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When the plane takes off, why doesn’t the tail hit the runway? (thegigamax.com)
59 points by skellertor on Oct 16, 2017 | hide | past | web | favorite | 64 comments

Interesting write up. I was just watching a video yesterday which had a pretty good example of the testing aircraft manufacturers do for this scenario. It’s called a velocity minimum unstick test. Some impressive flying.


"They put the plane into a stall to make sure it can recover" CAN YOU IMAGINE? lol Could you imagine being the guy who wakes up in the morning and is like "Today I get to put a plane into stall to make sure it can recover" shivers

This is a normal part of pilot training. I think it's less common in large aircraft but for small planes it's not uncommon.

Normal pilot training does not involve testing aircraft limits. Stall training happens in a plane with a known stall speed and behavior. The quote is about finding that limit for the first time.

It really doesn’t feel like anything special is happening either, and recovery is quick and easy. It’s a non-event at altitude.

Spin training though, no thanks!

Well, the nice thing about most planes is that they don't want to stall, and most of the time the correct action to recover is "stop doing things and let the plane recover". It's when you keep messing with it that you make things worse and get toward unrecoverability.

I'm going to reply here because multiple people said it:

I'm aware that stall training is a common occurrence but the difference here is that you're testing with a plane that is massive and may have no nearly been tested as much before. What struck me was the "Make sure it can recover" it's not a test for the pilot's training to see if he can recover it. It's testing the plane's capability to recover. Sure the pilot could still end up recovering it if it doesn't but the sheer size of this plane is what mostly made me surprised!

I'm fairly sure that the engineers have figured out a pretty good estimate of the stall speed before they send a pilot to go test it

Recovering from a stall is something you learn very very early into flying

I'd say impressive commitment to QA'ing your product! I wish software in general, is tested to this degree.

Testing costs money. If software in general was tested to this degree, we would still be stuck in the CLI-only world of 30 years ago.

Or, we would have long ago found better ways to adopt design and development strategies that more generally lend themselves to rigorous and easily repeatable testing.

We would have found Fred Brooks' missing silver bullet?


I don't know what that means, but I'm going to upvote you and go find out what interesting reading material I have missed!

Edit: As a rails dev, I know that there is no silver bullet, but I also know that some strategies are objectively better than others, and some strategies produce software that is easier to verify than others.

You can write heaping mounds of Javascript that you pile on top of each other, and pile more and more tests on top of each other and run them within a CI framework between each change (or don't), to build confidence that you don't break things that you previously guaranteed from one commit/release to the next...

Or you can write tiny functions with an obvious and wholly singular purpose, and build them into micro-services that deliver one small fraction of the whole service, and test at each layer, and build composable units of the final service that you intended to guarantee.

One strategy is easily verifiable if you keep it up without ceasing (and the other is not, but the two strategies are usually easy to tell apart.) Unfortunately it's probably true, for example, that neither strategy can ever be said to (obviate essential complexity! Fred Brooks) – to totally guarantee that the tail does not hit the ground on either takeoff or landing, which is a complex problem that probably can't actually be solved in units.

We would be reusing the hell out of everything and we wouldn't have every single company on the internet building their own CMS.

The tailskid (physical tailstrike protection [1]) was removed from the 777-300ER in favor of software-based mitigation [2,3].

[1] http://www.boeing.com/news/frontiers/archive/2004/december/i...

[2] http://www.airliners.net/forum/viewtopic.php?t=775483

[3] http://aviationweek.com/advanced-machines-aerospace-manufact...

If there is a suspected tailstrike in an airliner, the tailskid might reduce the damage but it still requires an emergency return and engineering inspection for damage.

Most severe tailstrikes occur on landing, and the tailskid isn't going to help reduce damage.

The cockpit recording from Japan Airlines Flight 123 (which crashed due to improper repairs of tail strike damage 7 years earlier) is chilling. https://www.youtube.com/watch?v=Xfh9-ogUgSQ

Wow, that was a scary recording.

From the wikipedia article [1]:

> Casualties of the crash included all 15 crew members and 505 of the 509 passengers

> ...

> deadliest single-aircraft accident in history, the deadliest aviation accident in Japan, the second-deadliest Boeing 747 accident and the second-deadliest aviation accident after the 1977 Tenerife airport disaster.

> ...

> During the investigation, Boeing calculated that this incorrect installation would fail after approximately 10,000 pressurization cycles; the aircraft accomplished 12,318 successful flights from the time that the faulty repair was made to when the crash happened.

> ...

> In the aftermath of the incident, Hiroo Tominaga, a JAL maintenance manager, killed himself to atone for the incident, while Susumu Tajima, an engineer who had inspected and cleared the aircraft as flight-worthy, committed suicide due to difficulties at work.

[1] https://en.wikipedia.org/wiki/Japan_Airlines_Flight_123

> > In the aftermath of the incident, Hiroo Tominaga, a JAL maintenance manager, killed himself to atone for the incident, while Susumu Tajima, an engineer who had inspected and cleared the aircraft as flight-worthy, committed suicide due to difficulties at work.

That sucks. If ever there were two people that knew first-hand how important it was to get right and would have worked to make sure that accident, and likely others as well could never happen on their shift, those were them. Suicide as atonement is a stupid, counter-productive cultural norm (and hopefully it's much less of a norm in any modern society where it exists).

Interestingly, at the end of WWII, when Tojo was captured by the Americans, he shot himself in the abdomen--creating referencss fo seppuku--and apologized that "I am taking so long to die."

Not long after, he was tried for war cimes and executed by hanging.

I'm sure he would have rather have died from the gunshot.

Whether right in some cases and wrong in others, I think it's difficult to say cultural norms are simply and plainly wrong.

I'm not sure comparing a case where the person has a high likelihood of dying anyway is necessarily appropriate based on what I was referring to. I don't fault the skydiver that failed to pack their parachute correctly and causes it to fail for committing suicide before hitting the ground, I do fault a system that would cause the person responsible for re-checking the parachutes to commit suicide because of the death.

I also didn't say the cultural norm was wrong, just that it was stupid and counter-productive. I meant stupid as an enhancement to counter-productive, and I meant counter-productive in relation to actually advancing a society to the point where the problem that caused the suicide in the first place is less common.

As someone who lives and works in Japan, it's absolutely shameful how people do this, when they are pressured so much from above to bot only work insane hours, but to take the entire responsibility upon themselves. It's as if there is a magical white line, where you can pass orders down through, but there is no responsibility for errors passing back through.

I've just been reading a bit on the aftermath and what is amazing to me is that Boeing apparently paid nothing in compensation or liability, but JAL did, despite the accident being nearly entirely the fault of Boeing!? Does anyone know why?

Based on my reading, the fault lies with JAL for executing the wrong repair procedure. Why do you think the fault lies with Boeing?

Boeing specifies: "repair procedure is like so" and due to misunderstanding, pressure to bring equipment back into use, failure to acquire the correct parts or some sort of similar problem [all my speculation btw], JAL maintenance executes another repair procedure that seems equivalent to them (or at least adequate).

Boeing technicians did the repair on behalf of Boeing. JAL did not do the repair.

And if you read your own link you would see that it was Boeing's own repairmen that caused the faulty repair. JAL didn't do the repair.

Oh man, that captain screaming for more power [9:30] while the "pull up" alarm is going on, that is bonechilling. Thanks for the link.

Why did he want flaps AND power? Wouldn't flaps slow the plane making it more likely to stall?

Flaps do increase drag (especially at higher speeds) but they also decrease the stall speed which is why they're deployed during takeoff and landing-- they allow a slower takeoff speed. In effect, at lower speeds, the lift increase has a bigger effect than the drag.

See also https://www.quora.com/Why-does-deploying-flaps-reduce-stall-...

Flaps reduce stall speed as well as inducing drag; in the very short term, they prevent stalls.

I already had SEVERE fear / anxiety of flying before this video. I'm not sure I'll ever fly again. FML.

Note that this is a historical accident that hasn’t happened since and that accidents in aviation are extremely uncommon. You’re significantly more likely to get T-boned by a driver on their phone browsing Facebook than you are to encounter a minor incident in the air.

You should read Cockpit Confidential; it’s a great book written specifically to address your concerns

thank you, I'll take a look.

Well cars don't have drive recorders, they seem to cause a lot more deaths and probably should.

I think a lot of people have anexiety for flying, I useto for a while. The best recommendation I could give to get over that (or at least to mitigate it a little), is to do some flight lessons. I actually conpletly switched deom being nervous to wanting to fly fairly quickly :-)

I know for a fact that I would have far less fear (maybe even NONE) if I were the one flying the plane. One of these days I might take your advice and go for some flying lessons.

I know that the issue at its heart, is about control. In a commercial airline flight I have no control over anything, and that's the root of the fear. It's why I'm not afraid of driving, despite knowing my risks are statistically MUCH higher. At least when I get behind the wheel, I feel like I have the ability to do something about risks as they arise, even if my chances of reacting in time are extremely small, at least I can do something.

I couldn't help but think about being on that flight, for 30 minutes, knowing it was going to crash and being completely unable to do anything about it. I've always wondered what would be going through other people's minds? I would be having a crisis, and possibly would die from a heart attack before the plane even crashed.

For what it's worth, I'm a huge proponent of self driving cars BECAUSE I recognize the potential for a much safer world.

Tail-draggers died out for larger aircraft partly because the slanted cabin when on the ground was inconvenient. The DC-3 was the last successful tail-dragger airliner.

Wolfgang Langewiesche, in his 1944 classic, "Stick and Rudder", writes that the tail-dragger arrangement is a poor landing gear, but a good takeoff gear for underpowered aircraft. It gives the effect of flaps on takeoff for planes that don't have flaps. Tail-draggers are prone to nose-plant accidents and ground loops.[1]

Worst landing gear ever - the U-2. Two inline wheel sets.[2] That's the result of extreme weight reduction.

[1] https://www.youtube.com/watch?v=q5trygRQaV0 [2] https://www.youtube.com/watch?v=-ELjCkG4Gl0

Why aren't people reading the article? Yes, as engineers we tends to rationally think and come up with seemingly plausible explanations but like 3 comments out of the current 8 seemingly didn't even bother validating their theory or verifying whether the article offered an explanation! News for hackers indeed!

Yes, this is a frustrating trend. It would be nice to see ~2-week long posting bans handed out for this sort of behavior

Note that insinuating people haven’t read the article is itself against HN’s guidelines [1].

[1]: https://news.ycombinator.com/newsguidelines.html

This always reminds me of the rule that in parliament, MPs cannot accuse each other of lying [1]. People do it, we all know they do it, and it's a genuine problem that they do it - but we're not allowed to talk about it!

[1] https://www.theguardian.com/notesandqueries/query/0,5753,-22...

The solution there is the same as here. Point out how people are wrong, and if egregiously so, make it obvious that is the case. Replying "The article mentions this exact case and explains it" Is sufficient.

Is it accuse people of lying or present proof that they are either wrong, or knowing lying?

Otherwise I could just had me and a few friends constantly telling everyone that anything I don't like, is lying.

Well I have read the article, I have nothing to add directly, yet I have commented twice in reply to other comments.

Should I get a 2 week ban for bot commenting directly? Perhaps people want to discuss some issues raised or some side issue/interest about the article?

We are here to discuss afterall, and I am more than a little disappointed to see someone being upset for comments that may be to the side of the article.

If they were all political posts, okay I could understand, but they arnt.

Edit: I am reading the top third comments, most popular threads bottom thirds are, well ignored for a reason(and hence downvoted)

i read it, and now i am looking for articles on the 4 survivors of Japan Airlines Flight 123

I remember seeing somewhere that some planes were fitted with some wooden ball on the tail so it can touch the ground.

I think Concorde had a wheel on the tail.

And the Soviet Il-62. It was actually smarter than the more elegant British VC-10 as it permitted the centres of pressure ( wing position ) and gravity to be optimised for cruising rather than remaining in its main gear whilst in the ground.

i feel like it doesn't take a whole page to explain that planes are moving forward faster than they are gaining lift when taking off.

Perhaps an entire page is needed to explain that what you suggest is not at all the reason :)

horizontal velocity has nothing to do with it. It's because they gain a bit of lift before increasing angle

Horizontal velocity and lift are at least correlated. The reason the tail of the plane does not strike the ground in a proper takeoff rotation is because the pilot make sure the aircraft has sufficient speed (and indirectly, lift) to perform the rotation maneuver. The airspeed at which the rotation can happen is calculated based on weight and loading.

Or that the tail doesn't hit the runway because it's angled upwards.

I guess you can make it hit the runway, if you want. I watched a doc with them testing planes and they, quite literally, put some lumber on the tail to protect it from damaging the metal when they hit the runway with the tail. As in, they were intentionally trying to hit the runway with the tail.

Yes, the actual answer to the question is "because the pilots are trained not to hit the tail, since it's expensive and makes the passengers nervous."

It's a decent little article but it seems to not quite be on the same topic as the headline suggests.

Yes, pilots are trained, and the design helps too.

You first rotate the airframe at Vr speed (velocity rotate). Pilots are trained on their aircraft how much to rotate, and the design of the rear fuselage allows for initial rotation.

Once you have rotated (ie. nose up) you wait for positive rate of climb, and you depart the earth, and possibly even increase your rate of climb. All without hitting the runway.

Yeah, someone has added a video of this and it's currently at the top. I don't think I'd like to try that.

I know of at least one major crash caused by a tail strike, although the problem took years to manifest after a bad repair job: https://en.wikipedia.org/wiki/Japan_Airlines_Flight_123

(Worth noting that this airplane's tail strike happened on landing, not takeoff, but it's bad either way.)

Definitely best to avoid them if you can....

"Explosive decompression": https://youtu.be/awMHJ_ZZF5Y

That doesn't prevent tail strikes. The article provides many examples of how the (angled) tail of an aircraft can strike the runway during takeoff and landing.

Omg, scary stuff. How can we check the planes we are boarding have never had this airstrike repair? Sounds crazy.

You can't and without specialized experience you probably wouldn't know what to look for anyway. This is why we have regulatory structures in place to ensure airworthiness.

The tail wont hit the ground because the engineers designed the tail in a way so it wont hit the ground.

It is very easy to cause a tail strike. The article provides multiple examples of how this can and does happen.

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