Bud,
It sounds like you could 'kill two birds with one stone' by adopting the
design of fuselage reinforcements that the Swiss taildragger uses. If
you've
not seen these I'll send you an isometric sketch.
Duncan McF
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Bud Yerly
Sent: 24 January 2011 23:09
Subject: Re: Europa-List: Re: Main wing bushings
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 <mailto:ami-mcfadyean@talktalk.net> & Ami
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
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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