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Lift pins



 
 
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  #1  
Old July 25th 19, 12:33 AM posted to rec.aviation.soaring
jp
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Default Lift pins

I have not yet found a description of "lift pins" that I understand but they apparently are pretty important.

Can someone please tell me what lift pins are?
  #2  
Old July 25th 19, 01:00 AM posted to rec.aviation.soaring
[email protected]
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Default Lift pins

If you try and fly without your Lift Pins, you won’t find ANY LIFT!
;) JJ
Actually, the 4 lift pins attach the wings to the fuselage............rather important, I’d say!
  #3  
Old July 25th 19, 01:09 AM posted to rec.aviation.soaring
Tony[_5_]
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Default Lift pins

Yea they are the pins that the fuselage hangs off of.
  #4  
Old July 25th 19, 01:24 AM posted to rec.aviation.soaring
Scott Williams
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Default Lift pins

On Wednesday, July 24, 2019 at 7:09:32 PM UTC-5, Tony wrote:
Yea they are the pins that the fuselage hangs off of.


I'll bet they look a lot like SSA Diamond pins:-)
  #5  
Old July 25th 19, 03:36 AM posted to rec.aviation.soaring
[email protected]
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Default Lift pins

OK- nobody really gave a decent description of the lift pins, so I will give it a try.

Your wings are held together inside the fuselage by large composite spars, either with an interlocking fork and tongue and dual main spar pins (like Schleicher) which carry the load of the glider in flight, or a fore/aft spar arrangement with one main pin, generally located at the center of the spar junction, in the middle of the fuselage. The carry-through load is handled by pins extending through the ends of the spar stub that fit into sockets at the root of each wing. This is a characteristic of Schempp-Hirth gliders..

Both design methods have been utilized by other manufacturers. Interestingly, Jonker Sailplanes use the two main pin configuration on the JS-1, while the single pin and lateral spar pin/socket design is used on the new JS-3.

Now, the lift pins. Since the main spar is designed to carry the load of the aircraft laterally, there must be a way to constrain the wing and keep it in horizontal alignment with the fuselage. This is handled by the pins extending from the fuselage ahead of and behind the main spar. (Although Jonker prefers to have the pins extending from the root rib and fitting into sockets in the fuselage.)

Essentially, the lift pins keep the wing in proper alignment relative to the fuselage while in flight, while the spars and their retaining pin(s) hold the wing together and carry the load of the aircraft.
  #6  
Old July 25th 19, 06:23 AM posted to rec.aviation.soaring
Surge
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Default Lift pins

On Thursday, 25 July 2019 04:36:26 UTC+2, wrote:
Essentially, the lift pins keep the wing in proper alignment relative to the fuselage while in flight, while the spars and their retaining pin(s) hold the wing together and carry the load of the aircraft.



I'm not an expert but I thought the lift pins (for and aft pins at wing/fuse junction) carry the full load of the fuselage on gliders. They're not there just for keeping things aligned.

That is certainly the case on my Nimbus 2 where the main spar is joined and secured with a main pin but can still essentially float around in the fuselage if it were not for the lift pins on the wings.
Hence the name "lift pins" - they carry the fuselage load.
  #7  
Old July 25th 19, 08:19 AM posted to rec.aviation.soaring
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Default Lift pins

"while the spars and their retaining pin(s) hold the wing together and carry the load of the aircraft."....and transfer this load to the fuselage by AIR!!
  #8  
Old July 25th 19, 01:00 PM posted to rec.aviation.soaring
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Default Lift pins

That is certainly the case on my Nimbus 2 where the main spar is joined and secured with a main pin but can still essentially float around in the fuselage if it were not for the lift pins on the wings.
Hence the name "lift pins" - they carry the fuselage load.


Yes, I guess that's probably more correct, as the lift pins are mounted to the internal structure of the glider. (Generally, a steel tube cage that incorporates the landing gear and all other structural components.) The spar carry-through hole is primarily surrounded by composite structure only.

My bad.

  #9  
Old July 26th 19, 02:25 AM posted to rec.aviation.soaring
Sky Surfer
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Default Lift pins

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*
  #10  
Old July 26th 19, 02:50 AM posted to rec.aviation.soaring
Bob Kuykendall
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Default Lift pins

On Thursday, July 25, 2019 at 6:25:44 PM UTC-7, Sky Surfer wrote:

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?


That is indeed the case for the vast majority of modern high-performance sailplanes, including the ones I design and make parts for. I have an hour-long sermon about the why of it, but it boils down to performance. The best overall performance is achieved by optimizing the performance of the infrastructure/sailplane/pilot system as a whole, and not just the performance of the sailplane itself.

Isolating the spars from the fuselage incurs a modest weight penalty in exchange for simplified assembly with fewer opportunities for misalignment or misassembly. The payoff is less fatigue accrued during pre-flight phases and more energy available for in-flight strategy and tactics.

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*


There may be such out there, but they must be pretty rare because I almost never see them in modern sailplanes.

--Bob K.
 




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