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Question About Aircraft At Cruising Alttitude  
User currently offlineMike89406 From United States of America, joined Mar 2007, 1464 posts, RR: 3
Posted (6 years 11 months 3 days 2 hours ago) and read 6438 times:

Looking at this picture below its evident the aircraft is flying somewhere over the arctic I've always wondered how cold the temperature is flying over the arctic region at say FL 400 which I presume is a good estimate of where the pictured aircraft is flying.

I guess this could be a loaded question I know that flying anywhere else over the US or EU for example it would be say -40 to maybe -60 F at cruising on average.

My point of the question is flying over the arctic would the temperature be much different than anywhere else based on surface temperature at the same cruising altitude as pictured? I presume it would be much colder flying over the North Pole but then again I'm not a weather expert.

http://www.airliners.net/open.file?i...4%2FRE&Wm=0&WdsYXMg=Pbagvaragny%20
Nveyvarf&QtODMg=Va%20Syvtug&ERDLTkt=Vagreangvbany%20Nvefcnpr&ktODMp=Znl%201%2C%202005&BP=0&WNEb25u=Zvpunry%20Znagbhqvf&xsIERvdWdsY=A77006&MgTUQtODMgKE=RJE-UXT.%20PB%20Syvtug%2099.%20Guvf%20syvtug%20gbbx%20hf%20qverpgyl%20bire%20gur%20trbtencuvpny%20abegu%20cbyr.%20Ba%20guvf%20cvpgher%20lbh%20pna%20frr%20gur%20ynfg%20ovg%20bs%20ynaq%20orsber%20jr%20ernpu%20gur%20cnpx-vpr.%20Gur%20ivrj%20jnf%20fghaavat%20jvgu%20fabj%20naq%20vpr%20nf%20sne%20nf%20bar%20pbhyq%20frr%20naq%20n%20qrrc%20oyhr%20fxl.&YXMgTUQtODMgKERD=218893&NEb25uZWxs=2005-05-17&ODJ9dvCE=&O89Dcjdg=29476%2F183&static=yes&width=1024&height=724&sok=JURER%20%20%28nvepensg_trarevp%20YVXR%20%27Obrvat%20777%25%27%29%20NAQ%20%28nveyvar%20YVXR%20%27Pbagvaragny%20Nveyvarf%25%27%29%20%20BEQRE%20OL%20cubgb_vq%20QRFP&photo_nr=2&prev_id=0945545&next_id=0532410&tbl=WINDOW_VIEW

Having asked the question above I presume the leading edge of the wing is heat treated 7076T aluminum or high strength aluminum alloy with the extremely cold temperatures up there coupled with the wind chill of the airspeed over the leading edge how does the aluminum stand up to say bird strikes or objects? Aluminum is a malleable metal until mixed with other alloys but the cold temps would make the skin of the aircraft or leading edge very brittle.

Being an Airframes Mechanic were not too inadated with scientific theory just metallurgy and hydraulic flight control systems but I always admit I have been intrigued by how the aircraft stands up to the elements.

Regards, Mike

[Edited 2007-09-26 04:36:05]

25 replies: All unread, showing first 25:
 
User currently offlineDoug_Or From United States of America, joined Mar 2000, 3402 posts, RR: 3
Reply 1, posted (6 years 11 months 3 days 1 hour ago) and read 6412 times:

Wind chill does not affect anything that does not produce heat. The friction and compression of air caused by the aircraft speed will actuly increase the temperature.


wind chill

http://en.wikipedia.org/wiki/Wind_chill

To answer your original question read:

http://en.wikipedia.org/wiki/Atmospheric_circulation

Basicaly, there are three circulation cells (equator-30 [hadley cell  warm ], 30-60 [Ferrel cell,  moderate ], and 60-pole [Polar cell  cold ])



When in doubt, one B pump off
User currently offlineBoeingfixer From Canada, joined Jul 2005, 530 posts, RR: 0
Reply 2, posted (6 years 11 months 2 days 23 hours ago) and read 6394 times:

Quoting Mike89406 (Thread starter):
Having asked the question above I presume the leading edge of the wing is heat treated 7076T aluminum or high strength aluminum alloy with the extremely cold temperatures up there coupled with the wind chill of the airspeed over the leading edge how does the aluminum stand up to say bird strikes or objects? Aluminum is a malleable metal until mixed with other alloys but the cold temps would make the skin of the aircraft or leading edge very brittle.

As Doug_Or stated above, windchill does not effect aircraft. Ram rise, which is the effect of the aircraft flying through the air, actually increases the temperature of the airframe. At M0.82, the ram rise is approximately 32 degrees C. An example is If your SAT at M0.82 cruise is -60C, your TAT will be only -28C. As for bird strikes, you don't have to worry about them at cruising altitudes and temperatures of -50C. The temperature effects the fuel more than anything on long range polar flights and is a concern if the fuel gets too close to its freezing point (-40C for Jet-A and -47C for Jet-A1).

Cheers,

John



Cheers, John YYC
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 3, posted (6 years 11 months 2 days 23 hours ago) and read 6390 times:

Quoting Mike89406 (Thread starter):
My point of the question is flying over the arctic would the temperature be much different than anywhere else based on surface temperature at the same cruising altitude as pictured?

There is a significant temperature swing. Aircraft using Jet-A have to watch their fuel freeze point when doing polar routes because Jet A can cloud up during a polar flight if you're at the high end of the spec.

Quoting Mike89406 (Thread starter):
Having asked the question above I presume the leading edge of the wing is heat treated 7076T aluminum or high strength aluminum alloy with the extremely cold temperatures up there coupled with the wind chill of the airspeed over the leading edge how does the aluminum stand up to say bird strikes or objects?

There aren't really any birds or FOD up at cruise altitude; that's only a climb/descent concern. Not sure what happens if you're operating out of a far arctic base though.

Tom.


User currently offlineScooter01 From Norway, joined Nov 2006, 1201 posts, RR: 8
Reply 4, posted (6 years 11 months 2 days 23 hours ago) and read 6384 times:
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Quoting Mike89406 (Thread starter):
My point of the question is flying over the arctic would the temperature be much different than anywhere else based on surface temperature at the same cruising altitude as pictured? I presume it would be much colder flying over the North Pole but then again I'm not a weather expert.

Depends on what time of the year.....  sun 

Scooter01



"We all have a girl and her name is nostalgia" - Hemingway
User currently offlineRwessel From United States of America, joined Jan 2007, 2342 posts, RR: 2
Reply 5, posted (6 years 11 months 2 days 23 hours ago) and read 6380 times:
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Quoting Boeingfixer (Reply 2):
As for bird strikes, you don't have to worry about them at cruising altitudes and temperatures of -50C.

Well, it's not a big concern, but the highest recorded bird strike was with a Griffon Vulture over the Ivory Coast at some 37,000ft.  eyepopping 

Hope the bird was using oxygen!


User currently offlineMike89406 From United States of America, joined Mar 2007, 1464 posts, RR: 3
Reply 6, posted (6 years 11 months 2 days 23 hours ago) and read 6380 times:

Quoting Doug_Or (Reply 1):
Wind chill does not affect anything that does not produce heat. The friction and compression of air caused by the aircraft speed will actuly increase the temperature.



Quoting Boeingfixer (Reply 2):
As Doug_Or stated above, windchill does not effect aircraft. Ram rise, which is the effect of the aircraft flying through the air, actually increases the temperature of the airframe.

Ok so it heats up a little, interesting

Quoting Boeingfixer (Reply 2):
As for bird strikes, you don't have to worry about them at cruising altitudes and temperatures of -50C.



Quoting Tdscanuck (Reply 3):
There aren't really any birds or FOD up at cruise altitude; that's only a climb/descent concern

Yeah I wouldn't expect any birds or foreign objects that high was just wondering about the effect on the structure I should have used a better depiction.

[Edited 2007-09-26 07:21:13]

User currently offlineSEPilot From United States of America, joined Dec 2006, 6883 posts, RR: 46
Reply 7, posted (6 years 11 months 2 days 17 hours ago) and read 6314 times:

Actually, I would suspect the biggest concern might be the possibility that extreme cold might make the aluminum brittle and lead to cracks when encountering turbulence, instead of flexing. Obviously it does not get cold enough for that to happen, as we haven't had any planes breaking up during polar flight.


The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 8, posted (6 years 11 months 2 days 16 hours ago) and read 6294 times:

I don't remember the temp being all that much colder on the last polar flight I made than any other flight. As far as fuel temp goes the closest I've gotten to being concerned was CDG-SFS in the winter. That was 12 hrs at cruise and we did have "cold fuel recirculation".

User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (6 years 11 months 2 days 11 hours ago) and read 6205 times:

Quoting SEPilot (Reply 7):
Actually, I would suspect the biggest concern might be the possibility that extreme cold might make the aluminum brittle and lead to cracks when encountering turbulence, instead of flexing.

Aviation aluminum alloys have very high yield points (relative to ultimate strength) and they're never supposed to go above yield during normal flight. Within the elastic range, you don't really have to worry about brittleness.

Tom.


User currently offlineSEPilot From United States of America, joined Dec 2006, 6883 posts, RR: 46
Reply 10, posted (6 years 11 months 2 days 10 hours ago) and read 6194 times:

Quoting Tdscanuck (Reply 9):
Within the elastic range, you don't really have to worry about brittleness.

This is true; I have heard, however, of steel parts in extreme cold breaking under comparatively light blows. It is anecdotal, and might be exaggerated.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlineLaminarFlow From Canada, joined Aug 2007, 72 posts, RR: 0
Reply 11, posted (6 years 11 months 2 days 6 hours ago) and read 6130 times:

Quoting Mike89406 (Thread starter):
My point of the question is flying over the arctic would the temperature be much different than anywhere else based on surface temperature at the same cruising altitude as pictured? I presume it would be much colder flying over the North Pole but then again I'm not a weather expert.

Theoretically, an aeroplane cruising at 40,000' over the North Pole could be in equally warm or warmer air than an aeroplane flying at the same altitude over the equator due to the decreased altitude of the stratosphere, throughout which the air temperature actually begins to increase with altitude as the air is heated by the absorption of UV rays by small amounts of ozone. The stratosphere can generally exist as low as 26,000' over the poles, and as high as 60,000' over the equator.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 12, posted (6 years 11 months 2 days ago) and read 6079 times:

Quoting SEPilot (Reply 10):
This is true; I have heard, however, of steel parts in extreme cold breaking under comparatively light blows. It is anecdotal, and might be exaggerated.

It does happen with certain alloys. Fracture toughness can be temperature dependant so, under impact, a blow that would normally cause a dent may cause a crack. Still have to go above yield for that to kick in though. Impact stress is also hardness dependent so it's worse with steel than aluminum (for the same impacting object).

Tom.


User currently onlineStarlionblue From Greenland, joined Feb 2004, 17019 posts, RR: 67
Reply 13, posted (6 years 11 months 1 day 23 hours ago) and read 6064 times:

Here is an interesting article about considerations on Polar routes: http://www.boeing.com/commercial/aer...magazine/aero_16/polar_story.html. Right from the horse's mouth if you will.

Quoting CosmicCruiser (Reply 8):
I don't remember the temp being all that much colder on the last polar flight I made than any other flight. As far as fuel temp goes the closest I've gotten to being concerned was CDG-SFS in the winter. That was 12 hrs at cruise and we did have "cold fuel recirculation".

JFK-HKG - 16½ hours flying time, and it grazes the pole. That's a lot of time in the cold. But I'm sure those clever dispatchers and pilots knew what they were doing. We got there in one piece in any case. Far more worrying was "handling" our 23 month old and our 5 month throughout the flight. Not quite the flight from hell but we were pretty tired when we got there.  Sad

Quoting Tdscanuck (Reply 12):
It does happen with certain alloys. Fracture toughness can be temperature dependant so, under impact, a blow that would normally cause a dent may cause a crack. Still have to go above yield for that to kick in though. Impact stress is also hardness dependent so it's worse with steel than aluminum (for the same impacting object).

In other words, don't hit any birds at cruise. Big grin



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineElpinDAB From United States of America, joined Apr 2005, 473 posts, RR: 4
Reply 14, posted (6 years 11 months 1 day 23 hours ago) and read 6063 times:

Quoting LaminarFlow (Reply 11):
Quoting Mike89406 (Thread starter):
My point of the question is flying over the arctic would the temperature be much different than anywhere else based on surface temperature at the same cruising altitude as pictured? I presume it would be much colder flying over the North Pole but then again I'm not a weather expert.

Theoretically, an aeroplane cruising at 40,000' over the North Pole could be in equally warm or warmer air than an aeroplane flying at the same altitude over the equator

Very true. The air temperature above the planetary boundary layer (which is the part of the atmosphere directly affected by the Earth's surface, ranging from the surface to between about 1,000ft to 10,000ft) is not significantly affected by day and night heating or changes in latitude. So, often you'll see similar temperatures at 40,000 ft from the equator all the way to the pole. This is because the Earth's atmosphere is mostly heated from below, from radiation that has been absorbed by the Earth's surface and then heats the surrounding air in the planetary boundary layer. The remainder of the atmosphere at a given altitude remains at a fairly constant temperature, and even more so the higher you go. So, down around 25,000ft or so, you'll see a little more difference in temperature with changes in latitude.

To illustrate, here are three current atmospheric soundings for the same day. (altitude on the vertical axis, temp at the bottom on the horizontal axis, temperature line on the right, dewpoint on the left.)

1) Manaus, Brazil, near the equator: http://weather.uwyo.edu/cgi-bin/soun...TH=09&FROM=2700&TO=2700&STNM=82332
Temp at 12,000m (about 40,000ft): -50C


2) Denver, CO, USA, middle latitudes:
http://weather.uwyo.edu/cgi-bin/soun...TH=09&FROM=2700&TO=2700&STNM=72469
Temp at 12,000m (about 40,000ft): -50C


3) Barrow, AK, USA, north of arctic circle:
http://weather.uwyo.edu/cgi-bin/soun...TH=09&FROM=2700&TO=2700&STNM=70026
Temp at 12,000m (about 40,000ft): -50C

All are at about -50C at 40,000ft even though the surface temperatures vary greatly between the locations. On the Barrow, AK sounding, you can also plainly see the temperature inversion that occurs at the top of the troposphere, the tropopause, because of the presence of ozone that absorbs solar radiation. Interesting, this temperature inversion also prevents thunderstorms from growing to enormous heights.


User currently offlineAnalog From United States of America, joined Jul 2006, 1900 posts, RR: 1
Reply 15, posted (6 years 11 months 1 day 21 hours ago) and read 6046 times:

Quoting Doug_Or (Reply 1):
Wind chill does not affect anything that does not produce heat.

I don't think that's true. Take a puddle of water. It does not produce heat, but wind [chill] definitely affects the rate at which its temperature changes.


User currently offlineRwessel From United States of America, joined Jan 2007, 2342 posts, RR: 2
Reply 16, posted (6 years 11 months 1 day 19 hours ago) and read 6039 times:
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Quoting Analog (Reply 15):
Quoting Doug_Or (Reply 1):
Wind chill does not affect anything that does not produce heat.

I don't think that's true. Take a puddle of water. It does not produce heat, but wind [chill] definitely affects the rate at which its temperature changes.

The original statement is correct, but entirely clear.

If there's no local airflow, you have a stable boundary layer of air attached to any object, and all heat loss is convective through that layer. What wind does is blow the warmed boundary layer away and replaces it with fresh cold air. This can significantly increase the rate at which heat is sucked out of the object. So you will freeze faster as your ability to produce body heat is overwhelmed, a puddle of water will freeze faster, or an object will cool down faster.

But that only apply to an object with a temperature above the (actual) air temp. So if the air temp is -20C, a warm block of aluminum will cool to -20C more quickly than with a good breeze blowing than in calm conditions, but in both cases they'll stabilize at exactly -20C. If there is a heat source inside the aluminum block, then the no-wind stable temp will be higher than in the wind.


User currently offlineAnalog From United States of America, joined Jul 2006, 1900 posts, RR: 1
Reply 17, posted (6 years 11 months 1 day 15 hours ago) and read 6001 times:

Quoting Rwessel (Reply 16):

The original statement is correct, but entirely clear.

But you go on to give an example that shows it is incorrect. Wind chill does affect non-heat producing objects. Perhaps not in the steady-state, but that's not really important.

Quoting Rwessel (Reply 16):
So if the air temp is -20C, a warm block of aluminum will cool to -20C more quickly than with a good breeze blowing than in calm conditions, but in both cases they'll stabilize at exactly -20C.

If wind chill does not affect objects at the same temperature as the air, why do people sweat when the outside air is below 37 degrees? Because the wind still chills your body (evaporation). You can make ice in a hot desert using wind chill.


User currently offlineBoeingfixer From Canada, joined Jul 2005, 530 posts, RR: 0
Reply 18, posted (6 years 11 months 1 day 15 hours ago) and read 5989 times:

Quoting Analog (Reply 17):
If wind chill does not affect objects at the same temperature as the air, why do people sweat when the outside air is below 37 degrees? Because the wind still chills your body (evaporation). You can make ice in a hot desert using wind chill.

The confusion is in the terminology. Wind Chill was devised to be a measurement of how the human body feels the air temperature based on wind speed in freezing temperatures. It wasn't meant to be a term to describe the rate of temperature change due to wind speed. That is called Temperature Transference. This Temperature Transference can be used to calculate the rate of temperature change to bring an object from one temperature to the temperature of the surrounding air. Obviously if the air is moving or circulating the temp. will change faster. The OP had assumed that wind chill would make the aircraft skin colder than the outside temp. This is not physically possible.

Make ice in the desert by just blowing wind? Not likely unless there is some pretty hefty energy transfer going on. A 30 knot wind at 50C is still 50C. It may cool you off by evaporating sweat quicker but you're never going to make ice cubes without massive energy extraction and volume expansion.

Cheers,

John



Cheers, John YYC
User currently offlineAnalog From United States of America, joined Jul 2006, 1900 posts, RR: 1
Reply 19, posted (6 years 11 months 1 day 2 hours ago) and read 5894 times:

Quoting Boeingfixer (Reply 18):

Make ice in the desert by just blowing wind? Not likely unless there is some pretty hefty energy transfer going on. A 30 knot wind at 50C is still 50C. It may cool you off by evaporating sweat quicker but you're never going to make ice cubes without massive energy extraction and volume expansion.

You can cool things below ambient temperature using evaporation. Many air conditioning units (evaporative coolers) work like that.

In retrospect I think the trick of making ice in the desert works by radiation (insulated container, open to space at night).


User currently offlineBoeingfixer From Canada, joined Jul 2005, 530 posts, RR: 0
Reply 20, posted (6 years 11 months 23 hours ago) and read 5839 times:

Quoting Analog (Reply 19):
You can cool things below ambient temperature using evaporation. Many air conditioning units (evaporative coolers) work like that.

You never mentioned evaporation in your post. You specifically said:

Quoting Analog (Reply 17):
You can make ice in a hot desert using wind chill.

Wind chill and Evaporaion cooling are two completely different things and have no correlation to each other. Lets not confuse this post more than it already is.

Quoting Analog (Reply 19):
In retrospect I think the trick of making ice in the desert works by radiation (insulated container, open to space at night).

 Confused

Cheers,

John



Cheers, John YYC
User currently offlineAnalog From United States of America, joined Jul 2006, 1900 posts, RR: 1
Reply 21, posted (6 years 11 months 23 hours ago) and read 5827 times:

Quoting Boeingfixer (Reply 20):
Wind chill and Evaporaion cooling are two completely different things and have no correlation to each other. Lets not confuse this post more than it already is.

Please explain. Wind chill is partly due to evaporative cooling. They are highly correlated (in so much as causation is correlation).

http://www.straightdope.com/mailbag/mwindchi.html
http://www.newton.dep.anl.gov/askasci/phy99/phy99116.htm


User currently offlineBoeingfixer From Canada, joined Jul 2005, 530 posts, RR: 0
Reply 22, posted (6 years 11 months 16 hours ago) and read 5765 times:

Quoting Analog (Reply 21):
Please explain. Wind chill is partly due to evaporative cooling. They are highly correlated (in so much as causation is correlation).

http://www.straightdope.com/mailbag/mwindchi.html
http://www.newton.dep.anl.gov/askasci/phy99/phy99116.htm

Two very simple explanations there. I will however concede on that point but it is a much more complex issue than your links express and simple evaporation plays a partial role along with other factors.

BTW, you still can't freeze water in the desert just by wind chill  Wow!

Now I'll let this thread get back on track  Yeah sure

Cheers,

John



Cheers, John YYC
User currently offlineAnalog From United States of America, joined Jul 2006, 1900 posts, RR: 1
Reply 23, posted (6 years 11 months 11 hours ago) and read 5721 times:

Quoting Boeingfixer (Reply 22):

BTW, you still can't freeze water in the desert just by wind chill

Antarctica is a desert.  Wink

I tried searching for the answer to this question... no luck so far. If the air is 1deg C, can one freeze water using wind? In retrospect I think that you are right about that (No).


User currently offlineChksix From Sweden, joined Sep 2005, 345 posts, RR: 4
Reply 24, posted (6 years 11 months 6 hours ago) and read 5683 times:

Air that flows through an expanding nozzle at high speed will cool enough to cause the bound moisture to form ice chrystals. It can happen in smoke diving air pressure regulators despite them being used in very hot zones if the main valve isn't opened fully for example.


The conveyor belt plane will fly
User currently offlineBoeingFixer From Canada, joined Jul 2005, 530 posts, RR: 0
Reply 25, posted (6 years 11 months 5 hours ago) and read 5649 times:

Quoting Chksix (Reply 24):
Air that flows through an expanding nozzle at high speed will cool enough to cause the bound moisture to form ice chrystals. It can happen in smoke diving air pressure regulators despite them being used in very hot zones if the main valve isn't opened fully for example.

That's pretty much what I said in reply 18:

Quoting Boeingfixer (Reply 18):
Make ice in the desert by just blowing wind? Not likely unless there is some pretty hefty energy transfer going on. A 30 knot wind at 50C is still 50C. It may cool you off by evaporating sweat quicker but you're never going to make ice cubes without massive energy extraction and volume expansion.

Volume expansion is exactly what you get from compressed air being released at high speed.

Cheers,

John



Cheers, John YYC
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