This has sparked an extremely interesting and thought provoking debate.
The only real solution is to model the aircraft using Finite Element
Analysis to truly see how the airframe moves under differing load
conditions.
Any Europa builders use FEA?
Nigel
On 24/01/2011 23:19, GRAHAM SINGLETON wrote:
> Not convinced Duncan. The spar resists bending and the leverage is
> enormous, from the centre of lift of the wing 30% span? The load on
> the root ribs is shear and some bending of the pins. Don't forget the
> lift load is a spread load whereas the spar bending of the tangs is a
> point load applied by the spar pins.
> You are right about the stiffening of the fuselage side. We really
> should have flexible sockets at the LE as well as the TE.
> I still believe the lift pins (in the root rib) should carry all the
> lift loads and the spar pins all the bending loads. That's why the
> tangs needed to be strengthened on the glider.
>
> Graham
>
> ------------------------------------------------------------------------
> *From:* Duncan & Ami <ami-mcfadyean@talktalk.net>
> *To:* europa-list@matronics.com
> *Sent:* Monday, 24 January, 2011 21:58:21
> *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? Lets
> 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 201112:34
> *To:* europa-list@matronics.com
> *Subject:* RE: Europa-List: Re: Main wing bushings
>
> In support of Bud and Petes 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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