Description of the issue: The true airspeed TAS is different on the G1000 display than the tas number in the dev mode speed debug or simvar or the outside view HUD.
Using online calculators or good old math it looks like the G1000 number is the correct one.
This would mean the whole simulator is using a wrong speed number and this sould cause an untold number of problems in navigation / performance calculations ect.
Example:
Clear Sky weather template
C208B
20000ft altitude
G1000 say TAS is 156
Every other mentioned TAS variable say 163
I plotted the difference from 100ft to 24000 ft every 2000 ft this is the result:
|KTAS|G1000 KTAS|
|158|157|
|159|158|
|160|159|
|162|160|
|163|160|
|164|161|
|166|162|
|167|163|
|166|162|
|165|159|
|163|156|
|160|153|
|157|148|
If applicable, which aircraft is experiencing this issue:
I tested with the C208B
[PC Only] Did you remove all your community mods/add-ons? If yes, are you still experiencing the issue?
Yes , clean community folder, no change, still experiencing the issue
FREQUENCY OF ISSUE
Constant, 100%
REPRODUCTION STEPS
Please list clear steps you took in order to help our test team reproduce the same issue:
Select free flight
Select Clear Sky weather preset
Select a G1000 equipped aircraft like the C208B
Climb
keep checking the g1000 TAS speed (under the speed tape) and compare it to the TAS speed in the outside view HUD
[PC Only] Are you using Developer Mode or have you made any changes to it?
Used dev mode to open the aircraft debug speed section to compare may findings.
The speed debug window TAS number is the same as the outside view HUD, higher then the speed displayed by the G1000
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Did some more testing and something is VERY wrong here.
The internal TAS calculation looks like dependent on thrust or indicated airspeed range (at lower speed the error is bigger)
Here are some numbers, C208B ISA atmo.
I did tests with 50% 70% and 90% thrust lever position.
At 10000 ft density altitude it looks like this
50% 142.8 TAS simvar True Airspeed 137 TAS on the gps 5.8 knots difference
70% 164 TAS simvar True Airspeed 161 TAS on the gps 3 knots difference
90% 180.75 TAS simvar True Airspeed 179 TAS on the gps 1.75 knots difference
So if there is not some big hole in my aeronautical knowledge we have a big problem in the simulation.
If this is true that means EVERY aircraft performance is totally wrong.
But maybe I’m just wrong here and I’m missing something obvious, I very hope so.
Interesting. I noticed weird TAS outputs like this in the first iterations of career mode when the sim launched.
To verify which one is correct, you can fly a course with zero windspeed and see which TAS your groundspeed more closely matches. I’d also back this up with a timer to ensure the GS is correct.
Method: Pick two GPS waypoints at a known distance. Stabilize everything - speed, altitude, and course before overflying the first waypoint, start the timer as you overfly, and stop the timer at the next waypoint. Then do it again at different altitudes and/or indicated airspeeds and see what changes.
Make sure wind is zero, altimeter is 29.92 (1013mb), and temperature is ISA at every altitude you fly.
I’d make a spreadsheet with several columns - altitude, OAT, IAS, G1000 TAS, simvar TAS, GS, start time, and stop time. I don’t know if power settings will correlate, but you could put those as well.
I didn’t do the distance time measurement yet (will do later) but I checked different simvars, and the gps ground speed is same as the internal TAS number variable, so I suspect that distance time test will show the exact speed.
The problem is if I calculate TAS with an online calculator or E6B or by hand the G1000 TAS number is the correct one.
Example for the test I’m doing right now
24000 ft 29.92 115.5 indicated airsped
E6B give me 169 knots true , and that is exactly what the TAS speed says on the G1000 under the speed tape.
0 wins but by ground speed is 176 and the AIRSPEED TRUE simvar say 176
And to be honest I will believe the E6B before I believe anything from the sim
You’re right that the TAS on the G1000 matches the IAS for that altitude and the atmospheric conditions displayed, but true TAS should be based on calibrated airspeed (CAS). What’s the CAS for that aircraft at that IAS, in those conditions, at that altitude?
FWIW, given the environment, a CAS of 121 should produce a TAS of 176.
Ye KCAS … I’m stupid, totally forgot about that one , the G1000 calculates the TAS from the indicated , why the simvar and outside hud uses calibrated.
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