In nature, anything that flies has
symmetry. And in the early days of human flight, mimicking nature made sense.
But as we pushed on to ever higher speeds, our stubborn insistence on symmetry might’ve
been a mistake. In the 1950's, a brilliant NASA engineer began to push for a radical new approach.
Proving theoretically and with prototypes, that aircraft didn't have to be symmetrical.
The implications of his work are profound. It suggests we should be flying a lot faster
and more efficiently than we are today.
Since the dawn of flight, aircraft had been
getting faster. In 1920, the fastest plane could barely reach 300 kilometers an hour.
By the 1940's, they were already flying three times as fast. But there seemed to be
a limit beyond which they simply couldn't go. Pilots called it "the sound barrier".
Above a certain speed, aircraft stopped accelerating, control became increasingly
difficult, and stress forces could even cause an aircraft to break apart in mid-air. But in
1947, a daring test pilot flew an experimental plane beyond the speed of sound. Proving that
the sound barrier wasn't a barrier at all.
It’s just that supersonic flight revolved around
a different set of aerodynamic principles.
In the decades that followed, engineers
mastered the physics of flying supersonic, pushing speeds ever higher. But a new challenge
emerged. Designing an aircraft that would perform well in both flight regimes. Any aircraft
optimized for supersonic flight, would by definition, fly poorly at subsonic speeds.
Because the ideal wing at lower speeds was long and straight. But for supersonic flight,
it was thin or sharply swept. A shape that struggled to generate lift at lower speeds.
Engineers struggled to find a solution. Eventually coming up with a kind of wing
that could transform in mid air. Functioning more like a straight wing at subsonic speeds
and sweeping back for supersonic flight.
But variable sweep wings created their own set
of problems. Pivot mechanisms had to bear immense lift, rotational, and bending forces. Shifts
in the center of lift had to be compensated for with larger stabilizers or other systems. All
of which added weight and complexity, largely undoing performance gains. Variable sweep wings
were only successfully applied to a small number of military aircraft. None of which are still
produced today. The sound barrier might not have been an actual barrier, but it seemed that flying
faster would always involve serious trade offs.
By 1955, Robert Jones had made a name for
himself as one of NASA’s top aeronautical engineers. His groundbreaking work on
the delta wing, once met with skepticism, had led to the greatest aerodynamic
transformation since the very invention of the airplane. But his life-long passion lay
in an entirely different kind of design.
It was called an oblique wing. A radical concept
consisting of a single wing that rotated on a center pivot. Intuitively, it looks all wrong.
As if it would simply corkscrew its way through the sky. But through wind tunnel tests and with
radio-controlled prototypes, Jones proved that they were surprisingly stable and controllable.
Because when it comes to generating lift, the air doesn't really care whether a wing
is swept forward or backwards. So it can fly. But why build an aircraft like this?
Intuitively a highly swept arrow shape seems like the correct way to minimize drag. But that’s
simply not the case. Jones demonstrated that at transonic and supersonic speeds, the
same wing when arranged asymmetrically, had a much lower predicted wave drag.
And so there was no rational reason to favor bilateral symmetry, when it was actually
less efficient. But Jones’s oblique wing had another important advantage. It could
also perform optimally at lower speeds by transforming itself back into the ideal straight
wing. And compared to variable-sweep wings, oblique wings would be easier to build. With a
single pivot mechanism handling just one force, it would be lighter and less complex. And the
center of lift would remain virtually unchanged regardless of the wing’s position.
Secret German documents uncovered after World War Two suggest that oblique wings
were even studied as far back as 1942, although no prototypes were ever built.
On the verge of an aeronautical breakthrough, Jones and NASA engineers were about
to change aircraft design forever.
This is not an ordinary plane. It has a
scissor-like design. By the mid-1970’s, NASA moved beyond wind tunnel
tests to develop a large-scale, remotely operated model that could evaluate
the oblique wing’s real-world performance and handling characteristics.
Meanwhile, leading aircraft designers Boeing and Lockheed were also asked
to study oblique wings and evaluate their potential for future commercial aircraft.
Both concluded that they could lead to faster, more efficient air travel. But it was Boeing’s
study that really caught NASA’s attention.
Because by 1975, the dream of mass supersonic
air travel had all but faded as Concorde looked set to become a commercial failure. And
it had everything to do with the wing.
Engineers had spent more time developing
Concorde’s advanced delta wing than any other part of the aircraft. But it was
still hopelessly inefficient at low speeds, producing so little lift that Concorde needed
fuel-thirsty afterburners to take off.
And when countries banned supersonic flights
over their airspace due to concerns over loud sonic booms, flying slower wasn’t really
an option. Concorde wasn't designed to cruise at subsonic speeds, where its
operating economics were terrible.
But Boeing concluded that an oblique wing
airliner would have none of these problems.
Because it would be capable of flying efficiently
at a range of speeds and cruise at up to Mach 1.2 without even generating a sonic boom that could
be heard on the ground. And that would allow for transcontinental flights over populated areas 50
percent faster than existing airliners.
Power requirements for takeoff, landing,
and holding around busy airports would also be a lot lower, dramatically cutting
noise and pollution around airports.
NASA was impressed enough to take the next leap
forward. In 1976, development began on a scaled down version of Boeing’s design. Not a remotely
operated model, but the world’s first human piloted oblique wing aircraft.
NASA’s objectives were ambitious, but the AD-1 was modest in design, built mostly
from fiberglass-reinforced-plastic and foam core. Two tiny jet engines provided less than five
hundred pounds of thrust for motivation. The cockpit had only the bare essentials. No fly by
wire or computer assistance, it would be flown entirely by the skilled hands of a test pilot.
Built on a shoestring budget, many at NASA were cautious about investing huge resources into a
still unproven concept. But the AD-1 would back up NASA’s research with real-world data. In a total
of 79 test flights, the AD-1’s wing was gradually pivoted from zero all the way to 60 degrees.
Even flown entirely by hand, control was fairly straightforward. And at lower pivot angles, any
reasonably skilled pilot could manage. But above 45 degrees, maneuvering was more challenging,
with a phenomenon called cross coupling becoming an issue. Pitching the AD-1 up or down
caused it to roll left or right. While rolling left or right caused it to pitch up or down.
At a full 60 degrees, pilots had to continually bank and yaw to the right to keep the
aircraft flying straight and level.
None of these issues were all that surprising,
and data gathered showed that the AD-1 would have handled significantly better with
an improved wing structure and the help of a computerized flight control system.
But the AD-1 maxed out at just 320 kilometers an hour, nowhere near the transonic speeds,
where oblique wings could begin to show their potential. For that, NASA would have to
turn to a renowned Navy fighter jet.
By the 1980's, the U.S. Navy had also taken an
interest in oblique wings. Because an oblique wing fighter could offer superior take-off performance
from a carrier and increased loiter time. Both were prized capabilities for a next generation
fleet defense fighter to replace the F-14.
In 1984, the Navy and NASA signed a joint
partnership to develop the first supersonic oblique test-bed. And the F-8 Crusader was an
ideal place to start. Its high wing could be modified to accommodate an oblique wing and
NASA had already experimented with the F-8 to develop fly by wire technologies.
A modest thirty six million dollars were allocated to the project. Design work was
to finish by 1986, construction by 1990, and the first flight was planned for May 1991.
But after a successful design phase, the aircraft never got off the ground. By 1986 the Navy, caught
up in deep budget deficits and cost overruns on other experimental programs, suddenly pulled
funding. NASA couldn't carry the program alone, nor could it find a new partner. In 1987,
the project was officially canceled.
After nearly half a century,
intensive research into oblique wing aircraft largely came to an end.
Jones never gave up on the oblique wing. He continued his research into the 1990’s, even
at the age of 80. Eventually shifting his attention to the development of a pure oblique
flying wing, a concept that promised to be the pinnacle of aerodynamic efficiency and fly at
Mach 1.5 with operating economics approaching that of a modern subsonic transport.
Over the years, dozens of studies have demonstrated the potential of the oblique
wing. And in NASA’s own words, it remains a viable concept for large transports.
But real-world advantages at transonic and supersonic speeds have yet to be tested
in flight, and the challenges of flying at extreme wing pivots remain. Modern flight control
technologies would go a long way to help realize the advantages. But the aviation industry
is conservative by nature. Aircraft today look strikingly similar to those designed
over a half century ago. The reality is, it’s less risky for the industry to spend billions
eking out single-digit gains in efficiency with a proven design, than it is to start from scratch
with a radical concept like the oblique wing.
That’s why well funded research programs like
NASA's AD-1 are invaluable to the advancement of aerospace. Jones passed away in 1999, having
made some of the most important discoveries in the history of aerodynamics. And his groundbreaking
research has left many convinced that despite obstacles, it’s only a matter of time
before oblique wings take to the skies.
Aviation is full of big ideas. But some of
them are a little bigger than others. In 1969, Lockheed set out to determine just how
large an aircraft could get, and what it would mean for U.S. airpower. Lockheed's six
thousand ton nuclear powered flying aircraft carriers are some of the most fascinating
and bizarre aircraft ever imagined.
You can learn about the incredible CL-1201
in my latest video, now on Nebula.
Nebula is where you’ll find hours of exclusive
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Engineers are confident that the reactor will be fail-safe, even in a head-on
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