As Bud says, a suitably reinforced larger hole can be quite acceptable. His
approach
sounds thorough and considers the conservative stressing methodologies of
Mr Niu et al. He could also have mentioned Bruhn (the stressman's bible),
NACA/NASA
papers, Roark & Young and the implementation of those Gentlemen's work
by Bill Gran, Richard Abbott, etc.
There are dangers in using the numerical programs (finite element based), as
with
most tools they need to be used properly. I came into stressing in the early
80's became attracted to FEM/FEA techniques and taught myself Nastran, Patran
and a lot of other programs since). Having since used FE techniques to analyse
many thousands of objects (from paper clips to A380 wings) there is still
a risk of getting things wrong. However, with careful planning, incremental
implementation
and a robust approach to V&V (verification and validation) a great
deal can be gleaned from these simulations.
I developed the structure for the Europa tail dragger (McCallum/Flyer initiated
in the UK), this was done with a partial fuselage FE model, using the factory
layup (pre-XS days). Material data from Martin Hollmann's books is conservative
but good for basic strength calcs. That design is flying now as G-MLXP (the
LAA, as is normal, insisted on beefing up the optimal structure l had
specified).
Going back 'on topic' l think the layup details Bud gives can be used as a
guideline
for reinforcement of a Europa fuselage access hole. In the UK any deviation
would need to be cleared as a Mod (preferably before it is applied to the
aircraft).
--------
John Wighton
Europa XS trigear G-IPOD
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