Wind correction for GC steering
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JP : the issue is that when you align the tadpole (“têtard”) inside the FPM, your FPM is not aligned with the waypoint, the nose is.
Edit : that is what you meant with GCSC, Blu3wolf, right ? Because I couldnt find this acronym in the Dash-1. For me it is always called the tadpole.
Yup, GCSC = blu3wolfspeak for Great Circle Steering Cue, was meant to save me typing that out constantly. Should have just wrote tadpole as that would have saved everyone a lot of hassle!
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Yup, GCSC = blu3wolfspeak for Great Circle Steering Cue, was meant to save me typing that out constantly. Should have just wrote tadpole as that would have saved everyone a lot of hassle!
I actually found the name Great Circle Steering Cue in the dash-1. But it is pretty much always called the tadpole.
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has anybody commented on whether wind correction for navigation will be implemented in the next update?
it will
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well, its here NOW, so Im happy, now. I was actually thinking about that bug about a month ago, trying to correct for winds by not following the tadpole…. its a bit painful. Now, I dont need to worry about it!
Actually, I do still need to check to see if the tadpole ‘tail’ is misaligned from directly up in high winds, as it should be.
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We probably need to check with an actual authority. I know this has been changed in the code several times as understanding has, shall we say, varied over time….if we’re going to mess with it again, let’s make sure it’s really right this time
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I can appreciate that. Theres certainly no shortage of contradictory tales of ‘how it works’.
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nooooo its back
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The tadpole is not aligned with the FPM, even though the FPM is aligned with the STPT diamond. This is the bug described above in the thread.
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OK - my 2 cents (and at current exchange rate 2 pence as well). Are you sure it is a bug? Just thinking about this for about 10 seconds, the tadpole should never be aligned precisely - the reason being that the tadpole follows a great circle, and the steerpoint diamond is line of sight… Now whether that is the same as your bug I am not sure…
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The STPT diamond is line of sight. Great circles are also line of sight. No issue.
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The STPT diamond is line of sight. Great circles are also line of sight. No issue.
Not quite true. A straight line between two points on a sphere is a great circle, where a line of sight is not viz: https://www.flightradar24.com/blog/flight-paths-and-great-circles-or-why-you-flew-over-greenland/
It might not be the issue, nor might it be how the STPT is mechanised (however I believe it is, otherwise why have both a tadpole and a stpt?), however the straight line in RL is not Lat2-Lat1^2 + Long2-Long1^2 on the surface of a sphere.
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Rhumb vs. GC line should be super tiny at that dozen miles.
I’m curious if GCSC isn’t aligned as expected from any direction and what happens if you actually follow the GCSC exactly. Do you miss the waypoint? Do you fly a curved path?
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Rhumb vs. GC line should be super tiny at that dozen miles.
I’m curious if GCSC isn’t aligned as expected from any direction and what happens if you actually follow the GCSC exactly. Do you miss the waypoint? Do you fly a curved path?
Rhumb lines cross all lines of longtitude at the same angle. It is an approximation of a great circle (and has a great advantage that it can be drawn in a mercator projection chart as a straight line).
As a great circle (equivalent to a straight line on a plane) is the shortest distance over a sphere between two points, you will not miss the steerpoint, as the great circle will be between your current position, and the steer point if you steer a great circle.
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Great circles happen to be straight lines on a sphere. Line of sight also happens to be a straight line on a sphere.
Also, for BMS, a rhumb line and a great circle are identical, because there is no curved earth navigation code. Geometrically? It is flat. On a flat plane, line of sight, great circles, and rhumb lines are simply straight lines.
If you follow the tadpole, you fly a curved path (not a great circle) which does overfly the waypoint. The degree of curvature is proportional to the amount of wind perpendicular to your flight path. As a result, your heading changes over time. In short you are blown off course by the wind.
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This post is deleted! -
Ok … we neeeeed … someone …
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I thought this was what the DRIFT C/O switch was for…if it is OFF (HUD “caged”, in my lingo) you’d fly the arcing path to/over the steerpoint, and if it is in NORM that the system will show you the wind corrected steering to fly?
…which is a reason I prefer to land with it in OFF. For VFR approaches, anyways.