Aerospace & Defense Technology - August 2022 - 22

Vibration Testing
NASA's X-57 Maxwell
Electric Aircraft
I
t's not only automobiles that are
going electric - airplanes are as
well! And, to prove that aircraft
can be electrically powered, NASA
has developed the X-57 Maxwell, its
first all-electric X-plane. The X-57 airplane,
currently in the Mod II configuration,
is a modified version of the
Italian Tecnam P2006T. In place of the
usual gasoline-powered motors, the
X-57 has two all-electric motors powered
by traction batteries. The X-57
Maxwell project has some lofty goals,
including lower energy consumption
(the X-57's motors use one-fifth the
energy of a gasoline-powered aircraft),
reduced emissions, and lower noise
during flight.
The Challenge: Making It Real
As NASA engineers design new electrically
powered aircraft, they must ensure
that their designs not only use energy
efficiently but also that the aircraft can
fly safely. One way they do that is to
build an analytical model of the aircraft
structure and simulate the stresses the
aircraft will experience while in flight.
By doing this, they can uncover weaknesses
in their designs and fix them
before making expensive prototypes.
There's no substitute for physical ground
testing, however. At some point, engineers
must strap an airframe to a shaker
and take some measurements. These
physical tests are essential for validating
the simulation models and understanding
the structural characteristics of any
new aircraft design.
A ground vibration test, or GVT, is performed
before the first test flight is made.
During a GVT, test engineers subject the
aircraft to a number of different vibration
profiles while measuring the response at
hundreds of points around the airframe.
Analyzing these measurements helps
engineers identify the modal frequencies
and mode shapes of the airplane in a
flight-ready configuration. This allows
them to validate and update the aircraft's
finite element model (FEM), which they
will then use for flutter analysis predictions.
In the end, the flutter analysis tells
them whether or not a structure has the
necessary aeroelasticity and flutter margins
necessary for airworthiness.
Safety First
When running a GVT, it's important
that the test article be as close to the
final design as possible. This can lead to
some interesting challenges for the test
team. For example, during the GVT, the
heavy and high-voltage electric motor
batteries were not real. In normal operation,
sixteen traction battery modules
power the twin electric motors and
amount to nearly a third of the airplane's
total weight. To be safe, however, battery
22
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Aerospace & Defense Technology, August 2022
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Aerospace & Defense Technology - August 2022

Table of Contents for the Digital Edition of Aerospace & Defense Technology - August 2022

Aerospace & Defense Technology - August 2022 - Intro
Aerospace & Defense Technology - August 2022 - Sponsor
Aerospace & Defense Technology - August 2022 - Cov1
Aerospace & Defense Technology - August 2022 - Cov2
Aerospace & Defense Technology - August 2022 - 1
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Aerospace & Defense Technology - August 2022 - Cov3
Aerospace & Defense Technology - August 2022 - Cov4
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