[Music]
>>An average person's access to technology increases every year.
Maybe even every day.
So does their use of energy.
People around the world are driven to find faster, more efficient, and cleaner ways to
utilize energy so that it can be accessed sustain-ably on an even greater scale.
Some are doing it with power.
Others are revolutionizing automobiles.
Engineers at NASA are working on a better airplane.
[Music/Background noise]
>>We are looking at ways for more efficient travel.
One way to do this is with ultra-efficient lift wings that are built with new and lighter
material.
[Music/scribbling]
However, this type of wing could have an issue with flutter.
[Music]
>>Flutter is a type of unstable interaction between a structure and the air that is moving
around it.
[String plucks]
All structures vibrate at their own fundamental frequencies, with their own harmonics.
Simple structures, like guitar strings, have relatively simple harmonics, which allow for
the production of a clean, clear musical note.
[String plucks]
More complex structures have more complex harmonics, but they still vibrate according
to the same laws of physics.
The air around these objects is a fluid, and even though you can't see it,
it exerts a force on everything moving through it.
Flutter occurs when the forces from the air interact with the structural vibrations in
such a way that they to grow.
Sometimes these unstable interactions can have catastrophic consequences.
Even very large structures can be affected by these types of destructive
phenomena.
[Music/Tarmac noise]
Flutter phenomena in modern transport aircraft is well understood as a result of decades
of research.
Today's aircraft wings are built to account for flutter by building them relatively rigid.
The problem with rigidity is that it makes airplanes heavier and less efficient
than they would be with more flexible wings.
There is an ever increasing demand for greater speed, better fuel efficiency, and passenger
comfort, but as we push the limits of what is possible with current technology we must
find ways to achieve these gains without sacrificing the hard-won and impressive safety record
of today's aviation industry.
One promising technology that may make it possible to improve both aircraft safety and
performance is active stabilization of flutter using advanced flight control systems.
Current aircraft use passive means to avoid flutter.
They carry around extra structure and limit operational speeds, basically avoiding the
conditions where flutter occurs.
[Music]
Consider this wine glass.
[Ding]
The structure of the wine glass resonates, or vibrates, at a characteristic frequency.
If we excite those frequencies with enough energy, the structure of the wine glass will
break.
Now think about the airplane structure like the wine glass.
It vibrates at few characteristic frequencies, and if we fly fast enough, like turning up
the volume, and we are exciting those wing frequencies the wing can break similar the
wine glass.
By building the wings stiff, and flying slower we prevent the wings from being destroyed
by flutter.
However, as we try to fly faster with lighter weight more flexible wings we can no longer
just avoid flutter.
We have to improve our prediction and analysis tools and come up with clever innovative solutions
to the flutter problem.
One promising solution to the problems we encounter with flutter as wings become lighter
weight and we fly faster is to take an active role in suppressing those structural vibrations
with the control system. We can utilize advanced sensors, software, actuators, and computers
to sense the wing vibrations and proactively manage flutter.
This is what we're trying to accomplish with X-56.
We are preparing to flight test control systems that actively suppress flutter, and investigating
advanced sensors, such as these fiber optic strain sensors that may give us a more detailed
picture of the motion within the aircraft structure.
But to actively control something you have to understand how it works.
We are developing more detailed and accurate math and physics models of aircraft and validating
those models with as much test data as we can get our hands on.
It's essential that we understand exactly how our aircraft moves.
How loads affect wing bending,
how forces and moments from various sources affect aircraft motion,
And at what frequencies does the X-56 structure vibrate?
[Music]
By answering these questions, the team can model how the X-56 will behave in flight.
We can make predictions about flutter-induced instability, and we can create controls to
respond to these dynamics.
And by predicting how the aircraft will behave in flight and how it may flutter, the team
can begin to develop accurate control strategies and software.
[Music/Background noise]
Once the control software is written and the airplane is once again ready to fly, flight
tests will attempt to purposefully put X-56 into flutter conditions to investigate the
performance of the active control system.
Can these control systems actively suppress flutter?
But before that, there still is much to be done.
The active controls must be tested on the ground, the control room must be prepared,
and communication equipment tested and validated.
And Active Controls are not the only way to suppress flutter.
NASA engineers and their partners are working on a multitude of methods to deal with it,
with the hopes of coming to one, integrated solution for the future of flight.