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MPusz
Aquila imperiale
Poland
683 Posts |
 Posted - 11/01/2010 : 08:05:04
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According to the XCSoar manual blue arrow (when visible in LK8000) should account for "Drift during climb". I do not think it works correctly. Please check following scenario:
1. Click goto on a distant waypoint (more than 100km away)
2. Set a strong side wind (you should see a blue arrow now deviated from desired course)
3. Now start to increase altitude. While doing that I would expect that the arrow would turn to the waypoint's direction (because shorter time is needed in circing). The result I get is that arrow disapears when the waypoint becomes reachable, but until than it doesn't move.
If I am a few meters below the final glide slope I would have glide for hours in a wrong direction if I would choose to circle at the end of the cruise. Doing that I would do much longer way home.
What is your opinion on that? |
Edited by - Coolwind on 09/02/2010 02:04:18 |
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Coolwind
Moderator
Italy
8957 Posts |
Posted - 11/01/2010 : 13:02:34
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Have check it months ago, it works correctly (had a couple of small bugs, fixed). In final glide the blue arrow is not used: no more thermals if you are in final glide, just head to the destination. Aldo (cernauta) may explain it better than me...
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MPusz
Aquila imperiale
Poland
683 Posts |
Posted - 11/01/2010 : 13:14:26
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| Final glide mode is enabled when you have a finish as your waypoint and that doesn't mean automatically that you are above glide slope. If you are below you have to climb and that is the scenario described above. Please try to reproduce it and see that blue arrow doesn't change its direction. |
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Coolwind
Moderator
Italy
8957 Posts |
Posted - 11/01/2010 : 18:41:26
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Oh I understand.. I will check that the blue arrow disappears in final glide only if the glide slope is positive. I might have missed it.
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MPusz
Aquila imperiale
Poland
683 Posts |
Posted - 11/01/2010 : 22:23:47
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It is like you said. It disapears only if the arrival altitude is positive.
The problem is that for all the time it is negative, not matter how much, it points to the same direction. I think it should point more and more towards the waypoint when you gain height closing to the final glide slope. |
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bo.
Pterodattilo
843 Posts |
Posted - 18/01/2010 : 19:17:24
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I can confirm the blue arrow behaviour reported my MPusz. The blue arrow changes gradually with wind speed and direction, and with MC setting, but not with altitude. Altitude only affects it when above the glide slope, then the blue arrow disapears.
Edit: 1.19b PC Sim |
Edited by - bo. on 18/01/2010 19:19:16 |
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MPusz
Aquila imperiale
Poland
683 Posts |
Posted - 18/01/2010 : 19:25:51
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| Thanks bo. |
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Coolwind
Moderator
Italy
8957 Posts |
Posted - 18/01/2010 : 19:34:09
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| May you check if this is a problem of LK or it was since years like that inside xcsoar? Since I don't use the blue arrow I have no idea how it was working before. |
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D-HIJU
Pulcino
Germany
88 Posts |
Posted - 19/01/2010 : 17:28:50
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Why should it change with altitude?
See XCsoar user Manual page 81 chapter 5.11:
"In order to help reduce the cross-track error when flying between
non-final waypoints, XCSoar calculates an adjustment to the cruise
track, called the ’optimal cruise track’. This track is adjusted so
that it compensates for the wind drift incurred when circling, and
as such it needs to estimate the proportion of time spent circling
according to classical MacCready theory.
The optimal cruise track is displayed on the map area as a large
blue arrow, and it recommends the glider steers so that the glider’s
track is lined up with the blue arrow during cruise. For example, if the display is oriented ‘Track-Up’, then steer so the blue arrow
points directly up.
The glide computer accounts for wind drift during circling to provide
an ‘optimal cruise track’ vector, which indicates the track the
glider should follow during cruise such that it will arrive at the
waypoint in minimum time. This vector is displayed on the map
as a blue arrow. When the wind is negligible, or when the computer
is in final glide mode, this arrow will point along the black
line that indicates the track to the next waypoint.
The calculation and display of optimal cruise track is a unique
feature of XCSoar. Commonly, when cruising between thermals,
glide navigation systems direct the glider to steer so that the glider’s
track points directly at the target. Ideally, the glider’s track is
collinear with the line from the previous to next waypoint, such
that the cross-track error is small and hence the glider travels the
minimum distance between waypoints.
However, because the glider usually has to stop cruising in order
to climb in lift, whilst circling the glider drifts downwind and
therefore the cross track error can increase. After several cycles of
cruise-climb, the overall track becomes curved.
For the case where the final waypoint is active and one is above
final glide, circling is not necessary so this simple scheme is optimal." |
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bo.
Pterodattilo
843 Posts |
Posted - 19/01/2010 : 18:08:25
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When the pilot approaches the required altitude to reach the final destination, less time will have to be spent in the thermal, drifting away from the original track. Thats why the blue arrow should converge with the black line as the required altitude is reached. This also explains why increasing the MC setting will move the blue arrow towards the black line (less time spent in thermals when the themals are stronger).
The blue arrow should only move with altitude when approaching the required altitude. Now the arrow suddenly disappears when above the glide slope (as it should, but gradually).
At least thats my understanding. Im hope i did not misunderstand something here? |
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MPusz
Aquila imperiale
Poland
683 Posts |
Posted - 19/01/2010 : 18:26:53
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| I agree with bo. Lets assume that you are only 10m below final glide slope and you decide to gain altitude at the very end of the cruise. In such a situation you will spend a lot of time flying in a wrong direction. |
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D-HIJU
Pulcino
Germany
88 Posts |
Posted - 19/01/2010 : 19:52:29
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Do you really need the blue arrow to fly in the right direction in a GLIDER?
You are also drifting while direct approach to destination. Without wind correction angle you miss the target. It depends on the wind angle. The black line is the track. I think blue arrow is the heading and this depends on the wind and your speed and therefore the McCready. |
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bo.
Pterodattilo
843 Posts |
Posted - 19/01/2010 : 20:16:33
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No, the blue arrow is not supposed to give heading or correction for drift during glide. Note that while above the glide slope, the blue arrow disappears, as it should. The blue arrow is only showing the amount of deviation needed to correct for drift while thermalling.
I have not evaluated this feature in flight, but it seems to be slightly wrong at the moment. Someone should check previous version as Coolwind suggested. |
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MPusz
Aquila imperiale
Poland
683 Posts |
Posted - 19/01/2010 : 20:20:59
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I may not need it, but I am a tester and I would like that feature to work as designed. Otherwise it may be the best to remove it.
Wind correction while cruising is handled by other means in LK8000, but I assume you know it from the documentation you quoted above. If you will follow waypoint direction indicators you will have that shift handled properly (the correct glider angle is shown on LK8000 screen but you even do not need to think about that).
The blue arrow is about additional direction shift to count for the time you have to spent drifitng in thermals to gain altitude. |
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MPusz
Aquila imperiale
Poland
683 Posts |
Posted - 22/01/2010 : 12:46:35
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| Can someone move that thread to bugs section? Thanks |
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parapenT1sta
Pterodattilo
Portugal
1866 Posts |
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Topic |
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(LOW) XCSOAR Blue arrow problem
