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It's Too Hot For Some Planes To Fly In Phoenix (npr.org)
In Phoenix on Tuesday, temperatures were forecast to climb as high as 120 degrees Fahrenheit, causing more than 40 American Eagle regional flights out of Phoenix's international airport to be canceled. NPR reports: American Airlines said in a statement that the Bombardier CRJ aircraft used on some shorter routes have a maximum operating temperature of 118 degrees. For bigger jets, the threshold is higher. The carrier says that, for example, Airbus aircraft have a maximum operating temperature of 127 degrees and that for Boeing, it is 126 degrees. As USA Today reports: "Extreme heat affects a plane's ability to take off. Hot air is less dense than cold air, and the hotter the temperature, the more speed a plane needs to lift off. A runway might not be long enough to allow a plane to achieve the necessary extra speed." Bianca Hernandez, a meteorologist with the National Oceanic and Atmospheric Administration, tells NPR that Phoenix is seeing an unusually strong high-pressure system, which is causing the soaring temperatures.
This actually isn't all that uncommon around the world, at least to varying degrees.
Hot air, at high(er) altitudes is less dense, which will affect the performance of an aircraft to various degrees. The usual effect is that reduces the aircraft's MTOW (Maximum Take Off Weight). If it drops below a certain point, it's either uneconomical to fly the plane, or it can't carry enough fuel to do its job.
Many years ago, Air Canada used to fly to India using Airbus A340s. At certain times of year, it was hot enough in Delhi that they could not take off with sufficient fuel to do DEL->YYZ direct, and instead they would have to make a technical stop in Turkey to refuel the aircraft. This is also one of the reasons why most long-haul international flights fly in and out of Delhi at night. The air is cooler, giving the airliners better performance.
...si hoc legere nimium eruditionis habes...
Phoenix has only had three previous days with a temp of 120F or higher, all occurring in 1990 or later. Such temps were not recorded there any other time since 1890s.
And you're perpetuating a common falsehood, that's been thoroughly debunked.
It's a nice story, but it's not true. The origin of the scale comes from Ole Romer who set freezing of water at 7.5, and human body temperature at 23.5, and boiling point at 60. Fahrenheit didn't like this scale because of the fractions so he just bumped everything up by 0.5. Freezing at 8, body temperature at 24. Later on he multiplied everything by 4. Freezing now becomes 32, body temperature 96, boiling at 212.
But there's probably more to the story, since 1oF increase in temperature increases the volume of Mercury by 1 part in 10,000. Did this play into it? No one knows.
Interesting story. I highly recommend Veritasium's video on the subject:
https://www.youtube.com/watch?...
I'm up at 0315 for a training flight in a balloon this morning. Sunrise is at 0450. I intend to have landed by 0730, and this has little to do with the heatwave we're experiencing.
The reason balloons operate near sunrise and sunset is not specifically to do with the temperature, but actually to avoid thermals, which are generate by temperature differences (strictly, different heating rates of areas on the ground). Thermals that would be fairly pathetic for a glider pilot (which I used to be), say anything up to 200 ft/min up or down, would be enough to cause issues for balloons. Meaningful thermals (more than 200 ft/min up or down) would make the balloon very hard to control, since up and down control is the only way a balloon pilot can steer and uncommanded up and down movements (especially on landing!) mean you don't know where you're going to end up.
As far as temperature is concerned, the balloon flies a bit better in summer but can carry less weight. The balloon is less buoyant in hot air which is thinner as the parent(s) point out, so in general you can carry more weight in winter (or at lower altitudes - "pressure altitude" is still a relevant thing to look up). The big deal with temperature for me is actually that the fuel pressure drops a lot with falling temperature (liquid propane expands and contracts far more than water does). This means that in winter, less fuel is supplied each time I burn, meaning less heat output per burn. I have to burn more frequently to maintain level flight, or constant climb/descent rates.
I knew I needed to stop reading Slashdot and finish my PhD when I started to miss articles by Bennett Haselton.
The core value of metric is not just the decimal calculations, but that the units for different measures, such as weight and volume, fit together in an easily comprehensible way. No more medieval mess of fluid ounces, cups, pints and gallons.
The original measurement was that 0C was the freezing point of water at sea level. This has since been changed so that 0.01C is the triple point of water, exactly -- or more specifically, 273.16K . (The triple point of water is the temperature and pressure at which water can exist in all 3 states simultaneously, which is 273.16 K (0.01 C) at 0.611657 kPa (0.00603659 atm)).
This was chosen because the triple point is at an exact temperature AND pressure. If either the temperate or the pressure are changed then water cannot exist in all 3 states. There's no "at sea level" here, as that can be somewhat arbitrary, thus leading to a fluctuating 0C.
https://en.wikipedia.org/wiki/..., if you want to read more.
The vast majority of SI units are specified so that they can be measured in a lab -- the kilogram being an obvious exception to this, but that is something that should be resolved soon. The definitions of all of the SI units is actually fairly fascinating, and I recommend reading at least the Wikipedia article about them.
https://en.wikipedia.org/wiki/...
This lists the original measurements (such as the metre being 1/10,000,000 of the distance from the North Pole to the Equator (through Paris, for some reason)), and how the definition changed until the current definition was reached (a metre is the distance light travels through a vacuum in 1/299,792,458 seconds).
It gives reason to all of the measurements, and shows how they are all (mostly) interlinked, again with the obvious exception of the kilogram.
Incidentally, the inch, which is the basis for all imperial units of measuring, is 25.4mm exactly. So all measurements in the US are actually based on SI units. https://en.wikipedia.org/wiki/...
All weights are also based on SI units: https://en.wikipedia.org/wiki/...