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Old June 27th 19, 01:01 PM posted to rec.aviation.homebuilt
BobW
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Posts: 504
Default Sailplane wing joint

On 6/26/2019 7:21 PM, Sky Surfer wrote:
Thanks for the response, Bob W. As a new poster, I did notice the
spammers' infestation of this forum, which I thought was really informative
when it was more active. Just wondering if the spammers or a decline in
amateur aircraft homebuilding is more responsible for this site's near
demise.


Interesting question to ponder,,,but I have no idea!
- - - - - -

At about the time I posted, Jim M. replied to my email. He said, "why
throw other unknown forces into a joint when you don't have to", which
mirrors what you said. That reasoning does help my understanding.


Difficult to get more succinct than that! "What Jim M. said," is what I had in
mind, too.
- - - - - -

Though, I'm picturing the Schreder wing spar "knuckles" joint where one of
the connecting pins goes through the knuckles AND an anchor tab welded to
the midpoint of fuselage cross tube. I guess that anchor mostly aligns the
knuckles for rigging and maybe makes the spar joint a little less
"plastic". Spar knuckles and tongues are different, but spar movement near
the fuselage centerline exist in both geometries.


I don't remember the HP-14 I had having a centerline anchor tab. In fact, I
can't remember the details of its fuselage center structure at ALL...just the
configuration of the top/bottom/longitudinally-oriented knuckles and their
"overly-long" (unsafetied!) pins. Dick Schreder's reasoning was there were no
in-flight fore/aft forces on them. I marked/taped 'em just to keep an eye on
Murphy! They never moved...though data/incidents/crashes exist in the
composite sailplane world - whose pins are generally NOT "overly-long" -
strongly suggesting (to me, anyway) that Murphy/repeated-spar-movement can do
wondrous things...

By the way, I expect you caught a misstatement I made about the Zuni's
spar-end pins. Each goes into a receptacle in the opposite spar's wing root
rib, not into the fuselage structure...as in it's possible to
completely-structurally-rig the wings without the presence of the fuselage.

Bob W.

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