Martin Hellman wrote:

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.


The best and most complete discussion of this issue is still Helut
Reichmann's Book "Cross Country Soaring".

Stefan