Rowland,
The manual 35_CBM - 35 FITTING DOORS from the Europa website, Fig 5 shows the
intended
design condition of the door hinge installation. The screws into the
upper hinge leaf are shown countersunk with a knife-edge condition (poor
practice
#1), the figure is probably not to scale but there looks to be significant
material for the counter-bore, a washer and the nut. It shows an almost flush
screw (i.e. less than 1 complete thread as normally required) (poor practice
#2). I note the lower hinge leaf has a protruding head fasteners with integral
washer.(AN525-10R10) and a non counter-bored retaining nut (good practice #1).
The critical failure mode as drawn is a head-side pull through (due to tension
and prying) of the upper screw. For high time aircraft this may be surpassed by
a tensile failure initiated by a fatigue crack between the countersinks. Hence
l think you could increase the depth of the counter-bore slightly to ensure
one protruding screw thread and a flush OML (outer mould line). Minimise the
countersinking.
Looking at my own aircraft l found both sides countersunk. This enables a
slight
over-parallel condition of the hinge leaves - to account for built tolerance
(in other words there is no room for the head of the AN525-10R10). This has
the slight benefit of ensuring both sides of the hinge flex a similar amount
- thereby reducing the likelihood of a fatigue crack on the more flexible side
(as drawn).
A redesign to today's interpretation of the regulations and compliance standards
would require adherence to best practice design principles. This would most
likely result in slightly thicker hinges, 130 deg countersinks with
corresponding
shallow head fasteners, a third fastener on each hinge (offset centreline
to alleviate the prying action).
JW
--------
John Wighton
Europa XS trigear G-IPOD
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