Hacker News Reader

Comment by darksaints | Hacker News Reader

I saw an F-14 during fleet week in San Francisco when I was still in high school...we were watching from the pedestrian pathway on the golden gate bridge. It broke the sound barrier, and I still remember the shock wave and the sound of the bridge cables vibrating for 5-10 seconds afterwards. It was terrifying...I seriously thought the bridge would be damaged from it. I'm still not sure what the story was behind it, whether it was an accident or an "accident", but it made me fully appreciate the reasons why supersonic flight is not allowed over land.

View on HN

Just as a point of note, the vapour cone often seen around fast jets at low level in humid conditions doesn't necessarily mean they're going supersonic themselves. Certain local areas of airflow do, however, which causes the drop in air pressure and thus condensation.

Not sure if that was an explanation for me, but I've seen it before and I wasn't basing it off that. This was obvious from the sound. The plane was too far away for me to see a condensation cone. It was probably somewhere over Angel Island at the time.

A sonic boom, on a small scale, isn't something impressive...bullets cause sonic booms, even the tip of a bullwhip will. I had been around high explosives before too, an oddity of my father's profession. This wasn't just a loud jet, it literally sounded like a bomb, and it resonated for what felt like 5-10 seconds.

You don't need supersonic anywhere to cause condensation. Watch the wingtips of a commercial airliner landing in high humidity; you'll often see swirls of fog caused by the low pressure inside the vortices.

But, the cone of condensation coming off the body of a plane is the supersonic shock wave.

> But, the cone of condensation coming off the body of a plane is the supersonic shock wave.

And shock surfaces can be present over the body due to local flow speed being supersonic even when the aircraft's velocity vector is strictly subsonic. Though to be fair, still in the transonic realm if you're seeing shocks.

Reply on news.ycombinator.com