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PFD Speed Tape - Mach Number Bug Position Offset


amahran
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When flying in Mach mode, the bug on the speedtape (only used as a visual reference) is in an apparently incorrect position:

  • The Mach bug is set to Mach 0.78
  • The aircraft Mach number is Mach 0.782
  • The Mach number is higher than the bug mach number, so you'd think that the arrow on the speedtape would be above the bug:

image.png.48e8bc7e85cee7dba9e5f61d888a6c1a.png

  • Lo and behold however, the arrow is below the bug.

The speedtape isn't in the incorrect position relative to the bug when IAS mode is enabled:

image.png.f6e584db2af39f0389b18d577a4a24e2.png

 

My interpretation is that, in Mach mode, the speed bug is trying to "snap" up to certain IAS integer values on the speedtape, rather than real numbers (e.g., Mach 0.78 corresponding to 241 knots instead of 240.1). This is just my wild guess, however.

 

Not sure which forum this should be posted in; I think it's a modelling/visual thing, but it may be Systems?

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  • 4 months later...

image.thumb.png.69ffde1fe97703df6eebc7d44fcb0b3f.png

 

After SU5, the issue is still ever-present. I tried to diagnose it and calculate it based on my inputs.

  • Speed bug is at Mach 0.74, its position on the IAS scale agrees with the Pressure Altitude and the SAT.
  • Current Mach (0.766 in white above the speed scale) and TAS agree given the Pressure Altitude and SAT.
  • TAS and IAS disagree given Pressure Altitude and SAT

It's the position of the IAS value on the scale (where the arrow is) that's incorrect, not the speed bug.

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  • CRJ Forum Moderator
5 hours ago, amahran said:

image.thumb.png.69ffde1fe97703df6eebc7d44fcb0b3f.png

 

After SU5, the issue is still ever-present. I tried to diagnose it and calculate it based on my inputs.

  • Speed bug is at Mach 0.74, its position on the IAS scale agrees with the Pressure Altitude and the SAT.
  • Current Mach (0.766 in white above the speed scale) and TAS agree given the Pressure Altitude and SAT.
  • TAS and IAS disagree given Pressure Altitude and SAT

It's the position of the IAS value on the scale (where the arrow is) that's incorrect, not the speed bug.

Our test team noted this same problem, which was exacerbated in SU5. A solution has been found, and the speeds should be working properly again in the update.

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  • 2 weeks later...

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