Cool pictures of F22 forming small clouds prior to breaking the sound barrier

[Queasy]

Whoa /neo

 

[91TTZ]

Why do people always assume that the jet is about to break the sound barrier when they see condensation?

This doesn't mean that the jet was going anywhere near the sound barrier. It's just condensation.

I see this misinformation posted all the time.

 

[Howard]

And what causes it to condense? I'm not sure if shock waves are hot, but as pressure increases, the temperature needs to be higher and higher in order for water to stay gaseous.

 

[91TTZ]

Originally posted by: Howard
And what causes it to condense? I'm not sure if shock waves are hot, but as pressure increases, the temperature needs to be higher and higher in order for water to stay gaseous.

The low pressure regions around the aircraft cause it to condense. You can commonly see it above the wings (regardless of what speed it's going), and anywhere else that's a low pressure area. Even if conditions aren't right for the clouds to form above the wings in level flight, a hard turn can cause them to form.

You can also see them on the wings of Formula 1 cars.

The position of the clouds in those pictures tells me that it wasn't going close to the speed of sound.

 

[noagname]

you do know that pics like that have been out there for years

 

[buck]

Originally posted by: 91TTZ
Why do people always assume that the jet is about to break the sound barrier when they see condensation?

This doesn't mean that the jet was going anywhere near the sound barrier. It's just condensation.

I see this misinformation posted all the time.

Isnt this condensation common right before breaking the sound barrier? (I am not saying its the only time)

*edit*
My comment is referring to the top picture. I am not talking about the little bit that forms on wings and whatnot.

 

[Kelvrick]

I wonder what kind of cameras take these pictures

 

[crab]

Condensation on a 757 wing I took this video a year or two ago...pretty neat, and we sure arent anywhere near the sound barrier.

 

[Howard]

Originally posted by: 91TTZ

Originally posted by: Howard
And what causes it to condense? I'm not sure if shock waves are hot, but as pressure increases, the temperature needs to be higher and higher in order for water to stay gaseous.

The low pressure regions around the aircraft cause it to condense.

Have you ever looked at a phase diagram for water???

 

[Queasy]

Originally posted by: noagname
you do know that pics like that have been out there for years

And it doesn't make it any less cool.

 

[skyking]

Local flow can indeed approach the sound barrier when the aircraft is quite a bit slower.
I see that phenomenon at the propellers of my plane while it is still on the ground accellerating.

 

[91TTZ]

Originally posted by: buck

Originally posted by: 91TTZ
Why do people always assume that the jet is about to break the sound barrier when they see condensation?

This doesn't mean that the jet was going anywhere near the sound barrier. It's just condensation.

I see this misinformation posted all the time.

Isnt this condensation common right before breaking the sound barrier? (I am not saying its the only time)

*edit*
My comment is referring to the top picture. I am not talking about the little bit that forms on wings and whatnot.

A jet traveling supersonically can make a condensation cloud, but not all condensation clouds are caused by supersonic flight.

Also, a common misconception is that a jet "breaks" the sound barrier and creates a boom the moment it breaks it. In reality, once a jet exceeds the speed of sound, it drags that wave along with it, so you'll hear the boom when the wave reaches you. If the jet travels a thousand miles supersonically, people on the ground all along the way will hear a boom. It's usually two booms, one of the nose and one for the tail.

 

[crab]

Good site explaining the effect.

 

[91TTZ]

Originally posted by: Howard

Originally posted by: 91TTZ

Originally posted by: Howard
And what causes it to condense? I'm not sure if shock waves are hot, but as pressure increases, the temperature needs to be higher and higher in order for water to stay gaseous.

The low pressure regions around the aircraft cause it to condense.

Have you ever looked at a phase diagram for water???

Not recently, maybe back in school.

 

[91TTZ]

Originally posted by: skyking
Local flow can indeed approach the sound barrier when the aircraft is quite a bit slower.
I see that phenomenon at the propellers of my plane while it is still on the ground accellerating.

The phenomenon that you're seeing has nothing to do with supersonic flow, though. Your prop isn't going supersonic.

You're just seeing the air condense on the low pressure side of the blade of the prop.

 

[91TTZ]

Just search for "Prandtl-Glauert cloud" and you'll find plenty of hits. This is common and doesn't indicate supersonic flight.

Here's a B2 with a cloud: pic

 

[skyking]

Originally posted by: 91TTZ

Originally posted by: skyking
Local flow can indeed approach the sound barrier when the aircraft is quite a bit slower.
I see that phenomenon at the propellers of my plane while it is still on the ground accellerating.

The phenomenon that you're seeing has nothing to do with supersonic flow, though. Your prop isn't going supersonic.

You're just seeing the air condense on the low pressure side of the blade of the prop.

That's true, the bulk of the effect is located mid-span of the blade. Actually, the tips are very close to supersonic speeds.
Listen to a 300HP 520 continental in the Bonanza or C185; it is a horrible racket at 2850 RPM on take off.
It is the limiting factor in propeller driven aircraft. Propellers get enormously inefficient in the transonic region. The reno racers are operating way out of the optimum range, but do it with exorbitant amounts of power and noise

 

[91TTZ]

Originally posted by: skyking

Originally posted by: 91TTZ

Originally posted by: skyking
Local flow can indeed approach the sound barrier when the aircraft is quite a bit slower.
I see that phenomenon at the propellers of my plane while it is still on the ground accellerating.

The phenomenon that you're seeing has nothing to do with supersonic flow, though. Your prop isn't going supersonic.

You're just seeing the air condense on the low pressure side of the blade of the prop.

That's true, the bulk of the effect is located mid-span of the blade. Actually, the tips are very close to supersonic speeds.
Listen to a 300HP 520 continental in the Bonanza or C185; it is a horrible racket at 2850 RPM on take off.
It is the limiting factor in propeller driven aircraft. Propellers get enormously inefficient in the transonic region. The reno racers are operating way out of the optimum range, but do it with exorbitant amounts of power and noise

I remember seeing an episode of Wings of the discovery channel where the air force tried making a fighter (a long time ago) with a supersonic propeller. They succeeded in making it more efficient, but a nasty side effect was that the sound was so horrendous that it made people sick. I hear that the old Soviet Bear bomber also had a horrible drone as its tips were close to supersonic.

 

[spidey07]

Originally posted by: 91TTZ

Originally posted by: Howard
And what causes it to condense? I'm not sure if shock waves are hot, but as pressure increases, the temperature needs to be higher and higher in order for water to stay gaseous.

The low pressure regions around the aircraft cause it to condense. You can commonly see it above the wings (regardless of what speed it's going), and anywhere else that's a low pressure area. Even if conditions aren't right for the clouds to form above the wings in level flight, a hard turn can cause them to form.

You can also see them on the wings of Formula 1 cars.

The position of the clouds in those pictures tells me that it wasn't going close to the speed of sound.

Bingo!

While the pics are really cool, they have nothing to do with breaking the sound barrier. When was that done anyway? 1955?

It has to do with the collapse/drop in pressure, forcing condensatition.

 

[Gibsons]

Originally posted by: 91TTZ

Originally posted by: skyking

Originally posted by: 91TTZ

Originally posted by: skyking
Local flow can indeed approach the sound barrier when the aircraft is quite a bit slower.
I see that phenomenon at the propellers of my plane while it is still on the ground accellerating.

The phenomenon that you're seeing has nothing to do with supersonic flow, though. Your prop isn't going supersonic.

You're just seeing the air condense on the low pressure side of the blade of the prop.

That's true, the bulk of the effect is located mid-span of the blade. Actually, the tips are very close to supersonic speeds.
Listen to a 300HP 520 continental in the Bonanza or C185; it is a horrible racket at 2850 RPM on take off.
It is the limiting factor in propeller driven aircraft. Propellers get enormously inefficient in the transonic region. The reno racers are operating way out of the optimum range, but do it with exorbitant amounts of power and noise

I remember seeing an episode of Wings of the discovery channel where the air force tried making a fighter (a long time ago) with a supersonic propeller. They succeeded in making it more efficient, but a nasty side effect was that the sound was so horrendous that it made people sick. I hear that the old Soviet Bear bomber also had a horrible drone as its tips were close to supersonic.

I've read that pilots in intercepting fighters could hear the Bear from a very long way away, over the noise of their own craft and through the headphones... I suppose the Bear crews must use a great deal of hearing protection, or maybe they're all deaf.

 

[Howard]

Umm... a drop in pressure would result in more water evaporating, not condensing.

http://images.encarta.msn.com/xrefmedia/aencmed/targets/illus/cha/T073590A.gif

 

[91TTZ]

Originally posted by: Howard
Umm... a drop in pressure would result in more water evaporating, not condensing.

http://images.encarta.msn.com/xrefmedia/aencmed/targets/illus/cha/T073590A.gif

But as the pressure drops, so does the temperature. The drop in temperature causes the water vapor in the air to condense.

Good read: link

^I think that's what you were looking for. Hope that helps.

 

[spidey07]

Originally posted by: Howard
Umm... a drop in pressure would result in more water evaporating, not condensing.

http://images.encarta.msn.com/xrefmedia/aencmed/targets/illus/cha/T073590A.gif

So you don't believe in fog then?

Interesting. Does fog not exist?

 

[noagname]

try this http://www.airliners.net/open.file?id=1...v_id=0188588&next_id=0925769&tbl=type2