Years and years ago it seemed amazing to me that wings can stay attached to a large airplane. But I was thinking about it wrong (I believe).
Would it be more accurate to say that the body of the airplane is attached to the wings, instead of the other way around? And that it’s not so much two wings, but one large structure that passes through the fuselage?
(the ‘Great Debate’ about 9/11 got me thinking about this)
I would say yes, mostly.
A plane without wings is just a pressurized storage locker on the ground.
A wing without a fuselage can still be made to fly.
But in the real world everything is designed to work together.
It is easier to visualize if you think of the fuselage as the section of the plane supported between the wings. That isn’t completely accurate (the entire tail section is made up of wings too) but it is the basic idea.
One engineering concept that will help is wing spars. They are some of the strongest parts of the aircraft and one of the most difficult to replace because the rest of the plane is built around them. They are extremely strong beams that make up much of the structural integrity of the aircraft.
Don’t worry about wings being strong enough either on any passenger jet. They look flimsy because they flex when taxiing but that is a feature and not a bug. Here is a stress test trying to make them fail under conditions that would almost never be encountered in the real world (it didn’t fail in that test).
I linked a youtube of that destructive testing in the 911 Great Debates page. And as I thought, the airplane is built around the wings. Could though, say, the primary wing be considered one piece instead of two. In that it effectively goes through the fuselage. I’m not the least bit afraid of wings falling off, but I do know some people that have a slight fear of flying. Would saying that the main wing is effectively one piece that the airplane is attached to be basically accurate? It would be an easy way to explain it?
It’s rare nowadays, but a wing can come off in flight. The Smithsonian Channel had an hour-long program recently about a crash of a Grumman Mallard amphibian in Florida. This plane had been built in 1947, and was still flying in airline duty from one of the Caribbean islands to the mainland. It was climbing to altitude on a return flight to the islands when the starboard wing literally snapped off - nobody survived that one.
Turned out that the spanwise stringers in the wing had corroded so badly that the entire wing was held on only by the wing skins, which unfortunately had finally corroded enough that the lower skin snapped in flight, with the inevitable results.
This eventually resulted in some stringent new inspection and maintenance procedures being instituted, especially for older airplanes.
Yes, for certain values of “effectively”.
Wings would essentially always be built separately, but then their spars are joined, resulting in what amounts to one continuous (very strong) spar, running pretty much from tip to tip.
You can also see this when you view the wings on the ground and compare to a plane in flight. On the ground, the wingtips are hanging lower than the fuselage. In flight, the fuselage is hanging lower than the wingtips.
I remember this Youtube video of a Hercules where both of the wings snapped off. No survivors in that one either.
Here’s the centre wing box of a B777, http://subaru-new-site.s3.amazonaws.com/styles/large/s3/boeing_engine.jpg. I think it’s fair to say that the wings plus centre wing box go together to form a solid unit, though each wing is still bolted on to the centre section.
The stress on the join between wing and fuselage (wing bending) is a significant design consideration and there are limitations on what the weight of the aircraft can be before fuel is added (zero fuel weight). Weight that is not fuel is mainly fuselage plus payload. The more this weight is, the more wing bend there is, so there is a limit to what can be loaded, that is, the number of people and bags that can be put on the aircraft. Any additional weight must be fuel because fuel is predominantly in the wings and therefore doesn’t contribute to wing bending. It is thus possible, with a light fuel load, to be well below your maximum take-off weight but to be unable to add any payload.
Another more obvious example of reducing wing bending is podded engines. Engines placed out on the wing reduce wing bending. The further out they are the more benefit there is.
Huh. Interesting.
Thanks everyone. Sheessseee that Hercules turned into a lawn dart.
Yes, but the longer lever makes the support work that much harder…
Starting from Richard Pearse’s post. …
What you really have is a single really beefy 4-way plus-shaped connector. Two long flat arms are bolted onto the left & right ends of the plus. Two long tubular arms are bolted onto the front and aft ends of the plus.
The whole time the thing is flying, the two flat parts (wings) are trying to break off upwards. Meanwhile the two tubular parts (fuselage) are trying to break off downwards. The plus and the connectors to the four extensions are stout enough that doesn’t happen.
At least until enough cracking or corrosion sets in, or somebody hamfists an overload, and then something breaks. Oops.
Nope. The wings are pulling up, not down. Putting weight farther out reduces, not increases, the stress concentration at the wing root.
At least in flight. You’re right that sitting at the gate an engine far outboard on a wing is inducing more downward bending than a similar engine mounted closer in.
Got it. First thought was sitting on the ground holding buckets at arms length…
Having participated in rigging and de-rigging several models of gliders, it seems that with some models, the wings are held on by little more that cotter pins and duct tape.
Each wing has a stout spar that sticks out a distance equal to the width of the fuselage. So this goes into the side of the fuselage and extends to the other side, but not out the other side. At the end of the spar of each wing is a stout pin (about an inch in diameter and sticks out about 3 inches) that fits into a matching hole in the opposite wing, to keep things lined up. Inside the fuselage, the two spars slide past each other, one in front and one behind.
Here’s as good a pic as I could find: The spar of one wing is visible, and the side of the fuselage that it fits into. If you look close you can see the pin sticking out of the end of the spar.
You’d think there would be some big holes in these spars that would line up, and big hungus bolts to go through those holes to bolt the two spars together. Well, maybe some gliders have that. Not the Grobs that I’ve been flying.
Then you have two large pins sticking out of each wing, maybe 1½" in diameter and maybe 4" long, that go into fittings in the fuselage. There’s a shallow groove around each of these pins about ½" from the end — looks like an O-ring type of seal would go into that. (Sorry, I wasn’t able to find some good pics on-line — I looked.) The pipe-like fitting it goes into has a ring of little ball-bearings around it on the inside. So then, you slide a sleeve over that fitting and screw it down, and that squeezes the ring of little ball-bearings into that groove around the pin.
And that’s what hold the wings on! :eek: Then the dive brakes and ailerons are connected to the cockpit controls and secured with some sort of cotter-pin-like clips. And, if anyone wants to bother, the joint where the wing butts up against the fuselage is sealed with gap tape. And that’s how some models of gliders are held together!
Imagine instead that you are holding your body up with your arms stretched out between some rails or something. If you could somehow distribute more of your body weight across your arms you’d find it a lot easier to hold yourself up.
This http://www.peacelovelunges.com/wp-content/uploads/2008/08/gym3.jpg is an airplane in flight. Notice how the beefiest part is the shoulder. If lots more of the weight was out near the wrists it’d be easier.
Related to this is the lateral distribution of lift on the wings. The wing root happens to be rather stout for structural purposes, but the chord there is also rather long compared to the wingtip, and because of the twist in the wing, the angle of attack is greater at the root (to help maintain good air flow over the ailerons at the tip even while the root is in stall). This puts the center of lift on each wing relatively close to the fuselage.
In reading recently about winglets, I found out that because they increase lift out near the wingtip, they move the center of lift on each wing out toward the tip. The total magnitude of lift remains the same (otherwise the plane would accelerate up/down), but the increased moment-arm results in increased bending loads on the wing structure. In the absence of any structural modifications this may decrease the G and or load limit for the aircraft. Boeing said that for the 737, winglets didn’t result in a need for more structural strength at the root, but they did create a need for reinforcement in the middle and outboard portions of each wing.
Actually, the wings are held on by those spars. In flight, those spars are going to be pressed against their housing by aerodynamic (and other) forces. The pins are only needed to keep them from vibrating or wiggling free.
Yup. When they retrofitted all our 757s and 767s with the Boeing winglet kit there was an issue with the speedbrakes / spoilers.
When those are deployed, they trash a bunch of lift inboard and trash relatively less outboard. With the effect of moving the CL outboard. In the early iterations Boeing believed the sum of what the new winglets were already doing full time plus what the spoilers would do if deployed at high speed plus an unlucky gust of turbulence would be too much for the structure as originally designed without winglets.
The solution was to install a limiter that would restrict the total spoiler extension to about 50% at very high speed and would retract them if they were deployed fully at a moderate speed but then you sped up.
After some operational experience with instrumented airplanes they later decided they’d been too conservative. So airplanes with the later version of the mod kit never got the spoiler limiter. It was proven unnecessary.
Going back towards the OP.
You can’t scale a dirigible beyond a certain point. Beyond some point your get: “Rigid, large, survives differential gusts. Pick 2.” Oops.
Likewise you can’t scale a wing-and-tube design airplane beyond a certain size. One way to move beyond those limitations, at least in terms of aerodynamics, is the span-loader. See AeroVironment Helios Prototype - Wikipedia for an example. If each bit of wing carries just the load directly in/under it, the thing can scale out a long, long way. At least in theory, and if you don’t need it to operate from existing airports.
The “blended wing body” or BWB Blended wing body - Wikipedia is a more plausible stepwise move from pure tube-and-wing to pure span-loader.
There’s not much doubt the military and the cargo airlines will be operating these things in a decade or two. Whether they ever become part of the passenger fleet is debatable.
