High-speed cameras
28 DECEMBER 2019 \\ AEROSPACETESTINGINTERNATIONAL.COM
2 // Final preparations for
the test took three days
3 // The Fokker is the largest
aircraft dropped using the
gantry at NASA Langley
4 // Justin Littell, engineer at
NASA Langley’s Structural
Dynamics Branch
2
“The camera can show
4
you that a dummy sunk in
its seat and that’s why
there’s a high load
measurement on the load cell”
during the drop was both horizontal and
vertical. Planning for a complex test like
this begins by asking yourself a series of
questions, says Littell.
“We ask: What kind of impact conditions do
we want? What kind of instrumentation do we want?
What is technically feasible within the constraints of the
facility? From these questions we develop all the
different areas of the test.”
Instrumentation used in the test either monitored
the aircraft or monitored the anthropomorphic test
devices, the crash test dummies, on board.
LIFE OF A DUMMY
Littell’s team used a number of crash test dummies
ranging in body types, from infants to obese male
adults. The dummies were placed throughout
the cabin. Special attention was put on the
positioning of the dummies conforming
to the 50th percentile, because this is
the body type that the FAA uses in
its regulations.
The dummies were fitted with
accelerometers in the head, chest
and pelvis and load cells in the
spinal column and neck. The load
cells measure force, says Littell,
“indicating compression in the spinal
column and whiplash in the neck.”
As well as the sensors inside them, the
dummies were also monitored using cameras
mounted inside the cabin. The cameras allow researchers
to correlate measurements from the body-mounted
sensors with movements the dummies make.
“For example, the camera can show you that a
dummy sunk in its seat and that’s why there’s a high load
measurement on the load cell,” says Littell. “It is able to
give us a complete picture of what the dummies
experience on board.”
For the Fokker test, high-speed ruggedized cameras
were trained on all the dummies except for the pilot. The
cameras, which are designed to withstand high g-forces,
were mounted to the cabin’s overhead racks using a
gimbal system.
Littell’s team also used several high-definition 4K
cameras to monitor both the dummies and deformation
to the cabin that occurred during the impact. The
aircraft was also fitted with accelerometers throughout
the airframe – in the floor, in seat bases and overhead
bins, and in the engine, tail and nose.
Such a high volume of instrumentation produces a lot
of data. In total, the data acquisition system for the crash
test used 300 channels. Outside of the aircraft, a further
set of ground-based cameras were used to monitor the
fuselage using a technique known as digital image
correlation (DIC).
SEEING DOTS
The DIC process involves painting the exterior of the
fuselage with black dots. Littell says, “We then run a
calibration procedure on the cameras, which allows
them to track the movements of these dots throughout
the crash,” he says. “By measuring how the dots move
relative to each other, we can calculate fuselage strain
and deformation.”
Before DIC, displacement was measured by fitting
strain gauges to the fuselage, an expensive and labourintensive
process, says Gerardo Olivares, director and
senior research scientist at the US National Institute for
Aviation Research (NIAR) in Wichita
State University, USA. But DIC – helped by
ultra-high-speed cameras, some of which
can take up to half a million frames per
second – allows for far greater definition,
giving researchers a much clearer picture
of “how stress and strain waves travel
through the structure during a crash”,
says Olivares.
To help clarify this picture software is
used to analyze and display the level of
displacement in color-coded graphics.
The NIAR provides certification
testing for aircraft OEMs, many of which
have a manufacturing presence in
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