Hacker News Reader

If it's any kind of open track, it'll have problems with sonic booms. 400 miles in 30 minutes is 800 mph, a speed which exceeds the speed of sound at sea-level (~ 760mph). The neighbors aren't going to like that.

View on HN

Supersonic vehicles have been designed that minimize the size of the sonic boom. For example, the Lockheed Martin SAI produces a sonic boom 1% as big as the Concorde (http://en.wikipedia.org/wiki/SAI_Quiet_Supersonic_Transport).

Hmm. Maybe it won't be a problem after all. The size of the sonic boom seems to correlate positively with the size of the wing surface. Since a track (or tube) based system wouldn't need much of a wing, it ought to have a pretty small boom.

However, I do want to point out that rifle shots are supersonic and are annoying to the neighbors, and they have no wings at all.

I'm pretty sure a subsonic rifle shot is still pretty loud. :)

A friend has a rifle in 300 AAC Blackout. Subsonic ammo is far quieter than supersonic -- but you'd still want hearing protection. With a suppressor attached, it's quieter still -- you can fire it without wearing earplugs. But it's not "Hollywood quiet" - that's a movie myth.

Reply on news.ycombinator.com