Inter-thermal cruise speeds?

On Feb 10, 5:35*am, wrote:
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- Hide quoted text -

- Show quoted text -

Ingo is a great pilot so I wouldn't quibble that his technique works
for him in the conditions he was thinking of when he gave this advice.

That said, I can say from personal experience that I have seen world-
class pilots pursue very different strategies with great success under
conditions that may or may not be similar to what Ingo was thinking
of. In particular I see a lot of very good pilots in the high desert
of the western US make significant deviations from courseline to seek
out lift. This may have something to do with the topography of the
site and the lift distribution on any given day.

With respect to speeds, it all depends on what Ingo means by "low and
weak" versus "strong". His speed ranges cover the gamut and in the end
the basic idea is right - don't fly the speed director.

9B

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).

According to a fellow club member (Discus 2), if the day is booming, fly
80 kts, if the day is good, fly 70 kts, if the day is so so, fly 60 kts.
YMMV.

Tony V.

On Feb 12, 8:01*pm, Tony Verhulst wrote:
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).

According to a fellow club member (Discus 2), if the day is booming, fly
80 kts, if the day is good, fly 70 kts, if the day is so so, fly 60 kts.
YMMV.

Tony

Those sound like east coast conditions with no water. They correspond
to 2.5, 1 and 0 knot McCready settings on my ASW 27 - a D2 wouldn't be
too far off.

It would have to be a truly weak day for me to fly best L/D (60 kts)
all the time.

Andy

On Feb 7, 6:50 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)

As someone who changed from an LS4 to an ASW27 last year I did wonder
about this quite a bit and how best to learn to fly in a different
speed range. I like the idea of 3 speeds as mentioned by some other
writers, tip-toeing (best glide), normal (75-80 kts) and flat-out
(90+kts), because it's easy to do. I like setting Macready and just
using it as guidance, because it's easy to do. I like paying attention
to other gliders around me and seeing how they're getting on, because
it's easy to do.

All that leaves you with plenty of capacity for the important jobs -
picking the right pieces of sky, making an excellent job of climbing
if you choose to stop, and changing to Plan B if you get the first 2
jobs wrong. After several beery evenings analysing flight traces, it
seems I perform best late in the afternoon when you either correctly
find, reach and use the few large thermals that are left or you don't
get home before the bar closes. If only I could apply that selection
process at other times of the day I'd be getting somewhere.

And I think I go faster on Condor because if you get it wrong you can
just hit restart.

For those of you who enjoy other's mistakes, see if you can spot an
example of Plan B taking it's time to kick in ...
http://www.bgaladder.co.uk/dnload.asp?DSN=77TC3IR1.igc

Martin (UK)

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

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