Wind correction for GC steering
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TBH DJ what you are saying has no sense.
tadpole should guide the AC to the waypoint !!! so when everything is fine tadpole / fpm and diamond aligned.
else tadpole is useless:!
BUG for me
Agree!
However, on some a/c (mine) in some case, the “tadpole” (flight director equivalent) can give you a steering command to stay on your “TRACK” … what I mean about “track” here, is the route defined between two waypoints. So, it won’t give you command to steer direct to the WPT, but to make you intercepting the “route/track” between the two WPT, and then, one back on route, give you a command to apply the correct drift. (same behavior than the course deviation needle of the HSI, or the LOC of the ILS. … in F-16, it would be equivalent to the CMD STEERING CUE in HUD when performing an ILS)
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Whatever, IMO, you re correct, and the tadpole is should act as in “direct to”, hence, the three symbols (Waypoint diamond, tadpole and FPM) should be overlapping when you are on the proper route.
So, I would say that I agree … probably a bug here.
The fact that the tadpole is on the same level as the FPM, and not the guncross for example, is in JP’s favor, IMO.
The tadpole should be an indicator of where to go to overfly the waypoint : ie, putting the FPM on it means you are goind directly toward the waypoint regardless of drift and where is your nose pointed at.
Agree.
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Its easier than it looks Jinro, just go for it.
Freferf, the other thing is that if you have any wind, on a long leg flying ‘straight’ using the AP, your heading will graudually increase or decrease as you approach the STPT. This was what ticked me onto it originally.
haaa…if GCSC is the tadpole
Yes, the other thing “captain’s bars” on the heading tape you see on many airplanes is not on the F-16 except in ILS mode for landing, at least the OFP this manual is for. However there is a indication on the corner of the MFD like a capital “W” for steering if FPM off HUD. Also if drift c/o is on you can always put FPM on GCSC. Also if you put ground speed option on HUD heading tape = ground track tape.
Agree!
However, on some a/c (mine) in some case, the “tadpole” (flight director equivalent) can give you a steering command to stay on your “TRACK”
Yes, many aircraft have a concept of steering intercept to desired course line. F-16 does this to command 45-degree intercept to ILS LOC.
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sorry but i think there is a misunderstanding here.
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The DIAMOND marks the physical location where the AC shall fly over : DO YOU AGREE ?
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The FPM reprensents the velocity vector, in other words this is where the AC is flying to , taking into account wind and turbulence or even beta side slip : DO YOU AGREE ?
1 + 2 = to fly over the physical waypoint location , the FPM SHALL be aligned with the DIAMOND
the GCSC is the marker line on the heading tape, correct ? (i think it is , i am no specialist here with acronyms)
to me the GCSC shall indicat the heading where the noze shall be put in order that the FPM be align with diamond, simply because when there is a lot of drift , fpm can not be seen , so the only way to know is to indicate the pilot the heading relatively to the NOZE => GCSC
so in your picture the GCSC should be around 29 / 30 (i.e. on the right…) and pilot should align his noze to it
according to my memories , this is exactly what BMS does and i dont understand how it could work otherwise ?
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The STPT DIAMOND marks the location of the STPT - it is what we intend the aircraft to overfly. So far, so good.
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the FPM represents the direction of the velocity vector, i.e. where the airplane is flying to, taking into account wind, turbulence, alpha, beta, etc - all good.
ergo, to fly over the STPT DIAMOND, the FPM needs to be aligned in azimuth with the DIAMOND. All hunky dory so far!
The GCSC is my own abbreviation for the Great Circle Steering Cue (or tadpole). I don’t think its found in the manual.
The tick mark on the GCSC indicates the direction the plane needs to turn to find the diamond, and is used for coarse steering. The circle aligns with the FPM when your ground track (track - in the sense that track is heading corrected for wind - so your ground track in this sense is EQUAL to the azimuth of the FPM) is the same as the required ground track to overfly the STPT DIAMOND. The circle is used for fine steering.
What I think you have all concluded, and am hoping you can confirm, is that the FPM and the STPT diamond should coincide in azimuth, when the Great Circle Steering Cue is aligned with the FPM. The nose should point upwind of the STPT DIAMOND.
Instead, what happens in BMS is that the nose points directly to the STPT diamond.
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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.