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Thanks, Alex
Great to have your research/knowledge on the topic. Now I know why the
aluminum foil seemed to work so well.
Ed Anderson
> >
> > 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
> >
> >
> >
> > >> Homepage: http://www.flyrotary.com/
> > >> Archive: http://lancaironline.net/lists/flyrotary/List.html
> >
> >
> > >> Homepage: http://www.flyrotary.com/
> > >> Archive: http://lancaironline.net/lists/flyrotary/List.html
> >
> >
> > >> Homepage: http://www.flyrotary.com/
> > >> Archive: http://lancaironline.net/lists/flyrotary/List.html
> >
>
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
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