280. An effect – could you explain the origin?
Uncategorized — By Dmitry Podolsky on February 21, 2009 at 11:04 pm
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While watching “Iron man”, I’ve got interested by the following episode: while Mr. Stark flies to Afghanistan to destroy Al Qaeda hideouts, he apparently develops supersonic speed at some point – at list, I’ve clearly heard a shock wave. At the very moment the shock wave comes, a cone of mist is developed around him.
It looks more or less like this (on the picture F18 does the same thing that Iron Man did in the movie):
Here is another example – F-14:
a) photo
and
b) video
A similar phenomenon can be observed at space shuttle launches during 25-33 sec after the launch (presumably when shuttle is nearly crossing sound barrier) as the following picture of STS-106 launch demonstrates:
Finally, some of the older readers of NEQNET might have seen the effect in these circumstances, too (although unlikely – those legendary figures are probably not internet savvy):
So, I have two questions:
a) what is the effect?
b) does it take place only at crossing sound barrier?
Update: Kudos go to Soumyadeep – this is Prandtl-Glauert vapour condensation due to a sharp gradient of pressure. Contrary to what many pages including Wikipedia say, effect is not related to the shock wave that appears at crossing sound barrier (the latter is sufficient but not necessary for the condensation to take place). Even if the speed of an aircraft is low, Prandtl-Glauert condensation may take place at low heights (and if humidity is high enough).
8 Comments
I was rather surprised to see the B52 with a shock wave like that. It seems from some preliminary Googling that that image may be a photoshop job.
Hi Jonathan,
although B-52 is subsonic (650 mph max < 767 mph), the issue whether the image is fake is actually related to my second question
Cheers,
Dmitry.
The comments about it appearing to be a fake seemed to be related to the fact that the tones in the background are very similar to another photo of an F16 with the same shock wave. This is unrelated to whether it is physically possible or not.
Most probably, the picture is fake (Prandtl-Glauert cones are almost similar), but I believe that the effect is possible even for B-52 – see below.
Cheers,
Dmitry.
http://blog.wired.com/wiredsci.....azing.html
Wow, thanks, really nice videos, my favorite is about liquid helium.
Hi Dmitry,
I read about a possible explanation for the effect here: http://en.wikipedia.org/wiki/P.....ingularity
As to question b, mist cones can develop at subsonic speeds.
Hi Soumyadeep,
Sure, questions were not that hard
The mist is due to the Prandtl-Glauert effect and is not necessarily related to the presence of shock wave contrary to what many pages including Wikipedia say (sufficient but not necessary). At low heights and high humidity Prandtl-Glauert condensation can take place even if speeds are rather low.
Cheers,
Dmitry.
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