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I read days before about the collision of the flight PSA Flight 182 on September 25, 1978. I was wondering how is it possible that a Cessna 172 can CUT Boeing's 727-214 wing. There is a video with the moment: video.

Is there an explanation of how this can happen scientifically?

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An airliner wing is built to be as light as possible. Its strength is calculated to withstand the stresses of flying, i.e. lift equally distributed over the wing, bird strikes on the leading edge.

The wing consists of one or more spars from the fuselage to the wingtip, ribs perpendicular to the spars and skin panels. All of these are made from thin aluminium: the spars (the main loadbearing structure) are a few mm thick outside the landing gear and engines.

Fire a one-ton object into the wing at a few hundred km/h and you can do a lot of damage. Even if that object is another aircraft with similar construction.

The damage gets worse if the wing hits the Cessna's engine block, but the accident descriptions I've seen don't say if that was the case.

Don't assume the animation is accurate. The Cessna won't slice cleanly through the wing, there would have been a collision in which both structures are crumpled and roughly torn apart.

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  • $\begingroup$ Is it possible that Cessna's flag would be stronger than Boeing's because of the much smaller size and thus more densely than Boeing's? $\endgroup$ – avionerman Feb 19 '19 at 8:47
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    $\begingroup$ @avionerman The Cessna would be subjected to far lesser loads under normal operation. To a first order approximation, the wings need to carry the maximum takeoff weight of the airplane, plus a margin for maneuvering and safety. That's going to be less for a small airplane than a large one. $\endgroup$ – a CVn Feb 19 '19 at 8:51
  • $\begingroup$ @a CVn So if we could give an example, the Boeing because of the long wings was like a paper and the Cessna because of its small wings (and with less weight) was like a pen and that is why it "pierce" it so easily. Is that right? $\endgroup$ – avionerman Feb 19 '19 at 8:54
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    $\begingroup$ Compare to a Coke can. You can easily dent a can from its side, but you can stand on top of that same can without it collapsing. $\endgroup$ – Hobbes Feb 19 '19 at 8:56
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    $\begingroup$ @avionerman Look up "wing loading". $\endgroup$ – a CVn Feb 19 '19 at 10:45
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Large objects are fragile. Pretty much any two airplane-sized objects, when colliding at airplane-like speeds, will both be damaged by the collision.

The reason for this is the square–cube law. As you increase the size of an object, its strength increases more slowly than its mass increases. So as a result, small objects tend to be very strong, and large objects tend to be very weak. That's why you can hurl a toy car into a stone wall at 10 mph and it will be completely undamaged, whereas if you run a real car into a stone wall at the same speed, it'll be damaged severely.

In a comment, you compare the two airplanes to a sheet of paper and a pen. I don't think this is a good analogy, since a pen is much stronger (relative to its mass) than an airplane is. A better analogy would be to imagine both airplanes as raw eggs.

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  • $\begingroup$ Thank you very much for your answer. I really like your example :) $\endgroup$ – avionerman Aug 24 '19 at 10:43

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