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Estimating Wind Speed with a GPS
On Wednesday, 26 April 2000 03:00:00 UTC-4, Tom Seim wrote:
I had a nice flight last Saturday in somewhat windy conditions. I have a new Garmin Pilot III that displays a fairly high resolution flight track. I noticed that I could estimate wind speed (and, of course, direction) by watching how much my thermal circles overlapped. Once set up in a thermal I fly a reasonably consistent bank angle and speed. This results in a circle diameter of 600-700 feet and a time period of 22 sec. This works out to a wind drift of 20 mph (17 kt) if the circles touch (a drift of about 700 feet per circle). The winds are 10 mph (9 kt) if the circles have a 50% overlap (ever other circle touches). This gives me a quick (and rough) estimate of the winds aloft. Obviously this will not work if your are continuously adjusting your circle position. You can calculate your circle diameter by: Diameter (feet) = 0.54 * Speed (kts) * Time Period (sec) The wind speed per circle is: Wind speed = 0.68 * Time Period (sec) / Diameter (feet) -- Tom Seim, 2G DG-400 Richland, WA Question: Is the speed at which a thermal drifts the same as the winds aloft? |
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