Hacker News Reader

Hacker News

Comment by flatiron | Hacker News Reader

Parent Full thread

flatiron

If you pop a window you lose pressure right?

You blow a fuel pump and can’t fuel the engines.

Wings fall off.

I dunno. I can think of a bunch of failure points on a modern airliner.

View on HN

Fuel pumps have backup pumps. Matter a fact, the whole fuel system is a lot more complex than this.

And as for “the wings fall off” part, makes me remember a quote of an engineer I once read that goes something like this: “The wings are the strongest part of the airplane. If you worry about them ripping apart or falling off, you have way bigger problems than that, like the rest of the plane missing”.

The flex test that the wings go through is pretty incredible:

https://www.wired.com/images_blogs/autopia/2010/03/index.jpg

Yes, I know! I don’t remember what video I saw but the wings were bent beyond imagination. Made me realise that what I saw while flying wasn’t even 30% of what they can withstand. Incredible engineering.

The Lockheed Elektra was infamous for its wings mysteriously coming off. Much research finally revealed that dynamic instability (flutter) was the cause. A great deal has been learned about how to prevent this, and a lot of effort goes into designing a wing that isn't susceptible to flutter.

I did the calculations for the 757 elevators to show it wouldn't flutter. And yes, it was also verified on the test stand.

There was an F-15 that had a mid-air collision, the entire wing ripped off, and it managed to safely land.

https://taskandpurpose.com/history/1983-negev-mid-air-collis...

The A-10 and it's redundant abilities are worth reading up on too:

- https://theaviationist.com/2017/08/16/the-crazy-story-of-the...

- https://en.wikipedia.org/wiki/Fairchild_Republic_A-10_Thunde...

The fuel systems at least are fully redundant. Each wing has its own system and then there’s redundant systems that allow fuel to be transferred or delivered from either wing.

I discovered this when trying to understand what the barking noise is on airbus planes.

The barking noise on airbus systems is the Power Transfer Unit which is about delivering hydraulic pressure across 2 independent systems, not fuel.

I thought the barking noise came from the Canine Transfer Unit in the hold. Thanks for clearing that up!

> If you pop a window you lose pressure right?

Right. But the plane drops oxygen masks and goes down to a lower altitude.

> You blow a fuel pump and can’t fuel the engines.

Multiple fuel pumps and multiple gas tanks.

> Wings fall off.

Wings have dual internal structure.

> I can think of a bunch of failure points on a modern airliner.

No single point of failure is an FAA requirement.

If you pop a window, everyone puts on their oxygen masks and the plane makes an emergency descent. The point isn't that nothing at all can go wrong, but rather that the plane will get its occupants onto the ground safely even if something does.

> I dunno. I can think of a bunch of failure points on a modern airliner.

not catastrophic failure, like you get with a rocket or a helicopter.

I'm not an expert but "wings falling off" seems like a pretty catastrophic failure for a typical aeroplane.

The wing root is the strongest part of any airframe. Wings falling off is way down there on the list of aviation risks, maybe next to getting struck by a meteor

that's not redundancy. can a plane fly w/ only 1 wing and for how long?

a plane without a wing is no longer a plane, realistically

Israeli F15 landed missing one wing but this was a fighter jet with super high thrust capability to help offset missing lift from the wings:

https://theaviationist.com/2014/09/15/f-15-lands-with-one-wi...

Low probability or not, if an airplane can't stay in the air with one of the wings missing that definitely counts as a "single point of failure". Whether that SPOF needs to be mitigated is a tradeoff based on other constraints like the expected risk, economics, and safety regulations (and in the case of the space telescope, maximum launch mass of the rocket).

That's kind of ridiculous. A terrorist bomb in the cargo hold is a "single point of failure" that will crash the plane, as is quantum uncertainty causing one wing to break off spontaneously. This says nothing about the actual SPoF engineering requirement, which is a very real, very relevant thing.

Wings don't just go missing. It would require multiple failures for a wing to "fall off" an airliner.

https://www.aopa.org/news-and-media/all-news/2018/may/16/nts...

Not as small of a risk as you’d expect (though not anything to seriously worry about). This metal fatigue grounded a large chunk of the US training fleet and similar cracks were frequently found in other Piper Arrows (including ours).

That is actually kind of scary.

How many cycles does the airframe have to go through in order for this to become a problem? I tend to think that if the FAA gave a shit about general aviation maybe we wouldn't be flying planes from the 1960s

For airliners, the airplanes are retired after a certain number of cycles. The 757 was designed for 62,000 flying hours, if I recall correctly. It's scrap after that.

My dad's B-17 in WW2 was scrapped after 30 missions, it was considered worn out.

The wings have dual spars.

Reply on news.ycombinator.com