Hi All,
Casting my memory back some ten years ago.... to the testing we [Europa] did
on the XS wings.... went something like this...
First we built a steel jig to hold a single wing on, so that it was
inverted, and tilted leading edge down , to simulate it flying normal way up /
leading edge up [ worst case load is positive angle of attack, I forget the
exact
angle,] wing was fixed with the normal [ at that time] non pip pin spar pins,
and the rigid drag pin sockets....... steel weights [10Kg & 5Kg] were then
placed on the lower skin, with a carpet underlay to give a non slip surface,
to a pre-determined plan to ultimately go past something like 12G.
We supported the wing with a scafold tower arrangement whilst we were adding
to the weights, going up in increments of ''G's'', taking away the support
at each stage to measure deflection and twist, so rather than the required
time [for the P.F.A.] unsupported of about 3 seconds, the wing was under load
each time for probably a couple of minutes.......It got to something like 7G
[at 1370 lbs AUW] the first try, before the tang of the spar ''walked off'' the
spar pin and dumped the 3000 or so lbs of weight onto my workshop floor.
[Hence my previous posting to the forum about leaving off the pip pin style
spar
pin in the port seatback bush?]
Wing / spar undamaged, but rib/ lift & drag pin plates ripped.
It was then decided to test wings in pairs, fitted to a fuselage, so a
fuselage was set up on a pedestal, supported by the seat pan / seatback /
baggage
bay areas, in the same nose down / inverted stance. The height was set to
allow spanwise deflection of the wings [ so the door sills were about 6' off
the
ground ] A strap was fitted to the port spar, in an attempt to contain the
''walking'' of the spars aft, and the swivel drag sockets and the ''tie bar''
were added. Loading [both wings together] went as planned, we were watching
the spars through access holes cut in the fuselage, the wings passed the test[
forget the figure, something like 9.8] but it was obvious the spar strap was
under stress. At this time, Francis Donaldson, and John Tempest [AKA Billy
Bunter] of the P.F.A. wanted to see another test [I am still convinced for
their own curiousity, rather than any truly technical reason] So we sourced and
fitted the pip pins [as supplied in the XS kit nowadays] and did the test
again. No problems, the pip pins were containing the aft movement of the spar
tang. We kept going with the test, again, I can't recall the exact figure we
went to, past 11G, I recall , when the wood core in the spar [between the two
pin bushings] ruptured, and let the rovings in the spars twist over [ top cap
to the bottom / bottom to the top] and something like 7000 lbs went on the
floor this time. The spar cap rovings returned to their original positions, no
visible damage, just the core was ruptured. So.... we picked up the weights,
had a coffee or two, and started to reload the wings, and got to more than 3G
before the spar cap rovings swapped place again.... so you can break the
wing at + 12G, unload and it will return to position, and as long as you keep
below 3G, fly yourself home. From memory, we did 3 sets of wings in during
testing,[ P.F.A. kept moving the ''goal posts''.] All tests gave similar
results.
Years later, I managed to catch Francis off guard, asking what R.V. had to
do to clear the RV10 to fly in the U.K ? His answer? Supply the paperwork to
support the stress calculations... and have a couple of them flying.......
when I enquired why Europa had to test 3 sets of XS wings, and dance through
even more silly tests to get the MG wings cleared for over here [ when there
were two allready flying in the U.S.A.] He went an embarrasing shade of
red.... no answer then ? [The MG wings have been tested on the same single wing
test rig [ beefed up, as we broke the rig itself the first time] to a much
higher G load than the XS wings. You will not break either sets of wings. .
re the VNE testing, Pete Clark did that, very carefully, increasing in
small increments, at high altitude with a parachute..... well past the limit...
but don't push YOUR luck in YOUR plane?
Cheers, Nev.
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