Another Airplane Physics Question

[crokett]

I was thinking about this on the flight home the other day. Supposing the 767 we were riding in was parked on the runway and a crane was brought in and strapped to the wingtips. Now supposing the crane started to lift the plane. We will pretend that the plane is perfectly balanced so it won't pitch backwards or forwards with no straps on the nose or tail. I was wondering where the wings would fail first? My guess was somewhere in the middle. It wouldn't be the root because that joint has to be strong enough to lift the fuselage when the plane is flying. My other thought was why doesn't somebody build a monster version of the stealth bomber that can carry passengers? A flying wing is the most efficient shape.

[Russianwolf]

I bet it would break at the point that it's attached to the straps.

Think about it. in flight the entire wing is being held up by air, but in your postulation all the force is being focused in two points. The wing isn't designed for this and should break at the point were the force is focused.

[Hoover]

The Boeing wing has a front spar and a rear spar. The wing is also the fuel tank. The area closest to the middle is where the engine pylon (aka strut) is located. There is also gussets inside the tank running from the front to the rear spar. This creates a box configuration.
The answer is the wingtips. The wing flexes up and down in flight. The wing also is tapered getting thinner as the distance from the fuselage is greater.

[parnelli]

Years ago PBS did a several part show on a Boeing being designed and tested....maybe the 767?

If you can find it, there was a test where they pull upwards on the wing tips until the wings break...It was VERY far- IIRC it was starting to look like a U shape before the violent snap.

Doesn't answer the question, but it was pretty cool.

[Hoover]

The wing stress test on the 747 did have the wings nearly vertical before failure. I don't remember the statistics on the forces, but seeing the test in the plant was really awesome.

I was a functional test inspector in final assembly 747 line. Got in on some cool tests, some were destructive testing, but mainly nondestructive testing was our tasks.

[LinuxRandal]

For the giant flying wing/passenger jet, the reason for that is airports. You have to be able to use and land on existing ones.

[crokett]

Yeah Randal, that is what I figured too. I know that was a constraint for that huge Airbus airliner. Even so, there are some airports it can't land at. I'd still like to see that flying wing passenger version though.

[jackellis]

I believe it was Jack Northrup who tried to build a flying wing bomber (B-47?) back in the 1940s. It was not a wildly successful airplane.

Another reason flying wings are not being built is because they would have too few windows and would be too unconventional. Peeps who fly like seeing outside.

As for the strength of the wings, they're built to withstand 150% of the ultimate design loading, which is a couple of Gs. Airplane wings are incredibly strong and on the very few occasions when they have failed in flight, it happens under 2 rare circumstances. First, there's an undetected crack in the spar. Second, some hot dog pilot (or someone who flies into a thunderstorm) stresses the airplane beyond it's ultimate loading limit.

[pelligrini]

If most of the discussion is true and if the wings are built to withstand 150% of the design loading and the crane was attached to the wing tips in a way that it wouldn't be a fastener failure the crane would probably just lift the plane.

I'm not totally convinced this would be the case as the lift forces when flying are distributed across the entire wing, not just a point load on the ends creating a rather large moment.

[jking]

Years ago PBS did a several part show on a Boeing being designed and tested....maybe the 767?

If you can find it, there was a test where they pull upwards on the wing tips until the wings break...It was VERY far- IIRC it was starting to look like a U shape before the violent snap.

Doesn't answer the question, but it was pretty cool.

That documentary was on the Boeing 777. We watched it in one of my college design classes in the mid-90's. The wing test was quite the thing to see on film, I can't imagine witnessing it in person. You know it's going to fail, but, you're just not quite sure when. I flew overseas in 1996 when the 777's were new. It's a very nice airplane.

I believe it was Jack Northrup who tried to build a flying wing bomber (B-47?) back in the 1940s. It was not a wildly successful airplane.

From what I remember Northrup had problems controlling the airplane. Flying wings are a different animal when it comes to flying. IIRC the B2 bomber would have some of the same issues if they removed the computer system from the plane.

[crokett]

From what I remember Northrup had problems controlling the airplane. Flying wings are a different animal when it comes to flying. IIRC the B2 bomber would have some of the same issues if they removed the computer system from the plane.

That's what I remember from reading about it. The wing is the most efficient shape since the entire surface is a lifting one but you need computers to keep it stable.

[pelligrini]

I saw a Vulcan at an airshow in '84 or so. It was around before computers. http://en.wikipedia.org/wiki/Avro_Vulcan

[Alex Franke]

This looks like it might be your test: wow.

http://www.youtube.com/watch?v=pe9PVaFGl3o

Looks like it broke about 1/3 the distance from the body of the plane.

[Mr__Bill]

Perhaps something like this? From Popular Mechanics

Here is the Northrup bomber

All the old Popular Mechanics are on line, just waiting for us.

Bill, on the Sunny Oregon Coast, who is getting real tired of all this fog

[Kristofor]

I suppose there are ways to accomodate all of the issues, but in addition to the airports needing to accomodate the planes and the lack of windows...

Evacuation in case of a crash may be more difficult with further distances needed to each exit. On most planes there will be an exit within ~10 rows of your seat. In the middle of a flying wing you may be 30 seats plus a row or three from the nearest exit.

More space wasted on aisles. Aisle seats are well liked by some (I'm a window guy generally) but even without that if you make it more than 5 seats wide per section there would be an increase in disruptions during normal flight (all the small bladder people, and getting stuff from the overhead bin people, etc.). Additionally in a crash again having to clear more people per section would increase evacuation times.