Aerospace & Defense Technology - August 2022 - 37

Tech Briefs
on the flight design to accomplish the
ideal objective to avoid operating any
particular flight hardware configuration
under any particular set of conditions
for the first time in flight.
Some flight environments (e.g., acceleration)
cannot be replicated during
ground test. Margin testing with respect
to the expected flight conditions should
be included to protect against known
and unknown uncertainties in the flight
conditions (e.g., ground-to-flight dispersions),
as well as known, anticipated,
and unknown hardware variations (e.g.,
manufacturing tolerances, non-conformances,
and undetected deficiencies).
If it is impractical to test or simulate a
particular flight condition on the
ground, then additional margin may be
appropriate. Furthermore, testing
should consider and account for engine
hardware experience and exposure
throughout all phases of the required
life cycle, including manufacturing,
acceptance testing, transportation, handling,
storage, vehicle integration,
checkout testing, launch preparations,
aborts, liftoff, and flight. Exceptions to
this approach should be carefully evaluated
and include a risk determination. It
is prudent that LREs be deliberately
designed to provide margins equal to or
greater than the specified margin test
requirements so as to provide high
probability for test success and high
reliability for flight operations.
A corollary to TLYF is the " fly-as-youtest "
approach. " Fly-as-you-test " means
that flight operation should remain
within demonstrated ground-tested and
qualified regimes, and that design and
process differences between qualified
test hardware and flight hardware
should be minimized and ideally avoided.
A successful development and qualification
program will anticipate all
potential flight conditions and ensure
those conditions are validated by a
robust test program. If an engine has
multiple applications, ideally the engine
should be developed and qualified to
the most demanding requirements,
however programmatic considerations
may dictate a phased approach.
Hot-fire testing to verify that an LRE
design is ready for flight typically consists
of four phases of major program
Aerospace & Defense Technology, August 2022
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activity: prototype testing, development
testing, qualification testing, and
integrated system testing. The first three
test phases typically occur at the component
level as well as the engine level.
The integrated system testing phase is
performed at the propulsion system
and/or vehicle level.
After an LRE design has completed the
qualification program (i.e., production
phase), each individual flight engine is
acceptance tested by hot-fire to verify
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Aerospace & Defense Technology - August 2022

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