Aerospace
The Canadian Forces EWT-33 wing
pylon structures were modified to reinforce the forward
and aft pylon legs to increase their load carrying
capability. The modification was required to enable
the safe carriage of new and heavy stores, such as
the ALE-503, needed to support the aircraft various
electronic warfare roles. The structural modification
consisted of the addition of gusset plates that are
welded to each of the pylon legs. Problems associated
with the embodiment of the structural modification
and quality of the welds had resulted in added maintenance
burden for the maintenance personnel.
Martec Limited was contracted to perform a loads
analysis and calibration of the modified EWT-133 wing
pylon and to perform the redesign of the pylon structure
to reduce the maintenance burden associated with the
weld inspection and to increase its overall performance.
Also, the new pylon was required to interface with
an existing bomb rack currently in the inventory to
improve its maintainability.
The project initially required Martec to develop
a Finite Element model of the pylon/store structure.
Early FE analyses had concluded that the original
pylon could not sustain required maneuver loads consequently
the pylon was strengthened through the addition of
gussets on both sides of each leg.
Following its instrumentation by the Aerospace Engineering
Test Establishment (AETE) with support from Martec,
the modified pylon was ground tested by Martec at
the Technical University of Nova Scotia (TUNS) in
order to validate the FE model, calibrate the instrumentation,
and derive strain/load transfer functions which were
used to determine flight test limits. The pylon was
mounted upside down on a rigid structure with a structurally
representative dummy store attached to it. Known loads
were applied at various locations/ directions on the
dummy store and measurements from the strain gauges
on the pylon and lugs as well as the load cells under
the swaybraces were recorded. The results of the ground
test permitted the derivation of 11 “Pylon Bending
Moment” transfer functions each using a different
set of strain gauges. Martec identified pylon bending
moments as a critical flight test variable thus a
large number of transfer function permitted the use
the most accurate function while maintaining numerous
alternate functions in the event of gauge failure(s).
In fact, once programmed into the flight test computer,
the transfer functions could be interchanged within
a few minutes, even during flight.
Overall, the CT-133 wing pylon ground test offered
good correlation with the FE model and its calibration
provided accurate transfer functions essential to
the proper conduct of the subsequent flight test.
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