Nice skyline article

Readers of this group might like a very nice article on turn radius and
handicapping by Judah Milgram

http://skylinesoaring.org/NEWSLETTER/2005/February/

Though mostly about handicapping, it also shows very nicely why you
should not thermal at the "minimium sink speed" corresponding to the
level flight polar, but instead should usually thermal right on the
edge of a stall. (Going slower means you can achieve the same turn
radius with a lower bank angle.)

John Cochrane

BB

On 24 Feb 2005 09:27:21 -0800, "BB"
wrote:

Though mostly about handicapping, it also shows very nicely why you
should not thermal at the "minimium sink speed" corresponding to the
level flight polar, but instead should usually thermal right on the
edge of a stall. (Going slower means you can achieve the same turn
radius with a lower bank angle.)

Try to thermal once at the edge of a stall in a glider like, say,
ASW-20, ASW-24, and you'll find out immediately that your conclusion
is not universally applicable.





Bye
Andreas

Andreas Maurer wrote:
On 24 Feb 2005 09:27:21 -0800, "BB"
wrote:


Though mostly about handicapping, it also shows very nicely why you
should not thermal at the "minimium sink speed" corresponding to the
level flight polar, but instead should usually thermal right on the
edge of a stall. (Going slower means you can achieve the same turn
radius with a lower bank angle.)


Try to thermal once at the edge of a stall in a glider like, say,
ASW-20, ASW-24, and you'll find out immediately that your conclusion
is not universally applicable.





Bye
Andreas
Ditto Std Cirrus - only time I dare go really slow is when there are big weak
thermals with no gusts. Otherwise it is only a case of when you are going to get
that auto rotation feeling. And the recovery from a wing drop when slow is time
and altitude consuming. As the article says, pays to attend to how the aircraft
flies. I am much more comfortable a little faster and a little higher bank angle
in the Cirrus.

As the article says, pays to attend to how the aircraft
flies. I am much more comfortable a little faster and a little higher
bank angle
in the Cirrus.

================================================== ==================================

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.

Terry Claussen
Estrella

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

Andreas Maurer wrote:
On 24 Feb 2005 09:27:21 -0800, "BB"
wrote:

Though mostly about handicapping, it also shows very nicely why you
should not thermal at the "minimium sink speed" corresponding to the
level flight polar, but instead should usually thermal right on the
edge of a stall. (Going slower means you can achieve the same turn
radius with a lower bank angle.)

Try to thermal once at the edge of a stall in a glider like, say,
ASW-20, ASW-24, and you'll find out immediately that your conclusion
is not universally applicable.


Bye
Andreas

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.
UH

"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

BB wrote:
Readers of this group might like a very nice article on turn radius
and
handicapping by Judah Milgram

http://skylinesoaring.org/NEWSLETTER/2005/February/

Though mostly about handicapping, it also shows very nicely why you
should not thermal at the "minimium sink speed" corresponding to the
level flight polar, but instead should usually thermal right on the
edge of a stall. (Going slower means you can achieve the same turn
radius with a lower bank angle.)

John Cochrane

BB

My LS1c climbed like a rock under 46kts. Think it has somthing to do
with a flow separation on the all flying tail. On the other hand, my
Ka8 went up like a rocket at 34kts indicated (min sink around 38). I
think you need to determine these things on a case-by-case basis.

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 use a different approach.
In case of my sHP18 I determent the minimum sink
polar for a know wing loading x 1.4 g load at a 45deg. bank angle. With that
I establish the speed for my bank. 43kt 8lb/sqft will give me a speed at
45 deg. bank of about ~ 51kt. This allows the glider to stay within the
sweet
spot and gives good control with the least amount of control drag.
Reducing the speed further would not gain anything.

My ASW24 previously owned by Hank has a minimum sink of 45kt at 6.4 lb/sqft
as per R. Johnson but the minimum speed in this case can be pushed back to
about
40kt. due to the relative flat bottom of the polar as well as better
winglets and modified
leading edge. this would give a speed of 43kt
at 7.4 lb/sqft. The 45 deg bank speed would about 51kt.
As it turns out, I fly it between 50-52kt.
Regards
Udo

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