Nice skyline article

Andreas Maurer wrote:
On 25 Feb 2005 05:59:35 -0800, wrote:

Comment: I've gotta dissagree with you on this. Both mentioned
gliders,
when properly tuned, respond very well to this kind of technique.
'20
in particular if flaps and ailerons are very well sealed and good
winglets are used. '24 needs improved winglets and ,in my opinion,
the
"B mod" on the leading edge. Do these and it climbs very well,
mostly
due to improved ability to pull harder thus giving smaller circle.
13 years in '20's, 13 years in '24. Lotza work done on both.

Interesting. What winglets do you use?
I got only about 700 hrs in the 20 and maybe 200 hrs in the 24, but
both didn't climb very well below 47-50 kts. The latter is equipped
with the factory winglets, btw.

The 20 was regarded as one of the best performing 20's ever (before
the ero of winglets). It climbed really well, but I made sure that I
stayed away from stall speed.


Bye
Andreas

Winglets I referred to are those I began developing in 1993. Udo uses
them on my old ship as do quite number of others. They significantly
improve the flow at the tip and permit much more agressive turning when
needed. Much better than the .4M factory ones. Thus my comment
differing with your opinion.
The '20 also responded very well when I added winglets. More than I
expected. Probably due to wide tip chord.
I'm off the track of this thread. John is very much correct in his
observations- as usual.
UH

"T o d d P a t t i s t" wrote in message
...
"Bill Daniels" wrote:

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.

You are missing the point. You don't reduce airspeed to get
a tighter turn radius. You reduce airspeed to get a
shallower bank in the *same* turn radius. The shallower
bank, even when flown at an airspeed less than the min sink
speed for that bank, produces a lower sink rate than the
same turn radius flown faster at a higher bank angle.
Flying at min sink for the bank angle is not the optimum.

See the Turn Radius Calculator:

http://www.soarcsa.org/thinking_page...n_rad_knots.ht
m

See Jud's article.

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.

A 45 degree bank at 43 knots results in a turn radius of 164.1 feet. For
me, that's a fairly standard thermalling turn that takes 14 seconds. That's
minimum sink in my Nimbus 2C if flown dry and it turns inside almost
everyone including the 12 meter ships.

At 40 knots and 40 degrees bank the turn radius is 169.3 feet. That
actually INCREASES the turn radius and it means I have to wobble along just
above stall at a high sink rate. That's a very bad deal from both a soaring
and safety standpoint.

Maybe if the starting point is someone that flies a 45 degree bank at 65
knots with a 375.1 foot radius, it looks different. Reducing the airspeed
to 45 while reducing the bank to 30 results in a radius of 311.3 feet or a
radius reduction of 63.8 feet. That's significant but just reducing the
speed to 45 knots turn is better still.

In fact, 45 - 45 is a good turn for most gliders. At a 45 degree bank,
there is little increase in G load so the sink doesn't increase much at all.
I'm beginning to think there is a big payoff for an angle of attack
indicator so we can just fly AOA and not have to compute these things.

Bill Daniels

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

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

"T o d d P a t t i s t" wrote in message
...
(snip)
IMHO, the best thermalling performance for your glider can
be found by flying against another glider, not by cranking
numbers. Nonetheless, Jud's article sheds some new light on
why I seem to find the best performance when flying slower
than min sink for my bank angle.


I agree with Todd. The best way to learn how to make your glider climb well
is by flying in gaggles with other gliders, especially during contests. You
will find out what works pretty quickly, and the best pilots are usually
willing to talk to you (after the contest!) to help you improve. Reading
charts and doing the math helps a lot with understanding "how things work",
and this was a very good article and well worth the read. To learn how to
really make a glider climb, however, you need to go fly one, preferably far
from home, where it really matters.

BTW, real world thermals are not usually like the model!
-Bob Korves