At 08:57 PM 24/11/2009, you wrote:
Hi,
I'm a newbie here........ but I have a question that has intrigued
me for some time....
I have read the GFA/AN53 regarding conspicuity markings, and wonder
why the large under surfaces of a glider are not recommended for
bright marking.
If heat is the issue with anything other than white, and presumeably
direct sunlight is the main source of heat....how do the boffins
reckon that the sun manages to heat the belly and under lower wing surfaces ?
If reflected or convected heat from a tarmac or concrete ground
surface is a problem, surely the fact that the patch under the
glider will be in shade, would greatly reduce this ?
One other thing, the "surface air temperature" is the temperature 4
feet above the ground inside a white painted (yes, it does matter
what kind of white paint) Stevenson screen, 100 feet from buildings
and roads over short cut grass.. On a bitumen runway in the sun on a
hot day?? Then there's the superadiabatic lapse rate near the surface
on such a day where the incoming heating is such that even convection
(a very good heat transport mechanism - much better than radiation
under most near surface conditions in daytime) cannot remove the heat
fast enough. So if the "surface air temp" is 40 deg C the temp at 18
inches will be much higher than at 4 feet and the surface much hotter
still (and radiating in the long wave IR).
Mike
Borgelt Instruments - manufacturers of quality soaring instruments since 1978
phone Int'l + 61 746 355784
fax Int'l + 61 746 358796
cellphone Int'l + 61 428 355784
email: [email protected]
website: www.borgeltinstruments.com
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