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Ticket #1803 (closed enhancement: duplicate)
Covering plane performance degradation
| Reported by: | DGFlija | Owned by: | |
|---|---|---|---|
| Priority: | normal | Milestone: | XCSoar 6.4 |
| Component: | Configuration | Version: | 6.3 |
| Keywords: | polar curve degradation | Cc: |
Description
It is a well known fact that a glider does not always reach its factory announced performance values. It is also a well known fact that unexperienced pilots cannot yet live up to use a plane at its top notch performance, even if the plane is perfectly sealed.
The most common way to take care of these issues is the way I learned to deal with them 45 years ago with a Ka6 and I still do it that way with an ASH and a DG800 : I start the final glide with excess altitude.
In my experience the extra altitude needed is more or less relative to the time to go, not the distance to go. Very surprising ;-). So, why not make that a feature : Have a configurable and persistent percentage value by which the required altitude to reach a goal is increased - on top of the configurable safety altitude for the landing pattern.
The precentage should be chosen individually by the pilot so that it works for him with small MacCready? settings (<= 0.5). When using higher MacCready? settings there is even more safety in the speed already. So there is no compensation required for high MacCready? speeds.
Then, I think, "bug degradation" and "polar curve" and "MacCready? setting", which have been discussed as means to handle bad performance, can be left alone for their proper purpose and set to the same values, the 302 or the VEGA or the Butterfly are set to.
Change History
comment:1 Changed 15 months ago by DGFlija
- Version changed from 6.3 to 6.2.5
- Milestone changed from XCSoar 6.2 to XCSoar 6.3
comment:2 Changed 15 months ago by apf
- Status changed from new to closed
- Version changed from 6.2.5 to 6.3
- Resolution set to duplicate
- Milestone changed from XCSoar 6.3 to XCSoar 6.4
If I understand your proposal correctly you want to introduce a time component into the arrival altitude calculation. Unfortunately that method would introduce a feedback loop with final glide STF (Speed to Fly) calculations leading not necessarily to the intended result (most probably it would converge to the planes STF for best L/D). BTW: The height saved by flying with MC 0 instead of MC 0.5 (assuming still air) is less than 2%, e.g. a 100km final glide in a Discus would arrive less than 40m higher with MC 0. That difference is negligible compared to real world differences.
Ticket #1551 is a request for a permanently stored degradation factor and is the solution we will most probably implement as a plane specific setting, i.e. stored within a specific plane profile (the settings currently available under "Menu -> Config -> Setup Plane"), which will also allow consideration of other factors like less than perfect plane condition.
If I have grossly misunderstood your proposal please reopen this ticket.
comment:3 Changed 15 months ago by DGFlija
Hi apf, yes, you misunderstood my proposal.
And it is my fault that I did not state my idea as simple as possible.
Restarting, I should not have said "relative to time to go", but "relative to required altitude".
But I think this is not the platform for discussions.
It is ok to close the ticket here.
I will find some other way to start the discussion.
