Just to clarify again few points from my original post, which some are missing:
1 - The reported wrong arrival altitude calculation was not just for the final
glide bar, but also for info boxes AND the waypoint detail. The labels do not
show when below glide so no problem there, but if you click on the alternates
to see your arrival altitude, you will see the same wrong number for the
"current MC" value.
2 -MC is not just for expected thermal. If your final glide is against the wind
as in these examples, you need to set your MC > 0 in your flight computer (eg
302) to get the best glide speed, even if you don't expect to circle again.
This is in fact why I noticed this problem, since I increased my MC to 0.5 in
my 302 (which automatically updates XCSoar) to compensate for the 12 knots
headwind, and as a result my arrival altitude instantaneously dropped by over
5000 feet. This can never be correct in any logical way. if it was correct I
would have landed out.
Thanks,
Ramy
>________________________________
> From: "xcsoar-user-requ...@lists.sourceforge.net"
> <xcsoar-user-requ...@lists.sourceforge.net>
>To: xcsoar-user@lists.sourceforge.net
>Sent: Tuesday, November 22, 2011 6:56 AM
>Subject: Xcsoar-user Digest, Vol 66, Issue 32
>
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>Today's Topics:
>
> 1. MC and thermalling drift (Andreas Pfaller)
> 2. Re: XCSoar 6.2.3 released (Olaf Hartmann)
> 3. Re: MC and thermalling drift (Olaf Hartmann)
> 4. Re: MC and thermalling drift (Max Kellermann)
> 5. Re: MC and thermalling drift (Tobias Bieniek)
> 6. Re: MC and thermalling drift (Max Kellermann)
> 7. Re: MC and thermalling drift (Andreas Pfaller)
>I simply think that this "do not consider wind drift" solution will help
>provide anything reasonable in many of the other calculations. Especially
>for low performance gliders like a Ka8 wind drift can be the absolute
>dominating
>factor even in moderate wind. By not considering it everything falls apart.
>Tasks may be shown as achievable when they are not, all the time calculations
>will be completely off (with the result that you might not make it back in
>time for sunset / end of lift) and what is even worse, if your outbound
>track is with a tailwind you will not even beware of the problems until
>you turn back.
>
>Instead of looking for a solution for papering over the effects
>of a deliberately provided wrong "MC" setting we should try to educate
>pilots not to use a MC setting as some kind of tuning knob to influence
>the calculations towards something the pilot wants to achieve.
>Take and use the MC setting simply for what it is, the expected lift of
>the next thermals and everything will just work and correctly tell
>you if something gets borderline/impossible. If you want to build reserves
>nothing prevents you to fly slower than the "Speed to Fly" which results from
>that MC setting. Sensible MC settings is all that is needed. For most gliders
>the range from 0.0 to 1.0 will not cause major different glide rates
>due to "Speed to fly" anyway however the drift will vary significantly in that
>range. Also in the presence of a headwind a slightly increased
>"Speed to Fly" above best glide-rate speed will even increase
>your glide range.
>
>And last but not least: This xcsoar behavior is not new. It is present
>since 6.0 and until now nobody seems to have had any problems with it.
>And it only effects the final glide bar and some of the infoboxes. The
>arrival heights in the map are completely unaffected since we only did
>show positive arrival heights anyway where drift does not need to be
>considered.
>
>This discussion has made me aware that "old habits" which were necessary
>and helped somewhat for the old generation simple glide computers are
>difficult to change. Instead of introducing yet another set of config
>options which will make understanding what really goes on in an
>already complex environment even more difficult try xcsoars method.
>Personally I think that xcoars calculations are far more useful
>since they are more realistic and will be appreciated by all who give
>them a chance. I have been very pleasantly surprised during my unfortunately
>few longer flights in windy conditions by the exact predictions of
>xcsoar (with MC set to AUTO).
>
>
>
>
>I guess at safety MC speed for still air mass. This would however add a
>dependency on the polar setup, which a geometric or ground L/D would not
>require.
>
>
>
>
>John Wharington <jwharing...@gmail.com> schrieb:
>Geometric + wind at what aircraft speed? The impact of wind will
>>depend on your airspeed.
>>These L/D required displays therefore all make additional assumptions.
>>
>>On Wed, Nov 23, 2011 at 12:54 AM, Sascha Haffner <s_haff...@yahoo.com> wrote:
>>> Hi
>>>
>>> I like Olaf's summary !!!
>>>
>>> As for the questions how other manufactures have implemented L/D req. I
>>> would venture a guess that LX uses geometric plus wind.
>>>
>>> Sascha
>>>
>>
>>>>________________________________
>>
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>>
>
>
>
>Andreas Pfaller <pfal...@gmail.com> schrieb:
>
>>This discussion has made me aware that "old habits" which were
>>necessary
>>and helped somewhat for the old generation simple glide computers are
>>difficult to change. Instead of introducing yet another set of config
>>options which will make understanding what really goes on in an
>>already complex environment even more difficult try xcsoars method.
>>Personally I think that xcoars calculations are far more useful
>>since they are more realistic and will be appreciated by all who give
>>them a chance. I have been very pleasantly surprised during my
>>unfortunately
>>few longer flights in windy conditions by the exact predictions of
>>xcsoar (with MC set to AUTO).
>
>No. IMHO XCsoar simply tries to be too clever here. With auto mc the required
>heights will fluctuate, so i will question them. In strong wind conditions it
>expects me to circle, wich i will very likely not do in the mountains.
>
>Olaf
>
>
>On 2011/11/22 15:36, Olaf Hartmann <olaf.hartm...@s1998.tu-chemnitz.de> wrote:
>> In strong wind conditions it expects me to circle, wich i will very
>> likely not do in the mountains.
>
>Without circling, there is no "expected lift in next thermal", and the
>MacCready theory is not applicable.
>
>Configuring a positive MacCready value or even AutoMC would not make
>sense if you do not plan/expect to circle. With MacCready=0.0, XCSoar
>will work as you expect it to.
>
>Max
>
>(P.S.: XCSoar is still doing several historic mistakes, for example
>the option that auto-increases the MacCready setting if you're above
>final glide)
>
>
>Max, I don't think that AutoMC option is a mistake. It works pretty
>well from what I have experienced... Using the MC value on final glide
>is simply a way of setting the speed-to-fly speed to a value where you
>would reach the goal. I'm not sure it has anything to do with the real
>MC theory anymore...
>
>Turbo
>
>
>2011/11/22 Max Kellermann <m...@duempel.org>:
>> On 2011/11/22 15:36, Olaf Hartmann <olaf.hartm...@s1998.tu-chemnitz.de>
>> wrote:
>>> In strong wind conditions it expects me to circle, wich i will very
>>> likely not do in the mountains.
>>
>> Without circling, there is no "expected lift in next thermal", and the
>> MacCready theory is not applicable.
>>
>> Configuring a positive MacCready value or even AutoMC would not make
>> sense if you do not plan/expect to circle. With MacCready=0.0, XCSoar
>> will work as you expect it to.
>>
>> Max
>>
>> (P.S.: XCSoar is still doing several historic mistakes, for example
>> the option that auto-increases the MacCready setting if you're above
>> final glide)
>>
>> ------------------------------------------------------------------------------
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>
>
>On 2011/11/22 15:47, Tobias Bieniek <tobias.bien...@gmx.de> wrote:
>> Max, I don't think that AutoMC option is a mistake. It works pretty
>> well from what I have experienced... Using the MC value on final glide
>> is simply a way of setting the speed-to-fly speed to a value where you
>> would reach the goal. I'm not sure it has anything to do with the real
>> MC theory anymore...
>
>Yes, it is a mistake! It's setting a bad example of "I'll change the
>MacCready setting to ridiculous values until the result matches my
>pre-defined expectations". And this kind of thinking is what causes
>the misunderstandings among users here.
>
>MacCready is for when you expect to circle, and nothing else. If you
>want something else (for example ridge soaring, or other types of
>soaring), you need a new theory with new formulas. XCSoar does not
>support that, neither does any other glide computer I know.
>
>Max
>
>
>On Tuesday, November 22, 2011, Olaf Hartmann wrote:
>>
>> Andreas Pfaller <pfal...@gmail.com> schrieb:
>>
>> >This discussion has made me aware that "old habits" which were
>> >necessary
>> >and helped somewhat for the old generation simple glide computers are
>> >difficult to change. Instead of introducing yet another set of config
>> >options which will make understanding what really goes on in an
>> >already complex environment even more difficult try xcsoars method.
>> >Personally I think that xcoars calculations are far more useful
>> >since they are more realistic and will be appreciated by all who give
>> >them a chance. I have been very pleasantly surprised during my
>> >unfortunately
>> >few longer flights in windy conditions by the exact predictions of
>> >xcsoar (with MC set to AUTO).
>>
>> No. IMHO XCsoar simply tries to be too clever here. With auto mc the
>> required heights will fluctuate, so i will question them. In strong wind
>> conditions it expects me to circle, wich i will very likely not do in the
>> mountains.
>>
>> Olaf
>>
>
>Sure. It was just a sample of worked well for me on those flights I did. If I
>expect conditions to get worse I would simply switch to manual MC and adjust MC
>to a "reasonable" value, i.e. the lift I expect in the future (and not some
>arbitrary low value). And for moutain flying, like max said, MC is not
>applicable anyway.
>
>Andreas
>
>
>
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