Aircraft skin temp

brien23

brien23

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How fast does a aircraft have to pass through air to increase the airframe temperature that is measurable around it.:rolleyes:
 
I've read that at WWII fighter speeds you get a measurable temperature increase. Can't cite a source for that, but do have a synapse dedicated to retaining that bit of not-too-useful information.
 
Until you're getting near the sound barrier, the skin temperature of most of the aircraft is not elevated. Most of your aircraft has airflow going over it nearly frictionless (drag is nasty stuff). You get a little temperature elevation on the nose and leading edges. Below 120 knots or so, even that is going to be negligible.
 
It's like TAS and IAS.

IAS goes up immediately above sea level but the difference is small at first. Above 10,000 it's enough to be a real factor and in the flight levels I can indicate 270 while doing 440.

Skin heating (it's from compression mostly, not friction btw) starts at one knot and increases with speed. At 250 it's you get about 8 degrees iirc, and 320 is closer to 20.
 
Btw, this is an excellent anti/de-ice procedure in many situations. Rather than turn on all the anti-ice which sucks massive air from the engine, instead speed up a few knots to get out of icing conditions.
 
brien23 said:
How fast does a aircraft have to pass through air to increase the airframe temperature that is measurable around it.:rolleyes:
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Measurable would depend on the instrumentation, but I would guess around .92 Mach you'll start seeing something noteworthy.
 
Henning said:
Measurable would depend on the instrumentation, but I would guess around .92 Mach you'll start seeing something noteworthy.
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Did you read my post or are you just certain your guess is more correct than my actual observation?

:D:confused::D
 
Captain said:
It's like TAS and IAS.

IAS goes up immediately above sea level but the difference is small at first. Above 10,000 it's enough to be a real factor and in the flight levels I can indicate 270 while doing 440.

Skin heating (it's from compression mostly, not friction btw) starts at one knot and increases with speed. At 250 it's you get about 8 degrees iirc, and 320 is closer to 20.
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That's the number I remember, somewhere about 8-9 degrees at 250 kts. I can't remember where I read that either.
We had to do that a few times flying the Sabre 60 which has slats and no de-ice on the wings.
 
0 MPH, or 0 knots/ph.

Just lean against any metal plane that sits on the ramp in Phoenix in the summer during daylight hours.
 
when the flow becomes "compressible" temps will elevate and become measurable....obviously transonic flows are compressible and do present heating....but it begins before that.

The hottest point will be at the stagnation point (front most point of the leading edge)....where the boundary layer is the thinnest.

Mach_Number_Flow_Regimes.png
 
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It looks like the steepest gradient is in the trans Mach region, if the temp ranges are evenly represented by color.
 
No....the colors on that chart do not correlate with temp change.....
 
I flew for Bob Greyell, a Korean War F-86 pilot.

He said that if they got into ice the'd just speed up to 350 KT and it would melt off.
 
kgruber said:
I flew for Bob Greyell, a Korean War F-86 pilot.

He said that if they got into ice the'd just speed up to 350 KT and it would melt off.
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760 mph is recognized as the speed of sound at standard conditions... mach....so 350 kts is about .5 which correlates to the lower ends of a compressibility flow regime.
 
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Checkout_my_Six said:
760 mph is recognized as the speed of sound at standard conditions... mach....so 350 kts is about .5 which correlates to the lower ends of a compressibility flow regime.
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350 indicated? At what temp? Cause 350 indicated would be super sonic at a lot of altitudes I fly...
 
Checkout_my_Six said:
where did you get indicated airspeed in any of that....?
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It was honest. Seldom do I use TAS. Plus, it's also seldom temperature is standard, so I'm trying to relate your post to flying and am hitting a wall.
 
champ driver said:
That's the number I remember, somewhere about 8-9 degrees at 250 kts. I can't remember where I read that either.
We had to do that a few times flying the Sabre 60 which has slats and no de-ice on the wings.
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Not the skin (where the flow is parallel) but leading edges and noses where the flow is perpendicular. Those you'll start seeing some elevation in the temperature. Skin temperatures don't rise until you get very near supersonic.
 
Captain said:
It was honest. Seldom do I use TAS. Plus, it's also seldom temperature is standard, so I'm trying to relate your post to flying and am hitting a wall.
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TAS is what the flow is "doing"...not indicated speed. You know indicated speed needs correction.....to allow for compressibility (density) and instrument error.

I mentioned standard conditions because altitude and temperature affects the speed of sound. It's a reference recognized by engineers to use for comparison.

What can you do with any of this?.....most likely nothing unless you're flying a transonic jet.
 
flyingron said:
Not the skin (where the flow is parallel) but leading edges and noses where the flow is perpendicular. Those you'll start seeing some elevation in the temperature. Skin temperatures don't rise until you get very near supersonic.
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All I cared about was the leading edges where the ice forms, I couldn't care less about any other part of the wing.
 
alfadog said:
I like the "simplification" to RR = V^2/87^2. Is that anything like V/87? :goofy:

edit: I went ahead and made the change on Wikipedia.
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Umm...I believe you're wrong.

Example

8^2/2^2 = 16

8/2 = 4

You might want to change it back and slink out of the room...

[edit: never mind, I removed it for you]

Or to make my example specific to the equation given:

V = true airspeed, so let's pick 250 for grins.

250^2/87^2 = 8.257

250/87 = 2.874
 
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champ driver said:
All I cared about was the leading edges where the ice forms, I couldn't care less about any other part of the wing.
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You can still get ice formation on the top and bottom of the wing due to "run back."
 
Wouldn't the increased air flow also increase the heat transfer away from the skin, like a radiator?
 
I can't recall the source, but I remember reading that temp increase was about 2- 3 degrees F at "routine" GA cruise of 150 knots. I assume it was friction at ".2 Mach", but I could be wrong. Yes, I know the value changes with temp and pressure. . .Can't imagine it matters much.
 
You guys who are still speculating obviously missed post #10!
 
no....I was thinking of going into a momentum equation derivation..... :lol:
 
You all need to become more educated about adiabatic cooling.

Take a class with Robert Fovell.
 
camel said:
Wouldn't the increased air flow also increase the heat transfer away from the skin, like a radiator?
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How will that happen? It is the compression of the air that heats the air, then the hot air transfers the energy to wing skin. The problem is the process is a radiator in reverse, and the airframe operates as the heat sink moving the heat to a cooler area where it can radiate away.

The SR-71, and rocket nozzles, use fuel to carry away the heat as well.
 
Problem is.....there isn't enough heat to conduct to the skin away from the stagnation areas. Without additional heat added to the skins behind the stagnation areas.....run back and refreezing is a concern.

Let's recall our Physics 101: The fundamental modes of heat transfer are conduction or diffusion, convection and radiation.
 
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