This topic is a moving target, a lot like fiberglass...
Most of the flex of the spars is in the thinner section reaching maximum
nearing the spar socket area. The spar at the root does not move, and
the forward root rib is really quite stiff, the aft root rib portion is
not as high so it tends to flex a bit as stated. The fuselage side on
the other hand is a bit flexi. After repairing a couple aircraft, the
aircraft flexing spots tend to be the area just behind the rudder pedal
step, just forward of the windscreen on hard landings (when the floor
flexes), and between the front socket and the spar. Interesting thing
is the Redux did not let go in any of the mishaps. Tough stuff.
Those looking at conventional gear, we must do considerable work to try
to get the landing gear loads closer to the fuselage sides to carry the
torsional load of the cantilever gear. The cockpit module seat is not
quite up to the task. To get a proper stance on the gear (read as
taller in height), the moment between the wheel and the fuselage on
rough surfaces is quite high, and a thin beam gear verses a wider gear
beam and the actual attach mechanism has to be analyzed and tested
properly.
All in due time.
Bud
----- Original Message -----
From: Duncan & Ami<mailto:ami-mcfadyean@talktalk.net>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Monday, January 24, 2011 4:58 PM
Subject: RE: Europa-List: Re: Main wing bushings
<<.. would stiffen the structure in such a way that it could lead to
overloading of the forward lift pin >>
Ian,
How does that work, if the lift pins are designed to carry the lift
loads in the first place, there being no greater load available?!
Actually, it was stiffening in bending that might restrain rotation of
the lift pin that was the issue, resulting in an additional bending load
(not lift load) being applied to the forward lift pin. The LAA were
offered a spherical socket that would articulate and remove the bending
load on the pin, but declined to accept that.
However, you are on right path, The earlier discussion in this thread
presumes that the spar flexes, as it indeed doe. But actually the spar
(loaded in this direction) is the least flexible part of the whole
system. What about the forward and aft portions of the root rib? Let's
say these ribs have equal section and 'I' as the spar, but being laid-up
at +/- 45 degrees have x1.41 the elasticity of the unidirectional spar
(in the direction of principal stress), added to which the length of
these flexing root ribs (between lift pin and spar) is longer than the
offset between lift pins and spar pins. So, as the root ribs will flex
more than the spar and it follows that the "leverage" effect between the
longitudinal offset of lift pin and spar pin centres is removed, or
reversed to the extent that the spar pins share some lift load.
As you say, the flexing of the fus side also contributes, albeit this
had to be stiffened-up to prevent pin disengagement.
Previously I have put a small finger down one of the (1/2") spar pin
holes with the wings rigged, while someone else rather violently loaded
the wing, albeit not even near to 1g. But there was no hint of the
"leverage" effect or the spar hole flexing downwards relative to the pin
hole in the seat back.
Rgds.,
Duncan McF.
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of G-IANI
Sent: 24 January 2011 12:34
To: europa-list@matronics.com
Subject: RE: Europa-List: Re: Main wing bushings
In support of Bud and Pete's notes I can confirm that flexing of the
fuselage is important. The LAA had considerable concerns that the tail
dragger conversion would stiffen the structure in such a way that it
could lead to overloading of the forward lift pin.
Ian Rickard G-IANI XS Trigear, 300hours
Europa Club Mods Specialist
e-mail g-iani@ntlworld.com
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