sausage said...NotWal said...Gestalt said...good stuff swoosh, not that i unsderstood it.
my questions.
does the wind gauge take into account density? if so wouldn't 15 knots on a cold day still read as 15 knots on a hot day. sure the real velocity on the cold day may be less but the additional density due to lower temps makes the effect on the gauge higher.
hope that made sense
I would guess that an impeller on a wind gauge would feel wind the same way a sail feels it. They are both foils. So the air speed on an impeller type gauge will be wrong but a very good indicator of available lift which is really just what we want to know
If I'm reading you right, you're saying a 15knot cold wind would read higher than a 15knot warm wind on the anenometer. Pardon my limited knowledge, but isn't this contrary to what Swoosh scientifically calculated above though i.e. the wind would read 15knots for both but the colder wind would pack more "punch" thereby requiring a smaller sail to get the equivalent lift force of a (slightly)larger sail in warm wind.
As Swoosh very ably showed us, the effects of temperature and pressure make an appreciable difference to lift. ie wind speed is not an accurate indicator of lift. However our anemometers are impeller driven gadgets. An impeller is a set of rotating foils. One would assume that what is measured is lift (or power) not speed. The gadgets are calibrated on the assumption that wind speed and wind power are linear covariants and this is good enough for everyday use. Even though the anemometers are reporting wind speed inaccurately they are reporting available lift accurately. They just call it wind speed.
