The “Switchblade” Wing: Feasible or Fantasy?
It’s arguable that there is no more intriguing fictional aircraft in the Ace Combat series than the X-02 Wyvern. Appearing as the lone “bonus” aircraft in Ace Combat 04 (2001), the X-02 positions itself well into the game’s more serious and professional tone than the installments preceding and following it. The X-02 derives clear inspiration from several types of real-world fighter aircraft. Under slung engine nacelles and vertical ventral fins from the Su-27 Flanker, chined edges and ruddervators reminiscent of the YF-23, and fuselage shaping not unlike a hybrid between the F-14 Tomcat and the F/A-18E Super Hornet.
To even an amateur eye, the X-02 seems atypically well designed. Compared to the mecha-influenced fictional aircraft before it like the XFA-27 and ADF-01, the X-02 “feels” real. There was quite a bit of thought and professional detail placed into the design of the aircraft by Ace Combat 04’s development team. This intuition is not unjustified. A more detailed look on the aircraft can reveal that the design seems to have come with an engineer’s influence. Everything from the center-of-lift and gravity to the internal dimensions of the aircraft has reason applied to it. That is perhaps a great deal of the appeal of its design. But it is, of course, the novelty of the aircraft’s signature—the “switchblade” wing—that gives the X-02 its dauntless allure.
So, beyond what you see in the game model, what exactly is a switchblade wing? Let’s break it down further. The removal of the switchblade feature alone actually reveals an equally novel wing configuration: the “W”-wing.
A “W”-wing planform is self-demonstrating. The wing itself forms an oblique W shape in its design. This planform remains generally untested and theoretical, appearing only in old NACA research papers dated 1950 and 1953, respectively. It also appears to have been considered by Nazi German aircraft manufacturer Blohm and Voss for their P.188 design during the final stages of World War II (Dan Sharp, Luftwaffe: Secret Bombers of the Third Reich, Mortons 2016, Pages 84-85.)
In the case of the P.188, the goal of the wing was to mitigate a known flaw in early swept-wing designs: a tendency for the aircraft to enter an ever-increasing pitch-up attitude as the outboard part of the wing stalls, eventually resulting in a loss of control of the aircraft as rudder surfaces became obscured by the wing and fuselage of the aircraft. The result is blocked airflow to these surfaces and, ultimately, a hull loss incident. The P.188 was passed up in favor of more conventional designs, but the wing configuration was not totally abandoned.
NACA revisited this design and fitted it to cheaply made rockets, which gave them the opportunity to study the resulting flight parameters of the wing, including its overall drag coefficient, the center of lift, and the results of aeroelastic flutter. Despite this, the wing was never applied in any realistic manner. The initial advantages of it—the ability to resist pitch-up—was no longer a concern with delta and swept wings by the 1960s, as designs had been produced to reduce or eliminate this danger entirely.
But the application of the W-wing in Ace Combat 04’s X-02 doesn’t concern itself with something so fundamental, or so technical. The W-wing on the X-02 is a representation of a single game mechanic: aircraft maneuverability. At first glance, this makes perfect sense. Like the Su-47 (in Ace Combat 04 carrying it’s Sukhoi DB project name of S-37), the swept-forward part of its design implies a real-world analogous feature of high maneuverability, and the X-02’s in-game mechanics exploits this, making the X-02 the most maneuverable aircraft available to the player.
The W-wing configuration does theoretically grant this, and may, in fact, be more suited for this statistic in reality over the simple swept-forward design due to the ability to increase structural integrity and reduce aeroelastic divergence - the tendency of the wing to want to bend upwards when force is applied, which risks structural failure. The swept-forward wing—and by extension the W-wing—take advantage of the ability of the inboard, rather than the outboard, portion of the wing stalling out first. The outboard, near-tip portion of the wing usually hosts the aircraft’s ailerons. So long as the ailerons receive clean airflow, they can allow the aircraft to maintain roll control. This permits the aircraft resistance to departure of controlled flight at high angles-of-attack. And an aircraft that can maintain these high AOA’s can inherently also achieve a tighter instantaneous turning radius, as it can present a greater surface area to the incoming air, increasing the force applied to the fuselage and wings. Additionally, due to the way that the air flows along the wings surface, it also lowers drag from the wingtips, theoretically granting sharper sustained turning rates with a well-engineered design.
So now we know what makes the W-wing itself special, but it’s the X-02’s “switchblade” function that really captures the eye. But is this where feasibility starts to fall apart for the X-02? The short answer is “Yes.” But let’s instead entertain the long answer: “It depends.”
The “switchblade” design is not entirely original. There is evidence of its study in 1999 by Northrop Grumman, as demonstrated in patents for an aircraft design.
Some might recognize this design as one that inspired the AI-controlled aircraft from the 2005 movie Stealth. But the X-02 precedes that design by over four years and is probably a more realistic application of the mechanics.
This is where the W-wing makes significant sense for the X-02 design—the inboard swept part of the wing works to conceal the forward-swept outboard portion in high-speed flight, quickly pivoting the wings inboard through a set of doors where there may traditionally be leading-edge slats on a swept-wing fighter. This does something that the Northrop Switchblade doesn’t: it eliminates an entire flight surface of the aircraft. In theory, this would not only provide structural integrity to the inboard wing but would also drop parasitic and wave drag considerably, enabling the X-02 to reach speeds that would not be possible with its higher aspect-ratio swept forward configuration. It is what grants the X-02 it’s seemingly contradictory statistics: it can pull double duty as a first-rate turning fighter while being able to also dash at high speeds limited by surplus engine thrust rather than drag. But what does this configuration mean in the real-world?
Let’s break-down the X-02’s wing-sweep procedure and see if we can pinpoint where physics rears its unwelcome head and puts the X-02 back into the realm of science fiction:
Between 0-450 knots the X-02’s wings remain locked in the long aspect ratio, swept forward position. This is a good configuration for this speed, granting low stall speeds and high maneuverability. The W-wing configuration mitigates the aeroelastic load on the aircraft, though the empty space in the inboard sweep does sacrifice some structural integrity but is bulked with an intelligent spar system.
Between 450-455 knots the wing configuration becomes a hindrance and needs to be changed, so a rapid series of adjustments start. The wing uses large servos to pivot the outboard wing inward. This lowers drag but puts stress on the wing’s aeroelasticity limits.
At 460 knots the outboard wing has its tips facing straight onto the airflow. The aircraft enters a light pitch-up due to the rapid change in center-of-lift and—
The wing shears off the aircraft.
What’s happening here? Well, by step two we’re already looking at undeniable stress on the wing. Coupled with the hollow inner wing, heavy center machinery, increasing airspeed, and resulting airflow, the wing encounters a structural limit. The force of the air on the ventral surface of the wing must obey Newton’s third law, and eventually the wing cannot sustain this force any longer. A subscale example of this failure is similar to what happens to a fixed, straight-wing aircraft like a Cessna 172 going into overspeed. The aircraft’s weakest points must yield to the forces applied to it, and the wing must either disintegrate or detach from the fuselage.
It is at this point that the X-02 Wyvern cements itself into the virtual world. But can this be fixed?
With what we currently know about aerodynamics and materials science, it’s unlikely. Stronger materials and more intelligent engineering might help, but there are fundamental forces at play that consistently produce damaging effects. This provides justification for the wing design of many modern aircraft such as the F-22, Su-57, and J-20, which stick with tuned, traditional trapezoidal wings. Ultimately, they provide acceptable performance while maintaining robust structural integrity. This is why swept-forward wings stay in the realm of technology demonstrator: the forces applied to the wing accelerate the stress on the weakest points of the wings attachment points on the fuselage, resulting in a higher need for structural maintenance and greater risk of catastrophic failure.
But despite this inherent flaw, do not discount the ideas presented by Ace Combat 04’s premier air supremacy fighter. It is certainly within the realm of plausibility that the aircraft’s designers constructed the aircraft knowing these flaws. But that doesn’t make the design any less impressive. The fact that they identified the possibility alone demonstrates a keen, intelligent rationale for the X-02’s addition to Ace Combat lore. Perhaps the designers of the fighter didn’t think that their fantasy idea would inspire such curiosity about its feasibility, but their approach did just that.
The X-02 will continue to spark questions for people discovering this series for the very first time and though just a thought experiment its design has the potential to inspire knowledge and discussion about the real-world physics at play, hopefully stoking the fires of people not just interested in Ace Combat, but perhaps delving into an interest in aviation as a whole.
About the Author
T.J. "Millie" Archer is Life-long realist and aviation enthusiast. Once the co-founding Administrator of the Electrosphere.info English Ace Combat Database. In the present day he is freelance, roving the internet in search of the latest aviation news and entertainment.