Article on glide strategy

On Tuesday, February 28, 2012 2:45:58 PM UTC-8, Ramy wrote:
On Feb 27, 7:15*pm, John Cochrane
wrote:
I wrote a new article on how to use computers to help judge glides.

http://faculty.chicagobooth.edu/john...ocs/safety_gli....

or the first item here

http://faculty.chicagobooth.edu/john...ndex.htm#maccr....

This will probably end up in Soaring sooner or later, but I always get
a lot of help from early readers. If it's not clear or you see
problems etc. let me know. (john dot cochrane at chicagobooth dot
edu0

John Cochrane

Finally! I've been arguing this with flight computer developers
(Winpilot, XCSoar) for years. STF MC, and safety MC are 2 different
things that needs to be decoupled. Use your STF Vario MC setting for
speed to fly, and keep a constant MC for safety (I use 4 which seem to
work for almost any situation) in your glide computer (i.e. PDA).
Problem is, that if you connet your 302 to winpilot/xcsoar (and
probably others) you could not decouple the two. The good news, is
that XCSoar 6.3 will give the option to decouple the two different MC
settings.

There is another solution though. Instead of setting a high safety MC
in your glide computer, you can degrade the polar using the bug factor
to achieve the same results. (typically 33% -50% degradation, depend
how aggressive you want to be). Probelm is, that some flight
computers, such as XCSoar, did not store this value, which means you
had to remember to set it before every flight. The good news is that
this is also addressed in 6.3, which will have persistent polar
degradation.

And last, this excellent article also demonstrate why just keeping a
safety altitude does not work, as it will be appropriate only for one
distance. The further you are the highest it would need to be. This is
why Safety MC, or polar degradation are better solutions, since they
are not depending on distance.

Ramy

So, assuming an undegraded polar, if the last thermal is 4 knots and your Safety MC is 4, at what speed do you go home and where is the safety?

David