Handyman
Hug someone you care about...
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Business, Economics, and Taxes: Capitalism. Yay? >=(
- Thread starter RaceBoarder
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Welcome to America :^p
Handyman
Hug someone you care about...
https://twitter.com/CNN/status/1380497176741175296
Doesn't sound like the hugest deal in the world...but bad headlines seem to follow this aircraft these days.
Doesn't sound like the hugest deal in the world...but bad headlines seem to follow this aircraft these days.
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I still have no idea how much I could actually be approved for. Ive always settled on a number I felt good about, and then went and got pre-approved for that. For fun, I've tried some "how much can you afford" calculators online, and they seem to always come up with something WAY more than what I would actually feel comfortable with.
Kepler
Cornell Big Red
I have a short bus E&M question.
How can the electrics in an airplane in flight be grounded?
I am mortified by how dumb this is. I'll hang my head in shame and listen.
French Rage
NICKERSON HAS [CENSORED]
If I'm understanding this correctly, you basically try to pass the current to the outside of the body so it can dissipate into the atmosphere: https://monroeaerospace.com/blog/how-are-airplanes-electrically-grounded/
Spartanforlife4
Generic Catchy Message
It took years and multiple elections at the Smithfield pork plant in NC to finally unionize. As long as this is the start of momentum and not a one-and-done moment, it'll happen eventually.
Kepler
Cornell Big Red
I'm sure they were made to understand that if they unionized they would close the facility. Ownership doesn't need to smash heads anymore -- they play the rubes off against each.
Handyman
Hug someone you care about...
Wouldn't that run afoul of the NLRB? Amazon doesn't want to tick off the Feds with a retaliation against legal unionization.
(asking legitimately I never understood Labor Law)
Ouch. Reading what laypeople write about technical topics that you are an expert on is like Yo-Yo Ma listening to a rendition of Bach's Cello Suite 1 by a 3rd grade recorder choir. Sure, some of the notes are recognizable, but dear god, my ears!
This is more-or-less impossible to explain without a whiteboard, but I'll try to get a few points across:
1. Your car is also not "grounded" to the earth (the only thing touching the ground are 4 pretty darn good insulators), so there's nothing all that special about airplanes in that regard.
2. While an airplane is in flight, or while your car is driving down the road, it definitely can build up static electricity that puts the vehicle at a different voltage from the ground. That either dissipates gradually over time, with electricity "leaking" very slowly via those highly resistive paths (via the tires or directly through the air - neither are perfect insulators), OR, when something does provide a conductive path from the vehicle to the ground, the electricity will discharge rapidly in a "static electricity" spark - exactly the same as when you scuff your feet on the carpet (building up charge on your body) and then touch a conductive doorknob (dissipating that charge very rapidly). You don't know this, but every single time your airplane comes into the gate, a ground crew member attaches a conductive wire to the airplane to do exactly that, so that nobody and no equipment gets sparked when the jetway touches the airplane or people disembark the airplane. If you drive a long distance, the same thing can happen to your car, and when you step out, you will become that grounding path and there will be a spark to your shoe - but you don't feel it, because of your shoe. This is why it is not a good idea to climb back into your vehicle while you're pumping gas - when you climb back out, there could be a spark. Sometimes you'll see trucks that carry explosive materials have a chain dragging on the ground, which is there to dissipate static electricity continuously, as soon as it is generated, so that you never get one big spark.
3. When we talk about "the" voltage of the airplane/car, that's a bit oversimplified, because of course there are many things at different voltages all over the aircraft. However, in general, what happens is that aircraft designers make sure that all the big metal pieces of the airplane (ribs, spars, skins, engines, etc) are electrically bonded together and that "chassis" becomes the "ground" for the airplane (car designers do the same thing). The electrical generator on board the aircraft has its negative terminal tied to the chassis, and then its positive terminal is the "hot" side that provides power out to all the devices on the aircraft that run on electricity. if you have a 270V generator, then your positive voltage will always be 270V above the chassis (whose voltage relative to the earth floats, as we've already talked about). Electricity leaves the generator, goes through various switches (remember this, it becomes important in a minute) and circuit breakers and finally to a pump or a flight computer or a cockpit display or whatever. Those devices "use up" the energy contained in the electrons flowing through it, and then return those electrons to the chassis and therefore to "ground" terminal of the generator, completing the circuit.
4. Those switches and circuit breakers in the loop are not all that different from the circuit breaker panel in your house - a "trunk" line of major power comes in from the generator, and then the electricity gets distributed out via the individual breakers to many different circuits. The biggest difference for an airplane circuit breaker panel is that the whole thing is computer controlled, so a control program can command individual circuit breakers to open and close (so long as they haven't already tripped due to over-current), which is how most devices on the airplane get turned on and off. So that "circuit breaker panel" is a pretty complex device in its own right. With lots of complexity, comes lots of failure modes. If "stuff" happens inside the box and electricity tries to go where it shouldn't, then that box needs to have a way to release those electrons safely back to the chassis, or too much electricity will build up inside the box. That eventually will get out, but if you don't have a designed-in path, then where it ends up going is pretty unpredictable, and chances are that it will end up putting more current through parts of the device than they can handle and those parts will burn. From what I can tell from news reports I've read (I have no insider information), 737MAX has an issue with the grounding of their circuit breaker panel, such there are probably a few bizarre, extremely improbable failure modes where the box would end up not able to dissipate the current back to the chassis. Who knows how they discovered this issue now, but these things are constantly being re-visited as airlines have trouble in the field with X or Y, and a new engineer gets asked to take a look at something and that new set of eyes sees something that the prior one did not.
5. Note that none of what I've talked about so far has anything to do with lightning. A lightning event (a huge current of electricity entering from outside the airplane) is nothing like what I described above, which would be called an "electrical fault" event. An electrical fault is simply when a piece of electrical equipment on board the airplane puts a moderate electrical current (that you generated intentionally in your generators) somewhere that it shouldn't be. When an airplane gets hit by lightning, the whole name of the game is to be sure that your skin (where the lightning enters) is electrically bonded so tightly to the chassis that the electricity hits the skin, immediately takes the path of least resistance through the chassis, and then exits the airplane at a different point on the skin. Lightning never "stops" at an airplane - it always just passes through. The idea is that you only want it to pass through the skins and the chassis, and not through any of the computers or other sensitive electrical equipment. If you do it well, a massive lightning strike can flow through the chassis, and none of the equipment (which all uses that chassis as a ground) will even notice - the equipment simply continues to "float" at +270V (or whatever your generator produces) above the chassis throughout the event. The chassis voltage will rise and fall as the lightning passes through, but the equipment won't care - it just floats along for the ride.
Well, that was more than I meant to write, but I hope it helped and was maybe even a tiny bit interesting in places....
Random aside: I’ll always remember my a-ha moment regarding layman journalists. At Cornell, I was friends with a polo team member who happened to be an English major. She did a summer internship at Polo Magazine (or whatever the premiere polo magazine is called). Out of the entire magazine staff, she was the only one who had ever even sat on a polo pony. The rest were just journalists with a gig - next week they might be writing for Gardening Monthly or the Journal of Gothic Tattoos.
Um.... that’s not how it works. ESD shoes keep your body from building up static charge while they are in contact with the ground - exactly like the chains that trucks drag behind. If you’re in a car with your feet off the ground, they don’t do squat - your body will eventually equalize to the same voltage as the car. When you step out of the car, you’ll still be at a different voltage from the ground and therefore have the potential (no pun intended) to generate a spark.
dxmnkd316
Lucia Apologist
I suppose you're right, because it's the car you're discharging not your body. So there are really two scenarios here. Grounding the car and anything you've built up by sliding across those sweet shag carpet seats, speaking for mookie of course.
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