In the early 1980s, the team behind America’s legendary F-16 Fighting Falcon had plans to literally reverse its wing design by adding forward-swept wings to the multi-faceted fighter. The goal wasn’t to put an exotic new design into service initially, but rather to create a platform DARPA (or the Defense Advanced Research Projects Agency) could use to assess just how viable this unstable approach to wing design could be in modern supersonic fighters.
The effort would ultimately result in the unusual-looking Grumman X-29 winning DARPA’s contract and securing funds for two fully functional prototypes, but not before General Dynamics could take a crack at making their broadly-capable F-16 fit the bill first.
Why choose the F-16 for an exotic wing experiment?
The General Dynamics F-16 Fighting Falcon may have begun in America’s air-to-air focused Lightweight Fighter Program, but it soon proved itself as a platform capable of far more than gun runs against enemy fighters in the sky.
By the time the F-16 entered service in January of 1979, the F-15 Eagle was already on its way to becoming the most dominant air superiority fighter of its century, and just two years later, F-16s rolling off the production line were already coming with structural and wiring provisions for attack missions. This shift would eventually lead to the F-16’s storied pedigree as an air-to-ground platform for nations all around the world, with many facets of its approach to air warfare improved upon and rolled into the design for the F-35 Joint Strike Fighter, thought of by many who fly it as a continuation of sorts of the F-16’s lineage.
In fact, the F-16 proved to be so cost-effective and capable that it would become the basis for a variety of proposed variants. The F-16XL was an F-16 that swapped its cropped-delta wing for the real thing, creating a fighter that could actually outperform the F-16 that was in service. This experimental aircraft proved so capable that it was pulled out of its experimental status and thrown into a competition with the F-15E Strike Eagle to see which would become America’s fighter-bomber of choice (a competition the Strike Eagle would ultimately win). But that wasn’t the only unusual F-16 proposal to garner Pentagon consideration.
The F-16 would also become the basis of the Vought 1600 proposal, which aimed to incorporate a landing hook and other changes into the Fighting Falcon to make it better suited for a new career at sea aboard the U.S. Navy’s aircraft carriers. The A-16 effort aimed to add more armor and hardpoints for Close Air Support Missions, and today, modern F-16s are given the radar-absorbent-materials treatment for Wild Weasel operations, which is the incredibly dangerous job of hunting for enemy air defense systems in contested airspace.
This aircraft has proven so capable, reliable, and affordable that the U.S. Air Force continues to operate a fleet of more than a thousand F-16s, with literally thousands more in service for nations around the world like Isreal, Pakistan, Denmark, Greece, Indonesia, and Norway.
So when it came time to field a fighter with its wings on backward, General Dynamics looked to their budget-friendly Fighting Falcon for the job.
What’s the deal with Forward-Swept Wings?
Forward-swept wings may look silly (or entirely rad, depending on which GI Joe toys you played with as a kid) but the prevailing wisdom of the ’80s suggested that flipping the wings of a fighter could offer a number of significant benefits in a fight. The most significant among them would be increased maneuverability thanks to an inherently unstable design.
“At the time, this maneuverability was believed to be absolutely essential to fighter superiority. If your airplane is going to stall before mine, I can shoot you out of the sky in a heartbeat,” explained Christian Gelzer, chief historian at the NASA Armstrong Flight Research Center
Better control in a stall
Air flowing over a traditional rear-swept wing flows toward its rear-most point, which is the wing-tip. As such, a stall in a conventional swept-wing aircraft often begins at the wingtip, causing a pitch-up that exacerbates the stall and makes recovery even more difficult. But in a forward-swept wing design, that air flows toward the wing’s root at the fuselage of the aircraft where there’s greater lift and stability. That airflow direction also allows the wing’s ailerons to function better in a stall than they might in a rear-swept wing, offering better control when a pilot needs it most.
Placing the wing roots at the rear of the aircraft also allowed for better weight distribution and a more efficient internal layout. In fact, with the wings rooted at the rear of the aircraft, most fighters could then carry more weight in the front of the fuselage without negatively affecting the jet’s center of gravity.
Forward-swept wings were thought to be more efficient while offering greater angle of attack
A dynamically unstable forward-swept wing fighter that leveraged computer-aided fly-by-wire controls could theoretically be incredibly maneuverable, something that wasn’t possible before computers made their way into fighter fuselages. An F-16 with forward-swept wings could also theoretically leverage a more aggressive angle of attack without stalling than an F-16 with a conventional pair of wings could match. NASA and DARPA further believed a forward-swept wing design could offer more efficient flying at cruising speeds and potentially even a reduction in aerodynamic drag.
But the biggest challenge DARPA and others faced with such a design was something commonly referred to as “aeroelastic divergence,” or just “divergence.” This divergence issue can probably be best summed up as a problem with wing bending. Forward-swept wing designs had a tendency to bend upward near the tip, which results in greater lift near the tip that would bend the wing even further. Because this issue worsens the faster you fly, traveling at high speeds with forward-swept wings could result in the wings bending so much that they structurally fail, resulting in the loss of the aircraft.
But by the 1980s, new composite materials promised to potentially solve this wing-strenth problem, making forward-swept wings potentially viable for high-performance applications. This prompted DARPA’s pursuit of technology demonstrators, and later, the Soviet effort to field the Sukhoi Su-47, a “stealth” fighter that leveraged forward-swept wings and ultimately competed with the Su-57 to become Russia’s premier 5th generation fighter.
Could the F-16FSW have been better than the F-16 we’ve got?
The short answer is probably not. The F-16FSW ultimately never made it off the drawing board, with Grumman’s X-29 instead securing DARPA’s contract to further explore the value of the forward-swept wing design. And while Grumman’s two X-29 demonstrators would go on to complete more than 400 successful test flights, their exotic design never made it any further that that.
DARPA’s tests concluded that you could indeed get a great deal of maneuverability out a forward-swept wing design, but the design’s shortcomings outweighed its benefits. The design was—to be fair—limited by the technology of the day, as evidenced by reports that the X-29 couldn’t actually offer any appreciable increase in acrobatic performance because the computer-pilot interface and subsequent control function of the aircraft’s flight surfaces simply couldn’t work fast enough to compensate for the aircraft’s instability while simultaneously allowing for dramatic maneuvers.
This issue could likely be overcome today, but there appears to be little reason to do so.
The common belief that a forward-swept wing design could be more efficient or offer a reduction in aerodynamic drag didn’t prove to be true in testing, limiting the significant benefits of this design to maneuverability, which was becoming both easier to pull off with other technology… and a whole lot less important.
According to NASA, the maneuverability offered by a forward-swept wing design isn’t really any better than can be accomplished through thrust-vector control (TVC), which is a technology leveraged on America’s F-22 Raptor as well as its 5th generation competitors in the Su-57 and now China’s J-20. Thrust vector control effectively allows the pilot to orient the outflow of the aircraft’s jet engine independent of the fuselage, allowing for a greater angle of attack and some absolutely astonishing maneuvers. In fact, by using TVC, a modern fighter can actually aim its nose and weapons down at a target as it continues to press forward in the sky past it.
But the F-22 also incorporates a different American-led technology that dramatically reduced concerns about maneuverability in general: stealth. The F-117 Nighthawk had secretly started flying years before DARPA’s forward-swept wing efforts began, and it wouldn’t be long before Uncle Sam began looking for ways to incorporate its groundbreaking ability to hide from enemy radar into actual fighter platforms. Once stealth made its way into fighters, America’s fighter priorities shifted away from dramatic close-quarters boxing matches with highly-maneuverable jets and toward engaging enemy jets from beyond visual range before they ever even knew they were there.
As exotic as the F-16FSW or the fully-realized X-29 may have been, the improved performance they may have offered can now be accomplished with more conventional designs, making it pretty unlikely that we’ll ever see a fighter with backward wings enter service for the U.S. or its competitors. But for those with too deep a love for this design to let it go, there’s always the Conquest X-30. It may not be a real aircraft, but it did make for one hell of a cool toy.