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The World’s Strangest Experimental Aircraft

Introduction

Aviation is an experimental industry, to put it mildly. You don’t get from not existing to breaking the sound barrier in just fifty years without some ingenuity, and a slightly carefree attitude towards health and safety. But what’s interesting about aviation is that, despite being a resource intensive industry, it gets a lot of room for messing around with crazy ideas, and more of those ideas than you might expect manage to make it from the design document to the runway.

Today, having gone through an obscene amount of aviation research in the last few weeks, we found quite a few designs that raise a few eyebrows, and it felt wrong to just let them fly under the radar. So, you’ll be getting the story of how, and why, they were made. These are some of the strangest experimental airplanes that have ever been made.

X-29

X-29 airplane
The No. 2 X-29 technology demonstrator aircraft is seen here during a 1990 test flight

Wings are important for flying. Yes, that is an obvious statement, thanks for noticing, but it’s important to establish that when talking about the first entry on this list. That’s because a simple photograph will tell you that it’s all about the wings with this one.

A bit of background, before we go on. It’s the 1980s, U.S. president Ronald Reagan has done his whole “evil empire” bit with the Soviet Union, and relations between the US and the USSR are at one of their lowest points in the entire Cold War, which is really saying something. Reagan has also made the call to start pumping more money into the armed forces, and some of that money is diverted towards R&D.

With that established, a team was put together consisting of a few giant groups, from NASA to aerospace company Grumman to the U.S. Air Force, to test a very interesting theory: see that plane? What if wings, but backwards? And so it was. In 1984, a test flight was flown of the prototype plane, designated the X-29, to explore the theory of so-called forward swept wings. It didn’t crash, which counts as a success when it comes to experimental planes, and testing continued up through 1991, when the program was discontinued.

Now, this begs the question as to why this would be done. What did this accomplish? What do forward-swept wings actually do for a plane that quote, unquote, “normal” wings don’t? It has to do, first and foremost, with airflow. Wings, as we’ve established with our first salient point, are important for flying. That’s because, as the plane moves, air flows over the wings and generates lift.

How airflow works on wings is fiendishly complicated; too complicated to explain in this video. Lots of math and equations and words like “vortices”. But thankfully, for our purposes, we only need to know a few things. First, when air flows over a wing that’s at an angle, some of the air is deflected. For a normal swept wing, like you see on most jet fighters, the air is deflected away from the plane. For a forward-swept wing, however, like the X-29, that air is instead directed towards the plane.

Well, what does that mean? To answer that, let’s now talk about stalling. Stalling is what we’re doing right now with this sentence, but it’s also when an aircraft experiences a loss of lift, which can result in a crash. Again, because of how airflow works, stalling doesn’t happen all at once; instead, it tends to start at the tips of the wings, and move along them. That’s important because the ailerons, the part of the plane that controls rolling, are generally located on the wing tips of the plane. As such, when a plane starts stalling, it will usually lose control at the exact moment when everything needs to be working.

This was the issue that the X-29 was intended to fix. For a backwards facing wing, the airflow is deflected the opposite direction. This has the side effect of causing the stall to start at the base of the wings, rather than the wingtips. This keeps the ailerons active, which gives the pilot precious time to regain control of the aircraft and get out of the stall before the plane starts careening down to Earth.

Did it solve this problem? Well, yes, it did. It also introduced entirely new ones, because that’s how engineering works. The most glaring problem with the aircraft was that it was unstable. Unbelievably unstable, like, “a big video game on launch day” unstable, or “your emotions after thinking about Hachiko” unstable.

Part of this instability came from the inherent design of the plane. The wings, you’ll notice, are positioned further backwards along the plane. This messed with the center of gravity, so already the aircraft is fundamentally unstable. Originally, this was touted as a feature, rather than a bug, since the fact that the plane could turn incredibly quickly was thought of in terms of high maneuverability. Granted, that maneuverability was only possible because of a flight computer that was making 40 corrections to the flight path every second (yes, you heard that right, 40 corrections a second), but hey, don’t hold technology against us.

As time went on, this assertion didn’t hold up to tests, as it became clear that 1) other aircraft could match it in maneuverability, and 2) the plane would tear itself apart if the flight computers ever failed. One historian for NASA went so far as to say that the plane was “literally unflyable.” For those reasons, the program was discontinued, and the idea was shelved as impractical.

But parts of the X-29 live on. See, the wings weren’t just more unstable, but more fragile as well, due to the higher amount of stress being placed on them. As such, they needed to be reinforced, but making them out of metal would’ve made the plane too heavy, so the engineers used some advanced materials, such as carbon-fiber and graphite epoxy. I don’t even know what those are, but they’re part of the same group of materials that make up the modern stealth planes of today, including the F-22 and the F-35. So in a way, the X-29 was the precursor to the fifth generation of jet fighters.

And America was not the only one to test this theory. Russia had its own forward-swept wing prototype, the Su-47, which was originally meant to be conducted around the same time as America’s, but was put in limbo when the USSR collapsed. It finally flew, however, in 1997, only to confirm that yes, it was just as unstable as when America tried it. It does look cool, though.

Bell X-5

Bell X-5’s variable-sweep wing
A composite photograph showing the Bell X-5’s variable-sweep wing

We’re still on with wings in this entry, and we’re also still with America. We are, however, going back in time a few decades, to when America first started running experimental airplanes.

With that in mind, it’s the years immediately following World War 2. America has confiscated a lot of science, and indeed scientists, from the former Third Reich, on everything from nuclear physics to rockets to aircraft. In terms of aircraft, the US recovered a prototype plane called the Messerschmitt P.1101 from an experimental facility. This design was a jet fighter that, interestingly enough, could change the sweep angle of its wings, mid-flight.

That was the vision behind it, at least; the plane itself wasn’t finished. But the US was intrigued by the idea, and in the early days of aviation experimentation that the Cold War was known for, this variable sweep wing was one of the first ideas that was seriously tested.

Six years after the plane arrived in America, the Bell Aircraft Corporation had finished studying the design and had come up with their own prototype, the X-5, which took its first flight in 1951. The plane had three sweep positions for its wings, at 20, 40, and 60 degrees, which it could switch between at any time. But why change the angle of the wings at all?

Again, it has to do with airflow. When the plane is on the ground or moving at low speeds, a wider wing is better to produce more lift and reduce drag. But when the plane approaches the speed of sound fast enough, a more narrow wing is preferable, as it reduces a different kind of drag. This design, if it worked out, would allow the best of both worlds.

And, rare enough for aviation tests, it worked. Despite problems with controls and the layout and positioning of parts, the actual concept it was designed to test proved successful, and variable-sweep wings were concluded to be practical for aircraft. The direct result of the Bell X-5 was the F-14 Tomcat, which included variable-sweep wings, and was by most accounts a perfectly satisfactory fighter.

Today, variable wings have fallen out of favor, since they require some very specialized mechanisms that weigh down the plane and make it more expensive. But some variable-wing planes are still in use; the Tupolev-160 bomber has variable wings, and the F-14 is still in use by air forces around the world, including, funnily enough, the Iranian Air Force. Talk about a deal with the devil. Get it? Because Iran calls America “Satan” all the time? Oh, forget it.

Antonov A-40

Antonov A-40
Designer’s model of the Antonov A-40

Throughout the history of aviation, many plane designs have been referred to as “flying tanks”: The Soviet IL-2 Sturmovik, the American A-10 Warthog. Generally, this is because the planes are quite durable and can take a number of hits before being shot down. Well, we have no time for metaphors with this entry, so here’s a literal flying tank.

The Antonov A-40 was a Soviet experimental plane that was tested to see if it was feasible to allow armored vehicles, such as a tank, to be flown into battle. It wasn’t. But let’s tell the story anyway.

It’s 1942, and it’s Hitler time in the Soviet Union. Germany has attacked and occupied large parts of the western part of the country, and there’s an ongoing guerilla war between the German armed forces and Soviet partisans. But the partisans are rather outgunned, having only rifles and explosives to work with, for the most part. Well, some mad lad by the name of Oleg Antonov came up with the idea of, “Hey, why don’t we go full Battlefield 2042, a century before 2042, and airdrop some tanks in for them?”

The Soviets had a bomber called the TB-3, and one of these was modified to be capable of carrying a glider, that in turn carried a T-60 light tank underneath it. It was envisioned that this plane would be able to carry the payload for a long distance and release the glider, which would then glide, interestingly enough, to the ground and deploy the tank behind enemy lines.

Did it work? No. The tank was too heavy for the plane to fly, as one might expect, and so the load had to be lightened by removing the gun, the ammo, the headlights, the crew, and the gasoline. Which… that’s not a tank at that point, that’s a big metal albatross around the neck. Oh, sorry, I said we didn’t have time for metaphors. The point is, even that wasn’t enough; the test plane had to ditch the glider to avoid crashing, although reports indicate that the tank itself was surprisingly aerodynamic, which is not a sentence the writer ever expected to write.

It wasn’t even the fundamentals of trying to fly a tank that doomed the project. Tanks themselves were rapidly being upscaled, and a light T-60 would have next to no chance against a German medium or heavy tank. As such, even if the project worked, it wouldn’t have much practical use. Add in the fact that all of the removed bits – the gun, the ammo, the crew, etc. – would have to be parachuted in separately, and you’re left with a great big, “Why bother?” And so, the project was cancelled.

Today, we actually can parachute vehicles; America does it with Humvees. We’re not quite to the point of video game gimmickry yet, but keep your eyes to the sky for any flying tanks. And have your complaints to the devs ready.

Vought V-173

The Vought V-173 "Flying Pancake" in flight
The Vought V-173 “Flying Pancake” in flight

We’re still in 1942 for this entry, but instead of Russians airdropping tanks, it’s Americans flying a pancake. Again, the writer’s breaking new ground on sentences with this one.

Our story starts in the 1930s, when an aeronautical engineer by the name of Charles H. Zimmerman came up with a concept he called a “discoidal” aircraft. “Disc” is the key part of the word, here, as you might have gathered from the photographs. The U.S. Navy developed some interest in the project, and gave Zimmerman resources to design a prototype in 1939, with full tests beginning in 1940-41.

What’s interesting about this plane, aside from, y’know, the whole “Flying Pancake” part, is the two massive propellors at the front. These propellors actually served an important purpose, and like the X-29 from earlier, it has to do with airflow.

There’s a force in aerodynamics called “lift-induced drag”, also known by the much cooler-sounding “vortex drag”. Say it out loud: vortex drag, it sounds like the name of a Formula 1 team. But anyways, vortex drag happens when airflow is redirected, creating vortices. Drag is bad for aerodynamics, and it’s in the interest of engineers to try and limit it as much as possible. The simple explanation is that the propellors of the V-173 cancelled these vortices out, reducing the drag and allowing the wings to be much smaller than they otherwise would’ve needed to be. This made them both stronger, and allowed the plane more maneuverability.

It’s solid stuff, really, but solid stuff on a creaky table will still collapse. The disc design created some issues for the plane at low speeds, which necessitated some extra designing to work around it. What’s more, the airframe of the plane acted as a giant airbrake when it pulled into a high angle of attack, which is something that pilots tend to do a lot when, say, dogfighting with other pilots. This limited the aircraft’s maneuverability, and made it more predictable in any envisioned fight.

It did fly, at least, and served as a proof of concept for Zimmerman’s discoidal aircraft frame. As such, it was requested that he design an updated version based on what they’d learned. What he came up with, the Vought XF5U, would prove to be much less successful than its predecessor. It never even managed to get off the ground, since it was larger and made entirely of metal (the V-173 was made of wood and canvas). In fact, the XF5U was so structurally solid that when the project was cancelled and it came time to scrap it, it had to be destroyed with a wrecking ball. Which counts as some kind of achievement, I guess.

NASA AD-1

The AD-1 oblique wing research aircraft was photographed during a wing sweep test flight.
The AD-1 oblique wing research aircraft was photographed during a wing sweep test flight.

We’ve saved the weirdest plane for last, and it’s America once again. But before we talk about America, let’s talk about Germany.

In 1942, an engineer for Blohm & Voss named Richard Vogt made a design to solve a specific problem; bear with us, because we’ll be retreading some earlier parts of the video here. Jet planes were just coming into production, and engineers created the swept wing to help deal with the high speeds that they could reach. But sweeping the wings comes with its own problems, particularly at low speeds during takeoff and landing. Variable swept wings were proposed, but as we’ve said before, they were complicated, they weighed down the plane, and they were expensive.

What to do? Well, Vogt came up with a middle ground. He designed something called an oblique wing – a variable wing that would have one wing sweep forwards, and the other backwards. He thought he had found a perfect middle ground solution: at low speeds, the wing would be perpendicular to the fuselage, providing better performance for takeoff and landing, and at high speeds, the sweeping of the wing would reduce the drag.

But it gets better. There are different types of drag, it turns out, and an oblique wing could theoretically deal with both of them. At low speeds, the aforementioned vortex drag is the most important kind, and longer, perpendicular wings help reduce its effect. This is why glider planes have such long wings. But at high speeds, so-called wave drag becomes more important; this is the drag that forms as a result of the shockwaves from sonic booms. These shockwaves are in the shape of a cone, starting from the nose of the plane, and sweeping the wings keeps them out of the shockwaves. This is why variable wings worked out. Lastly, think of drag like costing fuel. A plane affected by drag needs to use more fuel to stay at the same speed, so less drag means more fuel, which means a plane can stay in the air for longer. So that’s it, really: all of the advantages of variable wings, without the downsides.

Vogt was brought to the US under Operation Paperclip, where the US took a bunch of German scientists (many of whom were bona fide Nazis, it should be pointed out), and brought them to America. This is how Wernher von Braun ended up working for NASA. Speaking of NASA, they decided to explore Vogt’s oblique wing concept, and developed it further into the AD-1, which underwent test flights in 1979 through 1982.

How did it work? Well, you’ve probably detected the pattern for this list by now. As you can tell from just looking at this thing, the aerodynamics of the plane are thrown out of wack by this asymmetrical design. The control of the plane was incredibly difficult, almost as much as the forward-swept wings we talked about earlier. This was to be expected, considering the airflow was doing opposite things to each side of the plane, and was mostly solved with a flight computer that could compensate with other controls. It did rather limit the plane’s role, however; I mean, you’re not going to be dogfighting with this thing. Lastly, it was clear that if the plane ever lost control, it would be incredibly difficult to regain it due to the awkward wing configuration.

So, not much came from the AD-1, but NASA did acquire a suite of useful data from the many test flights it ran. And it never crashed; in fact, it’s currently on display in a museum in California. That’s something.

Challenging Assumptions

These were just five examples of how designs in aviation have been explored beyond their traditional constraints. In a sense, it’s fitting that aeronautics is one of the more imaginative fields of engineering, since the concept of human flight takes a bit of imagination. Maybe someday, we’ll have designs we can’t even imagine now taking us to skies unknown.

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The World’s Strangest Experimental Aircraft

Introduction Aviation is an experimental industry, to put it mildly. You don’t get from not existing to breaking the sound barrier in just fifty years...

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