>
> David, your observation was correct on the temperature of aircraft.
> However white paint would make be a bad shielding for the inside of a
> cowl.
> Here is what I got from my heat transfer book:
>
> A=solar absorptivity
> E=infrared emissivity & absorptivity
>
> Surface A E
> AL polished .09 .03
> AL foil .15 .05
>
> Stainless Steel Polished .37 .6
> SS Dull .5 .21
>
> Black Paint .97 .97
> Wight Paint .14 .93
>
>
> These numbers are very interesting. For shielding we want the lowest E.
> For trying to block radiant heat AL is clearly the best. Stainless steel
> is between 4 and 12 times worse at blocking radiation that AL foil.
>
> Trying to keep objects cool under sunlight is a special case. We want it
> to have a low A so that it does not absorb much solar energy but a high
> E so that it easily radiates any acquired energy away. Note white paint
> is great for this.
>
> The bottom line is that white paint is great for solar shielding on the
> outside of but bad for infrared shielding under cowlings and such. Al is
> the best for IR shielding.
>
>
> I am missing all the Greek letters so a am kind of mangling the
> radiation formula but here it is.
> Qrad= a*G*A + a*E*O(Tinf^4-Tsurf^4)
>
> Qrad=heat transfer (W/M^2)
> a=area of surface (M^2)
> G=solar radiation (W/M^2)
> A= solar absorptivity
> E= infrared emissivity
> O=5.67E-8 (W/(M^2*K^4)
> Tinf= temperature of the surroundings (K)
> Tsur= Temperature of the surface (K)
>
> NOTE temperatures must be in Kelvin
>
>
> Alex Madsen
>
>
>
>
>
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> Behalf Of Alex Madsen
> Sent: Monday, May 24, 2004 1:28 AM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Two problems solved, 2 more pop up...
>
> I am skeptical of this. Where the light colored aircraft composite? This
> would make a difference. The higher thermal conductivity of the AL would
> make it seem much hotter than composites. Both aircraft must be
> constructed of the same material. Were they?  Anyway off to look at my
> heat transfer book to see what it has to say on this topic.
>
> Alex Madsen
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> Behalf Of David Carter
> Sent: Sunday, May 23, 2004 11:49 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Two problems solved, 2 more pop up...
>
> I've noticed that shiney polished aluminum airplanes are quite hot in
> the
> sun, whereas white and light cream colored painted exteriors are quite
> cool.
> I used to think and "aluminum" finish would be best for reflecting heat,
> but
> I no longer think that.  I think the same situation would prevail inside
> the
> cowl.
>
> David
>
> ----- Original Message ----- > From: "Chad Robinson" <crj@lucubration.com>
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Sent: Sunday, May 23, 2004 9:25 PM
> Subject: [FlyRotary] Re: Two problems solved, 2 more pop up...
>
>
> <snip> Given that the primary goal is reflecting radiated heat (rather
> than
> "real"
> > thermal insulation) what's wrong with a coat or two of shiny silver
> paint?
> > It's not as good as polished aluminum but it's decent, and high on the
> > reflective scale. Sherwin Williams (and others) sells a product called
> > "Silver-Brite" that is marketed as "heat reflective" and "dry heat
> resistant
> > to 700degF". I haven't tested its adherence to epoxy so it might need
> a
> primer
> > coat to help it stick better (it's designed for metal) but that's not
> a
> > painful step. In any event, it would sure be a lot easier to apply
> than
> either
> > foil OR fiberfrax, especially to an oddly-shaped cowl.
> >
> > Unless real thermal insulation properties are necesary?
> >
> > Regards,
> > Chad
>
>
>
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