(JJ Sinclair) wrote in message ...
I fly a lot in the mountains and find MacCready speed-to-fly information,
completely worthless. Let me explain; Before crossing a ridge, I will fly
slower (below MC), so that I'm assured of making the next ridge. After crossing
the ridge, I may fly faster than MacCready. If I set the proper MC setting in
my computer. I am constantly bombarded with WRONG information coming from the
computer audio.

Something that is rarely said when MacCready speed to fly is discussed
(including texts on soaring!) is that there is a major assumption in
the math behind it: that you can stop at any point and immediately
find a thermal of the strength indicated in the MacCready window.
Wouldn't that make soaring easy -- and probably a bit boring.

There was an interesting article in Soaring Magazine about a year ago
which talked about related issues. Sorry I don't have the date, but if
memory serves me it's by a Biz School prof from Chicago. He argued
that you should use a lower setting when close to the ground because
you have less time to find a thermal and will almost surely have to
settle for a weaker one. Once you're high, you have more time to be
picky and can use a setting close to or even equal to the maximal
thermal strength of the day.

An earlier posting got close to these ideas when it pointed out that
the setting should be the expected strength of the next thermal --
which will clearly depend on how much time you have to be picky.

There is another point that needs to be mentioned: Maximizing speed
over a task is only one goal, so the MacCready math leaves out other
factors as well. How much emphasis should be placed on not landing
out? not landing out in a bad field and damaging the ship? not landing
out in hostile terrain and maybe getting killed? And so on. An
optimization that took all these factors into account is impossible,
which is where common sense (like JJ's not above) comes in.

Martin