Temperature Rise with speed
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Temperature Rise with speed
Looking for a Boffin to help me out...
Assuming level flight and ISA conditions, how much faster do you need to go to achieve 1 degree C temp rise?
Thanks guys
Assuming level flight and ISA conditions, how much faster do you need to go to achieve 1 degree C temp rise?
Thanks guys
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What you are describing is temperature gained due to kinetic heating of the aircraft as it moves through the air. The effect is not linear. It is neglible for speeds below Mach 0.3 or roughly 200KTS. Therafter the effect is increased as speed builds up.
Also a car temperature sensor doesn't hang off the car body, like a planes temperature probe does so I doubt you'll see the temperature display on your dash increase even if you managed to achieve a 250MPH cruise on the M1.
Also a car temperature sensor doesn't hang off the car body, like a planes temperature probe does so I doubt you'll see the temperature display on your dash increase even if you managed to achieve a 250MPH cruise on the M1.
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Superpilot....... I know why you got your name.... Thanks I forgot about the non-linear bits, thats obviously why the TAT doesn't change on the T.O. run.
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Wiki covers this quite well:
http://en.wikipedia.org/wiki/Total_air_temperature
http://en.wikipedia.org/wiki/Total_air_temperature
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As alluded to by earlier posters, there's no simple solution, the temperature rise is not linear, but exponential. The formula for temperature rise depends upon Static Temperature (SAT) and Mach Number, but, as these two inputs yield TAS, the formula may be much simplified by directly applying TAS......
Temperature Rise = (TAS / 87.1)^2 (For Temperature in Celsius, and speed in Knots)
If you're looking for the FIRST 1 degree rise, for an aircraft accelerating from zero speed, that will occur at 87.1 Knots TAS (100.2 MPH for those who live in the olde worlde).
Being exponential, further 1 degree rises will occur at decreasing speed increments, e.g.
+1 Degree at 87.1 Knots
+2 Degrees at 123.2 Knots (a further 36.1 Kt)
+3 Degrees at 150.9 Knots (a further 27.7 Kt)
+4 Degrees at 174.2 Knots (a further 23.3 Kt)
+5 Degrees at 194.8 Knots (a further 20.6 Kt), etc, etc....
As we approach typical jet aircraft cruising speeds, it requires a TAS of 477.1 Kt to achieve a Temperature rise above Static of +30 degrees, to achieve +31 degrees requires a mere additional 7.9 Kt TAS, increasing temperature rises require much decreased speed increments).
Strongly recommended that testing on the M1 is limited to a +1 degree temperature rise!!!!!!
Regards,
Old Smokey
Temperature Rise = (TAS / 87.1)^2 (For Temperature in Celsius, and speed in Knots)
If you're looking for the FIRST 1 degree rise, for an aircraft accelerating from zero speed, that will occur at 87.1 Knots TAS (100.2 MPH for those who live in the olde worlde).
Being exponential, further 1 degree rises will occur at decreasing speed increments, e.g.
+1 Degree at 87.1 Knots
+2 Degrees at 123.2 Knots (a further 36.1 Kt)
+3 Degrees at 150.9 Knots (a further 27.7 Kt)
+4 Degrees at 174.2 Knots (a further 23.3 Kt)
+5 Degrees at 194.8 Knots (a further 20.6 Kt), etc, etc....
As we approach typical jet aircraft cruising speeds, it requires a TAS of 477.1 Kt to achieve a Temperature rise above Static of +30 degrees, to achieve +31 degrees requires a mere additional 7.9 Kt TAS, increasing temperature rises require much decreased speed increments).
Strongly recommended that testing on the M1 is limited to a +1 degree temperature rise!!!!!!
Regards,
Old Smokey
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100.2 MPH for those who live in the olde worlde
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Temperature rise trivia...
Used to fly F-104G... 1965-1968 - Belgian Air Force, EBBE 1st Wing, 349/350th Squadron.
Often I was asked "what is your max speed", IAS, (TAS) or Mach...?
We gave "numbers" to be 2.3 Mach... but really it was not.
The real limit was a temperature
The correct answer is - Tt2 - Engine inlet temperature (J-79).
At Mach 2.3, the rise was about 150º...
At FL 600 or so, Mach 2.2, typical SAT was -60º, so Tt2 was about +90º.
Just a little red light that flashed next to the IAS indicator.
If I remember well, limit was 100ºC ram air temperature that triggered the light.
xxx
My turn to be curious... Did you have similar engine concerns in Concorde...?
Mach 2... FL 590...?
xxx
Happy contrails
Often I was asked "what is your max speed", IAS, (TAS) or Mach...?
We gave "numbers" to be 2.3 Mach... but really it was not.
The real limit was a temperature
The correct answer is - Tt2 - Engine inlet temperature (J-79).
At Mach 2.3, the rise was about 150º...
At FL 600 or so, Mach 2.2, typical SAT was -60º, so Tt2 was about +90º.
Just a little red light that flashed next to the IAS indicator.
If I remember well, limit was 100ºC ram air temperature that triggered the light.
xxx
My turn to be curious... Did you have similar engine concerns in Concorde...?
Mach 2... FL 590...?
xxx
Happy contrails
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Brian Abraham,
For heaven's sake, don't tell your daughter that knots are a part of the Metric system!
As long as the metric system continues to use the 360 degree circle, broken into 60 minutes per degree, and 1 Nautical Mile equals 1 minute of Latitude, the Nautical Mile remains metric!!!!
In the Imperial system, the Nautical mile is a surd, being 6076.11548....... feet to infinity, whereas in the Metric System it remains stuck at 1852 M exactly.
Now, if the metric system were to embrace gradians (the 400 degree circle, an eminently sensible idea), that would be a different matter altogether.
I wonder if the guy who invented knots considered WGS84?
Regards,
Old Smokey
For heaven's sake, don't tell your daughter that knots are a part of the Metric system!
As long as the metric system continues to use the 360 degree circle, broken into 60 minutes per degree, and 1 Nautical Mile equals 1 minute of Latitude, the Nautical Mile remains metric!!!!
In the Imperial system, the Nautical mile is a surd, being 6076.11548....... feet to infinity, whereas in the Metric System it remains stuck at 1852 M exactly.
Now, if the metric system were to embrace gradians (the 400 degree circle, an eminently sensible idea), that would be a different matter altogether.
I wonder if the guy who invented knots considered WGS84?
Regards,
Old Smokey
Mach 3
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Without wishing to be a pedant, the relationship also depends on gamma, the specific heat capacity ratio.
BelArgUSA,
If you check http://www.sr-71.org/blackbird/manual/5/5-8.php you can see the max Mach limitation for the SR-71 was also really a CIT of 427C. See also http://www.sr-71.org/blackbird/manual/5/5-10.php
I once worked out that in ISA-50C conditions (or thereabouts), this theoretically allowed for a Mach number of 4.
A significant number of SR-71 crews exceeded 3.5 I believe. Certainly, in the book The Untouchables you can read about a crew who did.
BelArgUSA,
If you check http://www.sr-71.org/blackbird/manual/5/5-8.php you can see the max Mach limitation for the SR-71 was also really a CIT of 427C. See also http://www.sr-71.org/blackbird/manual/5/5-10.php
I once worked out that in ISA-50C conditions (or thereabouts), this theoretically allowed for a Mach number of 4.
A significant number of SR-71 crews exceeded 3.5 I believe. Certainly, in the book The Untouchables you can read about a crew who did.
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Old Smokey - always regarded the knot/nautical mile as Imperial, going back to my navy days when a nautical mile was 1,851.66 metres. The Poms did invent this stuff didn't they? 
I know standards and conventions do change - look at the word gay
I know standards and conventions do change - look at the word gay
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As long as the metric system continues to use the 360 degree circle, broken into 60 minutes per degree
Last edited by perkin; 19th Dec 2007 at 08:13. Reason: didnt read a previous post fully
The metric system does use grads? I've come across them quite often in my line of work...
There are 90 x 60 nautical miles between the equator and the pole.
There are 100 x 100 kilometres between the equator and the pole.
The real fault here lies with evolution for cursing us with 2 fewer fingers than would be mathematically neat.
BelArgUSA
No temperature limit on the engine intake air on Concorde.
There was however a limit on the aircraft nose temperature TMO of +127ºC, which could easily be reached in warm air.
Couldn't understand how they'd arrived at that precise figure until one of the original design team patiently explained it to me at a reunion dinner.
The square, and square root, of the temperature came into various design equations, and so - in those pre-computer days - he said they selected +127ºC to make the mental calculations easier!
He must have seen the baffled look in my eyes.
Think Kelvin, he said!
Regards
Bellerophon
No temperature limit on the engine intake air on Concorde.
There was however a limit on the aircraft nose temperature TMO of +127ºC, which could easily be reached in warm air.
Couldn't understand how they'd arrived at that precise figure until one of the original design team patiently explained it to me at a reunion dinner.
The square, and square root, of the temperature came into various design equations, and so - in those pre-computer days - he said they selected +127ºC to make the mental calculations easier!
He must have seen the baffled look in my eyes.
Think Kelvin, he said!
Regards
Bellerophon
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Bellerophon - SR71 -
xxx
Thanks for the info -
I expected a limitation on the SST inlets...
And of course, the SR-71s, forgot about the masterpiece...
xxx
Thinking about SR-71's fuel temperature maximum as well.
In the 747, we are limited to +54.5º for Jet A-1.
But , limit is +43º for JP-4/Jet B...
Maximum never much of a problem.
xxx
Happy contrails
xxx
Thanks for the info -
I expected a limitation on the SST inlets...
And of course, the SR-71s, forgot about the masterpiece...
xxx
Thinking about SR-71's fuel temperature maximum as well.
In the 747, we are limited to +54.5º for Jet A-1.
But , limit is +43º for JP-4/Jet B...
Maximum never much of a problem.
xxx
Happy contrails
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electricdeathjet...
Try it...you'll like it!!!!
Again, I'm not contradicting any of the above....But, if you want a rule of thunb...it's ten knots---one degree.
All of the above is totally correct, I have no doubt.
PantLoad
Again, I'm not contradicting any of the above....But, if you want a rule of thunb...it's ten knots---one degree.
All of the above is totally correct, I have no doubt.
PantLoad
With all due deference to you scientists, all I know is that the speed-induced temperature rise was enough to stretch the Concorde by, as I remember it, 10 inches (25.3 or so cm?) at M2.
I was always amazed that the designers predicted it correctly, so that all the wires and pipes and stuff had the right amount of slack. I've never quite understood how the skin stretched with the frame, but no doubt someone can help with that.
I was always amazed that the designers predicted it correctly, so that all the wires and pipes and stuff had the right amount of slack. I've never quite understood how the skin stretched with the frame, but no doubt someone can help with that.