Hi
#1
Max sais - If you set a positive MacCready value, you tell XCSoar that you
want
to gain height by circling thermals. If you don't plan to do that,
don't set a positive MacCready value, because the whole point/basis of
the MacCready theory is the assumption of future lift.
This does not make sense to me. I often start a final glide "below glide"
and "bump" up on the way *without thermalling*. And I do this with a MC
well over 0. This is the normal way of doing FGs (in a competition) AFAIK.
But this seems to be at odds with what Max is saying. I dont get it.
#2
the Condor example seems to be missing something. 10K out at 1300m in an
LS8 with a 50Kmh headwind
> MC 0 = +11m above final glide
> MC 0.1 = +8m
> MC 0.2 = +3m
> MC 0.3 – 0.6 = no glide bar
> MC 0.7 = -596m (glide bar reappears)
> MC 0.8 = -266m
> MC 0.9 = -212m
> MC 1 = -195m
For this situation, these MC values are precisely where you would NOT be
flying. Notice how the glide is getting better with higher MC values then
MC 0.7. You should be at MC 3 or 4 I expect. So I am not sure what this
example is good for
#3
My vote is for changing XCSOAR to behave more like other flight computers
when it comes to this issue. I want to know if I am above or below glide. I
want a stable value so that I can tell if things are getting better or
worse. I quite liked the glidebar diagrams that someone posted earlier
Peter
On Wed, Nov 23, 2011 at 8:16 AM, Ian <ian-xcs...@zsd.co.za> wrote:
> Firstly let me express my thanks to all of those who have contributed to
> this project. The end product is much better than any single developer
> or manufacturer could be expected to achieve with resources justified by
> a "commercial" soaring product.
>
>
> On 22/11/2011 23:06, Alexander Swagemakers wrote:
>
> > MC 0 = +11m above final glide
> > MC 0.1 = +8m
> > MC 0.2 = +3m
> > MC 0.3 – 0.6 = no glide bar
> > MC 0.7 = -596m (glide bar reappears)
> > MC 0.8 = -266m
> > MC 0.9 = -212m
> > MC 1 = -195m
>
>
> If you are on a marginal final glide into a head wind, your focus should
> be on the following (not necessarily in this order, and not exclusively):
>
> 1) Flying the glider (obviously).
>
> 2) Identifying outlanding options.
>
> 3) Estimating change of headwind component with altitude, particularly
> when descending below the "operating" altitude to an altitude band where
> the glide computer has no historical data.
>
> 3) Looking for sources of lift and/or sink.
>
> 4) Managing conflicting traffic heading to and already on the
> destination runway.
>
> 5) Evaluating the go home/land out decision.
>
> If you do find lift and stop to thermal, you should be very aware of the
> effects of wind drift. It will have a direct effect on (2), (3) and (5)
> of the above. You must maintain climb at a rate which more than
> compensates for the effect of your drift. The glide computer can help
> determine if you are achieving this see (c) below.
>
> A glide computer cannot be expected to do any of the above. However what
> it can do very accurately and quickly is:
>
> a) Navigate you directly to your target (via GPS).
>
> b) Provide an accurate data of your distance to go (via GPS).
>
> c) Calculate the hight required to reach your target based on glider
> polar (corrected for bugs and ballast), nominated "mcready" speed,
> nominated or estimated head wind profile. This is most conveniently
> displayed to the pilot as the "arrival hight" relative to ground (or a
> pre-nominated safety hight above ground).
>
> Note, that while the speed to fly to optimize distance covered in still
> air is best glide speed, and a "speed to fly director" should be set to
> "mcready" zero, the speed to fly to optimize distance covered towards an
> upwind goal is faster than best glide and the "mcready" setting on your
> speed to fly director will have to be increased to a positive value to
> provide the correct guidance to the pilot. The glide computer can also
> be expected to help determine the optimal "mcready" setting for
> maximizing distance covered towards the upwind goal.
>
> However if the glide computer starts presenting information like that
> quoted above, there is no way the pilot can be expected to assimilate it
> and make good decisions. The pilot can well be expected to ignore it and
> then distrust the GPS navigation data too. This would leave executing an
> outlanding as the natural consequence of good decision making.
>
> I would not like to see the above displayed to the pilot on a final
> glide into wind using the default settings of XCsoar.
>
> Use of wind drift while thermalling in calculation of things like the
> optimization of "assigned area" tasks is a different matter altogether.
>
> I see this as an interface problem not a theory one. Perhaps the most
> important requirement for a program like XSoar is to provide the right
> information at the right time, not too much and not too little. There is
> a high learning curve associated with glide computers particularly as
> the learning is typically done while airborne. Thus the default settings
> should be intuitive.
>
>
> Ian
>
> PS: I know of one very experienced pilot who claimed that the most
> important instrument in his brand new open class glider was the
> mechanical vario. He claimed he always could rely on it to tell him if
> the glider was going up or down, irrespective of which page was
> displayed on the glide computer, whether it had setup errors, software
> bugs, a battery failure or lost GPS signal ...
>
>
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