“Designed as a pure lightweight fighter, evolved during development into a multirole fighter equally adept at air combat maneuvering and bomb delivery.”
Posted on September 26, 2017
By Raymond R. Panko | Ray@Panko.com | Pearl Harbor Aviation Museum
Single-Seat Multirole Fighter
The General Dynamics/Lockheed Martin F-16 is a light, fourth-generation single-seat fighter with unprecedented agility and, despite its small size, exceptional bomb load and range. Although named the Fighting Falcon, nearly everyone calls it the Viper. The F-16 was a showpiece of futuristic technology when it appeared, and has continued to stay at the cutting edge. The F-16 is equally adept at air combat and dropping bombs under almost any weather conditions.
General Dynamics created the F-16. In 1993, it sold its military aircraft division to Lockheed. In 1995, Lockheed merged with Martin Marietta to become Lockheed Martin [Simonson].
Why “Viper?” It got this nickname from the Colonial Viper space fighters in the original Battlestar Galactica series [Hillaker 1997].
More than 4,500 F-16s have been delivered since 1979, and Vipers have flown more than 400,000 combat sorties for 28 air forces around the world [Lockheed, July 2014]. In 2015, 2,691 Vipers were in active service, making it the world’s most widely used military airplane of any type [Hoyle]. America’s last F-16 was delivered in 2005 [Matricardi 394], but Lockheed Martin has continued to deliver Vipers to other countries. If F-35 production falters or is limited, Lockheed Martin is ready with a new version, the F-16V. The V stands for “Viper,” finally acknowledging the plane’s universal nickname [Lockheed Martin, Feb. 2014].
The Viper was prompted by the unhappy experiences of Air Force pilots in Vietnam [Hubbard, Ch. 2]. The F-4 Phantom II was designed as a bomber interceptor. It was enormously fast in a straight line and could fly long distances. Maneuverability was limited, however, and the big, smoky “Rhino” with its little wings had its hands full against the little MiGs flown by Vietnamese pilots. Worse yet, when F-4 pilots did manage to get on the tails of MiGs, their missiles had terrible reliability problems, and they had no guns for short-range combat until late in the war. For every two MiGs killed during Rolling Thunder, we lost one American fighter [Hubbard 469]. American fighter pilots said, “Never again.” They wanted an air superiority fighter like the P-51 Mustang in World War II and the F-86 Sabre in Korea.
In 1976, pilots got much of what they wanted in the McDonnell Douglas F-15 Eagle. This was an uncompromising air superiority fighter. The pilot sat high, surrounded by a clear canopy. It had a gun, heat-seeking missiles, and radar-guided missiles, allowing it to hit targets at any range. It could turn quickly, thanks to its oversized wing. (The Eagle was sometimes called the Flying Tennis Court [Panko]). This wing was designed to be optimal for turning at around Mach 1, where most air combat actually occurs [Hubbard 1048]. The Eagle’s size gave it the room for an extensive electronics suite that would help it survive over enemy territory. Size also gave it the fuel it needed to fly deep missions.
A separate version of the Eagle, the two-seat F-15E, was created for ground attack. It is easily identified by its two-seat cockpit and its darker blue color than fighter-only Eagles.
A group of Air Force pilots, defense analysts, and airplane designers that named themselves the “Fighter Mafia” argued that the F-15 was only a first step toward what they really wanted — a fighter consistent with Energy-Maneuverability Theory. EMT was developed by Col. John Richard Boyd and Thomas P. Christie [Coram, Hillaker, 1997]. Boyd, who was a fighter pilot with outstanding knowledge of air combat maneuverability, began with a practical insight. He realized that whenever he was in a position of advantage, his energy was higher than his adversary’s. Whenever he was at a disadvantage, the reverse was true [Hillaker, 1997]. Christie worked with Boyd to turn this and other insights into a formal theory that yielded quantitative tools for analyzing energy in air combat conditions [Coram]. Calculations based on EMT called for light weight, a high thrust-to-weight ratio, low drag, and outstanding pilot vision. With the proper combination of these and other characteristics, a pilot would be able to maintain an energy advantage over any opponent throughout a dogfight.
Figure 1: F-16 and F-4 Size Comparison
Air Force Historical Research Agency: USAF photograph.
In the past, light weight meant limited endurance. Small planes like the MiG-21 and F-104 had very short range. E-M Theory called for something very different in a small airplane. Obviously, light weight meant that the airplane could travel farther on a given amount of fuel, but EMT also focused heavily on slashing drag. Low drag gives far greater range as well as many other EMT benefits. One study estimated that a small aircraft weighing about 17,000 pounds would not only be twice as maneuverable as the F-4 but would also fly twice as far [Hillaker, 1997]. The eventual F-16 did, in fact, have only a third of the drag of an F-4 in level flight. At a high angle of attack in combat, it would have only one-fifteenth [Hehs]. It could therefore engage in air combat without burning through its fuel at the insane rates that big, draggy fighters did.
The YF-16 and production airplanes that followed demonstrated that the long range of light fighters was not an empty promise. Lt. Gen. Thomas Stafford, who was one of the YF-16 test pilots, said, “It’s amazing, this little airplane that weights half of an F-4 yet can carry the same bomb load as the F-4 twice as far using less gas” [Hubbard, 1177]. It shattered the myth that small airplanes necessarily had short ranges and little armament. Figure 2 compares drag and fuel consumption for the F-4E and the F-16A. The numbers are stark. Thanks to many innovations, the Viper can execute deep interdiction missions with substantial payloads and an unrefueled combat radius of 800 nautical miles.
Figure 2: Comparing the F-4E with the YF-16A
Source: Hillaker, 2014.
To explore Energy-Maneuverability Theory, the Air Force agreed to fund a prototype demonstration program for a Light-Weight Fighter. Only two companies would build prototypes, and there was no promise of a follow-on production contract [Hubbard 242]. General Dynamics worked closely with Boyd and the “Fighter Mafia” on using EMT to design the YF-16 [Hubbard 1073, 1149]. In fact, Henry Hillaker, who was General Dynamics’ chief designer, was himself a member of the Fighter Mafia [Hillaker, 1997]. The plane they built was a demonstration and vindication of the theory’s power. It did exactly what the theory said it would. It turned on a dime, climbed like a scalded cat, and flew extraordinary distances without refueling.
Figure 3: YF-16 Prototype, which Took to the Air Accidentally During Fast Taxi Tests
Source: U.S. Air Force photograph 1267828237_3142.
Lockheed Martin F-16 drawing and sketched outline 1363014422727.jpg
The F-16 was designed as a pure air superiority fighter. During its development, however, an international need emerged for a multirole fighter to replace such old aircraft as the F-5 Freedpm Fighter or the F-104 Starfighter [Hubbard 1139-1143]. The F-16 entered the competition and, to the surprise of many, won.
To meet the required changes for ground attack, the F-16’s weight grew a little [Hubbard 1254]. Boyd was deeply upset by this and retired in 1975 [Hubbard 1260]. While the Fighter Mafia was not crazy about this increase in weight, the Viper retained the prototype’s astonishing air combat abilities. As a ground pounder, the Viper can carry almost any type of ordnance the countries that use them have in their arsenals and deliver weapons with precision.
Figure 4: Viper Dropping Bombs at Hill Air Force Base
Source: U.S. Air Force photo at Hill Air Force Base.
The most important change to achieve multirole capability was installing the Westinghouse APG-66 multimode radar to give the F-16 ground attack capability while retaining the Viper’s air-to-air radar capability. Figure 5 shows that the radar required lengthening the nose by 10 inches and giving it a small droop. This design began in the first full-scale development aircraft and continued on later models. The top of the nose was kept constant to retain the downward visibility that is so crucial in pulling lead on the adversary.
Figure 5: YF-16 and Full-Scale Development F-16
Source: Lockheed Martin http://www.codeonemagazine.com/images/media/2014_YF16_F_Later_50_1267828237_2677.JPG
The Block 50/52 versions of the F-16 were created specifically for the demands of the suppression of enemy air defenses (SEAD). Their radar was uprated for the mission, detection and jamming avionics were added, and they were equipped to fire the deadly AGM-88 high-speed anti-radar missile (HARM) to take out surface-to-air missile sites. Integrated avionics allowed the single F-16 Wild Weasel pilot to do the work of the pilot and weapons systems officer in the F-105G and the F-4G Wild Weasels.
Figure 6: F-16 Wild Weasel
Source: National Archives. https://catalog.archives.gov/id/6630525.
Figure 7: F-16 Wild Weasel Fires an AGM-88 HARM Missile at Hill Air Force Base
Source: Hill Air Force Base, USAF photograph.
Not surprisingly, F-15 advocates were worried that the Air Force would drop the increasingly expensive F-15 in favor of the cheaper but less capable F-16 [Hubbard 1100]. In fact, fighter costs had been accelerating for many years, and the complex F-15 raised the fly-away price to a frightening degree. The F-16 would break this trend.
Figure 8: Unit Cost Trends
Source: Hillaker, 2014.
Concern only dissipated when the Air Force announced that it was adopting a high/low strategy that would use both airplanes [Hubbard 1126]. At the high end, the F-15 could fly deep into enemy territory and fight the best of the enemy’s fighters with long-range missiles. Before air dominance was achieved, F-16s would join in the air combat, presumably focusing on defeating smaller, agile MiGs with guns and heat-seeking short-range Sidewinders. Once air dominance was achieved, the F-16 would switch primarily to attacking ground targets. The high/low strategy made sense because the Air Force could not afford all the F-15s it would need to handle total air combat. Instead, it bought many F-15s but even more of the switch-hitting F-16s.
Everything about the F-16 screams “air-superiority fighter.” The pilot seems to be sitting on top of the cockpit, and the panoramic canopy is almost completely clear. Instead of having to deal only with “steam gauge” instruments, much information is now available on customizable multifunction displays. Figure 9 shows a later-model cockpit. For comparison, Figure 10 shows the original F-16A cockpit. To maintain situational awareness, the pilot can look mostly at the heads-up display in combat. This maintains eye contact with the enemy during complex maneuvers. Lockheed Martin also has developed a helmet-mounted cueing system that puts key information in front of the pilot wherever he or she looks. The pilot can even look at an enemy airplane not directly in front of the Viper and fire a missile at it without turning the aircraft. This helmet system is available on many newer F-16s.
Figure 9: Later Model F-16 Cockpit
Source: National Museum of the Air Force.
Figure 10: F-16A Cockpit
Source: National Museum of the Air Force
Figure 11: Lockheed Martin Helmet-Mounted Cueing System
Source: Lockheed Martin. http://www.codeonemagazine.com/images/media/34_JHMCS_A5V4032_copy_1267828237_7831.JPG
The plane was built to turn at a sustained 9 g-forces — even with full fuel tanks [Crosby 2003]. This was unprecedented at the time. It also meant that pilots needed help because they were going to be pinned downward by enormous weight. Figure 9 shows that the most important controls were put on the two armrests so that the pilot would not have to lift his or her arms up under high loads. The right armrest had a small computer control stick that took over the role of the traditional control stick between the pilot’s legs. The left armrest had the throttle. These two controls, furthermore, were studded with extra buttons for firing weapons and other functions. Today, HOTAS (Hands On Throttle And Stick) is common in advanced aircraft. To further help the pilot cope with g-forces, General Dynamics leaned the seat back 30 degrees to reduce blood flow from the pilot’s brain [Hubbard 1126].
Figure 12: Painting of North Dakota Air Guard F-16 over the burning Pentagon, Sept. 11, 2001
Source: Air Force Historical Research Agency 120515-D-LN615-001.jpg
The Viper’s stick and throttle are not linked to control surfaces by mechanical cables. Instead, they send electrical signals to the Flight Control Computer. The computer then sends commands, again electronically, to the correct motors on the wings and tail. The commands to the motors are much more detailed than the HOTAS input commands. To create those ultimate commands, the Flight Control Computer constantly receives sensor data on speed, atmospheric conditions, angle of attack, and other parameters to command the aircraft to do what the pilot intends.
Figure 13: Fly-by-Wire Control
Source: Raymond Panko (email@example.com).
A biggest advantage of “fly by wire” control is reduced stability. Before the F-16, all airplanes had positive static stability. If the aircraft received a small wind nudge, it would quickly go back to its original flight path. This is nice, but if the pilot needs to turn quickly, he or she must overcome this stability. This takes a tiny amount of time, but delay is death in air combat. Fly by wire with computer control permitted the airplane to be built with relaxed static stability. It still has slightly positive static stability, but it is close to zero. With relaxed static stability, the airplane is constantly thrown off course by small gusts of wind and atmospheric irregularities. Every time this happens, however, the Flight Control Computer, monitoring status data from sensors, recognizes the departure and sends appropriate commands to control surfaces to return the airplane to its previous trajectory. This happens instantaneously and without the pilot’s awareness [Hubbard 1173]. With relaxed static stability, the Viper almost seems to begin its turns before the pilot pushes the stick. Somewhat controversially, the Flight Control Computer will not allow the pilot to exceed the airplane’s capabilities or attempt maneuvers that would produce more than 9 g-forces [Hubbard 1168].
Cropped Delta Wings
Figure 14 shows that the F-16 wings look like a traditional cropped delta. It has a swept-back leading edge for high-speed flight and a straight trailing edge to give the wing the torsional rigidity of a delta. The cropped delta is extremely popular among fighter designers.
Figure 14: F-16 Wings and Other Lifting Surfaces (Front View)
Source: U.S. Air Force photograph 030322-F-7203T-019.
Figure 15: Wings and Other Lifting Surfaces (Top View)
Source: Lockheed Martin. http://www.codeonemagazine.com/images/media/2014_F16_Paint_06_F10_64251_1267828237_8539.jpg
What is not immediately obvious is that the wing has variable camber. Camber is the curvature of the wing. Traditionally, wings had fixed camber, which was better for some conditions and worse for others. One way to change camber dynamically was to give the wings variable sweep, as in the F-14 and F-111. However, a wing pivot mechanism is heavy, complex, and a maintenance nightmare. General Dynamics took this approach with the F-111, but it took a different approach to variable camber on the F-16. It simply changed its wing’s camber during a flight so that its camber was just right for the aircraft’s momentary speed and angle of attack. The F-16 achieved variable camber by using front flaps and rear flaperons. Figure 16 illustrates this approach. Normally, flaps are only on the trailing edge of the wing and used only during landings, to add lift by changing the wing’s camber and adding drag. In World War II, it was found that rear flaps could be used to change the wing’s camber in combat. Lowering the rear flaps all the way created a great deal of drag, but lowering the rear flap somewhat increased camber and therefore lift in turns while adding only a little drag. On the F-16, the rear flaps are called flaperons to indicate that they are used as both (maneuver) flaps and ailerons. In addition, the F-16 also had flaps on the leading edge of the wing. By changing these two control surfaces to different degrees, the wing could always have exactly the right camber for current conditions.
Figure 16: Variable-Camber Wing
Source: Raymond Panko (firstname.lastname@example.org).
Another lift innovation is the Viper’s blended wing-body. The wing essentially does not stop when it reaches the fuselage. It blends smoothly into the fuselage. The blend area gives the wing enormous strength, which it needs for 9-g maneuvers. It also provides room for fuel or equipment. Most important, the blend area adds lift. In fact, the entire upper body is a lifting surface. This blended design not only provides lift without adding a great deal of frontal area and therefore drag — it also allows the Viper to fly at a greater angle of attack than clipped deltas normally can without stalling. This is a massive gain for air combat maneuvering.
Figure 17: Lifting Upper Fuselage Surface on the F-16
Lockheed Martin: F-16 production in industry 12_F16_ProdLine_Turkey_01_1267828237_9796.JPG
In addition, there are strakes that flow from the forward fuselage into the wing root. These are essentially wings of tiny span. They add to lift, but their main job is to control the air flow over the wing root, as shown in Figure 18. Each strake creates a vortex that keeps air flowing cleanly at high angles of attack. This, combined with the blended wing-body, gave the Viper the ability to fly at then-unprecedented angles of attack. Today, innovations such as vectored thrust allow many fifth-generation aircraft to fly at even higher angles of attack, but the F-16’s ability to pick its nose way up without stalling was amazing at the time. The only angle of attack issue is that the fly-by-wire system will not allow an angle of attack over 26 degrees [Rogoway]. The MiG 29 had the same 26-degree design limit, but the pilot can override it to put the plane in a 40- to 50-degree angle of attack, albeit with some difficulty. Not being able to override the angle of attack limit on the F-16 is resented by many pilots.
Figure 18: Effect of the Wing Strakes
Overall, the wings gave the F-16 extreme agility. Figure 19 shows the contrails of an F-4 and an F-16 doing maximum-rate turns. One would clearly does not want to be in the F-4 in a turning dogfight against the F-16.
Figure 19: F-4 and F-16 doing maximum-rate turns
One reason for the F-16’s high endurance, beyond exceptionally low drag and weight, is its use of a turbofan engine. Turbofans drive air outside the combustion chamber, pushing the plane much more efficiently than the turbojets of F-4s and other previous fighters. Initially, the F-16 used the Pratt & Whitney F-100-PW-200 afterburning turbofan — a modified version of the F-100-PW-100 engine used in F-15s. Using the same engine reduced cost. Using only one engine to the F-15’s two further reduced cost. Later versions offered two options. One was improved F100-PW-200 engines. The other was General Electric F110-GE-100. Both engines were subsequently uprated multiple times.
When the F-16 was being developed, it had an M61 multibarrel cannon and Sidewinder heat-seeking missiles. In fact, Air Force generals specifically ordered that the F-16 should not have the radar-guided Sparrow missile because they did not want the Viper competing directly with the Eagle [Bjorkman]. Gen. John Michael Loh found a way around that restriction. He instigated a new radar-guided missile, the AAMRAM [Bjorkman]. It took a while for the F-16 to get the upgrades it would need to fire this missile, but after it received the AAMRAM, it had the long-range lethality that was supposed to be the Eagle’s distinguishing feature. Its radar kept improving over time as well, making the AAMRAM a very effective beyond-visual-range weapon.
Figure 20: M61 Vulcan Six-Barrel Cannon in an F-16 (Two Barrels Showing)
Figure 21: AAMRAM Missile on an F-16’s Wingtip Station
United States Air Force Photograph 981228-F-6082P-996.jpg. http://archive.defense.gov/dodcmsshare/newsphoto/1998-12/981228-F-6082P-996.jpg
Lockheed Martin has an excellent article about the many versions of the F-16. Here is a link to the article in Lockheed Martin’s Code One Magazine in 2015. http://lockheedmartin.com/us/news/features/2015/C1HistoryF16.html.
It is beyond the scope of this article to provide a detailed description of the F-16’s operational history. However, we will mention three important instances of its operational life. In 1981, Iraq was building a nuclear reactor that could produce weapons-grade plutonium. The French firm building it called it Osirak [Wikipedia, 2016]. Israel decided to hit it before its nuclear core arrived, because hitting it later would become dangerous to those near it. On June 7, 1981, Israel sent eight F-16s, each with two 2,000-lb. Mk 84 bombs, to destroy the two reactors at the site. Israel also sent six F-15s for top cover. In the early afternoon, the F-16s struck the reactor, and nearly every bomb hit its target, destroying the reactor. The biggest problem for the Israelis was that the reactor was almost a thousand miles away from Israel, even taking a short-cut through Jordanian and Saudi air space. The attack was a testament to both the Viper’s strike capability and to its incredible range for a small aircraft.
During Desert Storm in 1991, the United States deployed 249 Vipers. They flew almost 13,500 sorties — the most of any airplane in the Gulf War [Department of Defense]. They did an exceptional job of destroying Iraqi ground targets.
In 1983, the Thunderbirds upgraded from the T-38 trainer to the F-16 Fighter [Tirpak]. They have used Vipers ever since. In shows, they demonstrate the aircraft’s 9-g turning ability as well as performing negative 3-g maneuvers. Team pilots work out every day to be able to sustain this punishment. The team includes a pair of two-seat F-16s that team members use to give “influencers” rides to demonstrate the capability of the little plane.
Figure 22: Civilian “Influencer” (in this case, comedian Stephen Colbert) in an F-16B
For the future, the Air Force is trying to duplicate its high/low strategy with fifth-generation stealth aircraft. At the high end, the F-22 Raptor has the F-15’s air combat role. The F-35 Lighting II, in turn, is aimed at the F-16’s multirole job. To date, moving from the F-15 and the F-16 to the F-22 and F-35 has been controversial because the enormous cost of these airplanes compared to the F-15 and F-16. Congress has already limited the number of F-22s [Gertner], requiring the continuous maintenance of a large F-15 force. Will the F-35 face similar purchasing limitations? Many F-16s are still relatively “young,” so the Viper has the potential to endure if this is necessary. More intriguingly, Lockheed Martin now offers the F-16V specification with many technological improvements. It can both build new F-16Vs and upgrade older F-16s. However, if some enemy moves rapidly toward an all-stealth fighter and fighter/bomber mix, then we might see many more F-22s and F-35s built.
Figure 23: F-35 Lightning II and F-16
Source: U.S. Air Force photograph 161128-F-XX000-001.
Bjorkman, Eileen. “The Outrageous Adolescence of the F-16: The Viper was Small, Fast, and in Your Face,” Air & Space Magazine, March 2014. http://www.airspacemag.com/military-aviation/outrageous-adolescence-f-16-180949491/?all.
Coram, Robert. Boyd: The Fighter Pilot Who Changed the Art of War, New York: Back Bay Books, 2002.
Crosby, Francis. A Handbook of Fighter Aircraft, New York: Hermes House, 2002.
Department of Defense, Gulf War Air Power Survey, Volume 5, A Statistical Compendium and Chronology, Washington, D.C., 1993.
Gertner, Jeremiah. Air Force F-22 Fighter Program, Congressional Research Service, July 11, 2013.
Hehs, Eric. “F-16 Designer Harry Hillaker,” Code One Magazine, Lockheed Martin, April 15, 1991.
Hillaker, Harry J. “YF-16 Evolution: Design Evolution and Rationale for the YF-16,” Code One Magazine, 24 January 2014. http://www.codeonemagazine.com/gallery_slideshow.html?gallery_id=170.
Hillaker, Harry. “Tribute to John R. Boyd”. (This article first appeared in the July 1997 issue of Code One.)
Hoyle, Craig. Strength in Numbers: The World’s Top 19 Military Aircraft Types. www.flightglobal.com, January 9, 2015. https://www.flightglobal.com/news/articles/strength-in-numbers-the-worlds-top-10-military-air-407756/.
Hubbard, T. West, The Fighter Mafia: Vietnam, the Fighter Jet, and the Future of the Air Force, 2014. (Kindle.)
Lockheed Martin, F-16 Fighting Falcon: The Most Technologically Advanced 4th Generation Fighter in the World, July 2, 2014.
Lockheed Martin. The F-16: Then and Now, February 2, 2014.
Matricardi, Paolo. The Great Book of Combat Aircraft, New York: Metro Books, 2008.
Panko, Ray, McDonnell Douglas F-15 Eagle, PacificAviationMuseum.org, undated.
https://www.pearlharboraviationmuseum.org/pearl-harbor-blog/mcdonnell-douglas-f-15-eagle/. Undated. Last viewed January 23, 2016.
Public Broadcasting System. Air Performance in Operation Desert Storm. Frontline, April 1991. http://www.pbs.org/wgbh/pages/frontline/gulf/appendix/whitepaper.html.
Rogoway, Tyler. “How To Win In A Dogfight: Stories From A Pilot Who Flew F-16s And MiGs.” February 3, 2015. http://foxtrotalpha.jalopnik.com/how-to-win-in-a-dogfight-stories-from-a-pilot-who-flew-1682723379.
Simonsen, Erik. “Legacy of the Lightweight Fighter Competition,” Air Force Magazine, February 2017. http://www.airforcemag.com/MagazineArchive/Pages/2017/February%202017/Legacy-of-the-Lightweight-Fighter-Competition.aspx.
Tirpak, John A. “Thunderbirds,” Air Force Magazine, July 2016, pp. 44-54.
Wikipedia.org. Operation Opera, version of 4 December 2016.
For those who stay for the closing credits…
Figure 25: The Thunderbirds have used F-16s since 1983
USAF photograph 040130-F-0000C-002.JPG
Figure 26: A Study in Purple
Source: Lockheed Martin. http://lockheedmartin.com/us/news/features/2014/F-16-evolves.html
Figure 27: F-16s refuel over San Francisco Bay
Source: Air Force Historical Research Agency 110802-D-LN615-004.jpg
Figure 28: 30 Degree Seat Lean-Back
Source: Lockheed Martin. http://www.codeonemagazine.com/images/media/2014_YF16_A_Design_22A_1267828237_4821.jpg.
Figure 29: F-16 and human size comparison
Source: LANTIRN equipped block 40 F-16 (USAF photo).jpg.
Figure 30: Two-Seat versions of the Viper were used for training
Source: Lockheed Martin. http://www.lockheedmartin.com/us/news/features/2015/C12015Photos.html.
Harry Hillaker said that the riskiest part of the design was the fly-by-wire control system [Hehs]. In fact, the design had a fallback strategy if FBW failed to work out. The wings were connected to the fuselage by a special bulkhead that permitted wings with different planforms to be fitted. If fly-by-wire could not be made to work, an alternative wing design that moved the center of pressure back and so avoided relaxed static stability would have replaced the original wing. General Dynamics did not advertise this plan.