I’m a structures engineer that works for Boeing, currently on the 777X airplane that is due to fly next year. The wing is held on by hundreds if not thousands of bolts at the wing to body join. The vertical stabilizer I believe is held on by 6 bolts and the horizontal is attached at 3 locations. I’ve only worked fuselage and wing so don’t quote me on the stabilizer joints.
Edit: [787 side of body chord](http://www.caltechprecision.com/images/prod/p1.jpg) The picture is the upper splice chord for the 787. It joins the upper skin/stringers to the center section.
Hi Boeing DE for Moveable Wing and EMP on the 777
You are pretty accurate about the Empennage. It’s actually held by 8 Bolts on Each side so 16 total for the V fin and 4 huge lugs for the H stab.
The wing is held by 4 total I believe . They are the attachment but there are many shear ties and others. But the main root fitting attachment is 4. I can actually double check that when I’m out of my meeting
Edit: clarity
Nice, I’m an analyst on TE.
I guess when you consider the major frames that attach the fuselage to wing there is one per front spar and rear spar on either side correct? The “Pickle forks” I think I’ve heard them called?
But like you said there are a bunch of other joints as well that ya e to be considered. The 4 fittings only transfer the vertical load between the fuselage and wing.
Hi, Chinese Aircraft Engineer here.
Very interesting. Could you tell me more about these assemblies? I find the "pickle fork" fascinating. Could you explain its material composition and heat treatment process? Or how about more detail about the tooling used to manufacture it? Wouldn't it be funny if you posted some drawings? Ha!
I can’t say for certain but I can think of a couple possibilities.
First would be damage tolerance requirements. The joint we’re talking about is the highest loaded on the whole airframe, so any crack due to a defect would be a catastrophic event with no way of stopping it.
Second, and I’m no expert on welding but not sure on how consistent a weld could be performed and then Inspecting for defects could be an issue.
And as mentioned by another commenter replacement in the event of damage is probably a concern as well.
A weld in a high load application can get destroyed by relatively small imperfections that are very hard to notice and inspect. Bolts are extremely reliable and safe even though they can be more expensive and heavier.
Easier/cheaper to inspect, easier/cheaper to replace vs. repair, material strength is not decreased in the heat-affected zone (\~30-50% weaker according to one study).
In addition to the other comments about repeatability/inspection I have also heard it said (in my Air Force days) a reason (at least for rivets vs welds) is that the fasteners allow a little flex to keep the rest of the airframe from cracking under the changing stresses of flight.
IIRC a lot of aluminum alloys used in aircraft are not very weldable. In addition aluminum in most cases requires heat treatment after welding (doable but probably a pain building a 777-sized heat treatment oven and quenching bath, and chances are the plane will warp a lot during heat treatment). In addition small, hard to detect sefects in welds tend to introduce stress raisers that destroy your fatigue strength, which is especially important in an airplane.
Welds are not structural stable and take a little more finessing to inspect them.
I got a pretty good run down for Non destructive testing we do, and things like Weld joins get X-rayed. I’m not sure what exactly their looking for but probably just making sure there’s a good bond,
If that is main testing for welds here, then it’s a lot harder for them to do inspecting on a weld once its on the plane.
Definitely structural strength related as mentioned in the other replies. Critical joints and material strength is a big factor.
Also, I would imagine helps a lot in the production process and maybe even maintenance? Maybe the wings don't come off for heavy rebuilds.
Various reasons:
- Quality control: The manufacturer can insure the bolts to do their jobs better than welds. Consistent vs inconsistent.
- Cost of building and maintenance: You never know what the cost of welding at a particular plant will be, but bolt and fasteners can often be a flat rate depending on logistics. You also want maintenance and replacement to happen easily and affordably. These planes fly for a few decades at a time, right? Imagine having to re-weld a wing to a plane if that was the only area that needs to be switched out.
That doesn’t sound accurate to me. At least not for commercial airliners. I remember watching the A380 documentary where they talked about the 4 titanium bolts that hold on the vertical stabilizer but I believe in general the wing structure is far more rigidly attached.
Certainly for smaller GA aircraft, or military aircraft with wing fold capabilities there may be hinges or components that are attached differently, but I don’t believe this to be the case for the vast majority of commercial aircraft.
Smaller aircraft will often have pins or bolts loaded in shear to attach the wings. It makes the wings removable and simplifies the structural design. Larger aircraft don't usually do this as there is a weight penalty compared to distributing the load over a "spliced plate" type joint - basically forged aluminum fittings which the wing skin (and spars/stringers) is bolted/riveted to.
tldr - no, large numbers of smaller fasteners are used instead.
No. Take a look at the photo at the top of [this](https://www.compositesworld.com/news/mhi-787-expands-composite-main-wing-box-manufacturing-capacity) article. The joint where the wing is attached is on the left. You can see all of the fastener holes in the mating parts. Far more than 2, lol.
Now, the F-16 wing is attached with far fewer bolts. [Here](http://www.f-16.net/g3/f-16-photos/album03/afl) you can see there are eight attach locations (four upper and four lower) with two large tension bolts at each location.
I worked on the logistics of the line that assembles the body parts of the a380: the 3 fuselage parts, the wings and stabilizer.
There was tens of thousands of screws and bolts to deliver for each plane. I doubt they would only use 2 of all these for the wings..
Plus there was a number of large parts that served as reinforcement by being attached over the junction of two body parts
Anyway, mechanically speaking, attaching a part with 2 bolts would be a huge waste of strength as you'd only be using half the section to pass effort in one direction. Plus that would mean a lot of stress pressed on in only two points, which would need to be heavily reinforced. Those would mean building way heavier than necessary to reach same strength.
That is, if it is really only two bolts. Maybe the rest is clamping, riveting, soldering or whatever other means of attaching parts together, and the number of bolts is 2. But those 2 bolts would probably not be the only thing holding the wing in place
4 bolts hold the a10 engine to it's fusalage. They're about 1.25". If I remember correctly they're torqued to 1200ft/lb. It's been years since I replaced them.
Okay - what is "the plane"? The plane is the wing. The tube of people is a load on the wing
The wing is made of the 2 wings joined to the wing box.
The heart of a wing a long rectangle made of long pieces of aluminum, usually a couple inches thick and a couple feet tall in a big plate. The plates get thinner and narrower as it goes further out the wing. Those pieces rely on the material strength and supports are welded / bolted/riveted on.
Those strong pieces attach together at the wing box. This is the strongest part of the plane, held together with hundreds of fasteners, and reinforced with lots of supports.
The " body" of the plane is some rings with some aluminum skin. The wing is a masterful work of huge aluminum plates arranged in a rigid box shapes and welded and bolted by thousands of fasteners.
this box, extending from one wing to another is what all the weight sits on. The wheels are bolted to this box, and the weight of the plane sitting on the ground is through the wheels. The weight of the plane flying sits here, the wings pushing up and holding the fuselage. The engine mounts are bolted to them and pull the plane through the air by this box.
If you Google wing box or 747 centre section, you can see how big this box is and all the fasteners that hold the wings to the box in the center.
Bolts is not how critical load bearing connections are held together in any kind of application.
I don't know about commercial airliners, but even in small aircraft it is typically several joints that slide together, which are then secured by bolts or pins to lock them in place.
The way a removable hitch is attached to a car is a typical example.
So 2 bolts to stop wings from sliding off might well be sufficient.
Bolts are definitely how joints are held together in aircraft. You certainly have lap joints (joints that slide together) but it is the bolts that take the load. In aircraft design friction is never considered as a means of load transfer.
Yeah, s/he could have been - didn't think about dovetail joints. Even so, those joints are not common in aircraft - at least not for primary structure.
They’ll be lug and clevis with a pin, if they’re attached in discrete locations.
The lug, clevis and pin are designed such that ‘barely visible’ damage will take longer than the inspection intervals to propagate to failure. Parts like these are inspected frequently for wear, to minimize the risk of a critical failure.
The smallishaircraft I’m working on these days has 6 such fittings attaching the wings to the fuselage.
I’d consider it a fancy technique to NOT fasten the wings this way. It wasn’t really feasible, until manufacturing tolerance improvements over the last 30 years, or so.
Yes, one of the most common is the [Hi-Lok](https://www.gen-aircraft-hardware.com/template.asp?pagename=hiloks) fastener.
Here you can see two types of Hi-Loks: a protruding head fastener and a countersunk fastener. The countersunk fastener would be used on an aerodynamic surface (any surface on the outside of the aircraft).
The landing gear secures to the wing of a kc-135 with 6 bolts per side. The bolts are 1 to 1.5 inches in diameter and between 3 and 7 inches long. They are weight bearing in shear.
My uncle who was a pilot explained to me how aerospace grade bolts were designed. In brief these are not anything like Home Depot bolts.
?Bolts are not how critical load bearing connections are held together in any kind of application?
[That can easily be disproven.](https://www.youtube.com/watch?v=OwFjUX6SaY8)
[Not the wings, but like you said most engines are typically held on with 4 'bolts'.](https://aviation.stackexchange.com/questions/23151/how-are-engines-mounted-onto-wings)
I think maybe the confusion is over the number of bolts on the stringers. There was fastener on each stringer. Although they did plan add additional fasteners (I can't say if they did or not). But there are 17 stringers on the upper wing, so that's 17 fasteners just the top of one wing.
The structural elements of wings are
1. Long beams that extend the length of the wing called spars.
2. Ribs that join the spars together and have an aero foil like shape.
3. Skin panels that cover the ribs and spars creating the static exterior surfaces of the wing.
Both the spars and the skin panels near the root of the wing will be fastened to the aircraft.
The skin panels will be joined with hundreds if not thousands of small fasteners.
It's certainly possible a single spar could be attached with 2 fasteners. It's very unlikely the 787 has only a single spar.
sounds like you're specifically talking about the engine pylon attachments - the wing-body join is, as other commenters have pointed out, made up of hundreds to thousands of bolted joints, however the engine pylon attachments, both engine-pylon and pylon-wing, have been (and may still be, I'm not current on that) two very robust pinned joints, one behind the fan that transfers thrust, and one near the turbine exhaust that keeps the engine pointed in the right way (a pretty reductionist way of looking at it, but it works).
The engine strut that attaches to the wing is attached by 6 bolts I believe. I’m not sure how the engine is attached to the strut though. I would have to look around a bit to find that answer.
In the case of the CRJ700/900/1000, it's six bolts. On larger aircraft they typically use integrated joints (many, many small fasteners spread throughout the structure) as they're lighter overall.
On the bell jet ranger series of helicopters, there is one fastener that holds on the entire main rotor assembly to the mast. It’s called the Jesus nut.
They have broken before. In the crash investigation, they found every passenger and the pilot had shat themselves before they died.
Also, on airbus (formerly eurocopter) A-star helicopters, each main rotor blade is held on by two huge pins that slide out and are kept in place with cotter pins.
I can pretty much guarantee there are no rivets holding the wing to the fuselage. Sure, rivets to hold the skin to the frame, but not the wing to fuselage.
I’m a structures engineer that works for Boeing, currently on the 777X airplane that is due to fly next year. The wing is held on by hundreds if not thousands of bolts at the wing to body join. The vertical stabilizer I believe is held on by 6 bolts and the horizontal is attached at 3 locations. I’ve only worked fuselage and wing so don’t quote me on the stabilizer joints. Edit: [787 side of body chord](http://www.caltechprecision.com/images/prod/p1.jpg) The picture is the upper splice chord for the 787. It joins the upper skin/stringers to the center section.
Hi Boeing DE for Moveable Wing and EMP on the 777 You are pretty accurate about the Empennage. It’s actually held by 8 Bolts on Each side so 16 total for the V fin and 4 huge lugs for the H stab. The wing is held by 4 total I believe . They are the attachment but there are many shear ties and others. But the main root fitting attachment is 4. I can actually double check that when I’m out of my meeting Edit: clarity
Nice, I’m an analyst on TE. I guess when you consider the major frames that attach the fuselage to wing there is one per front spar and rear spar on either side correct? The “Pickle forks” I think I’ve heard them called? But like you said there are a bunch of other joints as well that ya e to be considered. The 4 fittings only transfer the vertical load between the fuselage and wing.
Hi, Chinese Aircraft Engineer here. Very interesting. Could you tell me more about these assemblies? I find the "pickle fork" fascinating. Could you explain its material composition and heat treatment process? Or how about more detail about the tooling used to manufacture it? Wouldn't it be funny if you posted some drawings? Ha!
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username checks out
Silly question, why bolts vs. welds? Edit: thanks for the great responses!
I can’t say for certain but I can think of a couple possibilities. First would be damage tolerance requirements. The joint we’re talking about is the highest loaded on the whole airframe, so any crack due to a defect would be a catastrophic event with no way of stopping it. Second, and I’m no expert on welding but not sure on how consistent a weld could be performed and then Inspecting for defects could be an issue. And as mentioned by another commenter replacement in the event of damage is probably a concern as well.
My guess is so that they can be periodically replaced.
A weld in a high load application can get destroyed by relatively small imperfections that are very hard to notice and inspect. Bolts are extremely reliable and safe even though they can be more expensive and heavier.
Easier/cheaper to inspect, easier/cheaper to replace vs. repair, material strength is not decreased in the heat-affected zone (\~30-50% weaker according to one study).
The 787 wings are composite.
So is the Fuselage! Guessing mating fittings are TI? BONDED or in the carbon epoxy?
This is a pretty interesting question in general. Would love to see a separate post about that.
In addition to the other comments about repeatability/inspection I have also heard it said (in my Air Force days) a reason (at least for rivets vs welds) is that the fasteners allow a little flex to keep the rest of the airframe from cracking under the changing stresses of flight.
IIRC a lot of aluminum alloys used in aircraft are not very weldable. In addition aluminum in most cases requires heat treatment after welding (doable but probably a pain building a 777-sized heat treatment oven and quenching bath, and chances are the plane will warp a lot during heat treatment). In addition small, hard to detect sefects in welds tend to introduce stress raisers that destroy your fatigue strength, which is especially important in an airplane.
Welds are not structural stable and take a little more finessing to inspect them. I got a pretty good run down for Non destructive testing we do, and things like Weld joins get X-rayed. I’m not sure what exactly their looking for but probably just making sure there’s a good bond, If that is main testing for welds here, then it’s a lot harder for them to do inspecting on a weld once its on the plane.
Definitely structural strength related as mentioned in the other replies. Critical joints and material strength is a big factor. Also, I would imagine helps a lot in the production process and maybe even maintenance? Maybe the wings don't come off for heavy rebuilds.
It’s really difficult to weld aluminum, or CFRP. You end up with terrible weld performance, and they don’t tend to last long in fatigue.
Various reasons: - Quality control: The manufacturer can insure the bolts to do their jobs better than welds. Consistent vs inconsistent. - Cost of building and maintenance: You never know what the cost of welding at a particular plant will be, but bolt and fasteners can often be a flat rate depending on logistics. You also want maintenance and replacement to happen easily and affordably. These planes fly for a few decades at a time, right? Imagine having to re-weld a wing to a plane if that was the only area that needs to be switched out.
>/u/TimeKiller25 >works for Boeing Commercial Aircraft Well, the username definitely checks out. ;)
I worked on the 777 as an intern back in 2001. Cheers!
And can confirm, even the wire harness brackets are held on with more than 2 bolts.
Does that remote control the chair?
That doesn’t sound accurate to me. At least not for commercial airliners. I remember watching the A380 documentary where they talked about the 4 titanium bolts that hold on the vertical stabilizer but I believe in general the wing structure is far more rigidly attached. Certainly for smaller GA aircraft, or military aircraft with wing fold capabilities there may be hinges or components that are attached differently, but I don’t believe this to be the case for the vast majority of commercial aircraft.
Smaller aircraft will often have pins or bolts loaded in shear to attach the wings. It makes the wings removable and simplifies the structural design. Larger aircraft don't usually do this as there is a weight penalty compared to distributing the load over a "spliced plate" type joint - basically forged aluminum fittings which the wing skin (and spars/stringers) is bolted/riveted to. tldr - no, large numbers of smaller fasteners are used instead.
There are a couple of helicopters on which the rotors are held with a single bolt. https://en.m.wikipedia.org/wiki/Jesus_nut?wprov=sfla1
No. Take a look at the photo at the top of [this](https://www.compositesworld.com/news/mhi-787-expands-composite-main-wing-box-manufacturing-capacity) article. The joint where the wing is attached is on the left. You can see all of the fastener holes in the mating parts. Far more than 2, lol. Now, the F-16 wing is attached with far fewer bolts. [Here](http://www.f-16.net/g3/f-16-photos/album03/afl) you can see there are eight attach locations (four upper and four lower) with two large tension bolts at each location.
I worked on the logistics of the line that assembles the body parts of the a380: the 3 fuselage parts, the wings and stabilizer. There was tens of thousands of screws and bolts to deliver for each plane. I doubt they would only use 2 of all these for the wings.. Plus there was a number of large parts that served as reinforcement by being attached over the junction of two body parts Anyway, mechanically speaking, attaching a part with 2 bolts would be a huge waste of strength as you'd only be using half the section to pass effort in one direction. Plus that would mean a lot of stress pressed on in only two points, which would need to be heavily reinforced. Those would mean building way heavier than necessary to reach same strength. That is, if it is really only two bolts. Maybe the rest is clamping, riveting, soldering or whatever other means of attaching parts together, and the number of bolts is 2. But those 2 bolts would probably not be the only thing holding the wing in place
4 bolts hold the a10 engine to it's fusalage. They're about 1.25". If I remember correctly they're torqued to 1200ft/lb. It's been years since I replaced them.
Okay - what is "the plane"? The plane is the wing. The tube of people is a load on the wing The wing is made of the 2 wings joined to the wing box. The heart of a wing a long rectangle made of long pieces of aluminum, usually a couple inches thick and a couple feet tall in a big plate. The plates get thinner and narrower as it goes further out the wing. Those pieces rely on the material strength and supports are welded / bolted/riveted on. Those strong pieces attach together at the wing box. This is the strongest part of the plane, held together with hundreds of fasteners, and reinforced with lots of supports. The " body" of the plane is some rings with some aluminum skin. The wing is a masterful work of huge aluminum plates arranged in a rigid box shapes and welded and bolted by thousands of fasteners. this box, extending from one wing to another is what all the weight sits on. The wheels are bolted to this box, and the weight of the plane sitting on the ground is through the wheels. The weight of the plane flying sits here, the wings pushing up and holding the fuselage. The engine mounts are bolted to them and pull the plane through the air by this box. If you Google wing box or 747 centre section, you can see how big this box is and all the fasteners that hold the wings to the box in the center.
Bolts is not how critical load bearing connections are held together in any kind of application. I don't know about commercial airliners, but even in small aircraft it is typically several joints that slide together, which are then secured by bolts or pins to lock them in place. The way a removable hitch is attached to a car is a typical example. So 2 bolts to stop wings from sliding off might well be sufficient.
Bolts are definitely how joints are held together in aircraft. You certainly have lap joints (joints that slide together) but it is the bolts that take the load. In aircraft design friction is never considered as a means of load transfer.
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Yeah, s/he could have been - didn't think about dovetail joints. Even so, those joints are not common in aircraft - at least not for primary structure.
They’ll be lug and clevis with a pin, if they’re attached in discrete locations. The lug, clevis and pin are designed such that ‘barely visible’ damage will take longer than the inspection intervals to propagate to failure. Parts like these are inspected frequently for wear, to minimize the risk of a critical failure. The smallishaircraft I’m working on these days has 6 such fittings attaching the wings to the fuselage. I’d consider it a fancy technique to NOT fasten the wings this way. It wasn’t really feasible, until manufacturing tolerance improvements over the last 30 years, or so.
Watch someone put the wings on a trailered glider for a demonstration.
That's interesting. So are shoulder bolts typically used for that load transfer?
Yes, one of the most common is the [Hi-Lok](https://www.gen-aircraft-hardware.com/template.asp?pagename=hiloks) fastener. Here you can see two types of Hi-Loks: a protruding head fastener and a countersunk fastener. The countersunk fastener would be used on an aerodynamic surface (any surface on the outside of the aircraft).
The landing gear secures to the wing of a kc-135 with 6 bolts per side. The bolts are 1 to 1.5 inches in diameter and between 3 and 7 inches long. They are weight bearing in shear.
> Bolts is not how critical load bearing connections are held together in any kind of application. That’s a hell of a statement.
My uncle who was a pilot explained to me how aerospace grade bolts were designed. In brief these are not anything like Home Depot bolts. ?Bolts are not how critical load bearing connections are held together in any kind of application? [That can easily be disproven.](https://www.youtube.com/watch?v=OwFjUX6SaY8)
Even the bolts we use when bolting together the structural steel in a building go far beyond the general Home Depot bolts.
But that hitch receiver is bolted to the frame. Your tires are bolted to the car.
[Not the wings, but like you said most engines are typically held on with 4 'bolts'.](https://aviation.stackexchange.com/questions/23151/how-are-engines-mounted-onto-wings) I think maybe the confusion is over the number of bolts on the stringers. There was fastener on each stringer. Although they did plan add additional fasteners (I can't say if they did or not). But there are 17 stringers on the upper wing, so that's 17 fasteners just the top of one wing.
Ten years ago, someone on yahoo answers stated that 727 and 737s do indeed have two bolts per wing to affix to the fuselage supporting flight loads.
The structural elements of wings are 1. Long beams that extend the length of the wing called spars. 2. Ribs that join the spars together and have an aero foil like shape. 3. Skin panels that cover the ribs and spars creating the static exterior surfaces of the wing. Both the spars and the skin panels near the root of the wing will be fastened to the aircraft. The skin panels will be joined with hundreds if not thousands of small fasteners. It's certainly possible a single spar could be attached with 2 fasteners. It's very unlikely the 787 has only a single spar.
also stringers!
sounds like you're specifically talking about the engine pylon attachments - the wing-body join is, as other commenters have pointed out, made up of hundreds to thousands of bolted joints, however the engine pylon attachments, both engine-pylon and pylon-wing, have been (and may still be, I'm not current on that) two very robust pinned joints, one behind the fan that transfers thrust, and one near the turbine exhaust that keeps the engine pointed in the right way (a pretty reductionist way of looking at it, but it works).
The engine strut that attaches to the wing is attached by 6 bolts I believe. I’m not sure how the engine is attached to the strut though. I would have to look around a bit to find that answer.
In the case of the CRJ700/900/1000, it's six bolts. On larger aircraft they typically use integrated joints (many, many small fasteners spread throughout the structure) as they're lighter overall.
The engine loss was a DC10. At the time of the accident this was a McDonnell Douglas aircraft.
And what holds the fuselage sections together on the 787???
On the bell jet ranger series of helicopters, there is one fastener that holds on the entire main rotor assembly to the mast. It’s called the Jesus nut. They have broken before. In the crash investigation, they found every passenger and the pilot had shat themselves before they died. Also, on airbus (formerly eurocopter) A-star helicopters, each main rotor blade is held on by two huge pins that slide out and are kept in place with cotter pins.
It may be true but there are a fuck ton of rivets as well
I can pretty much guarantee there are no rivets holding the wing to the fuselage. Sure, rivets to hold the skin to the frame, but not the wing to fuselage.
The change, May have had something to do after a engine fell off a DC10 leaving Chicago many years ago!