BoeingOnFinal
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Wing Mounting

Sat May 24, 2008 4:12 pm

Long time no thread starting..

I have always wanting to see detailed photos or drawings of how a wing is mounted onto the fuselage, either being a Piper, Boeing or Airbus.

An explanation would also be appreciated, with the particular specifics in mind:
1. How is the spar attached to the fuselage, and how does it fit into the wing (747 spar comes to mind)
2. Smaller aircraft that just use bolt attachment (no strut) must experience quite the moment at it's wing root, any number to present here? (Example could be the C-177 cardinal)
3. How are the duraluminum sheets (or other material used) mounted on the wing ribs? In particular how they are overlapping, sizes of sheets on particular type of A/C and so on..
4. I am currently working on the Mooney M20C questionare to get checked out on this aircraft, and studying the Mooney I came to read that the early productions featured wooden wings. How does this work, does this limit it's structural load factors? How is the wing skin mounted, and what are they made of? And being an educated carpenter myself, I know how flexible wood can be and I couldn't imagine anything else than a reduction in wing loading capacity. What becomes of the fuel storage units? And last, how are the wings mounted onto the fuselage?

I have seen a C-172 without it's wing, how the wing is attached with two bolts and the strut mounting. Any other example to show me? Both pictures or explanations would be appreciated greatly!
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tdscanuck
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RE: Wing Mounting

Sat May 24, 2008 4:42 pm



Quoting BoeingOnFinal (Thread starter):
1. How is the spar attached to the fuselage, and how does it fit into the wing (747 spar comes to mind)

On large airlines, the spars aren't meaningfully attached to the fuselage, they go right through. The center wing box carries the load from one wing to the other. The fuselage is, effectively, "sitting" on the center wing box. There is a very large cutout in the bottom center part of the fuselage to accommodate the wing box and the main landing gear.

The fuselage is attached to the wingbox along the top by frames, which fasten to the upper surface of the wing box, and along the front and back by stringers, which attach to the faces of the front and rear spars.

Quoting BoeingOnFinal (Thread starter):
3. How are the duraluminum sheets (or other material used) mounted on the wing ribs? In particular how they are overlapping, sizes of sheets on particular type of A/C and so on..

Most modern airliner examples I am aware of have stringers either fastened or integrally machined to the inside of the wing skins. The ribs then fasten to the stringers. Skins are butt spliced (not lap spliced) together using a stringer as a splice plate. I believe the wing skins on something like a 747 run the full length of the wing (until cut off by taper) and I think there are three upper and three lower skins on each wing.

Quoting BoeingOnFinal (Thread starter):
4. I am currently working on the Mooney M20C questionare to get checked out on this aircraft, and studying the Mooney I came to read that the early productions featured wooden wings. How does this work, does this limit it's structural load factors? How is the wing skin mounted, and what are they made of? And being an educated carpenter myself, I know how flexible wood can be and I couldn't imagine anything else than a reduction in wing loading capacity.

Wood is more flexible, but not necessarily weaker on a specific weight basis. Wood's actually a pretty good composite design material. For something like a simple box beam, wood can be very competitive. Wood is both weaker and less dense than metal...as a result, you can have similar weight structures in wood and metal but there will be more volume of wood present. Since cross-sectional area plays a much bigger role in structural stiffness and stability than material stiffness, you can end up with a better actual structure. The major thing that cripples wood as an aircraft material is durability and production variance.

Tom.
 
BAE146QT
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RE: Wing Mounting

Sat May 24, 2008 4:50 pm



Quoting Tdscanuck (Reply 1):
Skins are butt spliced (not lap spliced)

I assume this means that they are butted up next to one another, with a rib running underneath them to which they are both attached, (I build models in this fashion). This is opposed to overlapping sheets which might almost look like shiplap? (Forensic photos of the Aloha 737 are the only time I have actually seen such intimate details of aircraft construction).

If so, how are the joints between the panels sealed? Obviously the wing isn't pressurised, but presumably there are aerodynamic considerations?
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SlamClick
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RE: Wing Mounting

Sat May 24, 2008 7:10 pm

How it used to be done:

Not the best view for detail, I guess, but all I could find.

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Photo © Steven Mills
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Photo © Pablo Diez del Corral


The wing and attach points have machined surfaces that mate to carry loads but don't have an actual pin or bolts to secure the wing to center section. Instead, there is an exterior flange, seen just outboard of the engine in the second picture. This flange has 256 bolts on each wing to attach. The bolts are concentrated where the load is - densely concentrated on the underside at around 15-40% of MAC and more widely spaced on the upper surface near the trailing edge.

BTW that was an actual oral question at one operator - how many bolts? Obviously easy to inspect. Just as obviously draggy and subject to rain, mud, and other aids to corrosion. Drag not a big problem at a cruise of maybe 145 knots but still many Dougs had a fairing over the flange, like this one:

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Photo © Erik Frikke

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Starlionblue
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RE: Wing Mounting

Sun May 25, 2008 12:38 am



Quoting Tdscanuck (Reply 1):
Wood is more flexible, but not necessarily weaker on a specific weight basis. Wood's actually a pretty good composite design material. For something like a simple box beam, wood can be very competitive. Wood is both weaker and less dense than metal...as a result, you can have similar weight structures in wood and metal but there will be more volume of wood present.

For a cool wooden aircraft, see the De Havilland Mosquito. And of course my favorite wood composite examp


In the Far East, wooden scaffolding (specifically bamboo) is prevalent. There's some outside my window right now. As Tdscanuck points out it is weaker than steel but also less dense. So you need more structure but the total weight is probably about the same. A good example of using a (for this location) cheaper material to do the same job.



"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
tdscanuck
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RE: Wing Mounting

Sun May 25, 2008 5:04 am



Quoting BAe146QT (Reply 2):
Quoting Tdscanuck (Reply 1):
Skins are butt spliced (not lap spliced)

I assume this means that they are butted up next to one another, with a rib running underneath them to which they are both attached, (I build models in this fashion). This is opposed to overlapping sheets which might almost look like shiplap? (Forensic photos of the Aloha 737 are the only time I have actually seen such intimate details of aircraft construction).

You assume right. A butt splice buts the skins next to each other and runs something (rib, stringer, splice plate, etc.) between them to carry the load across the joint.

Lap joints indeed look like shiplap. Most Boeing's have lap joints on the longitudinal fuselage splices. Lap joints are lighter and, since those ones are parallel to the airflow, there isn't a significant drag penalty. Douglas used butt splices here due to higher durability (neither is right or wrong, it's just a different trade on weight vs. durability). Circumfrential splices (between fuselage sections) are butt splices to maintain the mold line.

Quoting BAe146QT (Reply 2):
If so, how are the joints between the panels sealed? Obviously the wing isn't pressurised, but presumably there are aerodynamic considerations?

With sealant! I'm not being facetious...there is a goop called aerodynamic sealant that's used to fill in fastener heads, fair joints between panels, fill any gap at a splice, etc., etc. It looks kind of like fuel tank sealant, only I think it cures harder.

Wings are actually pressurized a little tiny bit. The fuel system vent usually has a NACA scoop or other structure to provide a slight positive pressure inside the tank.

Tom.
 
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jetmech
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RE: Wing Mounting

Sun May 25, 2008 6:42 am



Quoting Tdscanuck (Reply 5):
With sealant! I'm not being facetious...there is a goop called aerodynamic sealant that's used to fill in fastener heads, fair joints between panels, fill any gap at a splice, etc., etc. It looks kind of like fuel tank sealant, only I think it cures harder.

True, I also vouch for this. We used to use sealant supplied by Courtaulds. There were two basic types as Tds noted, fuel tank sealant, and general purpose sealant used for panel gap filling and the like. Each type came in various sub-grades depending on the curing time.

As with anything aerospace, even the humble old sealant had much technology associated with it. Each tube of sealant came in its own sealed plastic pouch, which according to the blurb, was purged with nitrogen to assure freshness. The tube of sealant itself was wonderfully complex.

All aircraft sealant came as two separate chemicals, which you had to mix prior to use. Each tube of sealant looked somewhat like a small tube of household silicon sealant, except out of the nozzle end, you would find a shaft with a plunger sticking out. The shaft itself was hollow, and contained the hardener chemical.

To mix the two, you had to insert a plastic pusher tube into the hollow plunger shaft, and force the hardener into the second component of the mix. Once that was done, you withdrew the pusher tube and the real fun began. You had to push down and simultaneously twist the external plunger, which via the hollow shaft, pushed and twisted an internal mixing disc inside the main body of the tube.

To properly mix the chemicals, you had to twist and push until the plunger went all the way into the main tube, and then back out again. This was done numerous times until the colour of the mixture appeared to be homogeneous. The final step was to ensure the plunger was all the way in the main body of the tube. You then reversed the direction of twist to disconnect the hollow shaft and plunger from the mixing disc. Once fully unscrewed, you could withdraw the plunger and hollow shaft from the tube of sealant, whence you them screwed in the sealant nozzle.

You could buy a motorised mixed which did all the twisting for you, but you still had to move the tube up and down. The tube of sealant, now mixed and ready to set, fitted into a sealant gun in an arrangement very similar to a household sealant gun / silicon sealant tube arrangement, with one important difference. The ends of the sealant tube where hemispherical, not flat, so you could only use special aerospace sealant guns!

http://www.bergdahl.com/285-A%20Mixer.htm
http://www.bergdahl.com/basemkit.pdf

Regards, JetMech
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tdscanuck
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RE: Wing Mounting

Sun May 25, 2008 7:28 am



Quoting JetMech (Reply 6):
To properly mix the chemicals, you had to twist and push until the plunger went all the way into the main tube, and then back out again. This was done numerous times until the colour of the mixture appeared to be homogeneous.

"Numerous times" is an understatement. If you mix to the instructions (at least on BMS sealants), you'll basically wear out both arms. Not being one to cut a corner, I go to the full count but it sure seems like it was nice and homogenous a *long* time before the instructions let you off the hook.

Tom.
 
BAE146QT
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RE: Wing Mounting

Sun May 25, 2008 1:55 pm

Many Thanks Tom and Jetmech.

Quoting JetMech (Reply 6):
All aircraft sealant came as two separate chemicals, which you had to mix prior to use.

Like an adhesive and an activator? Sounds like an epoxy.
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474218
Posts: 4510
Joined: Mon Oct 10, 2005 12:27 pm

RE: Wing Mounting

Sun May 25, 2008 4:42 pm



Quoting JetMech (Reply 6):
All aircraft sealant came as two separate chemicals, which you had to mix prior to use. Each tube of sealant looked somewhat like a small tube of household silicon sealant, except out of the nozzle end, you would find a shaft with a plunger sticking out. The shaft itself was hollow, and contained the hardener chemical.

While it maybe true the all the aircraft sealant you have used came as two separate chemicals, this is not true. Aircraft production facilities us an enormous amount of sealants so mixing the two part sealants is time consuming and there is the possibility if not mixed sufficiently it will not cure correctly. So the sealant used at the factories comes from the suppliers premixed and frozen. When sealant is required, you just pop a tube in the microwave for a few seconds and it is ready to use.
 
MD11Engineer
Posts: 13916
Joined: Sun Oct 26, 2003 5:25 am

RE: Wing Mounting

Sun May 25, 2008 6:36 pm



Quoting JetMech (Reply 6):
As with anything aerospace, even the humble old sealant had much technology associated with it. Each tube of sealant came in its own sealed plastic pouch, which according to the blurb, was purged with nitrogen to assure freshness. The tube of sealant itself was wonderfully complex.

All aircraft sealant came as two separate chemicals, which you had to mix prior to use. Each tube of sealant looked somewhat like a small tube of household silicon sealant, except out of the nozzle end, you would find a shaft with a plunger sticking out. The shaft itself was hollow, and contained the hardener chemical.

To mix the two, you had to insert a plastic pusher tube into the hollow plunger shaft, and force the hardener into the second component of the mix. Once that was done, you withdrew the pusher tube and the real fun began. You had to push down and simultaneously twist the external plunger, which via the hollow shaft, pushed and twisted an internal mixing disc inside the main body of the tube.

To properly mix the chemicals, you had to twist and push until the plunger went all the way into the main tube, and then back out again. This was done numerous times until the colour of the mixture appeared to be homogeneous. The final step was to ensure the plunger was all the way in the main body of the tube. You then reversed the direction of twist to disconnect the hollow shaft and plunger from the mixing disc. Once fully unscrewed, you could withdraw the plunger and hollow shaft from the tube of sealant, whence you them screwed in the sealant nozzle.

You could buy a motorised mixed which did all the twisting for you, but you still had to move the tube up and down. The tube of sealant, now mixed and ready to set, fitted into a sealant gun in an arrangement very similar to a household sealant gun / silicon sealant tube arrangement, with one important difference. The ends of the sealant tube where hemispherical, not flat, so you could only use special aerospace sealant guns!

http://www.bergdahl.com/285-A%20Mixer.htm
http://www.bergdahl.com/basemkit.pdf

One reason why those Semkit tubes are being used is that many aircraft sealants are quite toxic and cancerogenous (containing chromates as corrosion inhibitor). The ready-to-mix tubes have the advantages that contact with the skin, if handled properly, is quite unlikely and that the ratios of the two components is clearly defined. Before the sealants and catalyst came in seperate tins and had to be mixed according to weight, making quite a mess and also the ratio wasn't always exact.


Quoting Tdscanuck (Reply 7):
Quoting JetMech (Reply 6):
To properly mix the chemicals, you had to twist and push until the plunger went all the way into the main tube, and then back out again. This was done numerous times until the colour of the mixture appeared to be homogeneous.

"Numerous times" is an understatement. If you mix to the instructions (at least on BMS sealants), you'll basically wear out both arms. Not being one to cut a corner, I go to the full count but it sure seems like it was nice and homogenous a *long* time before the instructions let you off the hook.

Tom.

During my apprenticeship I once had to scrape out a looong sealing joint, which didn't cure properly (still soft next day). Since then I always give a tube of sealant 80 strokes.

Jan
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tdscanuck
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RE: Wing Mounting

Sun May 25, 2008 7:35 pm



Quoting BAe146QT (Reply 8):
Like an adhesive and an activator? Sounds like an epoxy.

Similar concept, different chemistry. The activator kicks off the reaction that binds the molecules together. In expoy, I think it's a polymerization reaction. In sealant, I think it's a vulcanization reaction, or something like it (sulpher bonding between adjacent molecules.)

Quoting 474218 (Reply 9):
While it maybe true the all the aircraft sealant you have used came as two separate chemicals, this is not true. Aircraft production facilities us an enormous amount of sealants so mixing the two part sealants is time consuming and there is the possibility if not mixed sufficiently it will not cure correctly. So the sealant used at the factories comes from the suppliers premixed and frozen. When sealant is required, you just pop a tube in the microwave for a few seconds and it is ready to use.

I think the premix stuff is chemically the same, the reaction just gets so slow while it's frozen that it doesn't set in a normal time frame. I think this is why the frozen stuff has an expiration date, like prepreg.

Tom.
 
474218
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RE: Wing Mounting

Sun May 25, 2008 10:23 pm



Quoting Tdscanuck (Reply 11):
I think the premix stuff is chemically the same, the reaction just gets so slow while it's frozen that it doesn't set in a normal time frame. I think this is why the frozen stuff has an expiration date, like prepreg.

Correct.

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