On Feb 28, 6:22*pm, Max Kellermann wrote:
Ramy wrote:
Please explain why safety MC doesn't make a lot of sense.

Safety MC was implemented to degrade the polar, nothing else. *It has
no effect on speed suggestions or anything else related to MacCready's
theory.

So what you probably want is a third polar degradation setting:

1. "polar degradation" adjusts the configured polar to match your
* *real-world glider (persistent, new XCSoar 6.3 feature)

2. "bugs" adjusts the polar to match the dirty glider (not persistent,
* *has always been there)

3. "safety degradation" to replace "safety MC"; basically the same as
* *"safety MC" just with a name and definition that makes more sense.

I'm not 100% sure about this; these are just my unfinished thoughts
after weeks of reading XCSoar's glide solver code. *Maybe safety MC is
a setting to account for long distances of sink lacking any lift, and
the setting should be the expected sink value (and not the expected
lift value in the next thermal!).

Max

Max, I understand your points from pure theoretical perspective, but I
believe in practical most pilots use STF varios for speed, not PDA
flight computers, since STF varios are already doing this very well
and have audio signal as well. This is why the decoupling was
important. I also believe most pilots prefer to use MC for safety
degradation instead of polar degradation, or a combination of both.
But I guess one can just use the MC in XCSoar instead of safety MC.
Not sure about expected sink value, since this should be average sink,
and as such hard to predict or estimate (sink always seem stronger
than it really is, since we fly faster and see the combined result of
our increased sink rate and the neto sink).
Anyway, I think the most important thing here is the ability to
decouple the vario MC setting from the flight computer, or
alternatively use polar degradation. One thing is clear, using the
same MC for STF and glide calculation is a sure way to arrive short
without additional polar degradation.

Ramy