My education is in engineering (BS, ChE) and my industrial experience is in
metals (non-ferrous), so in that context this is an engineering analysis. I
did not "do the math" but from my understanding of the fundamentals of
statics (yes, I know, some of the loading is dynamic but the dynamic load
uses the same levers and arms), if the gear leg fits snugly into its socket
it will behave as a single member. Thus, you are correct in saying that the
fulcrum is at the fuselage skin. However, your assumption that the shorter
length inside the tube affects leverage implies a different assumption, to
wit, that the leg does not fit snugly in its socket. So, take your pick:
snug fit means that the socket is an extension of the leg, and loose fit
means the lever arm within the socket is the length of the leg within (and
the socket is loaded only at the lower end at the fulcrum, and the upper end
of the leg where the bolt goes through). As long as the leg within the
socket does not fail it transfers the same forces to the ribs under either
assumption about snugness of fit.
Perhaps a structural engineer will read this thread and comment.
Best regards,
Rob Housman
A070
-----Original Message-----
From: owner-europa@post.aviators.net
Subject: Re: Short Tri-gear legs
Rob, is this based on an engineering analysis? If not, I assume the
fulcrum is where the socket tube emerges from the fuselage, and if you
move the fulcrum, the leverage on the short arm inside increases at
least linearly.
Rather than engineering, any bets can be settled with the simplified
drop test in FAA regs. Load her to gross, hoist to 18.7 inches, and
cut the rope. Who gonna hold the bets? :)
Regards,
Fred F., A063
Rob Housman wrote:
>
> If the legs are snug in the sockets (and they are) the lever arm length
that
> affects the load on the leg sockets and therefore the plywood ribs, is the
> gear leg that is external to the fuselage. A shorter length inside of the
> fuselage, within reason, will not change the load that the ribs must
absorb.
>
> Best regards,
>
> Rob Housman
> A070
>
> ----- Original Message -----
> > I recall something like that, and it was about a 1/2". I just lowered
> > the fuselage in its cradle by 1/2", to preserve the other dimensions.
> > I figured there was little magic to the fuse height (except to result
> > in a little more nose up), but gear position fore/aft is important,
> > along with caster, toe-in, etc. Bonding the gear leg sockets as you
> > describe I think will increase stresses on wood ribs and fuselage. Of
> > course, you can always mitigate that with a panel placard, "Hard
> > Landings Prohibited." :)
> >
> > Regards,
> > Fred F., A063
> >
> > > My trigear gear legs are too short to reach FS 70 and 36.75" off
> midline.
> > >
> > > I've been told some trigear builders have ameliorated this problem by
> > > glassing the bottom flanges of the gear sockets below the belly of the
> > > plane thereby extending the reach of the gear legs towards FS 70.
> > >
> > > I'd like advice from someone who's done that or something similar.
> > >
> > > Also has anyone lowered the gear legs in the sockets a half inch or so
> to
> > > get a longer reach?
> > >
> > > Rob
> > > A162
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