Metrology
of the rails and its arc to the
water is carefully calculated.
Another method is an over
arching rig that controls the
model’s descent and impact.
Airbus mock-ups, Halbout says,
can be up to 3m long and weigh up
to 300kg.
The European manufacturer uses
cameras to capture the models’
performance, including for the SARAH
research project. “The model’s trajectory
was followed by a high-speed camera
system. We also had other cameras to
provide other fields of view. In total there
were seven cameras,” says Halbout.
DATA INCREASES
The SARAH tests involving Airbus included
emergency flotation systems. Pressure sensors
were built into the model’s inflatable floats and
there was a load sensor under the bottom of its
fuselage. There were also load sensors placed
between the floats and the fuselage and inertia
sensors inside the mock-up. Different flotation
systems were designed and tested. Halbout says, “It
was more than 50 or 60 channels to record with
different frequencies. We also did experiments with only
the fuselage,” Halbout adds. More than 200 tests were
performed with the water calm or with different wave
states. “Other parameters we varied was the nature of
the flotation system. We performed the impact with
rigid floats and inflated floats.”
“The blended wing body aircraft
model was found to skip across
According to Adden, fixed-wing aircraft have a
special way of coping with challenging sea states:
“They cover them by having very
conservative approach conditions for
the speed, the rate of descent and a
stable attitude.”
Helicopters are different because
the stability of the helicopter is more
important. Helicopters will capsize in
water without a flotation system and
so there is no benefit in the helicopter
fuselage staying intact.
Ditch tests feature multiple
high-speed cameras, sensors inside the
models and on flotation systems. The
36 DECEMBER 2019 \\ AEROSPACETESTINGINTERNATIONAL.COM
the water like a flat stone”
designs will be tested with them – SARAH also tested
blended wing model (BWB) designs. BWB airliners
promise dramatic reductions in fuel consumption. The
SARAH work sought to understand how these broader
fuselages coped with a ditch impact. “We also looked at
unconventional configurations to understand if our
current ditching simulation capabilities, which include a
lot of knowledge and a lot of engineering judgments
work,” says Adden. The BWB was found to skip across
the water like a flat stone, unlike the traditional tubular
aircraft which lands once.
For decades now, what has been understood about
ditching is that with a controlled approach an aircraft
can belly land, like in the Hudson River event, stay intact
and its passengers and crew escape. What would help the
industry is to understand how a testing process that can
reach that conclusion confidently can be
achieved without the expensive long test
lead times and physical tank work.
SARAH is a step towards that and
moves a costly part of the aircraft
certification process into the virtual world.
High speed cameras, modern
instrumentation and data acquisition
systems have also increased the quantity
and quality of data. With the use of this
data, simulation may increasingly provide
a real alternative for physically testing
such a rare event as ditching. \\
4 // CN235-300
ditch testing using
a scale model and
wave tank
amount of data is large and growing for projects like
SARAH and companies like Element. “The big change for
us is in the last ten years has been data acquisition,” says
Brown. “We capture, record data and then use small
logging systems to retrieve the onboard data.”
The data logging systems have allowed the number of
runs to be reduced because of the increased quality of the
data captured with each run, he adds.
The core methods for ditch testing are not changing
in the immediate future, even though radical aircraft
5 // Scenarios
considered by the
SARAH project have
included helicopters
with rigid floats
that inflate if the
aircraft ditches
4
5
/AEROSPACETESTINGINTERNATIONAL.COM