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My signals processing professor apparently knew one joke, and one joke only. "A LOT (Polish airline) airplane is about to land in New York City; as they align
by lb1lf 4y ago
My signals processing professor apparently knew one joke, and one joke only.
"A LOT (Polish airline) airplane is about to land in New York City; as they align for final approach, the first officer notifies the passengers that those seated on the right can now see the Statue of Liberty. A number of passengers get up from their seats left of the aisle and lean over the people seated on the right to get a glimpse of the statue. Plane promptly crashes.
Why? There were too many Poles in the right half of the plane.
I'll lead myself out.
- gugagore 4y agoThe article saying zeros (where the transfer function is 0) when it should be saying poles (where the denominator of the rational function is zero), right?
- themeiguoren 4y agoControls engineer here. The author’s control theory knowledge is correct - a RHP zero indicates that corrective action will begin in the wrong direction (which the article compares well with countersteering on a bike). The technical term is a “non minimum phase system”. It’s possible this will lead to instability, but in general the long term stability of a system is determined by the location of its poles (which is more applicable to the author’s ice cream example). Poles in the RHP will cause a system to blow up. My gripe with the article is that the author tries to wow you with some obscure technical points about a system which is unmodeled and he does not understand, to wave his hands at a vague conclusion. If he had made the same point using common English phrases that encapsulate the idea (“positive feedback loop”, “we have to let it get worse before it gets better”, etc), then it would be a lot clearer how wispy his argument is.
- l33t2328 4y agoI hate to be the guy to ask you to explain the joke, but why would that make the plane crash? I do know what a “pole” refers to, but I don’t follow the crash bit.
- ad404b8a372f2b9 4y agoThe weight imbalance from everybody rushing to the right made the plane unstable.
- 22c 4y agoInterestingly, I recently spoke to a loadmaster who told me that left/right side weight distributions are far less important than forward/aft, to the point that for the majority of aircraft they're loading, imbalance to the left or right side of the plane aren't accounted for at all.
- eftychis 4y agoYes you want the center of mass to be more forward than the center of lift. Otherwise, a small deviation in the pitch becomes hard to impossible to recover -- the system is unstable and stalls extremely easily. If that is a fighter plane of course you want that, so you make sure the opposite is true, and have a computer counteract that during normal flight.
- cwillu 4y agoI laughed the first time I made an airplane with the centre of mass behind the centre of lift in Kerbal Space Program.
- 2-718-281-828 4y agothis is the only answert to the question above and it's being downvoted? welcome to hacker news ...
- stephen_g 4y agoI didn't downvote it, because it's not a bad attempt at an answer if you don't know the context, but the actual joke is completely different and about calculus and control systems. The right side of the plane is double meaning for the right half of the complex plane in dynamical systems analysis, which is the area where the real part of every point is positive. If your poles are on the right half of the complex plane, then the system is unstable and the output will tend towards exponential growth (going out of control) for any change in input.
- dreamcompiler 4y agoDid we have the same professor? Mine loved that joke too. The students in the classroom next door always knew when Prof Lipovski told his joke because everybody along the hallway could hear the loud groan emanating from our room.
- a9h74j 4y agoHeard a varient at Berkeley from a professor of Applied Math, which you would probably no longer hear. Generic airline, specifically Polish people were asked to move to the left side of the plane. Because "Poles in the right half plane cause instability." (As for application in economics, economist Steve Keen, for one, explicitly models time delays and dynamics, with results worth learning from, AFAIK.)
- Natsu 4y agoI think all systems professors have the same joke book and there's only one page in it :)
- cperciva 4y agoThere was nearly a disaster earlier in that flight too, when the pilots got sick from food poisoning and the cabin crew had to ask if any of the passengers knew how to fly a plane. As it turned out, one of the passengers had flown many years previously, and offered to try. When he reached the cockpit, however, he took one look at all of the controls on the modern aircraft and realized that he wasn't going to be able to operate it. When the chief steward asked why, he replied, "I am just a simple Pole in a complex plane". I'll follow lb1lf out.
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- drekipus 4y agoNow this made me laugh like crazy
- danuker 4y agoIt has a grain of truth to it. Poland could donate MiGs to Ukraine, but other countries with US fighters could not, because Ukrainian soldiers didn't know how to fly them.
- Tuna-Fish 4y agoActually not true. Many Ukrainian fighter pilots have received training in the US, where they flew F-16:s. (That is, before the current phase of the conflict.) The hard part is actually the maintenance crews. A modern fighter plane requires constant intensive mainentance, they generally spend much more time being worked on than they spend actually in the air. And this maintenance work requires a lot of specific skills that don't necessarily translate well or at all between aircraft types.
- jacquesm 4y agoAnd a steady supply of parts.
- jacquesm 4y ago
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- ldite 4y agoAnd you know why the contour integral of Western Europe is zero? Because all the poles are in Central Europe. (sorry)
- jimnotgym 4y agoAs a resident of post-Brexit Britain, I was horrified as I read this expecting it to have the opposite punchline and to turn into an anti-immigration joke. For those that don't know, Polish (and other Eastern European) migration was a major issue raised by some in the Brexit campaign.
- kaashif 4y agoA more horrific and offensive version of the joke, which I actually saw recently as output from fortune [1], adds a part about the contour integral of the whole of Europe still being zero because the Poles are removable. [1]: https://en.wikipedia.org/wiki/Fortune_(Unix) https://en.wikipedia.org/wiki/Fortune_(Unix)
- samfriedman 4y agoThe version my professor told was, “Why is politics in Poland so volatile? Because all the Poles on the right are unstable!”
- selimthegrim 4y agoThe real answer is Ilyushin made terribly finicky engines and people skimped on maintenance but that’s another story.
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- chkaloon 4y agoThat joke is at least 38 years old, as I heard it in my controls class in 1984 :)
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