Skin Temp

[DavidHWalker]

I am not in aircraft design, but this looked like a good place to ask the question. We were flying to Armenia and we reached an altitude that I had not flown at before 44,000 or so. The ambient Temp -82 Celsuis at a speed of 680 MPH. What is the approx. skin temp (wing and/or fuelage) at that speed and temp.

 

[Zapster]

http://www.grc.nasa.gov/

http://WWW/K-12/airplane/atmosi.html

Take a look at the above calculator. For standard conditions temp at 44,000 feet is -69 degF. You stated 44,000 feet at -82 degC which is -115.6 degF. Are you sure about the temp? For standard conditions at 44,000 feet your speed of 680 mph would be slightly over Mach 1. Are you sure the speed is air speed and not ground speed? What were you flying in?

 

[debodine]

I agree with zapster. At that altitude in a commercial airliner (if that's what you were in), 680 MPH is a reasonable ground speed, but an impossible airspeed for a commercial jet.

If you were looking at an Airshow map (airplane symbol on world map) in the passenger cabin, you would have seen ground speed as the speed number, and 680 mph would be reasonable.

The airspeed would have most likely been around 325 to 350 KIAS (indicated airspeed) if you were looking at a flight deck airspeed indicator. If you were on the flight deck and saw an indicated airspeed of 680mph (unlikely since they are in knots) you would have lived about 1/2 second before the aircraft disintegrated.

If you were in a military aircraft that IS capable of 680 mph at 44,000 feet, you are probably not supposed to be talking about it. (he he, some humor there)

debodine

However, I don't know the skin temperature formula.

debodine

 

[debodine]

To finish my original thought, which I completely failed to do, since in your original post you only used the term speed (you did not say airspeed, so you used the term correctly, I was just having fun with you and zapster in my first post), I intended to say it was ground speed you saw and it would have to be converted to indicated airspeed before a calculation could be made as to skin temperature.

Sorry to hit send before I was done,

debodine

 

[DavidHWalker]

What ever speed is monitored on the flight screens, I s'pose that is ground speed. I am not doing an engineering job here. I only wanted a general idea of what the skin temp would be at thatt temp flying full speed for a commercial jet. I like the replies so far - interesting but I don't have my answer yet.

 

[IRstuff]

Was there something wrong with the applet that Zapster pointed you to?

TTFN

 

[kenvlach]

I liked the NASA simulator program from Zapster's link. For 600 mph, I got an ambient air T = -69^oF and a 'total' temperature of -5^oF.
The stagnation, or total, temperature "is the temperature of the airflow at a stagnation point, such as the leading edge of the wing or nose of the aircraft." But, I'm still uncertain of the remaining skin temperatures.

So, aero guys, is this 'total' temperature the maximum skin temperature on the aircraft? Does a skin temperature continuum between -69^oF and -5^oF exist for this aircraft depending upon surface flow?
There should be less heating due to air friction at a stagnation point. Some heat is generated by turbulence within the air. But, of course, also less convective cooling.
Answers?

 

[IRstuff]

Compression?

TTFN

 

[Sparweb]

For a good explanation and case study of aerodynamic heating:

http://www.hq.nasa.gov/office/pao/History/x15lect/structur.html

At a stagnation point, the air velocity is reduced to "zero", converting all of the kinetic energy to heat. At hypersonic speeds, the temperature change is tremendous. At sub-sonic speeds, it is measurable, but hardly an issue.

Steven Fahey, CET