Same aircraft, weight, Mach speed - yet different ground speeds?

Not sure if this is the right topic, because it really ain’t an issue, just something I’ve noticed and questioned about for quite some time.

A buddy and I were flying, we were in the B777-200ER on the sim. Same weights and same speed at cruise. Mach 0.84 at the same altitude of 35000. However, he was going some 5-10kts faster than I was at all times. Even with the same winds. Now, how is this possible? Is this some kind of glitch or technical error? It’s happened a few times as well, and I really can’t think of a reason to cause this, so I’m trining to y’all for some help on this…any ideas?

hmm that is odd

Only explanation I can give is that

Airspeed and Mach vary based on winds and other factors.

Ground speed is how fast you’re moving over the ground.

But I’m not sure if that would actually answer the question of why one o y’all was faster

It could be this: in the 777 family, I’ve seen the Mach instruments in the cockpit and HUD being 0.01 below what I set the autopilot on, so maybe your friend realized this and set it one higher than yours.

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Yea, I’ve noticed the same thing. But we both confirmed we had 0.84 on the autopilot and 0.83 on the PFD. So, as to what’s going on is beyond both of us at this point

Thing is, that isn’t necessarily exactly 0.83, it might be 0.832, which is rounded to 2 decimal places. So one might be doing 0.834 and another doing 0.826, but both show as 0.83. As for why, no idea. Which actually doesn’t explain anything sorry 🤣

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Temp! Check it out.

Actually, 5 degrees is worth about 5kt GS. But not sure that is the issue here… most likely a mix of temp and wind being slightly different.

I don’t think temp would effect it at cruise when everyone has the same live weather. We also confirmed that we had the same temp and everything was identical. I’m not too sure how the speed is coded into the game. So that decimal point issue might be the answer. But again, without actually knowing that info I can’t say that is the blame. Maybe someone who has more knowledge about that can take a stab at it and point is in the right direction

As you cannot have two aircrafts in one spot, wind and temperature might have been ever so slightly different at any time for the two aircrafts involved.
The formula for MACH/RELATIVE WIND/OAT I used for the litle spreadsheet matches otherwise what happens in IF, so I fail to see a reason for such a dramatic difference in GS.

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