Hi, the weather analyse is super but would it not be more correct to display the correct flight level acording to attached? Taken into account if it is a VFR or IFR flight. Regards Martin


Just another picture where the symbol on chart is different from symbol in Metar?

Why would that be more correct? The tool is designed to tell you the optimum altitude for your flight.

Ok Tim, we have to use the FL shown in chart therefore I think it would be a reminder to using correct FL when going east or west VFR or IFR😉 At the same time the wind analyse would also be more correct for the chosen altitude(minor). Skydemon is the tool to make flights more secure👍

The height above mean sea level (the datum) of any given Flight Level can vary significantly in relation to the datum depending on atmospheric pressure (QNH), whereas any given altitude is, by definition, and for all practical purposes, constant in relation to the datum, regardless of the QNH. Winds aloft cannot be forecast for a height above the datum which varies depending on the QNH, which is why forecast winds aloft always relate to altitude. Accordingly, I believe SD have got it right in this context.

Mike
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So the QNH is not taken into account when calculating best altitude - is that correct?

No. An altimeter set to a pressure setting of QNH (atmospheric pressure at MSL) indicates altitude (height AMSL). It doesn't matter what value the QNH is, providing the altimeter is set to that value, then the altimeter indicates altitude. It follows, therefore, that for any given altitude, the height AMSL is constant calculated by reference to the prevailing QNH. Altitude is therefore always calculated by reference to QNH. On the other hand, because Flight Level (FL) is calculated by reference to a standard altimeter pressure setting of 1013 hPa, the altitude (height AMSL) at any given FL will vary as the QNH changes. I hope this makes sense.

Mike
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Thanks Mike - "because Flight Level (FL) is calculated by reference to a standard altimeter pressure setting of 1013 hPa, the altitude (height AMSL) at any given FL will vary as the QNH changes" - yes it changes as QNH changes, but SkyDemon have access to QNH for the area according to flightplan and therefore should be able to calculate according to FL. Well if I am not right I will leave it at that😄

One further point. I may be wrong, but as far as I am aware, SD imports the forecast winds aloft from third party sources, so they have no control over how those winds are presented to the user.

Mike
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