wrote in message
oups.com...
I read the article and I don't agree with it. I think it's much
better to
fly the minimum sink airspeed for the bank angle. Lets do the math.

Bill Daniels

With a little reflection it is *obvious* that it cannot be optimal to
fly a given radius circle at a certain bank angle and airspeed if there
is a different combination of airspeed and bank angle giving a lower
sink rate for that radius of circle. If there is a different
combination yielding the *same radius* and *lower sink rate* then all
the higher sink rate combinations for that radius are not optimal.

If we are optimized then we are at the minimum sink rate for the circle
radius we are flying - period.

Judah's beautiful graphs and Reichman's 70's vintage "Cross Country"
both make it clear that the optimum will be found somewhat on the back
side of minimum sink speed for the optimal bank angle. Severe mushing
descent speed and sub-minimum controllable airspeed as potential
solutions are exagerated straw men.

But I did not understand from Reichman that the optimal speed actually
decreases initially with increasing bank angle/decreasing radius. So
this feature of the data in my ASW-20C pilot's manual was always a bit
of a mystery to me.

Thanks to Judah for graphing optimal speed versus radius directly for
several types, making the situation clear.

How to find the optimal radius though! Wouldn't it be a wonderfully
convenient coincidence if at the optimal radius the overbanking
tendency of the glider was exactly balanced by the lift gradient trying
to unroll the glider? Would this work out for some particular span? I
could probably notice when the stick was in the center, and it would
sure be nice to know I was flying right. Someone please do the math
and let me know.

Jonathan


The original issue was that gains could be achieved by reducing bank angle
and flying slower. More specifically, that the same radius could be
achieved at a lower sink at a lower bank and speed.

My point is that any gains are very, very small and likely to place the
pilot at risk of a stall/spin in rough air. (If I know a pilot is
attempting this, I won't be flying under him in a gaggle.)

All I'm saying is that small reductions in airspeed below min sink have
little effect on turn radii. Bank angle has a far larger effect. I've done
the math and plotted the results to scale to prove it to myself. A small
turn radius is good but it's best achieved with bank not reductions in
airspeed below min sink.

Accurate centering has a much greater effect on average climb rate than a
tiny reduction in turn radius achieved by a small reduction in airspeed.
Minimum sink is a solid airspeed that provides good control authority for
centering the thermal and is a much better bet for most pilots.

Almost any pilot will benefit more by practicing a "standard" 45 degree bank
at minimum sink airspeed for that bank angle than by reaching for a few feet
reduction in turn radius by flying slower.

Bill Daniels