The issue of load testing should be approached very carefully. as a30+
experienced
aeronautical engineer, Chief of Stress at Pilatus Aircraft hopefully l can
assist with a few pointers.
The design load level LIMIT loading is determined from the certification basis
(or approval basis) of the aircraft. For LAA projects this is likely to be
+4/-2,
without the consideration of gusts. The VN diagram submitted by Europa
for the original will be basis that needs to be used.
Additional factors applicable will include the ULTIMATE factor, usually 1.5,
Special
Factors, these could include a factor for composites (usually negotiated
as 1.5 to account for hot humid material property degradation), plus others that
are agreed with the approving/certifying agency.
For a wing bending test, which is important but NOT the only test that is
required,
the calculation for total load would be 621kg x 4 x1.5 x1.5 - (wing mass).
The wing mass can be left on and is conservative).
This makes a total mass of 5590kg or 2790kg per wing for Europa XS.
The next step is to determine the spanwise and chordwise distribution of this
load.
There are many issues to be considered here, however, a justification of
the distribution used, coupled with the correct angle of attach, is sufficient.
Other cases with loader total loading may be more critical, such as torsional
cases
driven by manoeuvre control inputs or flap loads should also be considered.
Typically for an aircraft of the Europa class the load calcs take around
200-1000hrs.
A test plan to cover the critical ones needs to be created and submitted
for approval (and often observation) by the authorities.
It is normal to correlate test data with predictive calculations (done using a
combination of finite element models and hand calcs). Hence the test is
normally
a confirmation of the predicted structural performance (deformed shape,
stress/strain
levels, failure locations if ULT+ loads are applied.
A light aircraft design and certification can absorb many 10,000 of man hours.
Typically around 20 to 50 times the retail price of the aircraft (rough guide
as the cost curve is exponential). Making the design certification cost of a
750kg VLA around 2 to 5 million.
Hopefully this has been useful to someone?
Regards
John
--------
John Wighton
Europa XS trigear G-IPOD
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