Temperature Rise with speed

[electricdeathjet]

Looking for a Boffin to help me out...:ugh:

Assuming level flight and ISA conditions, how much faster do you need to go to achieve 1 degree C temp rise?

Thanks guys

[PantLoad]

10 kts

PantLoad

[electricdeathjet]

Thanks,
But would that imply that at 70 mph on a motorway the temp. gauge will increase by about 6 degrees of so? :confused:

[mmciau]

I'd suggest that a car on the motorway isn't in level flight and under ISA conditions!!

Mike McInerney

[Superpilot]

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.

[electricdeathjet]

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.

[FE Hoppy]

Wiki covers this quite well:
http://en.wikipedia.org/wiki/Total_air_temperature

[Old Smokey]

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!!!!!!:eek:

Regards,

Old Smokey

[Brian Abraham]

100.2 MPH for those who live in the olde worlde

MPH? My daughter looked at me as if I came from another planet when feet, inches, MPH etc were mentioned (when in high school). All metric now. At least she is now learning to fly and understands knots.

[BelArgUSA]

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

[Old Smokey]

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!!!!:ok:

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.:ok:

I wonder if the guy who invented knots considered WGS84?:confused:

Regards,

Old Smokey

[SR71]

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.

[PantLoad]

Ten knots....


PantLoad

[Brian Abraham]

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? :8

I know standards and conventions do change - look at the word gay :oh:

[perkin]

As long as the metric system continues to use the 360 degree circle, broken into 60 minutes per degree

The metric system does use grads? I've come across them quite often in my line of work...

[bookworm]

The metric system does use grads? I've come across them quite often in my line of work...

Indeed. Which is why the nautical mile to kilometre ratio is so neatly close to 100/54. In the same way that the nm is a minute of arc, the km is a centigrad of arc.

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. ;)

[Bellerophon]

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. :confused:

Think Kelvin, he said! ;)

Regards

Bellerophon

[BelArgUSA]

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

[PantLoad]

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

[old,not bold]

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.

[Brian Abraham]

And the SR-71 engine grew six inches in length and 2½ inches in diameter. Wonder how in the world they managed clearances.

[galaxy flyer]

BelArgUSA:

An optimist was a F-104 pilot who gave up smoking!:}:}

[enicalyth]

G'Day Podeans and Auntie Podeans alike!
It isn't thermodynamics prompting my drift but the argument whether or not Ramanjuan has supremacy over Gauss when it comes to basic geodesy. A grave error was made when the international nautical mile was redefined. An error of 4.1045 Clarke feet.
I'm not saying any good maths undergraduate can blow apart the argument that perimeter is more important than surface area if it comes to modelling the earth as a smooth ellipsoid. Any child with a computer and access to the web can do the same.
In fact I first heard the argument in a pub where the matter under discussion was what would be the visible difference if God spliced an extra yard into a hoop which he had already fashioned to girdle the earth. Try it with a sphere of radius 20901500 feet for simplicity. Amazing! What was a tight fight before now has a clearance of five-and-three-quarter inches.
This proves that scientific definitions are best made with feet not metres, upon a bar, not of temperature controlled platinum but ice-cold Tooheys, Redback, Swan, Gage's or whatever is currently on offer at the The Lucky Shag in Barrack St Perth WA over the festive season. (Bring your own cormorant, it's that kind Shag).
Ron Hatch of GPS is correct. If anyone is looking for a better-fit, intellectual honesty, sounder mathematics and accurate cartography the best offer for the nautical mile is 6080.22ft. Which is coincidentally the old Admiralty Mile of Clarke, Bamford, Gauss, Andoyer, Weems and Lambert. But to redefine the nautical mile back more or less to what it was because t'committee goofed and got the form of the earth sized wrong would lead to too many red faces rather than Two Too many Toohey's.
Jeppesens are proud of their accuracy drawn to a scale of 1 inch to the old nautical mile. God went one better at twelve inches to the foot. Hatch has surveyed it and says the old boys with their glass and brass made a better fist of it than the bunch of academics in Bermuda. He also positions his satellites with a theory suggestive that Einstein didn't quite get everything right. (See his Ether Gage Theory). And now to raise the temperature of my next stubbie by one degree, how fast must my hand move again?
Festive Chiz
Mr and Mrs "E"

[ChristiaanJ]

Old Smokey,
Just being pedantic for a sec.... it's not exponential, but a simple square law.
But yes, it's non-linear, which is the main point.

For me as an engineer, it's still counter-intuitive, that, whether you barrel along at 2000 km/h TAS at sealevel or at 2000 km/h TAS at 60,000 ft, the temperature rise is the same, notwithstanding the far lower air density.

I'm not querying the formulae... worked with them long enough. It's just that it doesn't 'feel' right.

I expect the answer is elementary...
Temperature is a property of each individual molecule.
In a total temperature probe each indivdual molecule is brought to rest, so it experiences the same temperature rise, while the number of molecules does not enter into the equation.
Sounds right....

As a boffin, I now ask myself the question: to what extent does the air density affect the heat transfer, be it to the total temperature sensor, or to the structure.

To take an extreme case, think of the space station, where the total air temp works out at something like 30,000°C, but there are simply not enough air molecules to result in any significant kinetic heating.

CJ

[Sky Pilot]

Ah yes! But at what point does the wind chill factor become a ram rise?:}

[Beeline]

One of the Concordes still has a hat wedged in it from its final flight! Cant remember which one though!

[ChristiaanJ]

One of the Concordes still has a hat wedged in it from its final flight! Cant remember which one though!Not one, but several!
Alpha Fox at Filton for certain (I've seen it), Alpha Charlie at Birmingham almost certain, Alpha Golf at Seattle (was pulled out by a vandal, but they slid it back). Not sure about Alpha Delta in New York or Alpha Echo in Barbados.

IIRC, at Mach 2 there was a good two inches between the right side of the flight engineer's panel and the bulkhead, and less than hafl an inch on the ground.

[ChristiaanJ]

old, not bold,
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. 10 inches is 25.4cm. And thank goodness al the rest behind the .4 is zeros.
If that hadn't been the case I doubt we could ever have gotten all the French and British bits to mate....

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.Well, there are an awful lot of expansion joints and other tricks of the trade. :)

I've never quite understood how the skin stretched with the frame, but no doubt someone can help with that.Since you live in the UK, come down to Brooklands Museum in Weybridge sometime, and have a look at the fuselage section inside Delta-Golf that has been left "bare".
Lengthwise the skin IS the frame, the skin panels are machined from solid blocks, so when heated they expand uniformly.
Think of a beer can, or rather a tuna can in view of the proportions.
Top and bottom rim are the transverse frames which give the fuselage its shape and stiffness.
The wall is the skin, stiff enough so you can't crush it.
Now heat your tuna can. It just expands a bit in length and a little bit in diameter. No problem.
Same as Concorde.

And while everybody knows about 'spamcans', I don't think anybody has yet compared Concorde to a batch of tuna cans put end to end.

So I'm getting my tin hat and my coat, and I'm off for Christmas dinner.

Best wishes to everybody.

Christian

[Anotherflapoperator]

Err, I think you'll find Alpha Charlie is sat at Manchester Ringway, not Birmingham. Other than that, I'll have to look for the hat next time I take a peek inside....

[ChristiaanJ]

Anotherflapoperator,Err, I think you'll find Alpha Charlie is sat at Manchester Ringway, not Birmingham.Thanks, you're dead right. I make that mistake every time!