MIGHTY HISTORY

Why you won't see this awesome plane design in combat

Remember those super sweet toys from the 1990s, the planes with "backward" wings. The one that comes to mind for me is the old X-Men X-Jet. The new movies feature a plane that looks a lot more like an actual SR-71 Blackbird, but the old cartoons and the movie trilogy from the early 2000s had those distinctive, futuristic, forward-swept wings.


Well, those wings existed on actual planes, first in World War II and then in experimental designs through 1991. But you likely won't see the iconic wings on any real fighters or bombers overhead, even though they allow planes to fly faster while still directing air over the craft's control surfaces.

The inspiration for forward-swept wings dates back to World War II. As the warring powers developed faster and faster aircraft in the war, they eventually all found that, above a certain speed, pilots suddenly lost control of their aircraft. America tried to overcome this problem with brute force, and it backfired gruesomely in November 1941.

On November 4, Lockheed test pilot Ralph Virden was piloting a P-38 in a controlled dive when he activated spring-loaded servo-tabs that were supposed to help him regain level flight. Instead, they overstressed the plane and caused the tail to tear away. The plane crashed, and Virden was killed.

Eventually, plane designers figured out a more graceful solution to the problem. If they swept the wings, then the airflow would shift, and the shockwaves wouldn't form. But, when the wings are swept back, the new airflow creates a new problem. The air starts flowing quickly along the wings away from the body of the aircraft, creating stall conditions at the tips of the wings.

And those tips of the wings hold the ailerons. A stall in that region robs the pilot of the ability to roll the aircraft, a vital capability in combat.

So, in 1984, DARPA, NASA, and other agencies launched the X-29 for the first time. It was an experimental aircraft with its wings pointed forward from the body of the aircraft, same as the old X-Men jet. And the Germans actually had a design in World War II with similar characteristics, the Junker 287.

The Russian Su-47 had a similar wing design to the American X-29, but neither plane was adopted for combat use.

(Jno, CC BY 2.5)

The X-29 had some amazing characteristics compared to its more conventional brethren in the air. It had less induced drag, meaning that it had a better balance of lift-to-drag at high speed. And that allowed it to be up to 20 percent more efficient than it would be with wings swept to the rear. Best of all, the plane would be super-maneuverable even at high speeds. A Russian plane, the Su-47, saw similar advantages.

But designers found in their models, their wind tunnel tests, and actual flight tests, that the X-29's wings created a lot of problems.

First, the wings had to be made extra strong to deal with the additional stress of the wind hitting those leading edges of the wing far from the body. And, the plane had trouble maintaining its pitch, even with those canards mounted near the cockpit.

But worst of all, the air flowing over all these control surfaces was simply too chaotic for a pilot to control. So, in the X-29, pilots had three computers working together to adjust the flight surfaces 40 times per second. These computers worked to keep the aircraft stable so the pilot could give their inputs according to what they wanted the plane to do rather than constantly having to prevent crashes.

But, if the computers ever all failed in flight at the same time, it was likely that the pilot would encounter an irrecoverable spin or other emergency. So, when the computers all failed on the ground during testing, it sent a shudder through the program. A DARPA history page about the plane even calls it "the most aerodynamically unstable aircraft ever built."

Still, with all the advances in AI and computers, there might be a place for a design like the X-29 if not for one additional problem: forward-swept wings seem to be inherently less stealthy than wings swept to the rear or a delta-wing design like that of the B-2.

So, with the X-29 less stable and also inherently less stealthy than other designs, the U.S. decided to continue using rear-swept designs in combat aircraft, and it's unlikely that you'll ever look up to see something like the X-Jet supporting you from overhead.

But at least it looks cool in movies.