Temperature difference on a wing?

[Troubled_Coffee]

My curiosity has been peaked when a student asked me "how much colder the top of the wing is vs bottom"? Just wondering if anyone has done the math. I've googled the topic and as far as I've found, a 172 has a 4 degree spread but I'd like to back that up with some solid evidence.

[MichaelP]

Funny thing is that the frost always melts off the top surface first!

In flight it would depend on the Sun and the colour of the wing...

On a white aluminium wing would this temperature difference lead to a change in airfoil shape?

There used to be a question on the UK CPL exam about cable tensions summer and winter. Of course this question pertained to aluminium structures and not wood or composite ones but they did not say that.
We had to tighten the cables on the Condor as the temperature increased whereas in a Cessna you would loosen them.

[MG_]

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[AuxBatOn]

MG: can you define Cp for me? I don't quite understand why h =CpT.

It seems that the problem is much more complex than that, as you'd have to take into account the conduction (from the fuel), convection (surrounding air), friction, and radiation. I'll try to come up with something that would make sense when I have a little more time.

[Strega]

Auxbat,

H is enthalpy, and Cp is the "energy needed to raise the temp of a unit of gas one unit under constant pressure"


It seems we have another member of this forum that understands "thermo"...

Where are all the "engineers" to comment on this? Im sure all the AME training includes this.

[AuxBatOn]

Gotcha. I wasn't sure if it was that or something else out of the blue. I'm used to seeing that h as w.

We can't really say that

(v^2)/2+w=cst as it assumes there are no additionnal sources of energy. In this particular problem, there are are (convection, conduction, radiation on the top of the wing and friction). Plus, that equation actually gives us the temperature of the AIR above that point on the wing. With all the other factors taken into account, we CANNOT say that the temperature of the wing at that point will be the same as the temperature of the air. We could use that number to find the heat transfer from the convection. I'm thinking it could potentially be a fairly hard problem to solve. I'll have to get back into the books, which could really be interesting. Or someone could mount a probe on the wing to find out the actual temperatures

[Strega]

We can't really say that

I think its pretty close, enough so that we can say its close enough.

The other phenomenon are very small relative to the "thermo" changes in the gaseous flow around the wing.

[AuxBatOn]

We can't really say that

I think its pretty close, enough so that we can say its close enough.

The other phenomenon are very small relative to the "thermo" changes in the gaseous flow around the wing.

Sure, I can buy that for a slow aircraft, however we can't say the same about the heat transfer from other phenomenon on the wing itself. We eighter have to assume that the fuel doesn't warm the wing up (how fast does that fuel cools down again?) and that there is no radiation heat coming from the sun (we could probably say it's at night time and neglect the radiation of heat fron the wing to the atmosphere), or do it all. That's a whole lot of assumtions but, depending on what you need the info for, can be enough.

For a faster aircraft, we'll have to start taking friction into account and that would mean using Navier-Stokes.

[iflyforpie]

Where are all the "engineers" to comment on this? Im sure all the AME training includes this.

AMEs don't work on two-dimensional wings.

So would you expect to get the same results at W.S 57.12 and 172.00 on both the left and right wings?

[MG_]

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[Strega]

So would you expect to get the same results at W.S 57.12 and 172.00 on both the left and right wings?

you tell us... you seem to have a raft of knowledge in this area.

[SeptRepair]

Where are all the "engineers" to comment on this?

We are all out screwing the women you guys scare away when sitting around talking about mudane shit like this.