Composite materials, such as fiberglass and carbon fiber, are easily molded into
complex and aerodynamic shapes. They can create very strong structures tolerant to
wide variations in temperature and requiring little maintenance. Today, the use of
composites has replaced that of aluminum in many areas and is found in all areas
of aviation, from airliners to Light Sport Aircraft.
The use of composites, though, introduces different (not necessarily more complex)
structural analysis and testing methods that are often not well understood.
There are two primary purposes for testing aircraft structures: the first is to
validate computer models and confirm that the aircraft meets structural strength objectives
(discussed above); the second, more sophisticated objective is to simulate the effects
of long-term use on the airplane structure and develop a “useful life.”
Depending on the materials used this takes one of two directions: aluminum airplanes
emphasize fatigue testing (metal structures typically develop cracks after extended
use); the composite counterpart is damage-tolerance testing (composites don’t develop
fatigue cracks but can have hidden damage).
In both cases major aircraft assemblies are cycled through simulated takeoffs, cruise,
turbulence, landings (some good, some not so good!) and then taken to destruction and
shown to be strong enough to be “certified” even after this simulated lifetime. Premature
failures can be dealt with by regular structural inspections (if the parts involved can be
All this structural testing, both for strength and damage tolerance, on a Cirrus is performed
with major components built from sub-standard parts. This may not be intuitive but the idea
is to test the structure with all parts being at the minimum end of the acceptable range in
manufacturing - and then damaged further to allow for field incidents not visible during a
pre-flight inspection. You can be confident that an average Cirrus airplane comes from the
factory with much better components than the items we use for our testing.