Hacker News Reader

Comment by WalterBright | Hacker News Reader

When I worked at Boeing, I talked about autoland systems with my lead engineer. He said the autoland was too perfect, as the airplanes would touch down at the same place every time.

This caused that place in the runway to suffer severe fatigue damage.

View on HN

IIRC, there was a similar problem on aircraft carrier flight decks, where they had to induce some randomized amount of dispersion to keep the tailhook from hitting the same spot over and over again.

Hmm in distributed computer systems similar patterns exist, e.g. adding jitter to avoid thundering herd effects.

This feels like an essential pattern of the universe or something…

"Spread spectrum" is used in EE to spread out the frequency ranges used and reduce interference. The extreme version being CDMA.

Intriguing

I work at a self-driving car company and we observed a similar problem when we did some off-road testing on dirt tracks. The cars were too precise and they were cutting deep ruts into the soil. We too solved it by adding a pseudo-random offset to the track.

Before the current wave of automation there was a previous technology to automate buses using optical sensing and lines in the road which had the same issue.

If you want rails: build rails.

There are entire subway systems built with tire-on-concrete where the trains ride precisely the same routes down to the millimeter. Montreal’s is a famous one. These systems are not as efficient as rail, but they are quieter and gentler than the typical subway.

That's still rail. It's just not steel-on-steel.

Otherwise you'd have to seriously limit what systems you call "monorail".

The problem is that the optical guided bus was built with the intention of reducing cost, since painting lines is a lot cheaper than building rails.

The moment you have to build rail-like things you lose most of the cost advantages.

I believe Google Maps adds a bit of a rng in which route it will recommend when two otherwise similar in distance/time. Obviously the traffic input also affects this, but that's a slower feedback mechanism; better to distribute the cars all leaving the airport for downtown across the 2-3 possible routes upfront rather than dumping them all onto route A until it's a jam and then all onto route B until it's a jam, etc.

Annealing.

I'm sure Google Maps has had to put their thumb on the scale in numerous instances. I recall reading articles about it "discovering" more optimal routes between Point A and Point B only to find things like the new "optimal" route being down a neighborhood street, and then the locals started squawking.

Citation please. Doesn't pass the sniff test.

I suspect the ocean in its various states provides quite a bit of dispersion. Replacing deck plates on a ship is a normal part of maintenance. I find it very hard to believe they'd induce randomness rather than having just that one plate get a different hardness (I know some people will screech about that but trust me, the warship industry is well practiced at such things).

Not sure about the ocean industry but carrier landings have full autoland support for a long time (see e.g. magic carpet).

I wouldn't call it a "long time." MAGIC CARPET per se, especially as a default mode of operation, did not become mainstream until the last 10 years, and that's only for the aircraft that have it.

I interpreted the effect here not to be on the deck plates but to be the point of impact between the cable and the hook. Sudden bends in cables can wear them fairly quickly in the immediate vicinity. I'm sure you can extend cable life proportionally to the spread of the loading.

That makes far more sense.

Citation is my professional network as a former Naval Flight Officer who flew off aircraft carriers, and it's not the deckplates, it's the nonskid coating that goes on top of them. It's expected to wear and be replaced every so often, but when you have to do it more often than that, it becomes a pain logistically and operationally.

And the entire point of the system is to counter the dispersion the ocean provides, much like a Naval Aviator is already required to in order to trap successfully. You are literally flying through a very narrow window that is moving in three dimensions.

Similar problem with catenary wires on electric trains wearing into the contacts. The wires zigzag to distribute the wear.

Reply on news.ycombinator.com