Losing time in Cloud-Streets?

On May 18, 5:11*pm, "noel.wade" wrote:
A couple of things:

1) Thanks John, that's the kind of comparison/number-checking I was
looking for. *I know that cloudbase/working-band/lift-strength play a
factor in determining whether the tradeoff is worth it; but didn't
think to do a straight MacCready comparison (the idea of pushing the
glider to high speed while still in spotty lift under a cloud-street
is just still feels awkward - discounting the few times where I've
approached cloudbase and needed to "bug out")!

2) I thought flying "energy lines" was the consensus these days, and
"Dolphin flying" was out - given that variometers lag and its
incredibly hard to time your pushes and pulls when flying through
alternating narrow cores and strong sink. *If your strong cores are
separated by a couple of miles, their miniscule contribution (say a 50
- 150 foot height gain) when you fly straight through them doesn't
seem worth it (especially when you start considering the risks of
hitting nasty sink before accelerating back up to cruise speed;
possibly wiping out all of your gains). *I've always been much more
tempted to slow down under weak spread-out lift (for example, under a
cloud thats about to OD).

Now just to turn this around and look at it from a different
perspective: *For the fast guys out there, when (if ever) *do* you
start slowing down a lot while flying straight ahead? *What're the
combination of factors that encourage you to switch into this mode?

Thanks,

--Noel

Reichmann used the term "dolphin flight" to mean flying streets or
energy lines.

I will give you a simple was way to think about how fast to fly in
lift on a street. As always there are many other factors in tactics
that may make you do some things differently but those usually have to
do with some change in the conditions ahead (end of the street, big
blue hole, final glide, etc).

Lets take a simple MacCready STF ring set of numbers. These should be
about right for your DG.

0 60
-1 65
-2 70
-3 75
-4 80
-5 85
-6 90
-7 95

Invert the numbers to average base cruise speed (this is how most of
us determine our average cruise speeds so we are not just pushing and
pulling all the time.

0 60
1 65
2 70
3 75
4 80
5 85
6 90
7 95

Now on the cloud street use your target thermal strength, the one your
willing to stop for be your guide. Again let's use 5 knots. Subtract
the difference between your target speed and the STF for the lift.
Example you're in 2 knot lift, 85-(85-75)=75.

Vario Speed
0 85
1 80
2 75
3 70
4 65
5 60 (thermal if really below cloudbase)
6 55 (thermal if really below cloudbase)
7 50 (thermal if really below cloudbase)

On May 18, 3:25*pm, John Cochrane
wrote:
On May 18, 4:33*pm, "noel.wade" wrote:

All -

I've been flying with the assumption that flying slow in cloud-streets
is always a good idea. *

I disagree. It's always MacCready theory, if correctly interpreted.

Suppose the cloudstreet offers 2 knots up everywhere with occasional 8
knot cores. (Uvalde). Option 1: fly 50 knots without losing altitude.
You average 50 knots = 57 mph. Option 2: fly 85 knots, (I.e. cruise at
Mc 4 or so) , slowly losing, but stopping to thermal in the 8 knot
cores. You average 80 mph. (Typical uvalde winning speeds) The latter
is much faster. Reichmann offers the same advice.

John Cochrane

Agree!

Reichmann called Option 1 "Forced dolphin flight" if I remember
correctly.

Unfortunately this is what I most often do and I should stop.

David (GJ)

On May 18, 5:15*pm, John Smith wrote:
Read Reichmann, he explains everything.

While real life tactics may have changed, the mathematical basics are
still the same, and it's still good advice to start with strict McCready
and adopt only later when you have understood and mastered the basics.

One reason why it often pays to force yourself to fly straight ahead
rather than circling more than pure McCready theory would tell you is
that you rarely roll right into the core of a thermal. Often you spend
a number of circles getting centered and on occasion you completely
miss and make a circle in sink. The shorter the potential climb the
more this effect hurts you. Within a couple thousand feet of cloudbase
it hardly ever pays to take a circle. In theory you could roll this
into the McCready calculation, but people rarely do the extra math -
except BB.

I've found a similar effect on the last climb to make final glide -
climbing up to the altitude needed to match the McCready setting to
your climb rate almost always puts you behind the glider who leaves a
little earlier.

9B

On May 20, 6:50*am, Nine Bravo Ground wrote:
On May 18, 5:15*pm, John Smith wrote:

Read Reichmann, he explains everything.

While real life tactics may have changed, the mathematical basics are
still the same, and it's still good advice to start with strict McCready
and adopt only later when you have understood and mastered the basics.

One reason why it often pays to force yourself to fly straight ahead
rather than circling more than pure McCready theory would tell you is
that you rarely roll right into the core of a thermal. Often you spend
a number of circles getting centered and on occasion you completely
miss and make a circle in sink. *The shorter the potential climb the
more this effect hurts you. Within a couple thousand feet of cloudbase
it hardly ever pays to take a circle. In theory you could roll this
into the McCready calculation, but people rarely do the extra math -
except BB.

I've found a similar effect on the last climb to make final glide -
climbing up to the altitude needed to match the McCready setting to
your climb rate almost always puts you behind the glider who leaves a
little earlier.

9B

This is theoratically correct, but I found out more often than not
that the lift right below cloudbase (keeping FAR clearance of course)
is stronger and more widespread than couple of thousands below, which
allows much faster speed without loosing altitude.

Ramy

On May 20, 7:47*pm, Ramy wrote:

This is theoratically correct, but I found out more often than not
that the lift right below cloudbase (keeping FAR clearance of course)
is stronger and more widespread than couple of thousands below, which
allows much faster speed without loosing altitude.

Ramy

Okay, I broke out the polar and did some simple math for a "typical"
scenario.

Take a cloud street that is 16 miles long with 4 knot average thermal
strength and 10 knot peak thermal strength.

Pilot A pulls back to 70 knots and climbs in the average lift (2.4
knot net climb rate). It takes him 14 minutes to reach the end of the
street and he has gained 3,360 feet.

Pilot B climbs in the strong core, taking 30 seconds to center and
achieving a 8.4 knot average climb rate thereafter (note the higher
sink rate for circling flight). After 5 minutes he has climbed 4,250
feet. He then cruises at 110 knots for 16 miles, giving up 890 feet in
the process. Both pilots arrive at the end of the cloud street at the
same time and altitude.

Conclusion: stopping to circle in a thermal weaker than 10 knots puts
you behind the pilot who climbs straight ahead.

Taking Ramy's point about stronger lift closer to cloudbase into
account, let's assume you find an average 5 knots after a circling
climb instead of 4 knots for climbing straight ahead. In this case you
need a minimum 8.3 knot thermal before stopping to circle makes sense.
If you assume 6 versus 4 knots average lift cruising closer to
cloudbase then you only need a 6.6 knot thermal - but that starts to
feel like a pretty strong thermal strength gradient with altitude.

This analysis doesn't take into account a slight true airspeed
advantage for the pilot who climbs first due to his higher average
altitude.

Overall, I think this confirms that it pays to avoid circling under a
cloudstreet for anything but the very strongest lift. This is even
more true if you are heading into an upwind turnpoint.

9B

On May 22, 9:02*am, Andy wrote:
On May 20, 7:47*pm, Ramy wrote:

Overall, I think this confirms that it pays to avoid circling under a
cloudstreet for anything but the very strongest lift. *This is even
more true if you are heading into an upwind turnpoint.

9B

BTW, I'm not arguing against McCready theory. However, I do think you
need to account for the overall conditions and things like TAS and
lift strength versus altitude, thermal centering time, winds an
proximity of turnpoints. Not all of those factors are accounted for in
the base theory and some of the outcomes are quite a bit more extreme
that you might expect.

See BB's analysis of upwind versus downwind turnpoints as an example.
Using that advice gained me something like 4 mph on a long task where
the first turn was into a 30 mph headwind.

9B

On 5/18/2010 3:28 PM, Dave Nadler wrote:
On May 18, 5:33 pm, wrote:

All -

I've been flying with the assumption that flying slow in cloud-streets
is always a good idea. But in looking at some of my OLC flights I
wonder if my logic is faulty and I'm hurting my speed. Anyone with
lots of OLC or contest experience care to offer feedback? Details
below...

snip

A few weeks ago I flew 440 miles, around 15% circling, mostly during
the beginning of the flight and digging out of one hole (flew under OD
at 2nd turn):
http://www.onlinecontest.org/olc-2.0...htId=502072323

Suggestion: Go look at the log files of the fastest pilots during last
years 18m nationals at Ephrata !
But keep in mind, a modern ballasted 18 meter glider will not have to
circle nearly as often as your unballasted DG 300 will!

--
Eric Greenwell - Washington State, USA (netto to net to email me)

On May 18, 6:25*pm, John Cochrane
wrote:
On May 18, 4:33*pm, "noel.wade" wrote:

All -

I've been flying with the assumption that flying slow in cloud-streets
is always a good idea. *

I disagree. It's always MacCready theory, if correctly interpreted.

Suppose the cloudstreet offers 2 knots up everywhere with occasional 8
knot cores. (Uvalde). Option 1: fly 50 knots without losing altitude.
You average 50 knots = 57 mph. Option 2: fly 85 knots, (I.e. cruise at
Mc 4 or so) , slowly losing, but stopping to thermal in the 8 knot
cores. You average 80 mph. (Typical uvalde winning speeds) The latter
is much faster. Reichmann offers the same advice.

John Cochrane

I would only add that the other important factor is the view ahead.
Sometimes slowing in moderate lift for a while- maybe to max l/d or
something as opposed to min sink, can keep you in contact with the
lift without having to circle. Modern gliders don't give up much
straight ahead climbing ability when flown a bit above l/d max.
Qualifier- if you slow down so much that you climb to where you can't
read the clouds effectively, you have made an important mistake.
You ask good questions.
UH

On May 22, 10:02*am, Andy wrote:
On May 20, 7:47*pm, Ramy wrote:



This is theoratically correct, but I found out more often than not
that the lift right below cloudbase (keeping FAR clearance of course)
is stronger and more widespread than couple of thousands below, which
allows much faster speed without loosing altitude.

Ramy

Okay, I broke out the polar and did some simple math for a "typical"
scenario.

Take a cloud street that is 16 miles long with 4 knot average thermal
strength and 10 knot peak thermal strength.

Pilot A pulls back to 70 knots and climbs in the average lift (2.4
knot net climb rate). It takes him 14 minutes to reach the end of the
street and he has gained 3,360 feet.

Pilot B climbs in the strong core, taking 30 seconds to center and
achieving a 8.4 knot average climb rate thereafter (note the higher
sink rate for circling flight). After 5 minutes he has climbed 4,250
feet. He then cruises at 110 knots for 16 miles, giving up 890 feet in
the process. Both pilots arrive at the end of the cloud street at the
same time and altitude.

Conclusion: stopping to circle in a thermal weaker than 10 knots puts
you behind the pilot who climbs straight ahead.

Taking Ramy's point about stronger lift closer to cloudbase into
account, let's assume you find an average 5 knots after a circling
climb instead of 4 knots for climbing straight ahead. In this case you
need a minimum 8.3 knot thermal before stopping to circle makes sense.
If you assume 6 versus 4 knots average lift cruising closer to
cloudbase then you only need a 6.6 knot thermal - but that starts to
feel like a pretty strong thermal strength gradient with altitude.

This analysis doesn't take into account a slight true airspeed
advantage for the pilot who climbs first due to his higher average
altitude.

Overall, I think this confirms that it pays to avoid circling under a
cloudstreet for anything but the very strongest lift. *This is even
more true if you are heading into an upwind turnpoint.

9B

Andy,

Ok, I tried to take your scenario and put some numbers to it. I used
the polar for an LS-4 (no DG 300 numbers handy). I Assumed 4 knots of
lift along the 16 mile street and a 10 knot thermal at the end. The
glider starts at 3000 feet below the clouds and ends at cloud base at
the end of the street (similar to Reichmann). I added 20 seconds of
centering penalty and a 20% higher sink rate while thermalling.

Don't know if the table will get scrambled on most viewers but here is
the data. It shows that flying near MC speeds is optimum as long as
you can find the strong thermal ahead. If you expect to find a strong
thermal ahead don't slow down to minimum sink speeds. I think I will
use a MC speed of about (expected climb from thermal - average street
strength) as a good compromise MC setting to fly. In this case 10 - 4
= MC setting of 6 to fly.



MC miles/hr time minutes Average speed
45 14.99 64.05
50 14.53 66.06
55 14.14 67.89
0 60 13.80 69.56
1 68 13.34 71.96
2 76 13.18 72.84
3 84 12.62 76.05
4 90 12.33 77.86
5 94 12.18 78.80
6 98 12.07 79.55
7 104 11.95 80.35
8 112 11.87 80.85
9 118 11.87 80.88
10 124 11.90 80.66

TT

On May 26, 1:09*pm, Tim Taylor wrote:
On May 22, 10:02*am, Andy wrote:





On May 20, 7:47*pm, Ramy wrote:

This is theoratically correct, but I found out more often than not
that the lift right below cloudbase (keeping FAR clearance of course)
is stronger and more widespread than couple of thousands below, which
allows much faster speed without loosing altitude.

Ramy

Okay, I broke out the polar and did some simple math for a "typical"
scenario.

Take a cloud street that is 16 miles long with 4 knot average thermal
strength and 10 knot peak thermal strength.

Pilot A pulls back to 70 knots and climbs in the average lift (2.4
knot net climb rate). It takes him 14 minutes to reach the end of the
street and he has gained 3,360 feet.

Pilot B climbs in the strong core, taking 30 seconds to center and
achieving a 8.4 knot average climb rate thereafter (note the higher
sink rate for circling flight). After 5 minutes he has climbed 4,250
feet. He then cruises at 110 knots for 16 miles, giving up 890 feet in
the process. Both pilots arrive at the end of the cloud street at the
same time and altitude.

Conclusion: stopping to circle in a thermal weaker than 10 knots puts
you behind the pilot who climbs straight ahead.

Taking Ramy's point about stronger lift closer to cloudbase into
account, let's assume you find an average 5 knots after a circling
climb instead of 4 knots for climbing straight ahead. In this case you
need a minimum 8.3 knot thermal before stopping to circle makes sense.
If you assume 6 versus 4 knots average lift cruising closer to
cloudbase then you only need a 6.6 knot thermal - but that starts to
feel like a pretty strong thermal strength gradient with altitude.

This analysis doesn't take into account a slight true airspeed
advantage for the pilot who climbs first due to his higher average
altitude.

Overall, I think this confirms that it pays to avoid circling under a
cloudstreet for anything but the very strongest lift. *This is even
more true if you are heading into an upwind turnpoint.

9B

Andy,

Ok, I tried to take your scenario and put some numbers to it. *I used
the polar for an LS-4 (no DG 300 numbers handy). *I Assumed 4 knots of
lift along the 16 mile street and a 10 knot thermal at the end. *The
glider starts at 3000 feet below the clouds and ends at cloud base at
the end of the street (similar to Reichmann). *I added 20 seconds of
centering penalty and a 20% higher sink rate while thermalling.

Don't know if the table will get scrambled on most viewers but here is
the data. *It shows that flying near MC speeds is optimum as long as
you can find the strong thermal ahead. *If you expect to find a strong
thermal ahead don't slow down to minimum sink speeds. *I think I will
use a MC speed of about (expected climb from thermal - average street
strength) as a good compromise MC setting to fly. *In this case 10 - 4
= MC setting of 6 to fly.

MC * * *miles/hr * * * *time minutes * *Average speed
* * * * 45 * * *14.99 * 64.05
* * * * 50 * * *14.53 * 66.06
* * * * 55 * * *14.14 * 67.89
0 * * * 60 * * *13.80 * 69.56
1 * * * 68 * * *13.34 * 71.96
2 * * * 76 * * *13.18 * 72.84
3 * * * 84 * * *12.62 * 76.05
4 * * * 90 * * *12.33 * 77.86
5 * * * 94 * * *12.18 * 78.80
6 * * * 98 * * *12.07 * 79.55
7 * * * 104 * * 11.95 * 80.35
8 * * * 112 * * 11.87 * 80.85
9 * * * 118 * * 11.87 * 80.88
10 * * *124 * * 11.90 * 80.66

TT

Sorry found a sign error in my calculations. Here are the corrected
values:

MC miles/hr time minutes Average speed
45 14.99 64.05
50 14.53 66.06
55 14.14 67.89
0 60 13.80 69.56
1 68 13.34 71.96
2 76 13.25 72.46
3 84 12.90 74.43
4 90 12.75 75.27
5 94 12.70 75.57
6 98 12.69 75.68
7 104 12.71 75.54
8 112 12.82 74.88
9 118 12.95 74.11
10 124 13.12 73.16