On Jul 4, 3:55*pm, SoaringXCellence wrote:
Scott,

You need to read Johnnie Cochran's article:

http://faculty.chicagobooth.edu/john...search/Papers/

Down at the bottom of the page titled *"Just a little faster Please"

A very good description of the ideas promoted by many excellent
pilots.

Mike


Generally you should not try to minimize your % circling directly by
reducing your cruise speed - it will slow you down overall. Unless of
course you are flying too fast for the conditions in the first place -
and that is the rub.

Overall, you need to set your cruise based on McCready for your
expected ACTUAL climb rate, including centering time and other
considerations such as changes in climb rate at the top or bottom of
the climb (Cochrane explains this pretty well in his papers) -
different pilots estimate this in different ways, some computers give
bottom-to-top averages as well. The net effect is slower climb rates
than you might otherwise estimate based on staring at you 30-second
averager.

Next, you need to adjust your speed to optimize the tradeoff between
theoretical cross-country speed (as estimated above) and the odds that
you might have to take a weaker than expected thermal because you got
low before you found a good one. You might do this for the whole
flight (imagine a blue day with a lot of distance between good
thermals and a not very tall lift band). This is basically trading
off optimal cruise speed for a higher probability of getting a good
climb. You will see experienced pilots often "topping up" before
heading out into suspected soft areas or pressing low and passing up
weaker lift because they know they are likely to hit stronger lift in
a few miles. It is a big exercise in estimating odds.

The last thing to remember is that the biggest contributor to speed is
to find lift lines you can follow. This can be cloud or blue streets,
convergence lines, storm shelves, wave, ridge - all allow you to make
time without going backwards. You don't make this happen by slowing
down, you make it happen by picking your path well. If thermals are
hard to center and/or if you can make sustained climbs straight ahead,
you may elect to slow down to climb straight in lift, but only under
circumstances that are supported by the "adjusted" theory described
above (accounting for circling and centering losses, probability of
"false positives", etc.) In a modern ship on a day with clouds and
some modest streeting you can cruise at 85 knots and have achieved
cruise L/Ds in the 50-60 range and % climbing in the low teens.

Lastly, keep in mind that your achieved cross country speed has very
little to do with the cruise speed you pick - within certain bounds.
If you fly 15 knots slower than McCready optimal for the entire flight
it costs you 2-3% on cross-country speed. Taking a single 3 knot climb
instead of a 6 knot climb for 2500' costs you about the same amount.

9B