True airspeed calculations are not correct ?!

User Support Hub Aircraft & Systems
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1

I’m a bit confused
0 wind situation
G1000 TAS shows a different speed than the Ground speed or the dev mode speed debug window.

If I calculate my TAS by hand the G1000 shows the correct number not the internal variable of the simulation. This would be a major issue, since then the simulator calculates all kind of things based on wrong air speeds.
Example/reproduction steps
0 wind IAS (clear day preset)
C208B at 10000 ft
IAS: 138.6
GS: 164.3
TAS debug value: 164.3
TAS G1000 value: 161
TAS calculated by hand : 161

If I go higher the difference between TAS numbers grow
for example at 24000 ft it is 157 vs 148 knots.

Maybe I’m misunderstanding something here , but this looks like an important issue.

2

Moved to User Support Hub since not SU3 related and more appropriate for community support.

3

How did you calculate?

Useing the rule of thumb 2% / 1000 feet I get 166 KTAS. Also, what’s your pressure altitude because that’s the number you should be using?

4

TAS is dependent on pressure altitude and air temperature, both of which can vary from day-to-day. If you are using the clear sky preset, temperatures at a given altitude should be standard ISA, but you still have to take temperature into account when calculating TAS by hand.

5

Hey, this is clearly a bug since 2 simulation parameters gives different numbers
Even the outside view HUD says different TAS speed then the GPS in the cockpit!
Ignore the manual calculation part, this please move this to the appropriate BUG forum.

6

Does not matter what I calculate the simulator itself gives you 2 different TAS speeds that is clearly an error.

Also as I mentioned ISA atmosphere 0 wind.

7

I know, but how does this explain why the simulator itself calculates 2 different TAS number?
The tas on the G1000 say x while the outside view HUD says Y
Also the simvar TRUE AIRSPEED say the same as the outside view HUD.
So 1 of them is incorrect! That is the bug.
I only did a manual calculation to find out which one is the correct one.
And it looks like the G1000 is correct , but this means the simulator itself uses an incorrect TAS speed… that would be a huge problem , that would mean no aircraft in the sim works as it should.

8

If you think issue has been introduced in SU3 then you can created a new report in Sim Update 3 Beta | MSFS 2024 > Aircraft & Systems .
If you are not sure about previous point then you can create a report in Bug Reporting Hub > Aircraft & Systems

In both cases: please do not delete the provided template and fill in the required fields, in particular the “Reproduction Steps” section. All fields are important for the devs to reproduce the issue and users that want to contribute to your report. Thank you !

9

Will do, looks like this is not su3 specific I found similar reports from earlier but not properly explained. And I will leave out the manual tas calculation :slight_smile: to lessen confusion.

10

Ye, I’m stupid, totally forgot about calibrated airspeed being modeled: