ETA wrong: DA62 vs. TBM930 vs. CJ4

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Brief description of the issue:

From the world map, only TBM930 displays an exact ETA. DA62 and CJ4 display a shorter ETA than actual. And it’s off by around 25%.

For example, a flight plan is made on the world map. When DA62 is selected, it displays an ETA of 40 minutes but TBM930 displays 70 minutes. At 70% throttle, DA62 cruises around 145 kts and TBM930 at 202 kts. How can DA62 show a lesser ETA? When flown actually, TBM930 takes 70 minutes (accurate) and DA62, 90 minutes!

Same is the case with Citation CJ4. It displays an ETA on the world map of 60 minutes, but in actual, it takes 100 minutes, cruising at 240 kts at 70% throttle.

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The speeds you are talking about, are these IAS and if so: on which altitude?

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Since I was experimenting to make sure about this issue, I applied the uniform variables to all three aircraft.

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Interesting related topic that contains an explanation on how is calculated the ETE:

5

Thank you for the link but the answer has been given quite ambiguously. Doesn’t help.

For example, if I have only one hour to spend in flying, I pick a flight plan of 55 minutes or one hour. Excluding the TBM930, the other two aircraft would not finish in one hour.

By the way, the ETA is accurately displayed for Daher Kodiak 100, Cessna 208B, NX Cub, G36, and most other aircraft.

The discrepancy has mainly been observed only with DA62 and CJ4.

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This has been something I had been meaning to test. If you create a flight plan on the map screen, it shows you how long that flight will take, based on which aircraft you have selected. But what parameter is it using to work that out?

I’m guessing one of the reference speeds as listed in the flight_model.cfg, probably cruise_speed or maybe max_indicated_speed. If that’s the case, and some planes show erroneous values, either the speeds in the plane files are wrong, or the calculation on the map screen is. But if it’s the latter it should be wrong for all planes, which it probably isn’t.

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Per the link to the thread @DementedCorn327 posted, Asobo said it’s calculated based on the groundspeed derived from the reference speeds parameters in the flight_model.cfg

The cruise_speed and cruise_alt in those settings are single variables, with speed in KTAS and alt in feet MSL. However, we know that real-life KTAS will vary with temperature, altitude, and/or power settings. Recommended power settings at different altitudes can vary wildly between aircraft, so basing it on a single scenario is oversimplistic and can lead to the discrepancies you’re encountering, even after you control for the effect altitude and temp has on TAS and wind aloft has on groundspeed.

(This is why I eschew the flight planner in the world map and just do calcs on my own).

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I picked the TBM 850, and altered a few of the speeds, simply prepending a 1.

This was picked up in the sim.

image

But it didn’t seem to make a difference in the flight planning. The exact values I altered were:

cruise_speed = 1320 ; Knots True (KTAS)
max_indicated_speed = 1266 ; Red line (KIAS)
normal_operating_speed = 1266
airspeed_indicator_max = 1320

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Never mind, I get it. So it did pick up cruise speed as I would expect.

But it didn’t change the timing?

It will also calculate climb speeds, so if your flight didn’t have a long cruise segment, you might not see much of a difference.

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I was doing US East to West coast, so plenty of time for it to stretch its legs. I also changed the maximum size of the fuel tanks, and when I pressed resync this correctly showed in the W&B screen, but had no effect on its Endurance for some reason.

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Personal Comments and Observations

The World Map estimates…well I eschew those since I perform my flight planning in Little Nav Map. I find the Flight Plan time estimate there to be very close to what’s reported by my Pilot Logbook on flight exit.

It’s not so much a bug as it is a feature needing improvement. It’s all tied into the larger World Map needs that may be addressed in FS '24.

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