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albar965 / littlenavmap

Little Navmap is a free flight planner, navigation tool, moving map, airport search and airport information system for Flight Simulator X, Microsoft Flight Simulator 2020, Prepar3D and X-Plane.
https://albar965.github.io/littlenavmap.html
GNU General Public License v3.0
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Performance File Speed TAS Difference to the G1000 #1084

Closed Lewis2023 closed 5 months ago

Lewis2023 commented 5 months ago

Hi I work with the record of a performance file for a C172S. (LNM Version 3.0.1 beta) The climb Speed TAS is always 6 kts higher as the TAS value in the G1000. During the Cruise phase the value is also higher but only about 3 kts. Conditions: No Wind, Max Weight, Vy (IAS) = 72 KIAS constant with FLC to 7000 FT. Process: LNM shows at the beginning, 500 ft AGL a value of 79 kts and goes up to 86 kts at the altitude of 7000 FT. At the end I have an average climb speed of 86 kts and this is to high. What I am doing wrong?

albar965 commented 5 months ago

LNM uses the average which is good enough to calculate the climb. Do not confuse this with the actual values shown in the cockpit. They will differ after take off and before TOC.

TAS being above IAS and rising with altitude is normal due to thinner air at altitudes. The values are directly read from the simulator and therefore reliable. I use TAS in the perf because it is independent of wind.

Lewis2023 commented 5 months ago

Grüezi Alex Ok, I have taken the term "average" into account. If I fly from 0-12'000 then the average calculated by LNM is about 86 KTAS.

Let's look at LNM in the starting phase: 500 FT above the ground: the map shows IAS =72 kts and TAS = 78. A calculation gives TAS = 73 kts for the standard Temp 15°C. The shown 78 kts should be an average from 0 to 1000 FT ? This makes no sense. How do you calculate this 78 kts? Edi

Am Fr., 26. Jan. 2024 um 15:48 Uhr schrieb Alexander Barthel < @.***>:

LNM uses the average which is good enough to calculate the climb. Do not confuse this with the actual values shown in the cockpit. They will differ after take off and before TOC.

TAS being above IAS and rising with altitude is normal due to thinner air at altitudes. The values are directly read from the simulator and therefore reliable. I use TAS in the perf because it is independent of wind.

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albar965 commented 5 months ago

How do you calculate this 78 kts?

As I said above: It is not calculated but taken from every simulator as is. Average is calculated over time and you spend more time at the higher altitudes since climb is slower there. So the higher TAS is more dominant in the average.

Data sources:

BTW, next time read the text in the issue template:

Delete this text after reading before posting the issue.

What simulator do you use BTW and what G1000 is this?

Alex

Lewis2023 commented 5 months ago

Sim is MSFS2020 and G1000nxi, all latest version

albar965 commented 5 months ago

Does it also appear with stock G1000 or other aircraft? I still doubt this is an issue with LNM. I take the values as they are without any conversion.

Lewis2023 commented 5 months ago

ok, I will try the same testfile with gms50/gtn750 and with another plane to see if there is the same pattern. I will give you a short feedback

Alexander Barthel @.***> schrieb am Sa. 27. Jan. 2024 um 11:54:

Does it also appear with stock G1000 or other aircraft? I still doubt this is an issue with LNM. I take the values as they are without any conversion.

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Lewis2023 commented 5 months ago

Cessna 172S_G1000: Difference of 6 kts in TAS value G1000 and LNM is constant. All other values, especially fuel consumption are the same and near to the POH. Cessna 208: Same effect. Now the good news: I have tested with Kodiak100_G1000, Bonanza ATC36_GTN750, Tecnam2012P_G1000: No difference in TAS, all values are the same. Fazit:

  1. Not a problem of LNM, must be one with MSFS Cessna's profiles.
  2. For the Cessna 172 and Caravan: I think for the calculation of the fuel consumption this difference of 6 kts does not count. BTW: The fact that your program runs the performance in the background during the flight is a great feature for all which fly live weather. Merging makes it even better after each flight. Thanks for this great program!
albar965 commented 5 months ago

Thanks for getting back about this. :+1:

I have no idea what they are doing there. Normally the TAS is calculated and provided by the simulator. I'd expect aircraft add-ons to use and show this value and not calculate their own.

My last flight in X-Plane did show no differences. Values were spot on with the aircraft (A319).

Alex

albar965 commented 5 months ago

Checked MSFS with the stock DA-62 and saw no differences bigger than one knot from TAS up to 8000 ft. Most likely a problem with the aircraft systems. Closing. Feel free to reopen if you see issues.