Lift pins

Salto? I think it's spars pin into a fuselage fitting.

What about Diana 2? I know the stubs stick out the fuselage and the wings have sockets. Don't know how it pins.

I think the goal of the wings only touching at the lift pins simplifies the design's engineering. As things expand, contract, and flex there are fewer places where the forces are transferred.

I've always first explained glider assembly to new folks as the assembled wings are a structure all themselves that happen to get assembled passing thru the fuselage. Then mention the 4 pins hanging either the fuselage or wings depending
if flying or on the ground.

On Thursday, July 25, 2019 at 7:25:44 PM UTC-6, Sky Surfer wrote:
FWIW:Â* Jim Marske's Composite Design Manual, page F7, says of the lift/dagger pins, "There are four such pins located near the leading edge and rear spar (or trailing edge).Â* These four pins transmit all loads from the wing to the fuselage.Â* The main spar does not touch the fuselage structure anywhere."

Having seen (mostly from afar) plug-in wing spar tongues that are pinned together in the fuselage, that last sentence about the joined main spar not touching anything surprised me.Â* I wish I could look at many fiberglass gliders to see if the industry "standard" (if there's such a thing) is to float the joined spar freely accross the fuselage, but I don't have that ability.Â* So I emailed Jim about the importance of isolating the spar tongues from any fuselage structure.Â* He answered, "I once wondered about the same thing.Â* Why is the main spar suspended freely across the fuselage?Â* The spar is quite flexible - even across the fuselage, especially at the fuselage CL.Â* So my conclusion was, why throw other unknown forces into a joint when you don't have to.Â* However, motion near the fuselage side rails is quite small as it is close to the dagger pins so you may get away with it.Â* Don't fasten the spar to the fuselage on the fuselage centerline."

That all sounds reasonable.Â* So I'd like to ask the knowledgeable folks on this forum:Â* Is it true that the main spar tongues are pinned only to themselves and maybe to the opposite wing root, but they don't touch anything else in the fuselage?Â* Are there notable exceptions, like spar pins passing through not only the spar tongues but also through a fuselage bulkhead?Â* How about spar tongues that are pushed into a joining box or tunnel?Â* That would be the antithesis of isolating the main spar.Â* These are different but related questions to the original lift pins question.Â*Â*Â*

On the Phoebus (1st fiberglass production glider), the pin goes through the spar of both wings at the centerline, but also through the bulkhead behind the pilot's head. But this isn't a structural connection to the fuselage though, I don't think. The main connection is through the lift pins, even on this early model. And the wing is VERY stiff, so not much flex at all.

On Fri, 26 Jul 2019 10:39:48 -0700, John Foster wrote:

On the Phoebus (1st fiberglass production glider), the pin goes through
the spar of both wings at the centerline, but also through the bulkhead
behind the pilot's head. But this isn't a structural connection to the
fuselage though, I don't think. The main connection is through the lift
pins, even on this early model. And the wing is VERY stiff, so not much
flex at all.

Sailplanes 1945-1965 by Martin Symonds says that the Phoebus was closely
based on the Phonix (the first glass glider) and has a good drawing of
the wing mount (page 253).

This shows sharply tapered wing stubs that fit into a close fitting
structure built into the fuselage. The wings were pulled together by a
single, double-threaded bolt with opposite threads on each end and driven
by a (hex?) flange in the center. The axis of this is at right angles to
the fuselage centre line, so rotating it pulls the wings together and the
stubs into close contact with the matching fuselage structure.

There are two lift pins on each side of fuselage, which appear to lock
into the wing stub support structure. The pins project outwards to fit
into sockets on the root ribs.


--
Martin | martin at
Gregorie | gregorie dot org

On Friday, July 26, 2019 at 1:11:43 PM UTC-6, Martin Gregorie wrote:
On Fri, 26 Jul 2019 10:39:48 -0700, John Foster wrote:

On the Phoebus (1st fiberglass production glider), the pin goes through
the spar of both wings at the centerline, but also through the bulkhead
behind the pilot's head. But this isn't a structural connection to the
fuselage though, I don't think. The main connection is through the lift
pins, even on this early model. And the wing is VERY stiff, so not much
flex at all.

Sailplanes 1945-1965 by Martin Symonds says that the Phoebus was closely
based on the Phonix (the first glass glider) and has a good drawing of
the wing mount (page 253).

This shows sharply tapered wing stubs that fit into a close fitting
structure built into the fuselage. The wings were pulled together by a
single, double-threaded bolt with opposite threads on each end and driven
by a (hex?) flange in the center. The axis of this is at right angles to
the fuselage centre line, so rotating it pulls the wings together and the
stubs into close contact with the matching fuselage structure.

There are two lift pins on each side of fuselage, which appear to lock
into the wing stub support structure. The pins project outwards to fit
into sockets on the root ribs.


--
Martin | martin at
Gregorie | gregorie dot org

The Phoebus does not have this "feature". The tips of the spars have pins that mate to bracket holes in the wing root rib of the opposite wing. The left spar is forked and the right spar is a single tapered spar that fits between the forks of the L wing spar. Then there is a single pin that goes through all three and holds them together. The wing root ribs also mate to two lift pins on each side of the fuselage.

What is interesting/fascinating to me is that the fuselage is hanging from the root ribs (via the lift pins) only. That means the entire load of the fuselage, pilot (times 7.5G design loads) are being restrained by the root ribs (one rib per side). I'm just amazed what little material is there to transfer the loads to the rest of the wing structure. I would expect those poor ribs to be ripped out of the wing at high G loads. But alas they don't.. Pretty amazing design actually.

Dirk,
Those are not,�poor little root ribs�, in fact the designers have reinforced them with several layers of cloth running from the spars deep into the root ribs on both sides of the spar, so that they will transfer the fuselage load into the wings.
JJ

On Friday, July 26, 2019 at 5:50:02 PM UTC-4, wrote:
Dirk,
Those are not,�poor little root ribs�, in fact the designers have reinforced them with several layers of cloth running from the spars deep into the root ribs on both sides of the spar, so that they will transfer the fuselage load into the wings.
JJ

Wing skins also play a meaningful part in handling the loads.
UH

Interesting discussion.Â* Another question for Bob K. and other experts:Â* If you saw crosswise (cross section) through a typical sailplane's main spar tongue/stub what would it look like?Â* Mostly foam surrounded by many layers of fiberglass?Â* About how much glass versus foam?Â* Just trying to envision a vital structural component that most of us take for granted and never see the inside of unless one is a designer or fabricator.

On Saturday, July 27, 2019 at 1:02:23 AM UTC-4, Sky Surfer wrote:
Interesting discussion.Â* Another question for Bob K. and other experts:Â* If you saw crosswise (cross section) through a typical sailplane's main spar tongue/stub what would it look like?Â* Mostly foam surrounded by many layers of fiberglass?Â* About how much glass versus foam?Â* Just trying to envision a vital structural component that most of us take for granted and never see the inside of unless one is a designer or fabricator.

Two very strong beams(caps) at the top and bottom to handle tension and compression. Fillers(spacers?) between that handle the shear loads between the caps and also provide for strong pins that handle bending loads on many ships like Schleicher. Others(the "Glasflugel method) use pins on the ends of the spars that plug into sockets on the root rib of the opposite wing to handle bending.
In all cases there are many plies of cloth to tie the 2 webs together and handle shear loads. The "spacers" are commonly plywood or solid fiberglass for portions of high(pin)loads, and foam for the balance. Shear layers are most commonly glass.
UH