Timeline for Where does the difference between calculated and actual groundspeed come from?
Current License: CC BY-SA 3.0
5 events
| when toggle format | what | by | license | comment | |
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| Mar 11, 2017 at 17:28 | comment | added | Ron Beyer | No wind on the ground doesn't mean none at altitude. I remember talking off on a calm day and when I transitioned to slow flight at 2000', I was actually flying backwards relative to the ground, which meant I had a 45kt headwind. | |
| Mar 11, 2017 at 17:21 | comment | added | Paragliding | You are right but even flying in nil wind very early in the morning the Vg is not equal to Va calculated with the same method. I believe that one of the reasons has to be found on the fact that we do not have an engine to adjust thrust (just our body) and in real life the wind force/typology is never ideal, laminar and uniform. | |
| Mar 11, 2017 at 17:13 | comment | added | Ron Beyer | The wind speed, and direction, can be significantly different on the ground versus 50 meters in the air. When the air is close to the ground it is subject to ground friction. Wind is usually stronger as you go higher which would correlate with your measurements. | |
| Mar 11, 2017 at 17:08 | comment | added | Paragliding | I know the value of my trim speed from the paraglider manufacture 37-39km/h. Then I fly into the wind, no brakes applied, no position change, 50m above the landing area in which the Vw is 18-20km/h. Then somebody down calculates my shadow path from point A to point B, 100m straight line. Based on theory, I should have a Vg of 38-20=18km/h. Based on what we measured I had a Vg of 8-10km/h. The difference is quite important for a paraglider. We did some other tests in windy conditions and the result is that the Vg is less then Vg=Va-Vw. Even in calm conditions the Vg is never equal to Va. | |
| Mar 11, 2017 at 16:51 | history | answered | Romeo_4808N | CC BY-SA 3.0 |