Newbie question about aero-physics


#1

Hello, not sure if this is the right area, but I figured that if anyone could answer my question you guys could.

At RDU you can get a really good view of planes landing because the streets run right next to one side of the runway (23 right), so I enjoy going out there and watching the commercial airliners land. Sometimes, usually when it’s a larger plane (737 or MD80), about 10 seconds after it flies overhead, you’ll hear what sounds like the echo of a whipping or whooshing sound overhead for a few seconds. I know it’s not from the actual airplane/airport, so I was wondering if someone could tell me what this is called and/or point me in the direction of something that explains what causes it? You might say I’m curious.

Thanks!

Dan


#2

Not 100% sure, but I would guess you are hearing wing vortices.


#3

Yes, most definitely wing vortices. They form what are essentially mini-tornado like air funnels at the tips of the wing, and they slowly fall to earth after they are created. You hear them after it goes by because that is when they reach you on the ground. They sounds like anything from a whoosh to a cracking sound, and some planes have it more pronounced than others.

You can see these vortices in action here.


#4

Good picture on the vortices!

I’m sure that’s what locovaca was hearing. It’s kinda fun to wait and listen to them.

For those that haven’t heard them, find a place at the approach end of the runway. They are strongest from airplanes in the landing configuration and the larger the airplane, the better. They travel down, out and downwind from the airplane’s flight path, so the best place might be just off the end of the downwind side of the runway. It will have to be pretty quiet, they aren’t very loud, so traffic noise, etc. will probably drowned the sound out. But if you hear them, you will know it. They come 5-10 seconds after the plane passes overhead and are very distinctive in their sound. Happy listening! :slight_smile:


#5

Awesome, thanks guys (and gals)!