Inter-thermal cruise speeds?

On Feb 7, 5:00 pm, Mike the Strike wrote:
Frank:

One thing that classic MacCready theory doesn't take into account is
the depth of the working height band.

It would be a foolish pilot who set his computer/ring to MacCready 5
on a day with 5 knot thermals that topped out at 1,500 feet AGL, but
with cloudbases at 15,000 feet you could probably set it at 6 or
higher. Several pilots I know set their ring almost as a function of
height rather than thermal strength.

The chance of you hooking up with a good thermal increases with the
top of the lift and you can increase your speed accordingly. When you
get low, you need to slow down. There have been some good articles on
this if you search the databases.

Mike


Mike,

Working the bands is very common and I think of it as setting the MC
to the strength of the next thermal "I am willing to take". The day
average may be 6 knots, but if I am low and willing to accept a 3 knot
thermal I will set the MC to that. As I get lower the odds of finding
a good thermal are reduced and I am willing to take a weaker thermal
to get back up in the band or at least get the range to hopefully
reach a better thermal.

In the Western US there are many summer days where dropping below the
mountain height can cost you dearly in time to get back up. In the
14-18 K range I tend to fly MC+5, 12-14K MC for the average thermal
strength I am expecting still to find, 10-12 K I dial back to extend
range, 8 to 10K back further and below 8 back to zero. This is with
base elevation about 5,000 in the valleys.

Mike the Strike wrote:

It would be a foolish pilot who set his computer/ring to MacCready 5
on a day with 5 knot thermals that topped out at 1,500 feet AGL, but
with cloudbases at 15,000 feet you could probably set it at 6 or
higher. Several pilots I know set their ring almost as a function of
height rather than thermal strength.


My understanding of the theory is that you will ALWAYS be worse off if
you set a MC higher than the thermal strength and therefore fly faster
than optimum. Flying slower however does have several advantages, as
others have described.

Stephen

Stephen:

That is true if all thermals have the same strength. In reality,
thermals have a strength (and size) distribution. On a day with a 5-
knot average thermal strength you will find thermals as strong as 8
knots or as weak as 3 knots. More working altitude enables you to
pick the strongest thermals and maintain an effective MacCready higher
than the average thermal strength. The fastest pilots (which doesn't
include me) seem to be rather good at this.

Knowing when you can step up the speed and when to slow down is the
key to winning.

Mike

My understanding of the theory is that you will ALWAYS be worse off if
you set a MC higher than the thermal strength and therefore fly faster
than optimum. Flying slower however does have several advantages, as
others have described.

Stephen

I really liked John Cochrane's paper "A little Faster Please".

The message I took from that was that the MacCready setting can be used as a
general "optimism setting". I tend to set MacCready with a "gut check"
about how I feel conditions will be ahead.

If you are bumping along above 17,000 feet, there's no thermal that's worth
stopping for since you don't want to go any higher so M could be infinity.
On the other hand, if you are low in tiger country, you'll take any thermal
(M=0). There's a sliding scale in between.

I use GPS_LOG which can average the last three thermals and automatically
set M. That almost always gives me a M setting higher than my gut says I
should use. Maybe that's why I fly slow.

Bill D


"Mike the Strike" wrote in message
...
Stephen:

That is true if all thermals have the same strength. In reality,
thermals have a strength (and size) distribution. On a day with a 5-
knot average thermal strength you will find thermals as strong as 8
knots or as weak as 3 knots. More working altitude enables you to
pick the strongest thermals and maintain an effective MacCready higher
than the average thermal strength. The fastest pilots (which doesn't
include me) seem to be rather good at this.

Knowing when you can step up the speed and when to slow down is the
key to winning.

Mike

My understanding of the theory is that you will ALWAYS be worse off if
you set a MC higher than the thermal strength and therefore fly faster
than optimum. Flying slower however does have several advantages, as
others have described.

Stephen

Bill Daniels wrote:
I really liked John Cochrane's paper "A little Faster Please".

The message I took from that was that the MacCready setting can be used as a
general "optimism setting". I tend to set MacCready with a "gut check"
about how I feel conditions will be ahead.

If you are bumping along above 17,000 feet, there's no thermal that's worth
stopping for since you don't want to go any higher so M could be infinity.
On the other hand, if you are low in tiger country, you'll take any thermal
(M=0). There's a sliding scale in between.

I use GPS_LOG which can average the last three thermals and automatically
set M. That almost always gives me a M setting higher than my gut says I
should use. Maybe that's why I fly slow.

Maybe, but probably not - I think a lot of good pilots do the same. My
experience is, if I use a MC setting the same as the average climbs I'm
making, two things usually happen:

1) My speed director tells me to fly scary fast in medium or stronger
sink (like 110-120 knots), and

2) I get low frequently!

So, I usually set it as high as I can without getting stuck low
somewhere, and that's generally around one-third of the climb average. I
flew contests for many years, and the really good pilots weren't flying
much faster, if any, than I was, but they sure chose better places to
go, and they knew when to shift gears sooner than I did.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Mike the Strike wrote:
Stephen wrote:
My understanding of the theory is that you will ALWAYS be worse off if
you set a MC higher than the thermal strength and therefore fly faster
than optimum. Flying slower however does have several advantages, as
others have described.

That is true if all thermals have the same strength. In reality,
thermals have a strength (and size) distribution. On a day with a 5-
knot average thermal strength you will find thermals as strong as 8
knots or as weak as 3 knots.

McCready theory is based on what *you* get for thermal strength, not
what a random sampling of the thermals in the area would produce, so I
have to agree with Stephen. Set your MC higher than the thermals you are
encounter will slow you down. Of course, we're assuming you are flying a
classic thermal flight, and not convergence, wave, ridges, etc.

Probably no one reading this thread anymore - I was traveling and got
here late!
--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Feb 7, 5:00 pm, Mike the Strike wrote:
Frank:

One thing that classic MacCready theory doesn't take into account is
the depth of the working height band.

It would be a foolish pilot who set his computer/ring to MacCready 5
on a day with 5 knot thermals that topped out at 1,500 feet AGL, but
with cloudbases at 15,000 feet you could probably set it at 6 or
higher. Several pilots I know set their ring almost as a function of
height rather than thermal strength.

The chance of you hooking up with a good thermal increases with the
top of the lift and you can increase your speed accordingly. When you
get low, you need to slow down. There have been some good articles on
this if you search the databases.

Mike

On Feb 7, 11:50 am, Frank wrote:

I'm curious what others are using for inter-thermal cruise speeds for
modern 15m (and 18m I guess) gliders like the Ventus 2bx, Ventus 2cx,
ASW-27, ASG-29, Diana 2, etc (add models as necessary).

Here in the U.S. we have been moving toward cruise speeds much lower
than would normally be dictated by using straight McReady settings,
but how low is too low?

I've also been flying a V2bx & V2cxt in Condor a lot, and cruise
speeds there are all over the map, from 90kt to 125kt (fully
ballasted) in the same race/weather conditions, with varying results.

Any thoughts?

TIA,

Frank (TA)


I have also found John Cochrane's (BB) work in this area to be most
enlightening. Here is the link to the paper.

http://faculty.chicagogsb.edu/john.c...s/newmcred.pdf

It gets pretty technical but the gist is that he blends MC theory with
probability (of reaching the next thermal of a certain strength)
theory and proves it mathematically. A little calculus for those cold
winter months.....

Bob

On Feb 7, 11:50*am, Frank wrote:

Any thoughts?

I'm late to the thread but I have read the other posts. So far no one
has mentioned:

TAS effect (the advantage of better ground speed at high altitude)
Polar knees (the sharp fall off in performance at high speed seen in
some modern gliders).
Streeting
Wind shift with altitude.

Simple MC theory does not deal with any of this very well, or if it
does I missed understanding it.

Years ago I thought the only way to fly fast was to push forward on
the stick. I used to landout a lot. Over the years I got to fly with
many excellent pilots and was impressed by how slow many of them flew
and how seldom they stopped to thermal.


Andy

On Feb 7, 1:50*pm, Frank wrote:
I'm curious what others are using for inter-thermal cruise speeds for
modern 15m (and 18m I guess) gliders like the Ventus 2bx, Ventus 2cx,
ASW-27, ASG-29, Diana 2, etc (add models as necessary).

Here in the U.S. we have been moving toward cruise speeds much lower
than would normally be dictated by using straight McReady settings,
but how low is too low?

I've also been flying a V2bx & V2cxt in Condor a lot, and cruise
speeds there are all over the map, from 90kt to 125kt (fully
ballasted) in the same race/weather conditions, with varying results.

Any thoughts?

TIA,

Frank (TA)

The speed that gets you to the next acceptable thermal without hitting
the ground. Seems obvious
but each day we have to find a rythym that accomplishes this very
basic element.
I don't see the best pilots making drastic changes in how fast they
fly. This takes too much attention better applied to where to fly.
UH

Anyone else here see Carl Herolds talk at the convention a couple
years ago titled, If you fly Mcdready you will lose"? Actually, he
said that was a title just to get attention but that the real title
was Fly Slower to Fly Faster, or something like that. It was
fascinating to see all this graphs and flight traces. It was very
convincing to see his data that indicated staying high and not
circling was ultimately faster. I think there may be a threshold L/D
value particular to specific conditions in which his technique
worked. Regardless, I now circle as little as possible.

MM