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Old August 24th 10, 02:54 AM posted to rec.aviation.soaring
akiley
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Posts: 114
Default required LD versus required MC to make it home ??

snip

For typical days where there is lift available and as you become more
comfortable with thermaling I would encourage you to try to start with
Mc near 1. Mc == 0 means you really are in desperation mode and don't
really plan to go anywhere. See the discussion in Reichman about this.
Mc=0 quickly becomes a kind of boat anchor dragging on you. If you are
dialing the Mc into a flight computer (or STF ring on a winter vario)
it also starts giving you a feel for how excess Mc helps you if you
run into worse conditions than you expect. You can increase the Mc
setting you fly at up from there as you gain confidence, but dont' go
crazy with it. A rule of thumb often used especially for new XC folks
it to set the Mc conservatively at 1/2 to 1/3 of what you think your
next average climb will be - and even then its just to give you an
idea of average speed to fly, don't go chasing it. Sounds like you
have a good approach as is. The last thermal average climb stats in
SeeYou Mobile can be interesting to check, it will often be much less
than you think, and even then it often misses time wasted mucking
around trying to find lift.


This brings up something I may have overlooked as I described how I
get home safely. I use MC more as a way to judge my wiggle room to my
home airport rather than STF. If my SeeYou is showing 10mc to get
home based on winds and safety altitude, I generally don't fly that MC
unless I'm very close and can see I have it made. Instead I fly
conservatively within 10kts of best L/D and use that high required MC
as my safety margin. Sort of like always being within half your best
L/D to your target airport. akiley

BTW details of wind effects and Mc may not be obvious, search for past
r.a.s. postings by John Cochrane and others on this.

[snip]

Darryl