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Weather - Best altitude for flight


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Martin Bech
Martin Bech
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Hi

When planning a flight fro Denmark to Marocco in a Cirrus SR22T with indicated speed 170kt I get data for Best altitude. If I change to a Cessna 172 with indicated speed of 100kt I get no data. What is the correlation between speed and Best altitude?


Tim Dawson
Tim Dawson
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It's a lot more complex than that. Try actually planning the flight yourself with the Cessna at a few altitudes and look at virtual radar. You may find that its climb performance isn't enough to get over some terrain so accurate wind forecasts can't be determined for it, or similar.
Martin Bech
Martin Bech
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Thanks Tim, that make sense, but for someone that do not know the relation between performance data and Best altitude it will be a puzzle. Any chance to create a hint why it say Incomplete Forecast?

Now I can make better planning - great!
Tim Dawson
Tim Dawson
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Well, possibly yes. So what was actually the problem? Were you indeed flying through terrain?
Martin Bech
Martin Bech
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If I changed climb and/or decent rate - same result. If I change crusespeed to 124kt I get the result with first 4 altitudes incomplete. Changing speed to 130kt gives no incomplete. I can’t get the clue other than it has something to do with speed.

Martin Bech
Martin Bech
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Martin Bech - 3/5/2018 6:54:30 PM
If I changed climb and/or decent rate - same result. If I change crusespeed to 124kt I get the result with first 4 altitudes incomplete. Changing speed to 130kt gives no incomplete. I can’t get the clue other than it has something to do with speed.


I have now tested different situations and concludes that there must be an error i SD's weather calculations.
Entering the route as on the first picture gives no problem. If I then append LECO and LEMR to the route then I get Incomplete Forecast. Try then just to create the route LEVX‌ - LECO - LEMR, then no problem. Try also to change Power Settings to 150kt for the route on picture 1 - new result.
Why do the append give a problem when the LEVX, LECO, LEMR route don't? Why do a speed change change the situation?

Aircraft: Service ceiling 12.000ft, Climb Rate Sea Level 560ft/min - At Service Ceiling 100ft/min - Indicated 78kt, Decent rate -900ft/min - Indicated 100kt, Power Setting Airspeed 100kt Indicated

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Martin Bech
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Martin Bech - 3/8/2018 9:43:27 AM
Martin Bech - 3/5/2018 6:54:30 PM
If I changed climb and/or decent rate - same result. If I change crusespeed to 124kt I get the result with first 4 altitudes incomplete. Changing speed to 130kt gives no incomplete. I can’t get the clue other than it has something to do with speed.


I have now tested different situations and concludes that there must be an error i SD's weather calculations.
Entering the route as on the first picture gives no problem. If I then append LECO and LEMR to the route then I get Incomplete Forecast. Try then just to create the route LEVX‌ - LECO - LEMR, then no problem. Try also to change Power Settings to 150kt for the route on picture 1 - new result.
Why do the append give a problem when the LEVX, LECO, LEMR route don't? Why do a speed change change the situation?

Aircraft: Service ceiling 12.000ft, Climb Rate Sea Level 560ft/min - At Service Ceiling 100ft/min - Indicated 78kt, Decent rate -900ft/min - Indicated 100kt, Power Setting Airspeed 100kt Indicated

‌‌
‌‌


Sorry, the text should be: Try also to change Power Settings to 150kt for the route on picture 1 with added LECO and LEMR- new result
Tim Dawson
Tim Dawson
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This is something you need to work through with customer support, so they can try to pin down the exact thing which is the flight not to be modelled and then pass it on to the developers if necessary. Could you contact them?
Martin Bech
Martin Bech
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Tim Dawson - 3/12/2018 10:44:54 AM
This is something you need to work through with customer support, so they can try to pin down the exact thing which is the flight not to be modelled and then pass it on to the developers if necessary. Could you contact them?


Thanks Tim, I will contact customer support.
Martin Bech
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Martin Bech - 3/13/2018 6:56:46 AM
Tim Dawson - 3/12/2018 10:44:54 AM
This is something you need to work through with customer support, so they can try to pin down the exact thing which is the flight not to be modelled and then pass it on to the developers if necessary. Could you contact them?


Thanks Tim, I will contact customer support.


No error in SkyDemon. The reason to no weather data is that my unrealistic long route takes more than the weather forecasts can show - more than 24 hours. Thanks for help and a lot of good information about Best Altitude calculations. Thanks to support for a very quick response.

Last evening I had 22 pilots and 1 instructor for setup and education in SkyDemon. For those with other planning tools it opened up a new and better World.‌‌
GO

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