"Marc Ramsey" wrote in message
m...
"Bill Daniels" wrote...
I still don't think you guys get it. Yesterday, while flying over the
Rocky
Mountains in my Nimbus 2C I was seeing 5 M/S on the averager, yet if I
set
the M number to 5, the speed command would ask for 200+ MPH. Given the
level
of turbulence associated with 5 M/S lift and the fact that I was flying
dry,
I stayed in the green arc.

I would look carefully at the polar you are using and/or the instrument,
it's
calling for a lot more speed than I would expect. On the other hand, I
almost
always set my MC to half of what I'm expecting the next climb to be, and
it
seems to work pretty well.

The other thing that no one has mentioned is that, at the high altitudes
required over mountains, the True Airspeed calculation has a larger
effect
on average XC speed than the McCready calculation so flying slow and
staying
high gets you a higher real speed.

Be careful, though, polars are based on "indicated" speeds. Most modern
electronic variometers show something approximating a "true" climb rate.
Some,
but not all, glide computers assume you are setting the MC to a "true"
climb
rate, and actually convert it to an "indicated" (lower) equivalent climb
rate
before applying the speed to fly calculation.

In the mountains, structural limits, safe landing areas and terrain
clearance set maximum speed. McCready numbers are academic.

Perhaps, but I think the main problem is that many pilots fly far too fast
for a
given climb rate, due to instrumentation problems, incorrect polars, and
incorrect understanding of what the MC numbers actually mean.

I 've carefully verified the speed to fly calculations and corrections in
the
software I use in my LAK-17, and at 15K+ feet with full water and MC 5
(knots),
cruise speed to fly is normally less than 120 knots.

Marc

5 meter/second = 9.7 knots. I was setting M in meters per second. The
speed command just says push or pull. I think my computer is pretty well
set up. I think we agree on this: Most pilots fly too fast.

The point is that in mountain flying, total reliance on McCready speeds is
misleading and possibly dangerous if it induces a pilot to fly too fast.
Certainly, you don't want to base your strategic or possibly even your
tactical decisions on the McCready speed to fly. Be aware of it and factor
it in, but don't be a slave to it.

In a wide area of homogeneous airmass characteristics where thermals are
uniform in strength, diameter and spacing, the McCready speed to fly is a
major determinator of flying technique.

Flying in high mountain country is just the opposite. You had better be
ready for a complete weather change every few minutes. Thermic conditions
will cycle very fast and you may see blue sky, towering cumulus,
overdevelopment and back to blue in a single interthermal glide.

Bill Daniels