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Prandtl Glauert Singularity

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tigisfat

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The Prandt Gluert singularity is the reason for vapes, shock cones and a few other similar effects on aircraft. It's easily explained as moisture rapidly condensing in a pressure differential. There is a common trend that drives me nuts: TONS of pictures and videos of the singularity around fast moving subsonic aircraft labeled as supersonic. We should be smarter and better than that!! It seems every generation has often told lies passed as scientific fact, and this is fast becoming my generation's rediculous farse.

I distinctly remember a teacher telling us that if a penny were dropped off the Empire State building, it would easily kill someone. Gimme a break!! If you were to follow the same scientifically bankrupt reasoning, an automobile dropped from a thousand feet would easily beam a hole straight through the planet and come flying out of the ground somewhere in India. Then the danger is not as much having it fall on you, it's the hazard of having an object the size of an automobile come flying out of the ground if it was dropped onto the polar opposite of where you're standing. Anyone with any scientific background knows that there must be a terminal velocity for the penny and the car.

Back to the Prandt Glauert Singularity. Do your part and educate people!! Don't let your non-flying neighbors and family members think that moisture condensation means an aircraft must be flying at a million miles an hour.

Here are a few examples:

[YOUTUBE]iRGacDGUGtE[/YOUTUBE]

The worst is when a shock cone is called a "sonic boom:

[YOUTUBE]CF7h3EwBPjc[/YOUTUBE]
 
I've argued this one so many times with people that I've just given up now. Let people believe what they want to believe, if people are so ignorant as to not even accept that they may be mistaken then I can't be bothered wasting time discussing things with them.

If memory serves there is a cracking picture of B2 sporting a rather fetching singularity that can often be used to prove that it isn't a visual representation of breaking the sound barrier, that sometimes works.
 
Chris H said:
If memory serves there is a cracking picture of B2 sporting a rather fetching singularity that can often be used to prove that it isn't a visual representation of breaking the sound barrier, that sometimes works.
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I remember seeing a pic of an A-10 (and F-117's!!) in a similar state. :d
 
Goodpost, I must have been one of those misinformed youngsters who was told it happens when aircrafts hit 'supersonic'...as of this thread I am now a wiser man.
 
Hardly supersonic, but another 'Urban Myth'.
It's common (but less dramatic!) when a high performance car race is run in Malaysia or China under high humidity and temperate.
:173go1:
 
much worse are the peple who believe in chemtrails. i have a neighbor who has been trying to convince me of this for a long time. :angryfir:
 
cheezyflier said:
much worse are the peple who believe in chemtrails. i have a neighbor who has been trying to convince me of this for a long time. :angryfir:
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Argh, this one annoys me so much. I've had otherwise rational people whom I respect greatly try to convince me of mysterious chemtrails in the sky, usually with complete hysteria.
 
cheezyflier said:
much worse are the peple who believe in chemtrails. i have a neighbor who has been trying to convince me of this for a long time. :angryfir:
Click to expand...


I wouldn't even bring that up around Boxcar, he believes in them, and very strongly to boot.
 
Arrrgh, someone that stoopid should not be able to operate a camcorder, so I can only assume that some else filmed it whilst she drawled over the top.
 
What is the terminal velocity of a penny? Is it significantly different when it's dropped edge on versus flat side down?

I'm thinking a penny dropped from a high rise could be lethal. It has a rather high mass to aerodynamic drag ratio.

Flipping a coin several feet into the air and letting it rap you on the top of the head won't feel good, but I strongly suspect a penny doesn't reach terminal velocity in ten feet or less.

Cheers,

Ken

Edit: My favorite reality show (actually the ONLY one I watch) Mythbusters, did their scientific tests. They say a falling penny's terminal velocity is between 35 and 65 mile per hour. That's fast, but it seems not lethally fast. It might break skin and might cause a concussion, but should not be lethal. It can make a mar on concrete and dent asphalt. That's pretty significant. I certainly would not volunteer to put my noggin on the line for science!

http://www.mythbustersfanclub.com/mb2/content/view/26/27/
 
Ken Stallings said:
What is the terminal velocity of a penny? Is it significantly different when it's dropped edge on versus flat side down?

I'm thinking a penny dropped from a high rise could be lethal. It has a rather high mass to aerodynamic drag ratio.

Flipping a coin several feet into the air and letting it rap you on the top of the head won't feel good, but I strongly suspect a penny doesn't reach terminal velocity in ten feet or less.

Cheers,

Ken

Edit: My favorite reality show (actually the ONLY one I watch) Mythbusters, did their scientific tests. They say a falling penny's terminal velocity is between 35 and 65 mile per hour. That's fast, but it seems not lethally fast. It might break skin and might cause a concussion, but should not be lethal. It can make a mar on concrete and dent asphalt. That's pretty significant. I certainly would not volunteer to put my noggin on the line for science!

http://www.mythbustersfanclub.com/mb2/content/view/26/27/
Click to expand...

Ken, I figured you of all people would think Mythbusters is a crock of crap. They have no idea what they're talking about and their experiments are garbage. I used to love the show until the did the episode with the ultralights. That was it, and it tainted their credibility to me.

There have been other measures of a penny's 'lethality', and suffice it to say that you can throw a penny at someone harder than it would hit them if dropped. Either way, terminal velocity varies depending on how it falls, of which they identified four common ways for a penny to fall. The fastest recorded was not very much at all.

Ken, the penny is not likely to break your skin and give you a concussion.
1227953279246.jpg
 
Mythbusters frustrates me because the concept is fascinating, but they go for entertainment value over scientific accuracy too often. I would rather watch them work out formulas and try to determine the drag coefficient of a tumbling coin for half an hour than sit through the pseudo-science they sometimes try to pass.
 
djscoo said:
Mythbusters frustrates me because the concept is fascinating, but they go for entertainment value over scientific accuracy too often. I would rather watch them work out formulas and try to determine the drag coefficient of a tumbling coin for half an hour than sit through the pseudo-science they sometimes try to pass.
Click to expand...

Their science is pretty solid.

In the case of the penny, they constructed a variable speed wind tunnel where the speed near the wind source was 65mph and near the entrance where the pennies were dropped was 35 mph. The pennies hovered in the middle.

I think that's a very valid scientific method to judge the average terminal velocity of a dropped penny.

Of course a penny can be thrown faster than terminal velocity, and it then slows down until either gravity brings it to the ground, or wind resistance reduces the speed to terminal velocity.

Ken
 
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