nema
Posts: 479
Joined: Fri Feb 24, 2006 3:18 am

Hot Or Cold

Fri Jul 11, 2008 2:16 pm

We often see when flying on commercial aircraft, a screen telling us that the outside temperature is minus 45 degrees or so. At this time we also see our air speed as being around 550mph.

Yet, even though there would be wind chill to consider, Concorde for example, travelling at twice these speeds, actually got so hot on its outer skin that the fuselage stretched about a foot with the friction heat.

So my question, if i had strapped a joint of beef on the wing of a supersonic jet, would i see it freeze or would i see it cook at those high mach1 speeds / altitudes?


Thanks in advance,
There isnt really a dark side to the moon, as a matter of fact its all dark!
 
wilco737
Posts: 7279
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RE: Hot Or Cold

Fri Jul 11, 2008 2:23 pm

Nice question  Wink

The temperature shown on the screen to the passenger is the SAT (static air temperature). So, if you would stand still at that point then you would feel the -45°. But if you move, especially at very high speeds you will have higher temperature. On the leading edges of the wings, the nose, tail, all the front parts which "hit" the air first. There the air will be kind of compressed which let the temperature rise at that point. So the tempereature there would be higher. If SAT maybe is at -60, then the TAT is at -30 or so (depends on the speed). So the TAT is always higher than the SAT, when in motion. If standing still on ground, the TAT = SAT.

I remember something about the concorde, that at that leading edge points the temperature gets really high and that the concorde is about 20cm longer when she landed at the destination. So I guess, if you turn your steak several times, then you can enjoy it medium  Wink but this is only for very high speeds. The normal speeds flown by regular airliners in the normal altitudes would not be enough.

WILCO737 (MD11F)
 airplane 
 
flipdewaf
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RE: Hot Or Cold

Fri Jul 11, 2008 2:38 pm

The temperature of Concorde increased due (partly) to the compression of the air as it flew through it, just like a bike pump gets hot when you use it and a deodorant can gets cold when you spray it. The 747 gets hotter on the surface but because the heat generated through the speed squared there is much less of an effect on the subsonic jets (I once got a burn from grabbing the pitot on a tornado F3 after a mach 2 flight).

Fred

P.S. I'd go for it being slowly cooked at ~130 degrees C for 3hrs over the Atlantic although I wouldn't want to try it after the approach over the big smoke.

[Edited 2008-07-11 07:41:15]
Image
 
nema
Posts: 479
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RE: Hot Or Cold

Fri Jul 11, 2008 2:40 pm

Quoting WILCO737 (Reply 1):
WILCO737 (MD11F)

Thanks for your interesting reply, would like to hear any alternative views.

As always, i enjoy reading your imput on here Wilco so ive added you to my Respected list....i know with your rating its a bit like giving a millionaire a dollar but there you go...dont you ever work btw??

[Edited 2008-07-11 07:53:58]

[Edited 2008-07-11 07:54:23]
There isnt really a dark side to the moon, as a matter of fact its all dark!
 
wilco737
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RE: Hot Or Cold

Fri Jul 11, 2008 2:55 pm



Quoting NEMA (Reply 3):
Thanks for your interesting reply, would like to hear any alternative views.

As always, i enjoy reading your imput on here Wilco so ive added you to my Respected list....dont you ever work??

Anytime.

Me, never work? Nah  Wink Actually I work quite a lot, but most of the hotels have free internet Big grin

WILCO737 (MD11F)
 airplane 
 
Nicoeddf
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RE: Hot Or Cold

Fri Jul 11, 2008 3:36 pm



Quoting NEMA (Thread starter):
So my question, if i had strapped a joint of beef on the wing of a supersonic jet, would i see it freeze or would i see it cook at those high mach1 speeds / altitudes?

As I guess the temperature rise due to friction on the outer skin of the jet is very much limited to the area direct in contact with the surface, the beef would be black on the "skin"-side and frozen on the "air"-side.

On the other hand, I don't quite know the coefficient of hear transmission in beef  Wink
Maybe it is such a good performing heat-conducter, that it will be roasted thoroughly?  Wink
 
chksix
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RE: Hot Or Cold

Fri Jul 11, 2008 9:02 pm

Here's my favourite atmospheric calculator where you can try different speeds and altitudes to see when the beef would get ready quickest  Wink
http://www.aerospaceweb.org/design/scripts/atmosphere/
The conveyor belt plane will fly
 
wilco737
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RE: Hot Or Cold

Fri Jul 11, 2008 9:07 pm



Quoting Chksix (Reply 6):

This ones cool!  thumbsup  Thanks  Wink

WILCO737 (MD11F)
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josekmlb
Posts: 195
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RE: Hot Or Cold

Fri Jul 11, 2008 9:08 pm



Quoting NEMA (Reply 3):
Thanks for your interesting reply, would like to hear any alternative views.

As always, i enjoy reading your imput on here Wilco so ive added you to my Respected list....i know with your rating its a bit like giving a millionaire a dollar but there you go...dont you ever work btw??

same here Wilco really knows his stuff just like alot of people on here do and its hard to get everyone but since being on here I have learned more about airplanes even though I have worked the ramp since 1999 in KMLB it seems like I learn something new everytime I get on here thxs guys and gals
 
MD11Engineer
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RE: Hot Or Cold

Fri Jul 11, 2008 9:18 pm



Quoting Flipdewaf (Reply 2):
(I once got a burn from grabbing the pitot on a tornado F3 after a mach 2 flight).

No experience with Tornados, but isn't the pitot tube heated for anti-icing on these planes as well? (I once badly burned my hand when I tried to put on a pitot cover on a 727, the pilots had forgotten to switch off pitot heat. While standing still the pitot tubes can easily heat up to more than 150 degrees centigrade).

Jan
Je Suis Charlie et je suis Ahmet aussi
 
wilco737
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RE: Hot Or Cold

Fri Jul 11, 2008 9:22 pm

Quoting MD11Engineer (Reply 9):
No experience with Tornados, but isn't the pitot tube heated for anti-icing on these planes as well?

Yep, they are heated to avoid icing to be built up and show wrong data.

WILCO737 (MD11F)


[Edited 2008-07-11 14:28:40]
 
474218
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RE: Hot Or Cold

Fri Jul 11, 2008 9:23 pm

I don't know the answer to your question about a joint of beef strapped to the wing. However, the SR-71 crew would heat their high protein squeezable meals by holding them against the window for a few minutes.
 
josekmlb
Posts: 195
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RE: Hot Or Cold

Fri Jul 11, 2008 9:24 pm



Quoting WILCO737 (Reply 10):
Yep, they are heated to avoid icing to be built up and show wrong date.

Even before push back on a MD-88 I see the heat coming right off the pitot tube, but never grabbed one  Wink
 
KELPkid
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RE: Hot Or Cold

Fri Jul 11, 2008 9:32 pm



Quoting NEMA (Thread starter):
So my question, if i had strapped a joint of beef on the wing of a supersonic jet, would i see it freeze or would i see it cook at those high mach1 speeds / altitudes?

Or would it create so much additional drag that the aircraft would no longer be capable of supersonic flight?  duck  Sorry, couldn't resist  Smile
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tdscanuck
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RE: Hot Or Cold

Sat Jul 12, 2008 12:36 am



Quoting NEMA (Thread starter):
Yet, even though there would be wind chill to consider

No wind-chill. Windchill only happens when the surface is a significantly different temperature than the airflow. With an airplane skin, the heat source is the airflow, so the temperatures are very close.

Quoting NEMA (Thread starter):
So my question, if i had strapped a joint of beef on the wing of a supersonic jet, would i see it freeze or would i see it cook at those high mach1 speeds / altitudes?

Depends where you put it. Near the stagnation points it would get hot. On long areas parallel to the airstream it would get cold.

Quoting NicoEDDF (Reply 5):
As I guess the temperature rise due to friction on the outer skin of the jet is very much limited to the area direct in contact with the surface, the beef would be black on the "skin"-side and frozen on the "air"-side.

Not really...the friction that's heating the outer skin would be even worse on the surface of the beef (assuming your beef is rougher than a polished aluminum skin).

Tom.
 
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Starlionblue
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RE: Hot Or Cold

Sat Jul 12, 2008 12:36 am



Quoting WILCO737 (Reply 1):
that the concorde is about 20cm longer when she landed at the destination.

Concorde increased in length, but it decreased again when it slowed down. There were expansion points inside, including one in the cockpit. While supersonic, you could put your hand inside these points. When on the ground, there was no space.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Bartonsayswhat
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RE: Hot Or Cold

Sat Jul 12, 2008 1:12 am



Quoting Starlionblue (Reply 15):
Concorde increased in length, but it decreased again when it slowed down. There were expansion points inside, including one in the cockpit. While supersonic, you could put your hand inside these points. When on the ground, there was no space.

didn't all the flight engineers put their caps in these gaps and left them in their on their last flights? so that each concord has a hat stuck in the flight deck somewhere?
 
nema
Posts: 479
Joined: Fri Feb 24, 2006 3:18 am

RE: Hot Or Cold

Sat Jul 12, 2008 6:06 am



Quoting Bartonsayswhat (Reply 16):
didn't all the flight engineers put their caps in these gaps and left them in their on their last flights? so that each concord has a hat stuck in the flight deck somewhere?

Hey, a bit off topic but i hope its true...what a great idea!
There isnt really a dark side to the moon, as a matter of fact its all dark!
 
Nicoeddf
Posts: 513
Joined: Thu Jan 10, 2008 7:13 am

RE: Hot Or Cold

Sat Jul 12, 2008 1:28 pm



Quoting Tdscanuck (Reply 14):

Not really...the friction that's heating the outer skin would be even worse on the surface of the beef (assuming your beef is rougher than a polished aluminum skin).

Of course you are right...I totally forgot the friction that would heat up the beef itself...  Sad
 
SlamClick
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RE: Hot Or Cold

Sat Jul 12, 2008 4:36 pm

I suspect that your beef would be very dry when you landed. The water in the fiber would freeze, then sublimate at high altitudes. Possibly even, in the case of something as small as a steak, to the point of 'freeze-drying' the whole thing and having it blow away.

In short, airline food.
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jetmech
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RE: Hot Or Cold

Mon Jul 14, 2008 5:22 am



Quoting NEMA (Thread starter):

I remember a quote from a Concorde book I read many years ago. Apparently, the temperature rise and the mass of structure it effects, represents enough heat to boil either two pints or two quarts of water.

An English gallon is 4.546 litres, so I assume two quarts would be half of this, or 2.273 litres. The specific heat capacity of water is 4.184 J / (g.K). So assuming we have 2,273 grams of water, which needs to be raised by 80 Kelvin to boil, the quantity of heat required would be about 760.82 Kj.

Apparently, beef needs to be raised to a temperature of a bit more than 71 degrees Celsius to be well done, also, the worse case scenario specific heat capacity of beef appears to be around 3.18 Kj / (Kg / Celsius).

Thus, if my calculations are correct, there would appear to be enough heat generated on Concorde's exterior, such that one could expect about 4.785 kg of beef to be raised to a temperature of 71 degrees, assuming a 50 Kelvin temperature rise required to do so.

http://en.wikipedia.org/wiki/Beef
http://en.wikipedia.org/wiki/Water
http://www.engineeringtoolbox.com/sp...ific-heat-capacity-food-d_295.html

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .

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