ETOPS is (was) for planes with two engines. The thinking was that if one engine failed, you only have one engine in reserve. If it, too, fails, the passengers will be swimming for hours or days before help can arrive. Overland, the loss of both engines leaves the pilots with one final option before passengers are endangered: A dead-stick landing on the ground (See: "Gimli Glider"), or near enough to land for the passengers to be quickly rescued (See: "Miracle on the Hudson"). Flying out to sea, you can't expect a quick rescue after a forced landing. Regulatory authorities don't like it when you are operating with no redundancy left. They really hated the idea of twin engine aircraft flying over the ocean, just two failures away from catastrophe.

ETOPS initially said that If you wanted to fly a route that took you more than 60 minutes from land, you couldn't use a twin-engine plane. You had to find a plane with more than two engines.

You don't want to fly a three engines plane because it is less economical, but you are required by law to use at least three engines. You could use four, but that's even less economical. There was no practical need for three-engine aircraft (outside of extraordinarily rare double-emergency situations), but the law regulating twin-engine planes prohibited them from making these flights. Airlines needed three-engine planes to bypass this law.

ETOPS certification was incrementally expanded from 60 minutes to 370 minutes for some twin-engine aircraft and airlines. If you could prove your engines were reliable enough, and your maintenance program thorough enough, you could acquire additional certification to fly farther from land. With such certification available, more routes can be legally operated with twin-engine aircraft. Fewer routes legally require three engines. Presently, 99.7% of the Earth's surface is within 370 minutes single-engine flight time of a major airport. 99.7% of all possible flights can be undertaken with twin-engine aircraft. There was never much practical use for a three-engine aircraft in the first place; now there is only 0.3% of a legal requirement left. It's now cheaper to slightly alter one of the few remaining routes that twins can't legally perform than to maintain fleets of tri-jets to perform them. (Basically, they have to fly around the south pole, rather than directly over it, so they stay within 370 minutes of airports in South America, Africa, Australia, etc.)

Even 4-engine aircraft are being replaced with twins. Boeing ended production of the four-engined 747 in favor of the twin-engine 777 with nearly the same capabilities, because carriers prefer jets with two huge engines instead of jets with four smaller engines. Twins are simply more efficient to operate. The only thing that stopped them from using twins was the law, and the law has stepped out of the way.

You are correct that I don't understand your point, but I think the problem is that I failed to adequately explain the law. Your criticism doesn't seem to address a situation the law was trying to regulate.

Aircraft are designed with engine-out operation in mind. The vertical stabilizer provides sufficient yaw authority to operate with an engine out.

You don't shut down a good engine if you don't have to, because you might need it, and it might not start again. You might increase thrust on another engine on the same side, or reduce thrust in an opposing engine, but you're not going to shut a second engine down after one has failed.

The planes with single engines in the vertical stabilizer are due to a law that required twin-engine aircraft to always be within 60 minutes of an airport.This regulation came to be known as ETOPS: Extended range Twin engine Operation Performance Standards. (Or, "Engines Turn Or Passengers Swim)

This law did not apply to jets with 3 or more engines. If carriers wanted to fly longer, over-water routes, they had to follow coastlines, or fly planes with more engines. It's cheaper to operate 3-engined aircraft than 4-engined, so the market made 3-engined aircraft.

Planes with an odd number of engines can't divide them between the wings; they need the odd one in the fuselage. It has to point aft, so the tail is the natural choice.

With improved jet engine reliability, ETOPS standards have been extended from 60 minutes to 120 minutes in 1985, and 180 minutes in 1988. Some twin-engine aircraft are now certified to fly up to 370 minutes from a diversion airport. The era of trijets is rapidly coming to a close.

I don't know if adiabatic processes are responsible for the temperatures in the core, but if it is, it would be more accurate to describe this in the past tense, rather than the present tense that the other commenter used:

>"High pressure makes made the core hot"

You made the same distinction:

>the earth was pressurised

That being said, I doubt adiabatic heating plays a significant role. Adiabatic processes operate through compression, not pressurization.

Suppose I have a sealed tank of water. I put a balloon inside it. Then I pressurize the water to double the pressure in the tank. The volume of the balloon shrinks.

Here's the important part: Even though the balloon is half the size now, it still has the same amount of heat: none has entered or exited yet. The same amount of heat in a smaller volume means the temperature has risen. That's adiabatic heating.

Replace the balloon with an iron or nickel ball. When you double the pressure, the volume of the ball doesn't change. Increase the pressure a hundred times, a thousand times, it doesn't matter: the volume of the ball stays the same. The heat within the ball is not concentrated. There is no adiabatic process involved.

With the core of the earth being primarily comprised of non-compressible materials, I don't think adiabatic heating explains the temperature of the core.

The relationship between temperature and pressure does not work the way you are describing. A substance is not at a given temperature just because it is at a given pressure. Pressurize one cylinder of nitrogen to 30PSI, and another cylinder of nitrogen to 3000PSI. Leave them alone in a room for awhile, and they will both become room temperature.

The temperature of a given mass is not dependent on its static pressure, but on changes to its pressure.

You are (effectively) arguing that adiabatic heating is responsible for the heat of the earth's core. To make this argument, you will have to show that the earth's volume is shrinking, or otherwise demonstrate that the pressure at the core is not just high, but increasing.

Without a pressure change, we need to look at the heat entering or exiting the system. The simple fact is that relative to the total amount of heat within them, very little heat actually leaves the core and mantle. At the current rate of dissipation, it will take billions of years to remove a significant amount of that heat.

An owl certainly can kill a cat, but that is by no means a sure thing.

This owl ultimately suffered a dislocated wing, while the cat walked away without a scratch. In the wild, that's a fatal injury.

OP's owl weighs in at about 3 pounds. That cat, at least 10. If the owl were airborne and able to ambush the cat, the cat is toast. On the ground, that owl vs that cat? I'd put my money on the cat.

This is like a knife-wielding 10-year-old against an unarmed, full-grown adult. The kid wins every time, if he gets to ambush the adult. If he doesn't, the adult is probably going to get cut up a bit, but will ultimately prevail.

You're down voted, but I agree with you. House panthers are able little killers. That bird is posturing to make itself look big, but that cat is easily twice its weight, and much more nimble on the ground. Any altercation is going to be on the cat's terms, not the bird's.

Turn off the main water supply to the house. Also, close the supply valve to your water heater, just to isolate it.

Open an interior tap. Backfeed compressed air (about 20-40PSI) into the spigot. This will push the water down the supply piping.

When air starts spitting out of the interior tap, close the ball valve for the exterior line. Turn on the house supply, wait for the air to burp out, then shut off the interior tap and open the water heater.

I'd probably try digging some deep holes on the uphill side with a post hole digger, and just laying a paver or a flagstone over them. With some luck, frost heave will shove it back into place after a few freeze/thaw cycles.

No clue if it would actually work, of course.

As others have said, it is just convention. The convention relies on an implied order for summation and multiplication, and that can get you into trouble if you're not careful to provide the explicit order. For example, when for part of your problem, you come up with the equation X = 2Y + 4. In another part, you discover that Y = X + 4. You substitute X+4 for Y in the first equation and you come up with X = 2X + 4 + 4. This is wrong, but a student early in their learning might not immediately understand why. I should have used brackets/parenthesis around the substitute term when I replaced the variable. X = 2[X+4] + 4

If the implicit order of operations (the "DMAS" part of "BEDMAS") is causing you problems, I suggest eliminating it before you start working on the problem. Translate the problem from an implicit order of operation to an explicit order of operations: BRACKET ALL THE THINGS!

X = 2Y + 4 <-- Nah.

[X] = [ [2 * Y] + [4] ] <-- Yes!

It might be a crutch, like counting on fingers to add or subtract, but it was the only thing that worked for me. I still use it when I'm not completely sure that Excel and I agree on the implicit order in a formula.

False. Current code only requires lighting switches to have a neutral, and even then there are 7 broad exceptions listed in the code, and 3 of those exceptions could apply here.

404.2(C).

Neutrals are not required in "every" switchbox now. They are only required for switches controlling lights. Even then, there are seven broad exceptions listed in the code.

Look up NEC 404.2(C).

>I've seen tutorials showing that way, but then I've also seen some say that the new NEC updates for 2018(?) made it a requirement to use 12-3 and include a capped neutral... for whatever reason.

This is inaccurate. The NEC requirement is 404.2(C), and applies only to switches controlling lights. Even if it did apply to more than lights, you are not obligated to upgrade your switch wiring to the new code.

And even if it applied to non-lighting and you were obligated to update it, there are seven listed exceptions, and three of them would probably apply: #2, you have access to the wiring without removing finishing materials; #4, the switch serves only a specific appliance rather than the entire room; #7, receptacle loads. (If the switch controls a receptacle rather than a light, it does not require a neutral.)

The purpose of the NEC requirement is that "smart switches" need a neutral return to provide power for their circuitry.

The way they had it set up is not ideal from a maintenance and repair perspective (you have to pull the dishwasher to repair the disposal), but is perfectly fine from a wiring perspective.

Can you cite this? The only reference I've found is to 404.2(C), which clearly specifies that it applies to switches with lighting loads. A garbage disposal is certainly not a "lighting load".

Further, there is specific exception in 404.2(C) for "receptacle" loads, which is what OP is trying to set up.

The standard does not need to include any duration from when the clock starts to when the runner may begin moving. If they can figure out how to time it so that they start moving at the exact same instant that the starter is fired, it should not be considered a false start.

Lol, ok, add "Cunningham's Law" to your list. It is, actually, the relevant concept.

Oh, I'm thinking of Rule 34.

I thought the 80/20 thing was Hanlon's Razor.

Pretty sure it's the Pareto Principle.

Yeah, this is known as Godwin's Law.

Insurers are going to try to deny coverage on any grounds they can invent. Merely having a leak in the roof can result in a denial of certain coverage. Failing to adequately anchor the tarp can result in a denial of coverage, as well as open you up to liability if your weighted-and-not-anchored tarp goes flying in a storm and causes further damage to the house, cars, neighboring property, etc.

If it's leaking, the roof needs considerable repair anyway. There's little risk to anchoring the furring strips to the deck. If you're not going to anchor the boards to the roof, don't use them at all. Just tie off the tarp to anchors on the ground.

The more important factor is getting the roof properly repaired as soon as possible.

If you have any access to the attic, leave the door or hatch open. A fan in the attic area would also be useful.

I used to work in property preservation. That's exactly what I would do. Make sure you cover all the way from the peak down to well below where you think the leak might be.

If the weather isn't conducive to immediate repairs, I would advise laying down the tarps, then using 1x2" furring strips to hold down the edges. Just lay them down on the edges of the tarp, and screw them to the roof.