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What does flight mean to you?
Immediately, we think of birds.
Winged beings, high above.
But to think of ourselves flying,
we think of an airplane - tube, tail, wings.
Everyone knows that's how you fly, that's what we're used to -
following the same basic model the Wright brothers used.
After a century of innovation, we are still limiting ourselves
to the Wright's assumptions about manned flight.
As said by Sir Ken Robinson: "If you're not prepared
to be wrong you will never come up with anything original".
As engineers, we take that to heart and we believe it's time
to push the boundaries of aviation.
We believe in making the impossible possible
and are captivated by the idea
of enabling the future to exist today.
Since 1946, the Dryden Flight Research Center has been the
premier facility for atmospheric flight testing.
For over 60 years, the most advanced aircraft
of the day have flown here.
So much expertise, knowledge, innovation.
Surely the basics of flight are well understood.
But what if we missed something?
In the late 1800's people were thinking
about heavier than air flight.
Balloons weren't cutting it.
They understood the need for a force pushing you
up that would overcome gravity pulling you down.
See, when an airplane is in steady level flight,
it experiences four major forces: lift,
weight, thrust and drag.
Weight constantly tries to pull the airplane down,
and the airplane must produce lift to stay in the air.
Thrust provides enough force to overcome drag.
Now, drag is more complex.
There are three main types of drag: viscous, pressure
and induced drag - all acting
to slow the airplane from flying forward.
Aircraft designers are most concerned
with induced drag, a byproduct of lift.
Lift is generated by producing high pressure underneath the
wing, and a low pressure above.
But pressure acts in all directions, not just up or down.
Thus, while the plane is in flight, air will 'leak'
from beneath the wing and curl around the tip.
This spins the air as it moves around the wing.
This is called a wing tip vortex, and it looks
like a small tornado coming off the end of the wing.
This isn't good.
Making these takes a lot of waste energy; and if you think
of the air as water, it's like making big splashes in a pool.
Now, however you design your wing,
to get more lift you need a bigger difference in pressure.
The more lift produced, the more induced drag there will be
because more air will leak and curl around the wingtips.
In 1925, Ludwig Prandtl derived the first way to minimize drag.
His solution was the elliptical span load.
So a wing doesn't produce all of its lift in one place, rather,
it produces a little bit of lift everywhere.
And Prandtl came up with how much lift should be produced
at a particular location along the wing,
and visually his solution was a quarter of an ellipse,
where the most lift was at the root of the wing and tapered
to zero at the wingtips.
More than 85 years later, this is still the solution we use
when designing aircraft.
When the Wright brothers first flew their 1901 glider,
they could not get the airplane to turn.
Every time they rolled their aircraft in one direction,
it would turn in the opposite direction and crash.
As they rolled the airplane, one wing generated more lift,
but also more induced drag, forcing the nose to turn,
or yaw, in the opposite direction.
We call this adverse yaw.
To solve this, the Wrights put a rudder on their airplane,
which would angle more drag on the tail
that would directly oppose the induced drag on the wings,
forcing their airplane to yaw the correct way.
Controlled flight was solved!
Or was it?
After publishing his paper in 1925, Prandtl continued thinking
about minimizing drag.
He knew about adverse yaw and how the Wrights accounted
for it, but to overcome drag with drag?
He thought back to the inspiration for flight.
He wondered why he'd never seen a bird with a rudder.
How did they do it?
The Aeronautics Academies of 2012 and 2013
at NASA Dryden wondered the very same thing.
In 1932 Prandtl published another paper on induced drag.
By considering the strength of a wing rather
than just the wingspan,
he derived a new bell-shaped lift distribution
that would produce 11% less induced drag.
At the same time, two teenagers, Walter and Reimar Horten,
began designing all wing gliders, no tail at all.
To get Prandtl's bell shaped lift distribution they added
twist to their wing design.
They discovered as they turned their glider,
the nose FOLLOWED the roll of the vehicle,
they didn't need a rudder.
To explain their solution, I have to explain the work
of *** Whitcomb and his devices known as "winglets."
You've all seen them- little tips that point
up on Southwest jetliners.
These small vertical sections are actually the wings,
just pointing up.
They are also sticking straight
into the vortices we were talking about before.
They're making lift, same as the main wing, only now the force
of the lift is pointing, or pushing as you can imagine,
inward and a little bit forward.
This means we're actually getting a little bit
of extra push forward.
Normally it's only our engines that push us forward.
This works because the vortices start at the tip and curl
into our winglet; but if you folded them out horizontally
and kept the start of the vortex in the same place,
they would still work.
You would have flat winglets,
and Prandtl had figured this out, only accidentally.
The bell shaped distribution
of lift he derived caused inboard vortices
and the Hortens were seeing this.
But wait, you still have to account for adverse yaw.
The Horten aircraft will increase induced drag
as it rolls, and yaw the wrong way.
Wrong! The Horten wing actually uses adverse yaw
to its advantage.
When it rolls the lift on one wing is increased, and yes,
so does the induced drag, bigger vortices remember?
But now those vortices are hitting our flat winglet
and stronger vortices give the winglet more push forward.
The new thrust we are getting overcomes any induced drag
and we yaw the correct way!
The past two aeronautics academies
at NASA Dryden have built a prototype dubbed the Primary
Research Aerodynamic Design to Lower Drag
or the PRANDTL-D for short.
No data was initially collected until we were able
to instrument the vehicle
and record turning rates and accelerations.
What we found was better than we could have ever possibly
hoped for.
Roll and yaw occurred in the same direction,
and by definition, we were seeing proverse yaw.
We had demonstrated the fundamental principal
in a design that claims a 60% increase in aircraft efficiency.
We had found a viable aircraft for the future.
We'd all come from different schools and backgrounds -
brought together here by the love of freedom obtained
by flight, along with speed, power,
new frontiers, and knowledge.
NASA Dryden, though our work on the PRANDTL project,
gave us the ideal environment
to combine both the tangible elements
of aircraft flight testing with theory learned at school.
We weren't just witnessing a breakthrough in aerodynamics,
we were contributing to it.
We had challenged assumptions, conventions, and paradigms.
This was our first step.
We are the NASA Aeronautics Academy of 2013.