Aircraft Skin Temperature

[Dennis0312]

What is the simplest formula for calculating aircraft skin temperatures?:ugh:

[Goldenrivett]

Hi Dennis0312,

Skin temperature is the same as OAT, except for all the leading edges and the nose which are subjected to skin friction (almost negligible) and adiabatic compression.
See Total air temperature - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Total_air_temperature)

"With TAS in knots, a simple accurate formula for ram rise is then:
RamRise{total}={V^2}/{87^2}"

[JeroenC]

If Time > 120 then Tskin = OAT.
Sorry, no real useful help here. I wonder if this can be calculated, since it depends on, among many things, the amount of fuel in contact with the wing, so will be model specific.

[chksix]

This site is nice when looking at single cases:
Aerospaceweb.org | Atmospheric Properties Calculator (http://www.aerospaceweb.org/design/scripts/atmosphere/)
Can't help with the underlying formulas though.

[Mad (Flt) Scientist]

Except for some very specific cases, in general the skin temperature will be very close to the recovery temperature of the air; the heat loads from the inside 9whether it be cooling or heating) surprisingly work out to be small compared to the heat supplied or removed by the airflow.

(I'm recalling some IR signature work where it seemed to make no difference how we specified the temperatures in the bays - the skin temperature didn't change much if at all)

So assuming the skin temperature is TAT (rather than OAT) is probably a good start - it's probably a little lower, maybe 85% between SAT and TAT - but it's a good guess, IIRC.

[FLEXPWR]

Dennis 0312, I am not sure to understand at which location the aircraft skin temperature is measured for your question.

Aircraft skin temperature varies with location. A point measured along the fuselage skin (paralell to the airflow) would be nearly identical to OAT. A point measured perpendicular to the airflow (aircraft's nose, wing leading edge, TAT probe) would give OAT increased by the ram rise effect.

An easy -altough not terribly accurate- way to estimate the ram rise (difference between TAT and SAT) is as follows:

RR (ram rise) in degrees C = [TAS (in NM per minute)]^2 divided by 2

example: 420kt is 7NM per min = 7^2 is 49. 49/2= 24.5 degrees C

You can do the same with mach number (times 10), or an even easier one is IAS/10, but this last one works only at higher levels.

These examples are taken from the book "M3: The Mile, the Mach, the Minute / Mental Math for Aviators".

Note: Below 120kt, the ram rise is negligible and SAT TAT OAT are considered identical.

Is this what you were after?

[chksix]

Enter 85000ft, M3.2 into the calculator above and you get some impressive numbers. The Habus are still unmatched :8

A TAT of 404°C for example :E

[awblain]

The power of the air to deliver heat to a surface should go something not a huge distance away from density times speed-cubed per unit area. Close to shocks you might need to be careful, but that's the power there is in the flow.

When shockwaves form it gets more complicated, and the nature of the associated upstream changes in speed, density and temperature can be important.

The efficiency of cooling also affects the final surface temperature, so the surface and structural properties affect the answer too. Key components of short-lived items can cope if handled with conductive, ablative or radiative cooling.

[BUGS/BEARINGS/BOXES]

Dennis....does your question relate to environmental cold soaking and the LOUT of de-icing fluids? If so, model and and wing stored fuel overnight dependant. But recent NASA/FAA/EASA((?)can't quite remember whom) testing has shown differences of up to 10 degrees below OAT on some types and fuel amount combos, leading to pointless early type 1 fluid applications.