The Sound Barrier

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I've always liked this pic. Note the small halo behind the pilot.

"U.S. Navy F/A-18 approaching the sound barrier. The white halo formed by condensed water droplets is thought to result from an increase in air pressure around the aircraft at transonic speeds"

800px-FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29_-_filtered.jpg
 
That's a sweet pic. It looks fake. Not saying it is. Just sayin it looks like it.
 
^^ It's not. We see this sort of stuff routinely.

The small puff behind the canopy is likely a result of the shock wave of the leading edge root extension (LERX) of the wing interacting with a localized low pressure area as the fuselage diameter reduces behind the cockpit.


Willie

.
 
I still stand in awe of people like Chuck Yeager and John Glenn. They basically strapped a rocket to their backsides and said "Let's see what happens."
Click to expand...
If you have never read the book "The Right Stuff", by Tom Wolfe, it is time to rectify that shortcoming.
Written by a regular guy, who knows how to do his research. Published in 1979 or so, covers everything from Chuck Yeager's assault on the "sonic barrier" up to and through the space program.
Fascinating read, with a lot of real-world info.
 
The photo of the F-18 is real, I have seen the same thing many times while flying super sonic aircraft.

"At transonic speeds intense low-pressure areas form at various points around an aircraft. If conditions are right (i.e. high humidity) visible clouds will form in these low-pressure areas as shown in the illustration; these are called Prandtl-Glauert singularities. These clouds remain with the aircraft as it travels. It is not necessary for the aircraft as a whole to reach supersonic speeds for these clouds to form. It is also a build up of shock waves."

A low pressure area forms just behind the shock wave causing the moisture to condense.

The same effect may be seen with rifle bullets fired on a humid day, they will leave a visible trail-if it is not very humid it is possible to see a distortion in the atmosphere behind the bullet with good optics.
 
Same effect occurs whenever moisture-laden air drops in pressure*. The water condenses out, forming a cloud.

Example: The vortexes and clouds that form in front of the intake of a jet engine in the right atmospheric conditions:

9312.jpg

Video of the effect:
https://www.youtube.com/watch?v=SUKCp4pK5LY

You can also see these clouds while the aircraft is airborne, so it's not just sucking water up off the ground.

It's also basically the same principle that allows the Wilson Cloud Chamber to show nuclear particle tracks:

cloud4.gif

Video:
https://www.youtube.com/watch?v=MaAf6TTgEqw

What this shows is the little clouds being formed and disappearing as the radioactive particles from the object in the center zip through the saturated atmosphere in the chamber.

Terry, 230RN

* And/or temperature. Fog forms when the temperature drops below the dew point.
 
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I read "The Right Stuff" after I'd seen the movie. The book was the real eye opener. The movie was full of things that were hyped especially for the movie. I really wish that I'd read the book first.

The movie depicted Chuck Yeager as a "cowboy", when in reality, he was a cool headed test pilot who was a stickler for details, and paid attention to them. The first supersonic flight in the X1 was really a culmination of exacting tests and data gathering by these personnel.

When he tested the F104 rocket-powered plane, the movie made the flight out to be some joy ride. The truth was far from it.

Tom Wolfe made mention of the fact that some test pilots died because they stayed in the planes too long, gathering data. I know that some pilots may have been "hotdogs", but they didn't last long.

Thanks, guys. The information in this thread is fascinating.
 
Here is a series of photos I took of a large object, a 747, moving through a patch of humid air at high subsonic speeds, a little easier to see the flow here than a bullet. It is moving at about the same mach as a .45 ACP.

50e8f0ab.jpg


cc1ffae5.jpg


228e5e6d.jpg
 
The thing I like about shooting .50's is watching/spotting for others, the .50 is a big bullet and moves a lot of air. You can actually watch the bullet fly through the air and call the shot for the shooter, I tell people that it kinda like the movie the Matrix. Except the bullet is moving at real time speed and not in slow motion, the bullet flying through the air reminds you of how the bullets in the movie flew.

Watching them fly out to 7,8...1000+ yards and seeing the shockwave from the bullet is amazing. If its an API or other explosive round its cool to see it fly to the Target and then explode, if its a semi or full auto its even more amazing to see a bunch of bullets going down range. The more humidity in the air the better as it really helps to see how much air a bullet can move traveling down range.

What would be cool is if you could hook a camera up to your scope and get a picture or video of it. I know on some of the shows on guns, if you watch carefully and the cameraman has the zoom up, you can see bullets traveling down range.
 
With the sun behind me, I have seen the flat bases of my .45 bullets flying up on the Grasslands. Just a copper-colored streak that goes up and down in about 200 or 300 milliseconds at long ranges.
 
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In Vietnam the fighter flyers would do sound barrier passes right over communist sampans and the shock wave would sink the sampan.
 
O.K.

The one that puzzles me is footage of coast guard and other helicopters on TV during Katrina and other rescues.

What appears to be condensation / steam blowing out of the overhead air vents above the pilots.

I've had my butt hauled in the jump seats of Army Huey's and Chinooks a few laps around the track.

And I don't recall ever seeing that visible water vapor blowing on the pilots in the cockpit?

Is it just humidity related during hurricane weather.
Or do they all have really good A/C systems now?

rc
 
Willie Sutton said:
^^ It's not. We see this sort of stuff routinely.

The small puff behind the canopy is likely a result of the shock wave of the leading edge root extension (LERX) of the wing interacting with a localized low pressure area as the fuselage diameter reduces behind the cockpit.


Willie

.
Click to expand...
Youve got a pretty cool job brother! And I sell fruit.
 
O.K.

The one that puzzles me is footage of coast guard and other helicopters on TV during Katrina and other rescues.

What appears to be condensation / steam blowing out of the overhead air vents above the pilots.

I've had my butt hauled in the jump seats of Army Huey's and Chinooks a few laps around the track.

And I don't recall ever seeing that visible water vapor blowing on the pilots in the cockpit?

Is it just humidity related during hurricane weather.
Or do they all have really good A/C systems now?

rc
--------------------------------------------------------------------------


That is just humid air going through the A/C-most don't have a water seperator and if they are really cranking they can hit you with a few ice crystals, many modern military aircraft have great A/C and they need it because all that plexiglass works against it.

Older helos did not have A/C.
 
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