Comment by DrBazza | Hacker News Reader

Comment by DrBazza | Hacker News Reader

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If you keep scaling this up, you might naively think the tips of blades could reach Mach 1. They won't, due to a variety of reasons.

But that does remind of Thunderscreech: https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech

"The XF-84H was almost certainly the loudest aircraft ever built, earning the nickname "Thunderscreech" as well as the "Mighty Ear Banger".[16] On the ground "run ups", the prototypes could reportedly be heard 25 miles (40 km) away.[17] Unlike standard propellers that turn at subsonic speeds, the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards."

Do you know what's the speed of a blade at the tip? It's not mentioned in the article.

Speed of sound is 343m/s at sea level. The blade is 113 metres, so that's a circumference of 710m.

A quick google says large turbines can rotate up to 20 rpm, so once every 3 seconds, that's 710/3 = 236m/s, so Mach 0.68

(edit) I think 29rpm is when the tips of blades go supersonic for that turbine.

"The best way to get the correct answer on the internet is to give the wrong one". I look forward to being corrected...

>"The best way to get the correct answer on the internet is to give the wrong one". I look forward to be

Depends on the site and readers. As we've seen recently, wrong answers take on a life of their own and become gospel or canon to eliminate religious overtones.

Some have a max blade tip speed of 100-180mph depending on radius and wind speed[0][1]

(I use to work on utility scale wind farms with 100+ x 2.1MW turbines)

[0] https://www.semprius.com/how-fast-do-wind-turbines-spin/ [1] https://www.windpowerengineering.com/calculate-blade-tip-spe...

Assuming you're talking about the Thunderscreech: Mach 1.18[0]

0:https://www.airspacemag.com/how-things-work/zwrrwwwbrzr-4846...

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