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November 17

A lead zeppelin is your stairway to heaven?

In terms of fatalities per passenger-mile, and excluding combat losses during World War 1 (but including accidental losses during the same time period), which airships were more dangerous to fly in, those filled with hydrogen or with helium? I'm aware of the argument that helium-filled airships have a narrower flight envelope, which causes them to crash more often -- but, on the other hand, the flammability of hydrogen often had the effect of turning an otherwise survivable crash into one which is fatal for everyone on board, and also created the danger of explosion from lightning strike -- so between these two dangers, which one was the greatest? 2601:646:8082:BA0:CD5E:73B7:6DF6:2CF6 (talk) 03:41, 17 November 2024 (UTC)[reply]

Is there a source for the claimed explosion? It is not plausible, scientifically. --Lambiam 08:48, 17 November 2024 (UTC)[reply]

In what way not plausible? If your objection is to do with needing oxygen, that airship probably leaked: six months previously, "many small tears appeared". Card Zero (talk) 09:39, 17 November 2024 (UTC)[reply]

It would leak hydrogen out, not oxygen in. --Lambiam 10:16, 17 November 2024 (UTC)[reply]

So if a leak of hydrogen into air is hit by lightning, on top of a balloon made from sausage skin that's filled with more hydrogen, how do you imagine events would unfold after that? Hindenburg_disaster#Lightning_hypothesis says that airship fires have been observed under these kind of circumstances. I'm surprised that they were only fires, it makes the outcome sound mild, like lighting a gas stove. Card Zero (talk) 10:52, 17 November 2024 (UTC)[reply]

If there's a leak in the gas bags, it's plausible you may get an explosive mixture in the space between the gas bags and the outer hull. What exactly happened to Dixmude may never be known, but whether it was an explosion or rapid burning, too rapid for an orderly emergency landing (Hindenburg burned all its lifting gas in about half a minute), doesn't matter; all on board would be dead anyway. PiusImpavidus (talk) 14:00, 17 November 2024 (UTC)[reply]

That would indeed explain it. Without prior mixing with oxygen-containing air, hydrogen burns fiercely in a rapidly advancing front, as seen in the Hindenburg disaster, but not so rapid that there is an explosion. --Lambiam 16:46, 17 November 2024 (UTC)[reply]

I found a source, but no explanation. --Lambiam 10:30, 17 November 2024 (UTC)[reply]

According to the footnote in this republished 1923 article, there was an inquiry in January 1924, so maybe there is a report out there somewhere. Sean.hoyland (talk) 10:38, 17 November 2024 (UTC)[reply]

This is hard to say...

A helium-filled airship has less lift for the same volume, so it has to compensate somehow: fewer passengers and passenger-kilometres, giving more accidents per passenger-kilometre, or lighter skin, frame or engines or less fuel, all increasing accident rate.

A helium-filled airship is less likely to burn. The hydrogen fire itself isn't very lethal (except for those sitting high up in the envelope), but it can accelerate the destruction of the airship, leading to a faster crash, and set the skin and fuel on fire, leaving burning wreckage, which can kill passengers.

A third effect, which you didn't mention, is the heat capacity ratio. Helium has a heat capacity ratio of 1.66, hydrogen of 1.41, just like dry air, and moist air has an even lower heat capacity ratio. This means that on descent, helium heats up by adiabatic compression faster than hydrogen or the surrounding air, increasing the stability of the airship. When flying in slightly superadiabatic dry air, a hydrogen-filled airship is unstable in altitude. If it descends, the lifting gas heats up slower than the surrounding air, decreasing lift and accelerating the descent. This is no problem for helium-filled airships. Those have difficulty changing altitude faster than the time needed to equalise inside and outside temperature.

When looking at fatalities per passenger-kilometre, it's best to look only at passenger flights. Including military flights, test flights and accidents on the ground will increase the number of accidents without adding passenger-kilometres, making the airship appear more dangerous. Worse, those were the most dangerous occasions for airships. Ground accidents happened when the airship was grounded for bad weather, test flights were obviously more dangerous than regular flights and even when excluding combat damage, military flights were more dangerous as the airship was flown in weather and through manoeuvres that no captain would attempt on a civilian flight. However, excluding all military flights will exclude all helium-filled rigid airships, so no useful statistics are left. The safety record of those four helium-filled rigid airships of the US Navy doesn't appear too good though: three fatal crashes in only a third of the flight hours of Graf Zeppelin. PiusImpavidus (talk) 16:50, 17 November 2024 (UTC)[reply]

As noted in List of airship accidents, there is a variety of causes, a number of them being weather-related. The most successful airship was the Graf Zeppelin, which was filled with hydrogen, but never burned up or crashed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:55, 17 November 2024 (UTC)[reply]

There were no helium-filled passenger airships - they were all operated for naval reconnaisance. Alansplodge (talk) 15:56, 19 November 2024 (UTC)[reply]

There are some modern helium-filled non-rigid or semi-rigid passenger airships, used for sightseeing, but there are no hydrogen-filled modern airships, so there's no useful comparison possible. There are both helium-filled and hydrogen-filled gas balloons, but that isn't really the same thing. PiusImpavidus (talk) 09:57, 21 November 2024 (UTC)[reply]

Land surveying

Does modern land surveying (such as placement of streets after another, width of roads and blocks etc.) in take place using metric units in countries such as Canada, Australia and New Zealand, which have used metric distances for many decades now? Is there any English-speaking country that had already metricated when first surveys for 19th-century cities were done? Are there any downtown grids in English-speaking areas where streets are placed exactly 100 metres apart, and there are ten streets per one kilometre? In grids that place 16 streets per mile, the number of metres passed eventually deviates from number of 100 metres (hectometres) passed, since one mile is not exactly 1,600 metres. Placing ten streets per mile indicates number of miles passed by fourth-to last digit of house numbers, but does not indicate number of feet (or any other imperial unit) passed by whole number. By contrast, placing ten streets per kilometre indicates both number of kilometres passed by fourt-to last digit of house numbers and number of metres passed by whole house numbers. This placing is common in Argentina, but does it occur in any English-speaking country? --40bus (talk) 16:01, 17 November 2024 (UTC)[reply]

There are 100 meter blocks in Melbourne, Australia if I remember correctly. Mile/km/block-based addresses is not the original England way which was to count plots or buildings and call an unexpected new building in between the address of its neighbor suffixed with a letter or fraction. Manhattan's a hybrid: 1 address pair per 20ft plot of ownable (non-street) distance except 1 axis is 100 per block causing gaps like 153, 155, 201 except 3LPM5's 100 per 2 blocks cause Lex+Mad are new. Sagittarian Milky Way (talk) 05:48, 18 November 2024 (UTC)[reply]

The Melbourne blocks are 200 metres and then only by a coincidence; they are actually 10 chains or 660 feet, which happily converts to 201.17 metres. See Hoddle Grid for the details. Alansplodge (talk) 15:38, 19 November 2024 (UTC)[reply]

This is a new South Australian development near to where I live and the blocks are measured in metres, but not in nice whole metres. Zoom in and move the map to see details of the blocks. https://villawoodproperties.com.au/community/oakden-rise/find-buy/interactive-masterplan/ TrogWoolley (talk) 09:41, 18 November 2024 (UTC)[reply]

The same inaccuracy as 16 per mile then. Sagittarian Milky Way (talk) 01:29, 20 November 2024 (UTC)[reply]

Just to note that Australia, South Africa, New Zealand and Canada all began metrication in the 1960s or very early 1970s, so using metric measurements for any official purposes in the 19th-century would be highly improbable. Alansplodge (talk) 15:54, 19 November 2024 (UTC)[reply]

Is the any English-speaking country that already used metric measurement for official purposes in the 19th century? Was there anything that was measured in metric during Victorian times in the UK? --40bus (talk) 21:20, 19 November 2024 (UTC)[reply]

There was apparently a 6 mm government cartridge specification, the 6mm Lee Navy. I haven't dug up a contemporary source using mm, but it looks like it was so named even in 1895. (Note though the alternate .236 name.) Card Zero (talk) 06:26, 20 November 2024 (UTC)[reply]

The Abridgment: Containing Messages of the President of the United States to the Two Houses of Congress (1898) p. 480:

"Ten thousand 6 mm. Lee straight pull rifles have been supplied..." Alansplodge (talk) 12:44, 20 November 2024 (UTC)[reply]

On the subject of weapons, the QF 2-pounder naval gun of 1915 was made by the very British firm of Vickers and had a calibre of exactly 40 mm, but was known in British service by the weight of its shell in Imperial measure. The use of metric units here may be connected with the acquisition by Vickers of the Maxim Nordenfelt Guns and Ammunition Company in 1897, which although a British company, had its origin in the company owned by Thorsten Nordenfelt, a Swedish inventor. Alansplodge (talk) 12:33, 20 November 2024 (UTC)[reply]

A near miss though. Québec was a French colony using French units until 1763, switched to Imperial units after that, which was only 32 years before France metricated.

South Africa is an even nearer miss. It (or at least, the Cape Colony) was a Dutch colony until 1795, which is the year when the Netherlands metricated. The British then introduced Imperial units as they took over. Dutch rule was briefly restored in 1803–1806, but it appears this was too short to make the switch to metric. The Boers went their own way, continuing the use of traditional Dutch units (no longer used in the Netherlands) until Imperial units were made the standard in 1922: one of the last countries to switch to Imperial units. PiusImpavidus (talk) 19:31, 19 November 2024 (UTC)[reply]

How sampling rate in ADC adjusted or set ?

I am interested to learn how sampling rate in Analog-to-digital converter adjusted or set ? This page: Sampling (signal processing) didn't explain how it was adjusted. HarryOrange (talk) 18:36, 17 November 2024 (UTC)[reply]

Do you mean on a black box ADC (the sort of thing you have in a lab), or do you mean on an adc chip? Greglocock (talk) 22:00, 17 November 2024 (UTC)[reply]

@Greglocock I mean any typical ADC chip. How Sampling rate is adjusted? HarryOrange (talk) 05:03, 18 November 2024 (UTC)[reply]

I guess you read the data sheet for the chip. eg p41 and 42 here https://www.analog.com/media/en/technical-documentation/data-sheets/ad7768-7768-4.pdf Greglocock (talk) 06:04, 18 November 2024 (UTC)[reply]

An ADC sampling rate is determined by the data rate of the desired digital audio format. This article gives many examples of which 44.1 kHz, 48 kHz, 88.2 kHz and 96 kHz are typical. A designer simply ensures that an ADC chip receives a digital clock signal at appropriate frequency. Philvoids (talk) 20:17, 19 November 2024 (UTC)[reply]

Which is almost irrelevant to the question. An ADC chip or lab instrument can sample at many different rates. Greglocock (talk) 21:55, 19 November 2024 (UTC)[reply]