[stouset]

I seriously, seriously doubt it. The wings are so utterly critical to flight I can’t possibly imagine any situation they’d be engineered to snap off under. Further, that’s where the fuel is and any crash involving a wing rupture is dramatically more dangerous given the risk of fire.

Hell even in a crash landing like this you want the plane to stay upright and stable.

[evil-olive]

> The wings are so utterly critical to flight I can’t possibly imagine any situation they’d be engineered to snap off under.

I don't know enough about the details of the CRJ-900 to say for certain, but in general aerospace engineering does include considerations of this sort, where if a component breaks off you want to ensure that it separates in a specific way.

from an Admiral Cloudberg article [0] about El-Al 1862 [1]:

> The Boeing 747 engine pylon is attached to the wing by four fittings: one at the front, one in the back, and two in the middle (or midspar). Each of these fittings consists of a wing-mounted male lug and a pylon-mounted female lug, which are connected by a fuse pin. The four fuse pins are the weakest part of the pylon, but this is by design. Every airplane system and structure contains planned failure sequences which work to minimize damage in the event of an overload. In the case of the 747’s engine pylons, the fuse pins were designed to fail at a lower load threshold than the fittings themselves, ensuring that if the engine is torn off the wing — perhaps due to extreme turbulence, or a gear-up landing — the fuse pins will fail first, causing the engine to separate cleanly without ripping open the fuel tanks located directly above it. In theory, this should allow an engine to break off upon reaching its design load limit without starting a fire or otherwise compromising the plane’s ability to fly.

0: https://admiralcloudberg.medium.com/concrete-and-fire-the-cr...

1: https://en.wikipedia.org/wiki/El_Al_Flight_1862

[hugh-avherald]

The purpose of that engineering feature is to ensure the wings stay on.

[bfdm]

The comment was merely illustrating the concept in general being used on planes, or at least that's how I read it.

[stouset]

Yeah, but the whole point here is that the engines are very specifically designed to break off in a way that preserves the integrity of the wings.

The integrity of the wings is a function that supersedes just about every other possible thing on a plane. You can safely land without any engines. You can safely land without hydraulics. You can safely land without gear. Without wings, a plane is a brick.

[altairprime]

Here’s the bend test video for the Boeing 777: the wings can bend for something like a 45-degreee arc without breaking, so they ran it to breaking. https://www.homemadetools.net/forum/boeing-777-wing-flexibil...

[FabHK]

Indeed. And maneuvering speed V_A is designed such that as long as you don't exceed it, you will stall before breaking the wings off in case of turbulence or full control deflection.

[wkat4242]

I think you mean Vne?

[mrguyorama]

Nah, an engine getting ripped off will not tear off the wing since this is the level of force and flex they are designed to withstand: https://www.youtube.com/watch?v=--LTYRTKV_A

The engines are built to rip off cleanly, because when they don't, they have caused https://en.wikipedia.org/wiki/American_Airlines_Flight_191 and https://en.wikipedia.org/wiki/El_Al_Flight_1862 which were fairly serious and catastrophic accidents at least partially caused by the engines tearing off and damaging the wing in such a serious manner as to cause a stall and crash. The wings stayed on the aircraft in both instances. Interestingly, both accidents were caused by those same sheer pins being damaged in minor and unpredicted ways.

I highly doubt the wing is DESIGNED to cleanly separate. Planes are just very not rigid for something going such a high speed, and so tend to turn into confetti when faced with a harder surface, like a runway or a concrete building. Usually the only parts that survive serious crashes are the landing gear struts.

[victorbjorklund]

In the air. If the force applied is not the normal force expected from normal use it might be intended to snap off.

[stouset]

This is like suggesting that a boat's hull is designed to snap off in the event it encounters unexpected forces outside the water.

[account42]

I can see a boat's hull be designed to crumble as safely as possible under a headson impact. But the situation is not the same. Boats usually stay in water at all times. An accident might put them under water. The situation is different with airplanes: all airplanes are guaranteed to eventually impact the ground, just ideally in a controlled manner.

[victorbjorklund]

Parts of the boats are def made to snap off when unexpected force is applied.

[ambicapter]

An engine pylon is not a wing root?

[hinkley]

Look up stress to failure tests on commercial airplanes.

They know how much peak load is supposed to be for the airframe, then they go well beyond it to see how the plane fails. Generally you want the wings to break not the fuselage.

You can in a lot of situations land a plane with 1.5 wings. But once the spine cracks you’re just a ballistic object.

[WalterBright]

The parts are designed for "ultimate load" which is 150% of the worst case maximum load expected to ever see in service.

I used to work at Boeing on the 757 stabilizer trim system. There's the design group and the stress group. I was in the design group, the stress group double checks the design work.

One day the stress group called me on the carpet, and asked me why my designs consistently just barely exceeded 150%. I said I started with the ultimate load, and worked backwards to size the part. The stress groups said they prefered designs to be 10% over the ultimate load. I replied that I designed to the requirements, as adding 10% makes the airplane overweight. If they didn't like the design requirements, change them.

They grumbled, but I got my way :-/

A few months later, they offered me a position on the stress group. It was a nice compliment, as they normally required a masters' degree and I only had a bachelors. I told them I was honored by the offer, but my heart was in design.

Some time later, my parts were put on the torture rack to see if they passed the ultimate load test. All of them passed on the first try.

I also had the privilege in being mentored by some really fine engineers at Boeing, such as J Burton Berlin and Erwin Schweizer.

Am I proud of that? Yes. I love flying in the 757. Best airplane Boeing ever made. Whenever I fly in them I chat a bit with the flight crew, and they love it, too.

[WalterBright]

P.S. the jackscrew turned out to be stronger than I'd anticipated. The credit for that goes to Saginaw Gear, who made them. SG makes kick-ass airplane parts, beautifally made.

[throwaway173738]

> If they didn't like the design requirements, change them.

If anyone is wondering, this is always the correct answer when there’s a disagreement between reality and the specification and you’re following the spec.

[lenkite]

I always thought of you as the C++/D compiler guy - wow you did work in aerospace too!

Thanks for making the D programming language. If it did not insist on a GC and had a robust and stable GC-free stdlib, I believe it could have conquered the world.

[WalterBright]

D works just fine without using the GC. It can also work just fine with just the C standard library. It does not insist on it.

BTW, the GC makes the compile time function execution sweet and easy.

[tiahura]

757 stabilizer trim system

Have you shared your thoughts on MCAS? I feel like there are a lot of potential lessons that got missed for all the noise.

[WalterBright]

I've probably posted a hundred messages here on MCAS! Most were downvoted to hell. The actual 737 pilots I talked to agreed with me, nobody else did. Classic Gell-Mann Effect. The only truthful account of the crashes is the official NTSB report.

The 737 is an electric drive, with a manual backup. The 757 is a scaled down version of the 747's dual hydraulic drive, no manual backup.

More efficient wings and engines obsoleted the 757.

[carabiner]

Oh I was an aeronautical engineer (BS, MS aerospace engineering, concentration in fluid mechanics) for 8 years. Any pithy explanation of aircraft flight/engineering concepts that I post gets downvoted or ignored. Better yet, sometimes a java programmer tries to mansplain it to me in a worse way.

[WalterBright]

When I talk to airplane crews, their faces say "oh crap, another nut I have to be nice to". So I let slip into the conversation things only insiders would know, and they then relax and open up.

[747-8F]

Awesome! Thanks for commenting.

[easel]

I also love the 757, but never had as good a reason as you other than knowing the flight characteristics of the plane. Sad to see them disappearing from the icelandair fleet, is there anything else comparable? The modern 737 variants sure don't seem to be.

[stouset]

The fuselage isn’t being stressed in a wing load test. There is zero way the fuselage could stand up to the level of force being applied to the wings.

[hinkley]

I would submit to you that it’s impossible to load the wings at 150% of max load without transferring any of that force into the fuselage. Look at any finite element analysis of complex shapes. The force spreads out from areas of max tension or compression, and goes around corners.

[cycomanic]

Here's a video of a Airbus wing stress test. They seriously bend without snapping off. https://www.youtube.com/watch?v=7Ih9V0uobKc&t=7

[mjg59]

It's probably preferable to have the wing break off than for it to apply sufficient stress to the fuselage that the fuselage disintegrates - you're going to lose the wing either way and if you're in the air that's going to be bad, but if you're on or near the ground it's probably preferable to have an intact fuselage?

[stouset]

Wings don’t really transmit much stress to the fuselage. You can think of both wings as a single unit on which the fuselage rides.

The fuselage couldn’t take a fraction of the stress the wings are designed to endure.