Nice skyline article

"BB" wrote in message
oups.com...

The article dances around the question, at what speed do we thermal?

Students hate the "it depends" that this type of question drives, but
for my students, I say at the minimum sinking speed for your bank
angle. Since turning polars are not published I approximate this by
multiplying the minimum sinking speed by the load factor. Maybe not
completely and aerodynamically correct, but a workable rule while
flying around.

That's exactly what the article shows is wrong. I found it interesting
because I always found myself flying slower than "minimum sink adjusted
for bank angle". I noticed the same among most contest pilots, but I
always felt like I might be doing something wrong since I had been
taught the same logic.

By flying somewhat slower, on the "backside" of the polar (though not
of course to the point of losing control, buffeting, dropping wings
etc) you climb better. You want the minimum sink for a given TURN
RADIUS not a minimum sink for a given BANK ANGLE. By flying slower, you
get the same radius turn with a lower bank angle.

For example, in most standard/15 m gliders straightline "minimum sink"
is about 45 kts. Yet most pilots thermal at 45-47 kts even in 30-45
degree bank. These speeds are well below "minimum sink" for the given
bank angles.

John Cochrane
BB

John Cochrane BB


John, I'm sure there are situations where that applies but the reduction in
turn radius is not great for a small reduction in airspeed. For example,
reducing the airspeed from 50 to 45 knots in a 45 degree bank decreases the
radius by only a little more than 40 feet.

See the Turn Radius Calculator:
http://www.soarcsa.org/thinking_page..._rad_knots.htm


Bill Daniels