Inter-thermal cruise speeds?

Frank & all,

Great subject, it's my favorite and the essence of the "go faster"
game we all like to play. I certainly agree with Tim. Competing in
Gliders - Winning With Your Mind by Leo and Ricky Brigliadori is the
latest and greatest must have book in your soaring Library for the
"just a little bit faster please" (nod to BB) type pilot.

Here's the really interesting part concerning the answers (so far) to
your questions, every one of the comments are generally correct. The
theory of how and what to set your MC for inter-thermal runs and final
glides are generally known, the fact that most are setting MC slightly
less than the actual average achieved climb rate is well known, not
speed chasing the vario is a given today, height band evaluation,
adjusting for the conditions or obstacles ahead and long glides
chasing lift bands followed by climbing in only the strongest thermals
of the day all equate to faster XC speeds and the list goes on and on.
So you toss all that info in a blender then go flying and see what's
working today, be creative by varying the techniques.

So the real key and IMHO the most enjoyable part of what we do is when
we're tapping into our creative side. This is the side that quietly
informs us when to apply a little, slightly in advance of the obvious
gear shifting, creative wondering in lift bands or perhaps making that
90 degree turn and then finding just what you're looking for when
perhaps none of this was obvious to our right side of the brain. The
numbers side of the game, as I see it is really only a checklist
guideline, to be applied as an appropriate and important rule of
thumb. However the rewards are often found on the edges or perhaps
somewhat outside of the numbers. I doubt if many have won the day or
got around a 1,000k by just following the numbers. Having said that
somewhere between 70kts and 110kts sounds about right to me ;-)
21

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

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

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 8, 8:45*pm, wrote:
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

As had been already mentioned, there are a bunch of reasons why flying
slower than McCready theory makes sense. Some are consistent across
flying conditions, others are situation-specific.

Fist, in my experience, your perceived climb rate may not be your
actual climb rate - even using you vario or computer averager,
depending on how it calculates average. I consistently find average
climb rates looking at SeeYou to be a knot or more slower than was my
perception in the air. This is mostly because pilots (and perhaps some
instruments) don't adequately count the time centering a thermal with
no climb or include "trys", thermals that don't pan out. These two
effects reduce your realistic expected climb rate. Maybe your computer
properly adjusts for this maybe it doesn't, only some experimentation
can tell you for sure.

Flying slower keeps you higher, which has a number of direct and
indirect benefits that I've tried to quantify through the following
example. Imagine a flight where the lift band is 10,000' to 17,500',
the average (achieved) climb is 5 knots, the distance between climbs
is 35 miles and there are cu present. For my glider the theory gives
an expected cruise speed of 98 knots (dry) and an altitude loss
between thermals of 7,100'. If I slow down and fly 15 knots slower
(83 knots) instead, I end up with an altitude loss between thermals of
5,600' and an average achieved cross-country speed that is about 1.7
mph slower. So why fly slower? By staying higher my average cruise
altitude is 14,700 rather than 13,900 so I gain back about 1.5 mph in
true airspeed difference. You only need to find a 0.04 knot better
climb to close the remaining cross-country speed gap, or a 0.4 knot
faster climb if you ignore the TAS effect. Since we are flying higher
on average it is reasonable to expect you'll be able to do this under
the described conditions for several reasons. You will be closer to
the clouds and will have a slightly better change of aligining on them
to find lift. You will also be higher in the lift band so less likely
to fall into weaker lift or will be less inclined to accept weaker
lift as you get lower. You will have a greater search distance to find
better lift. If I fly McCready in this scenario I can go about 35
miles between thermals before I get out of the lift band. If I fly 15
knots slower I can fly 45 miles for the same altitude range. Lastly, I
have found that I have a somewhat harder time sensing and successfully
pulling up into and quickly centering thermals if I am cruising at 100
knots versus 85 knots. In the extreme case, flying faster ups you risk
of getting stuck down low and having to take a sub-standard thermal to
get back up or even landing out. Individual flying style will
determine which of these effects matters most for any individual
pilot.

How you think about this varies with the conditions of the day. If it
is blue with a very wide lift band, large, closely-spaced thermals
with very consistent thermal strengths you won't get as much benefit
from slowing down. The TAS effect is also reduced for lower altitude
lift bands. If the thermal strengths are lower overall, you actually
have to find a thermal that is more significanly above average (on a %
basis) to make up the cruise speed difference.

If I change the example to flying 20 or 25 knots slower than McCready
it gets harder to see the benefits because the incremental climb rate
you need to achieve to make up for the sub-optimal cruise speed goes
up substantially.

9B

On 9 fév, 12:54, wrote:
On Feb 8, 8:45*pm, wrote:

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

As had been already mentioned, there are a bunch of reasons why flying
slower than McCready theory makes sense. Some are consistent across
flying conditions, others are situation-specific.

Fist, in my experience, your perceived climb rate may not be your
actual climb rate - even using you vario or computer averager,
depending on how it calculates average. I consistently find average
climb rates looking at SeeYou to be a knot or more slower than was my
perception in the air. This is mostly because pilots (and perhaps some
instruments) don't adequately count the time centering a thermal with
no climb or include "trys", thermals that don't pan out. These two
effects reduce your realistic expected climb rate. Maybe your computer
properly adjusts for this maybe it doesn't, only some experimentation
can tell you for sure.

Flying slower keeps you higher, which has a number of direct and
indirect benefits that I've tried to quantify through the following
example. *Imagine a flight where the lift band is 10,000' to 17,500',
the average (achieved) climb is 5 knots, the distance between climbs
is 35 miles and there are cu present. For my glider the theory gives
an expected cruise speed of 98 knots (dry) and an altitude loss
between thermals of 7,100'. *If I slow down and fly 15 knots slower
(83 knots) instead, I end up with an altitude loss between thermals of
5,600' and an average achieved cross-country speed that is about 1.7
mph slower. So why fly slower? *By staying higher my average cruise
altitude is 14,700 rather than 13,900 so I gain back about 1.5 mph in
true airspeed difference. *You only need to find a 0.04 knot better
climb to close the remaining cross-country speed gap, or a 0.4 knot
faster climb if you ignore the TAS effect. Since we are flying higher
on average it is reasonable to expect you'll be able to do this under
the described conditions for several reasons. *You will be closer to
the clouds and will have a slightly better change of aligining on them
to find lift. You will also be higher in the lift band so less likely
to fall into weaker lift or will be less inclined to accept weaker
lift as you get lower. You will have a greater search distance to find
better lift. If I fly McCready in this scenario I can go about 35
miles between thermals before I get out of the lift band. If I fly 15
knots slower I can fly 45 miles for the same altitude range. Lastly, I
have found that I have a somewhat harder time sensing and successfully
pulling up into and quickly centering thermals if I am cruising at 100
knots versus 85 knots. In the extreme case, flying faster ups you risk
of getting stuck down low and having to take a sub-standard thermal to
get back up or even landing out. Individual flying style will
determine which of these effects matters most for any individual
pilot.

How you think about this varies with the conditions of the day. If it
is blue with a very wide lift band, large, closely-spaced thermals
with very consistent thermal strengths you won't get as much benefit
from slowing down. The TAS effect is also reduced for lower altitude
lift bands. If the thermal strengths are lower overall, you actually
have to find a thermal that is more significanly above average (on a %
basis) to make up the cruise speed difference.

If I change the example to flying 20 or 25 knots slower than McCready
it gets harder to see the benefits because the incremental climb rate
you need to achieve to make up for the sub-optimal cruise speed goes
up substantially.

9B



Hi,
Here's Ingo Renner rules to achieve fast x/c speed flying a Duo-
Discus.

-Ignore MaCready and fly one of three speed;
55 for thermaling, 70-80 kts for low weaker condition
90-110 kts for strong condition
-Fly straight to your goal with very minor deviation for lift.
-Slow down gently in lift and centre thermal in one circle or keep
going,
no second chance
-Leave as soon as climb falls off,
-Fly carefully with smooth control movement, no abrupt pull up or push
over.
-Always fly with the yaw string straight and centered.

Taken from a text entitle "Soaring with the master", by Ian Sutcliffe
in Free Flight,the Canadian magazine on soaring.
S6