[dduckwessel]

http://www.kettering...pler/mach1.html

In this photo, it looks to me as if there is a mini-sound barrier cloud just behind the cockpit. Can someone tell me what produced it?

[Qfwfq]

dduckwessel, on 06 December 2011 - 11:31 AM, said:

Can someone tell me what produced it?

The cockpit.

[dduckwessel]

Does that mean that whatever the size of the object, determines the size of the cloud?

[Qfwfq]

The size of the cloud surely depends on scores of things, but no doubt the size of the object plays a good role.

[phision]

dduckwessel, on 06 December 2011 - 11:31 AM, said:

http://www.kettering...pler/mach1.html

In this photo, it looks to me as if there is a mini-sound barrier cloud just behind the cockpit. Can someone tell me what produced it?

This is a type of Wilson Cloud, caused by, the pressure wave which condenses the water vapour in the air! It isn't necessarily associated with the "Sound Barrier", just the varying dew point of the air as it is compressed!

http://en.wikipedia....ert_singularity

[MacPhee]

The photo shows the F-18 carrying a load of stores under its wings. Can an F-18 go supersonic with that load?

[dduckwessel]

phision, on 07 December 2011 - 10:19 AM, said:

This is a type of Wilson Cloud, caused by, the pressure wave which condenses the water vapour in the air! It isn't necessarily associated with the "Sound Barrier", just the varying dew point of the air as it is compressed!

http://en.wikipedia....ert_singularity

Thank you for this. What would happen if there was a really big object that broke the sound barrier? How would that adversely (or not) affect the air around it?

[phision]

dduckwessel, on 08 December 2011 - 10:01 AM, said:

Thank you for this. What would happen if there was a really big object that broke the sound barrier? How would that adversely (or not) affect the air around it?

The bigger the object, the bigger the pressure wave! I'm not sure what you mean by adversely affect the air?

[CraigD]

dduckwessel, on 06 December 2011 - 11:31 AM, said:

http://www.kettering...pler/mach1.html

In this photo, it looks to me as if there is a mini-sound barrier cloud just behind the cockpit. Can someone tell me what produced it?

Because of the camera angle and its uniform whiteness, you don’t get an accurate impression of the shape of this vapor cone. From the wikipedia article, this photo

give a better view of its conical shape.

To understand how a little vapor cone forms near the FA-18’s canopy, consider that the shock wave that causes the low pressure region that causes the vapor is also conical, its angle depends on the shape of the plane’s nose. It appears the FA-18’s shock cone doesn’t fully encompass its canopy, so a second shock cone and resulting vapor cone forms.

phision, on 07 December 2011 - 10:19 AM, said:

This is a type of Wilson Cloud, caused by, the pressure wave which condenses the water vapour in the air! It isn't necessarily associated with the "Sound Barrier", just the varying dew point of the air as it is compressed!

http://en.wikipedia....ert_singularity

Vapor cones are also known as Wilson clouds, but they don’t form where air is compressed to a higher pressure, but where its pressure is lowered. That’s why they form not in the high pressure region of the objects shock cone, but well behind it, where the pressure is lower than ambient.

MacPhee, on 07 December 2011 - 11:33 AM, said:

The photo shows the F-18 carrying a load of stores under its wings. Can an F-18 go supersonic with that load?

These appear to be 3 330 US gallon drop tanks, which the FA-18 routinely carries to increase its range and time aloft. Though they appear heavy, even full of fuel, they increase the plane’s mass by only about 3000 kg, a fairly small added load for this airplane.

As these tanks are within the shock cone that appears when the FA-18 is transonic, the airflow around them remains subsonic, so they don’t cause an undue amount of drag.

Given all this, I’ve no reason to disbelieve the OP’s linked to article’s claim that the FA-18 in the photo is going supersonic, drop tanks attached.

dduckwessel, on 08 December 2011 - 10:01 AM, said:

Thank you for this. What would happen if there was a really big object that broke the sound barrier? How would that adversely (or not) affect the air around it?

You can watch what happens for yourself in several online videos, like this one:


Nearly all large rockets, like the Saturn-Apollo stacks and the Space Shuttle, go supersonic early in their flight (around 3 minutes into it), and like the FA-18 in the photo, form big, pretty vapor cones.

Neither shock nor vapor cones have any lasting adverse impact on the air, which returns to normal soon after.

[phision]

CraigD, on 08 December 2011 - 09:43 PM, said:

phision, on 07 December 2011 - 10:19 AM, said:

This is a type of Wilson Cloud, caused by, the pressure wave which condenses the water vapour in the air! It isn't necessarily associated with the "Sound Barrier", just the varying dew point of the air as it is compressed!

http://en.wikipedia....ert_singularity

Vapor cones are also known as Wilson clouds, but they don’t form where air is compressed to a higher pressure, but where its pressure is lowered. That’s why they form not in the high pressure region of the objects shock cone, but well behind it, where the pressure is lower than ambient.

Both the high pressure and low pressure regions are part of the pressure wave which cause the Wilson cloud.
The air is compressed at the leading edge of the pressure wave then transits to a lower pressure, the resulting temperature reduction causes the the Wilson Cloud to form if the Dew point(http://en.wikipedia.org/wiki/Dew_point) of the air is transited. The cloud evaporates when the temperature/pressure retransits the Dew point as they return to ambient conditions. See: http://en.wikipedia....densation_cloud

CraigD, on 08 December 2011 - 09:43 PM, said:

Neither shock nor vapor cones have any lasting adverse impact on the air, which returns to normal soon after.

Shock waves can cause notable noise pollution(http://en.wikipedia....Noise_pollution) and vapour cones can affect visibility. Both effects are temperary as CraigD has stated above.

[dduckwessel]

phision, on 08 December 2011 - 04:16 PM, said:

The bigger the object, the bigger the pressure wave! I'm not sure what you mean by adversely affect the air?

If a sonic boom (if such a thing is possible) was produced in space - what would happen?

[dduckwessel]

CraigD, on 08 December 2011 - 09:43 PM, said:

Because of the camera angle and its uniform whiteness, you don’t get an accurate impression of the shape of this vapor cone. From the wikipedia article, this photo

give a better view of its conical shape.

To understand how a little vapor cone forms near the FA-18’s canopy, consider that the shock wave that causes the low pressure region that causes the vapor is also conical, its angle depends on the shape of the plane’s nose. It appears the FA-18’s shock cone doesn’t fully encompass its canopy, so a second shock cone and resulting vapor cone forms.



Vapor cones are also known as Wilson clouds, but they don’t form where air is compressed to a higher pressure, but where its pressure is lowered. That’s why they form not in the high pressure region of the objects shock cone, but well behind it, where the pressure is lower than ambient.


These appear to be 3 330 US gallon drop tanks, which the FA-18 routinely carries to increase its range and time aloft. Though they appear heavy, even full of fuel, they increase the plane’s mass by only about 3000 kg, a fairly small added load for this airplane.

As these tanks are within the shock cone that appears when the FA-18 is transonic, the airflow around them remains subsonic, so they don’t cause an undue amount of drag.

Given all this, I’ve no reason to disbelieve the OP’s linked to article’s claim that the FA-18 in the photo is going supersonic, drop tanks attached.



You can watch what happens for yourself in several online videos, like this one:


Nearly all large rockets, like the Saturn-Apollo stacks and the Space Shuttle, go supersonic early in their flight (around 3 minutes into it), and like the FA-18 in the photo, form big, pretty vapor cones.

Neither shock nor vapor cones have any lasting adverse impact on the air, which returns to normal soon after.

Thank you. I was wondering about the effects that shock waves have on the atmosphere and ground (like sonar adversely affects whales and dolphins). Why is the vapor cloud in the first picture 'cone' shaped? Is this another example of the Doppler Effect?

[MacPhee]

CraigD, on 08 December 2011 - 09:43 PM, said:

These appear to be 3 330 US gallon drop tanks, which the FA-18 routinely carries to increase its range and time aloft. Though they appear heavy, even full of fuel, they increase the plane’s mass by only about 3000 kg, a fairly small added load for this airplane.

As these tanks are within the shock cone that appears when the FA-18 is transonic, the airflow around them remains subsonic, so they don’t cause an undue amount of drag.

Given all this, I’ve no reason to disbelieve the OP’s linked to article’s claim that the FA-18 in the photo is going supersonic, drop tanks attached

Aren't there also some dark objects, nearer the wingtips?

I'm surprised that the FA-18 can exceed Mach 1, in level flight, in dense low-altitude air, while carrying under-wing stores. Isn't the plane's max speed, supposed to be M=1.8? And that's presumably when it's flying in "clean" condition, in thin high-altitude air.

However the max speed of some planes seems mysterious. For example, the F-22. How fast can it really go? (with afterburners). I've seen figures quoted such as M1.8, M2+, M2.2, or "faster than the F-15" - implying at least M2.6 - which seems improbable. I suspect the wonder-plane is actually considerably slower than the old F-15. That would explain why the Air Force didn't like to be too specific! But now that the F-22 won't be bought in serious numbers, perhaps no-one will care any more about mentioning its inferior speed.

[Qfwfq]

dduckwessel, on 10 December 2011 - 01:47 PM, said:

If a sonic boom (if such a thing is possible) was produced in space - what would happen?

No, it isn't possible. Acoustic waves only propagete in materials.

dduckwessel, on 10 December 2011 - 01:50 PM, said:

Why is the vapor cloud in the first picture 'cone' shaped? Is this another example of the Doppler Effect?

It isn't the Doppler effect. It is just like the V shaped wave formation from boats speeding through water, except this is a two dimensional version while the cone is a three dimensional shape. Cherenkov light is another example of the same effect.