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Apr 22, 2013, 05:29 AM
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thermals, and stranger things...


i have been flying my planes for many years, but it has been in warm weather...until now.
in those years, i got into thermals regularly, and grew under the impression that it had to be warm weather in order to climb with the help of hot air (the so called 'thermals'). but recently i have been flying near freezing, and have witnessed my planes climbing and staying up there for a long time. some say that is the differential temperature that makes air go up. that is, if there is air at, let's say, -20c, and surrounding air is -10c, that mass of air will go up. so if in freezing air, and then we encounter not-so-freezing air, that makes planes go (or stay-up) there, why call them 'thermals'? shouldn't be more correct to call them something like 'rising air'? or 'risers'?
the original word comes from greek: therme=heat. see:
i found this in etymologies:
from Greek therme "heat," from PIE *ghwerm-/*ghworm- "warm" (cf. Latin fornax "an oven, kiln," formus "warm," Old English wearm; see warm). Sense of "having to do with heat" is first recorded 1837. The noun meaning "rising current of relatively warm air" is recorded from 1933.

and the last 1 brings the key word (relative), as i mentioned when i said that it is the differential temperature. 'relatively warm air' means that what matters is that some mass of air is warmer than the surroundings.
there is some interesting data about their shape here: https://www.rcgroups.com/forums/show...64#post4966743
and here: http://www.xcmag.com/2007/07/thermal...rt-1-thermals/
this is the 1st time i saw something about their shape:
http://soaringweb.org/Soaring_Index/...61_Apr_08.html (keep browsing through page 13)
jul 27, 2013: recently i have had the opportunity to fly my sailplanes in warm weather, so i reached some conclusions about thermals:
1.-we could find thermals in low temperatures (practically any temperature), as they develop from the difference in temperature between areas.
2.-as thermals form from the heating of certain areas, even if at -20c we can find some.
3.-but as temperature rises, the possibility of finding them increases. that is, in warm weather the sun heats more the soil and therefore there are more areas where thermals develop. and the longer the sun is on, the more areas get the heat. i have confirmed this now that i have been able to fly in warm weather, especially in the afternoon. even if there are no clouds.
Last edited by phil alvirez; Jul 27, 2013 at 10:32 AM.
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