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Plog IAS & GS


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VH-DUX
VH-DUX
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I am using the ipad version and I am delighted, but:

When I prepared a route and looked at the Plog, it had used the current winds, which is OK, but then I set the flight for three days hence and all of the winds went to zero, which is also good, but the GS values are still significantly different to the IAS.

Is there something I'm missing?

VH-DUX

VH-DUX
acassata
acassata
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Did you compare the GS with the TAS (true airspeed) ?
I remind that the IAS is equal to TAS at sea level in standard atmosphere condition.

SD team can provide more details about the calculation.


Alexandre
Based at LSGL (Lausanne - La Blécherette, in Switzerland)

Edited 12/2/2015 1:59:47 PM by acassata
VH-DUX
VH-DUX
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Yes I have compared the GS with the TAS and I still find an unexplained difference with no wind at 3000 feet. I am using only 3000 feet or less and I've gone to the trouble of calculating the TAS for the IAS, and I still expect the TAS and IAS to be much closer to the GA for no wind at all.

If I can understand this point, I can utilize this plan on any day and trust that it will adjust for the winds on that day. At the moment I don't trust it.


VH-DUX

VH-DUX
ckurz7000
ckurz7000
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SD takes into account climb and descent speeds you defined in the aircraft profile. They will be part of a leg and won't show up in the IAS but in the calculated GS (which is distance over time spent between waypoints).

-- Chris.

Tim Dawson
Tim Dawson
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SkyDemon models the flight in quite some detail, which may make the calculations initially appear to differ from a simple, naive calculation.

Broadly speaking in a nil-wind situation the other factors are IAS-to-TAS correction and taking into account the climb and descent phases, over which of course the GS will vary.
VH-DUX
VH-DUX
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Thanks Tim and Chris,

You've both identified the point I had been missing, and that is my climb and descent speeds. I will play with them and restore my confidence.

VH-DUX

VH-DUX
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