“Synchronizing correctly the instant you
release the mock-up and targeting the impact
to a specific zone of the wave is difficult”
3
AEROSPACETESTINGINTERNATIONAL.COM // DECEMBER 35
retrieved and a small hatch opened for it to be connected
to a data logging system.
WAVES ON REPEAT
Ditch testing typically involves around 125 runs into the
tank. Engineers are normally most interested in the
acceleration of the model before it hits the water, but
testing does assume a controlled landing on water. The
number of runs, how the model is expected to accelerate
and its angle to the water are specified by the aircraft’s
designers and determine what needs to be measured. A
test plan will state how many runs are needed and what
types of setups will be carried out, for different angles of
attack, for example.
Most of the runs that can be conducted will be in
simulated calm water conditions. This helps engineers
work out how to alter the setup for the model drop and
to understand how the results change. Then the waves
can be introduced. “We’re looking at how the model
reacts when we’re landing it on the trough of the wave,
on the face, on the rear of the wave, and on the peak of
the wave. The very final test is we ditch into head seas,”
3m long
Typical length of a test
rig for ditch testing
2.5m long
Maximum size of a
model for ditch testing
60
Channels of data for
Airbus Helicopters’
ditch testing of flotation
systems
says Brown. A head sea is a
mass of waves coming directly
at the front of the aircraft.
Targeting a specific zone of the
wave for the model to impact is
something that Airbus Helicopters also
deems necessary. There is no
fundamental difference between fixed
wing and rotorcraft testing, they both
need to know the forces acting on the
fuselage on impact, depending on how
that impact occurs. Halbout says,
“Synchronizing correctly the instant you
release the mock-up from the top of the
launcher and targeting the impact to a
specific zone of the wave is difficult.”
The attitude of the model to the wave
on impact also needs to be adjustable with trim and yaw
variations for fixed wing aircraft.
To control the path of the model to the wave, the
aircraft can be fixed to a trolley on rails and accelerated
as the trolley travels. The model is thrown off at the end
Metrology
3 // Pressure and
load sensors
provide data for
analysis by
engineers during a
ditch test
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