect on speed); and specific excess power (a measure of an aircraft's potential to climb, accelerate, or turn at any flight condition). Another parameter of interest is transonic acceleration time (for example, the time needed to go from Mach 0.8 to Mach 1.2). Comparing these characteristics for two fighters shows which one should have the tactical advantage in a maneuvering engagement.

STOL/STOVL/VTOL

The ability to operate an aircraft from battle-damaged runways was yet another characteristic evaluated in the early ATF studies of the 1970s and 1980s. Designs incorporating this capability are referred to by a number of terms, including short takeoff and landing, short takeoff and vertical landing, and vertical takeoff and landing (STOL, STOVL, and VTOL, respectively). The benefits of abbreviated takeoffs and landings are, however, less clear than benefits associated with stealth, speed, and maneuverability.

Incorporating a short or vertical takeoff and landing capability comes at a high price. Establishing the need for the capability is very complex. "How much of this capability is needed depends on the size and effectiveness of an enemy's offensive counter air [the ability to destroy adversary aircraft before they take off] and runway-busting weapons," Moran explains. "It also depends on the number of runways that an enemy needs to wreck to significantly affect the other side's ability to fly and on its ability to quickly repair runways and get back into operation. Most importantly, it depends on the effectiveness of defensive counter air forces in stopping enemy sorties from reaching a base in the first place."

Whether to bomb concrete or whether to bomb airplanes on the ground further complicates the issue. The effectiveness of aircraft shelters and the accuracy of intelligence about where airplanes are at any given time play a role in the latter approach. "The United States and its NATO allies were busy developing a variety of air-to-ground weapons for busting large expanses of concrete," Moran continues. "We reasonably assumed that the Warsaw Pact would reply in kind."

"Short Snort" and "Jiminy Cricket" were two General Dynamics designs that addressed short takeoff and landings more directly. Short Snort vectored thrust from the engine over the wing to produce a fighter with runway requirements of only a few hundred feet. The concept employed ducts and ports that diverted engine exhaust out spanwise along the top of the wing. The approach generated tremendous amounts of lift at very low speeds. The ducting, however, was very heavy, and ultimately proved impossible to incorporate in a high-performance supersonic fighter.

Jiminy Cricket attacked the short takeoff and landing problem with multiple engines. The design had a main lift-cruise engine that provided thrust for lift and for up-and-away flight, and it had auxiliary engines mounted vertically that provided lift for takeoffs and landings only. The aircraft could have either short or vertical takeoff capability, depending on the size of the engines.

A fighter designed for supersonic flight and high maneuverability has a thrust-to-weight ratio and wing loading that produce a fair amount of inherent short airfield capability. That capability can be improved with the addition of rough-field landing gear (for operating on repaired runways), oversized brakes, and thrust reversers. The weight of the improvements, however, decreases the thrust-to-weight ratio available in air combat.

ATF originally had a very difficult STOL requirement that called for the use of some of these features, most notably thrust reversing and thrust vectoring. The takeoff and landing distances were relaxed during the demonstration/validation phase of the program to eliminate the need for reversers as well as their extra weight and cost. Thrust vectoring was retained since it improves aircraft performance in several ways. Thrust vectoring can be used to shorten takeoffs by rotating the nose of the aircraft up at a lower speed than would be possible by using tail surfaces alone. In cruise flight, vectoring can be used to supplement the trim normally provided by tail surfaces. Vectoring, therefore, allows smaller tails or allows cruise with tails set to a position that produces less drag. Thrust vectoring can also augment control power at high angles of attack or during aggressive maneuvers.

The Challenge

Integrating stealth, speed, and maneuverability became the fundamental challenge of the ATF program. No one had ever attempted such a complex combination before. As the F-117 had shown, stealth affects every aspect of a design. Internal weapon carriage, a must for a stealthy design, increases the cross section of an airplane. Larger cross sections increase supersonic drag and work against supercruise. "A stealthy airplane requires a big weapon bay," explains Hardy. "And the landing gear and the inlet duct want to be in the same place as the weapon bay. You wind up with a guppy that won't go supersonic unless you make it very long with huge engines. Such an approach is a nonstarter because the airplane would be way too expensive."

Maneuverability requirements tend to increase the size of the wings and tails and make the engines bigger than necessary for supercruise alone, all of which make stealth more difficult to achieve. Those few pilots who were briefed on the F-117 knew about compromises in speed, maneuverability, payload, and other capabilities that went along with an all-out approach to stealth. Fighter pilots who would be flying the ATF would not willingly sacrifice these capabilities for stealth.

Nine airframe companies and three engine manufacturers responded to the challenge when ASD reentered the game and issued its request for information for an ATF in 1981. At this early stage in the program, the Air Force had not decided whether the new aircraft would emphasize air-to-air or air-to-ground missions. The Air Force invited industry to share ideas for a new fighter.

The companies submitted a wide range of configurations in their responses. Lockheed's response favored a derivative of the YF-12A (what most people would recognize as a single-seat SR-71). This aircraft, designed for air-to-ground missions, carried several kinetic-energy penetrator weapons in a central weapon bay. The weapons would be released at supersonic speeds at high altitudes and guided by a laser. The approach, which was worked through spring 1982, built upon technical data gathered from a series of air-to-air missile launches from the YF-12A conducted in the mid- to late-1960s. The YF-12A had fired seven Hughes AIM-47 missiles at altitudes up to 80,000 feet at speeds over Mach 3. The shots, at aerial targets at ranges of over thirty miles, were highly successful. The high-altitude, high-speed approach was also one of Lockheed's candidates for the F-X program, what became the F-15.

Like Lockheed, Boeing took a supersonic approach in replying to the request for information. The designs favored air-to-ground missions. "After studying a broad spectrum of airplanes, including flying wings, canards, four-tailed airplanes, two tails, side inlets, and nose inlets, Boeing homed in on a design fairly quickly," recalls Hardy. "We thought the aircraft should be designed for higher speed, so we concentrated on designs with a higher fineness ratio.

"It was also obvious that we needed a good maneuvering airplane," Hardy continues. "When the prime mission of the airplane later shifted to air-to-air, we quickly got rid of those things that did not have good control authority." Boeing also stressed stealth with clever internal arrangements and weapon bay designs that carried munitions semi-submerged.

The response from General Dynamics favored two of the four concepts originally developed in the 1976-78 studies for the Flight Dynamics Lab. One was a Plain Jane derivative called Model 21. This design was a forerunner of the conventional family of configurations the company would explore in the next phase of the ATF program. Model 21 looked like a traditional member of the modern fighter family, but it wasn't totally conventional. It had frontal shaping and treatment to reduce its radar cross section, strut-braced wings, a rotating nose that combined a radar with an infrared search and track system. Composite materials comprised forty percent of the aircraft structure. Its air-to-ground loadings included glide bombs with square cross sections.

The other candidate was a descendent of Sneaky Pete. General Dynamics, however, was not allowed to show USAF officials actual drawings of this design because of its classification. The company substituted surrogate drawings of a notional fighter that USAF officials soon dubbed "the marshmallow." The real design was the starting point for all-wing studies explored in the next phase of the program.

After a year of study and report writing by industry, ASD performed mission analyses on four generic fighter designs that spanned the variety of aircraft investigated by the companies. The aircraft were labeled N, SDM, SLO, and HI. N (numbers) was a small, cheap concept that could be bought in quantity. SDM (supersonic dash and maneuver) emphasized speed and maneuverability. SLO (subsonic low observables) was based on a flying wing design. HI (high-Mach/high-altitude) represented a large missileer. The results, which were presented to all participants, favored the flying wing. The more conventional SDM fighter placed second in effectiveness. The missileer and inexpensive minifighter did not rate well in the analyses.

Momentum And Funding

As the RFI results were announced, the ATF program gained momentum and funding. A mission element need statement, a required document that characterizes a particular mission, was issued in late 1981. Tactical Air Command (which later became part of Air Combat Command) created a corresponding statement of need-another required document that addresses threats, theaters of operation, and capabilities needed to accomplish the mission described in the mission element need statement. The statement of need is largely credited to Col. Mike Loh, the deputy commander of the requirements branch at TAC Headquarters (he later became a full general and ACC commander). The fifty-page document was provided to industry for comment in the summer of 1982. The requirements formally made the ATF a replacement for the F-15 in the air-superiority role. An ATF System Program Office was formed at Wright-Patterson AFB in 1983, and Col. Albert Piccirillo became its first director.

A request for proposals for the ATF engine was issued in May 1983. General Electric and Pratt & Whitney were awarded contracts to build and test competing engine designs. The General Electric engine was designated the F120; the Pratt & Whitney engine was designated the F119. At the same time, USAF requested proposals for a concept definition investigation for ATF.

Boeing, General Dynamics, Grumman, Lockheed, McDonnell Douglas, Northrop, and Rockwell responded to the request and prepared proposals for submittal in mid-June 1983. Just before the deadline, ASD announced a week delay and informed contractors to await further instructions. At the end of June, the companies were asked to add another volume to their proposals to describe stealth-related skills and experience. Any detailed discussion of stealth technologies had evaded the ATF program to this point. The original proposals were limited to thirty pages. The stealth addendum - to be submitted as a separate, highly classified volume - had to fit on five pages.

"Originally, the ATF program did not contain stealth," explains Al Piccirillo, the director of the ATF System Program Office at the time. Piccirillo is now the manager of the technology division at ANSER, a government consulting firm in Washington, D.C. "People on the program were aware of what was going on in the F-117 and the B-2 programs," Piccirillo continues. "We would have been really stupid to develop an advanced fighter without using this new technology. Without stealth, I am not sure the Air Force could have justified ATF."

Including stealth set an unusual security precedent. The security level of the original request for proposals for this phase of the program precluded any details on stealth, a topic that was highly classified in the early 1980s. Companies could claim that low-observable technologies would be considered in a design, but they couldn't reference any actual experience or techniques in their proposals. Stealth technologies were considered "black." Such programs did not exist to anyone not cleared on them. The last-minute change to the request for proposals placed the program in both worlds: black and white.

The proposals from most companies for the concept exploration phase showed how they would narrow down their previous approaches for achieving air superiority. This work would lead to the next phase of the program, the demonstration/validation phase, in which they would have to prove their technologies and refine their designs. Lockheed, however, took a radical departure from its high-speed, high-altitude design and started from scratch with an F-117 derivative in its proposal for the concept definition phase.

"Clearly, ATF was going to be superstealth and not a cousin of YF-12 or SR-71," explains Osborne. "I stopped the YF-12 derivative effort, and we started working on an F-117 derivative for ATF." The design submitted in the Lockheed proposal looked like a larger and elongated F-117 with some significant differences. It had a high wing rather than low wing and four tails instead of two. The inlets were placed below and behind the leading edge of the wing. The highly faceted airplane weighed around 80,000 pounds and was far from aerodynamic.

"We knew we would have serious problems with the supersonic requirements," recalls Osborne. "Our design could go supersonic, but it was a real dog of an airplane. With enough power, you can make a brick fly. We did not know how to analyze a curved stealthy shape in those days. The software wasn't sophisticated enough, and we didn't have the computational capacity we needed. We had our hands tied by the analytical problems. Lockheed had become convinced that, if we could not analyze a design as a stealthy shape, then it could not be stealthy. We would not break through that barrier until 1984." Lockheed's submittal for the concept exploration phase was not received well by the Air Force. The company placed last in the field of seven.

Each of the seven companies that bid on the concept exploration phase of the ATF program, including Lockheed, received a contract for about $1 million. This phase ran from September 1984 through May 1985 when the Air Force received many briefings and thousands of pages of reports that would take the program into the demonstration/validation phase. In the dem/val phase, four winning companies would be given about $100 million each to demonstrate technologies needed to build their ATF. The request for proposals for the dem/val phase was issued in September 1985. The deadline for the proposal was set for that December.

The Lockheed Design

After a poor showing in the concept exploration phase, Lockheed had to turn around its ATF program before the next proposal was due. The company had just lost what became the B-2 with a faceted design to a more aerodynamic flying wing design from Northrop. Lockheed had also been cut from consideration in the Navy's Advanced Tactical Aircraft program after entering that competition with a highly faceted design. The Air Force's response to Lockheed's concept exploration proposal forced the company to rethink its commitment to faceting for stealth.

"We simply started drawing curved shapes," recalls Osborne, "even though we could not run the designs through our analytical software models. When we went to curved airplanes, we began to get more acceptable supersonic and maneuver performance. Instead of relying on software models, we built curved shapes and tested them on the company's radar range. The curved shapes performed quite well in the radar tests."

The Lockheed configuration quickly progressed from faceted to smooth. The configuration just preceding the company's final dem/val design, called Configuration 084, was smooth except for a faceted nose. "We knew how to make a stealthy flat radome," recalls Osborne, "but we didn't know until early 1985 how to make a stealthy curved radome. We started drawing them in late 1984, before we knew how to analyze them."

The proposal configuration, called 090P, had a streamlined nose, trapezoidal wing planform with positive sweep on both the leading and trailing edges, and four tail surfaces (two horizontal and two vertical). The large vertical tails were canted outwards. The leading and trailing edge sweep angles of all of the surfaces were aligned at common angles. The design had a wide strake that ran in a straight line from the wing leading edge outboard of the inlets to the point of the nose.

One requirement that drove all of the ATF designs was a wide field of regard for sensors. The requirement called for a 120-degree radar field of regard on each side of the nose. A forward-looking infrared search and track capability was also desired. Lockheed approached the field-of-regard requirement for the radar with three radar arrays placed in the nose of the aircraft (one facing forward and two facing sideways). Each wing root carried an infrared search and track system that operated through faceted windows.

The aircraft carried six air-to-air missiles in a rotary missile launcher. The launcher was loaded away from the aircraft. (Lockheed also designed a version of the launcher that could be used independently for airfield defense.) When closed, the bottom of the launcher became the lower skin of the aircraft.

Lockheed built a large-scale model of a curved configuration to test on the company's radar range. The data from these tests went into the company's proposal for the dem/val phase. "The real question USAF had was whether Lockheed could design a curved stealthy airplane," Osborne explains. "We showed them with the range model that we could do curves." Lockheed's biggest advantages going into the dem/val competition were its revamped approach and its vast stealth experience. Lockheed had also earned a fine reputation for rapid-prototyping in a variety of programs, most recently in the Have Blue program.

The Boeing Design

The Boeing concept was a larger aircraft than the designs submitted by Lockheed or General Dynamics. The company retained the higher operating speeds assumed in its previous work. The most notable features of the design were twin vertical tails located well aft on the fuselage behind a trapezoid planform wing. The vertical tails were sized to provide the same vertical and horizontal control power as four tails. "Our designers argued most over two tails versus four tails," Hardy says. "The whole Boeing company got involved in the argument. We had special teams set up to study the problem. Two tails won out. Our higher operating speeds led to a longer airplane, which produced a longer moment arm for the tails. So we didn't need as many tail surfaces. We thought we could meet all the requirements with two tails, which gave our design a lower signature and a lighter weight."

Boeing designers focused on the weapon bay and essentially designed the airplane around it. Wind tunnel results, especially those related to flight at high angles of attack, affected the arrangement, size, cant angles, and placement of the tails. The design used a single chin inlet with an internal splitter to feed the two engines. The inlet had an internal variable ramp (combined with the splitter) to reach its higher design speeds. Boeing designers moved the nose landing gear aft of the inlet in one of the later design changes. The company had been working on advanced composite materials for USAF labs and in some classified programs in the 1970s and 1980s. As a result, the design used a unique thermoplastic manufacturing process and material for the wing.

The Boeing design carried its air-to-air weapons internally, though larger air-to-ground weapons were carried partially submerged. Heat-seeking missiles were carried in separate bays placed forward in the fuselage. The weapon bay concept relied on quick-change pallets to position the munitions so they could be loaded quickly to meet quick turnaround requirements. The Boeing design had three radars in the nose, one large forward-facing array and two smaller side facing arrays, to meet the 120-degree field of view requirement. Two infrared search and track sensors were placed near the nose as well.

Boeing had done well in the previous phase of the program, placing high in the field of seven. Its design was also well developed and wind tunnel tested. Further, the company had extensive experience in integrating avionics. This experience, which dated back to the AWACS program, had been more recently refined in the B-2 bomber program. The company also had an impressive production capability developed in its commercial airline work.

The General Dynamics Design

The General Dynamics design for the dem/val phase evolved from a variety of inputs. During the previous program phase, the company had focused on three separate families of aircraft: conventional, all-wing, and semi-tailless (denoted in the configuration studies by C, W, and T, respectively). The conventional family derived from the Model 21 designs of the previous studies. The all-wing family strove to carry Sneaky Pete's minimum observables into the supersonic regime. The semi-tailless family, which had a single vertical tail, fell in between these two extremes. After a series of internal design competitions and trades, the company went with the semi-tailless approach.

The wing planform and airfoil design were chosen to minimize weight while providing the maximum turn capability and supersonic cruise. The single vertical tail, however, presented problems in achieving a totally stealthy design. General Dynamics ran many wind tunnel tests to find a location and shape for twin canted vertical tails on the T configuration. The vortex flow off the forebody and delta wing produced unstable pitching moments when it interacted with twin tails. Without horizontal tails, the aircraft did not have enough pitch authority to counteract these moments. A single vertical tail and no horizontal tails was finally identified as the best overall approach to the design despite the degradation of radar cross section in the side sector. The proposal configuration was designated T-330.

General Dynamics took a unique approach to the sensor requirements, using two radar arrays and one infrared search and track sensor. (Boeing and Lockheed had each used three arrays and two IRST sensors.) One IRST sensor was placed in the nose of the aircraft and the two radar arrays were located aft of the cockpit. The radar beam from each array could be steered sixty degrees from the face of the array, allowing each radar to cover the area from straight ahead to 120 degrees aft. The arrays were located just above the engine inlets.

The General Dynamics configuration achieved a high state of detailed design. The company built a full-scale mockup and was finalizing a half-size pole model for testing the design's radar cross section. Preliminary structural designs were developed, along with locations for manufacturing breaks to allow the aircraft to be divided among potential partners. General Dynamics had done well in the concept exploration phase of the program, placing very high in the field of seven. Among General Dynamics strengths were its extensive experience in fighter design and manufacturing gained in the F-16 program. The company also had experience with rapid prototyping: the YF-16 was an unsurpassed program in this respect.

Amended Request

A few months before the proposals for the dem/val phase of the program were to be submitted, the Air Force amended its proposal request. The change significantly increased the importance of stealth in the design. Lockheed, with a stealthy configuration derived from the F-117, made no modifications to its design as a result of the new requirements. Boeing made some slight modifications to the design of their inlet to address the increased stealth requirements. The company was, however, satisfied that its twin-tail design would meet the stealth requirements.

The upgraded requirements forced engineers at General Dynamics to again reconsider twin tails in a variety of locations, including out on pods on the wing. The trailing edge of the wing and the control surfaces were cut into chevrons aligned with the leading edge, giving the wing a bat-like look. In the end, no acceptable location for the twin tails was found, and the design was submitted with a single centerline tail and a serrated trailing edge. The new final configuration was labeled T-333.

Another Delay

As it had done with the proposal for the previous phase, the Air Force delayed the submittal date for the dem/val proposals. This time the deadline was put off for prototyping. The amendment required contractors to build two prototypes: one with the F119 and the other with the F120 engine. The last-minute change resulted from a reaction to a report released in the early-1980s by a congressional commission headed by electronics-industry pioneer David Packard, who had been asked to look at reforms in Pentagon acquisition practices. The report, influenced by the recent success of the F-16 program, favored prototyping for new military aircraft.

"Initially, the proposal request did not contain prototypes," Piccirillo explains. "ATF was patterned on the F-15 program, which did not have prototypes. The Air Force has gone back and forth over fifty years on the value of prototyping. In the 1960s, through the F-15 program, we did not prototype. We performed studies, ground testing, and wind tunnel testing and went right into full-scale development work. We built test airplanes, but they were very close to the production configuration. After the amendment, the dem/val phase of the program called for best-effort concept demonstrators. We left it up to the contractors to decide how they would demonstrate the critical technologies behind their concepts for an ATF. One of the most critical was shaping for supersonic flight and low observables."

"We had actually finished the proposal and were within a few days of turning it in when we got Modification Request MR-006 to the RFP," recalls Moran. "Instead of approximately $100 million contracts for four winners, the Air Force added flying prototypes to the program and would award only two contracts of about $700 million each. We were directed to write one more proposal volume describing how we would design, build, and test two flying prototypes-one with the Pratt & Whitney F119 engines and the other with the General Electric F120 engines. We were also required to build a ground-based avionics test lab, and we could offer a flying avionics testbed if we thought that was desirable." The companies were given sixty extra days to modify their proposals.

About the time the request for proposals for the dem/val phase was amended in late 1985, USAF sent out a letter to the competing companies to encourage teaming. "The amended proposal request had a cover letter that encouraged teaming," recalls Piccirillo. "The Air Force encouraged teaming because it wanted the best resources from industry to be brought to bear on the program. The program was going to be expensive and big. The more commitment we had from industry, the more likely the program was to succeed."

A complicated dance among the contractors began immediately to see who wanted to partner with whom. Representatives from Boeing, General Dynamics, and Lockheed signed a teaming agreement in June 1986. Northrop and McDonnell Douglas announced their team two months later. The two remaining companies did not team.

The teaming agreement among Boeing, General Dynamics, and Lockheed called for the winning company to be the team lead. The teaming deal was done "blind," none of the participants got to see the other contenders' aircraft or program plans before the contract was awarded. Boeing, General Dynamics, and Lockheed each identified a group of twenty high-level managers who would travel to the winning company's site the day after the award was announced.

The $700 million announcement came on 31 October 1986, naming Lockheed and Northrop as the top two contenders. Representatives from Boeing and General Dynamics met their Lockheed counterparts for the first time on Sunday 2 November as partners at Lockheed's Skunk Works in Burbank, California. The team would be competing against Northrop and McDonnell Douglas for the Air Force's next-generation fighter.

Eric Hehs is the editor of Code One.
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