Losing time in Cloud-Streets?

On May 26, 2:16*pm, Tim Taylor wrote:
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

Nice job Tim. At what speed do you get to top of lift before you
reach the 10-knotter?

The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not.

I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.

My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.

9B

On May 27, 4:28*am, Nine Bravo Ground wrote:
On May 26, 2:16*pm, Tim Taylor wrote:





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

Nice job Tim. *At what speed do you get to top of lift before you
reach the 10-knotter?

The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not.

I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.

My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.

9B

Just as a hypothetical, I figured out how much "centering loss" you
might experience rolling into a 10-knot thermal. If I assume 1/3 of
the time you get 10 knots from the first turn, 1/3 of the time you
spend a turn at 2 knots and a turn at 5 knots before centering and 1/3
of the time you burn a circle on a thermal that turns out not to be
there, then the expected centering loss is the equivalent of 40
seconds circling at zero sink.

9B

On May 27, 8:25*am, Nine Bravo Ground wrote:
On May 27, 4:28*am, Nine Bravo Ground wrote:





On May 26, 2:16*pm, Tim Taylor wrote:

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

Nice job Tim. *At what speed do you get to top of lift before you
reach the 10-knotter?

The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not.

I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.

My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.

9B

Just as a hypothetical, I figured out how much "centering loss" you
might experience rolling into a 10-knot thermal. *If I assume 1/3 of
the time you get 10 knots from the first turn, 1/3 of the time you
spend a turn at 2 knots and a turn at 5 knots before centering and 1/3
of the time you burn a circle on a thermal that turns out not to be
there, then the expected centering loss is the equivalent of 40
seconds circling at zero sink.

9B

Andy,

I agree with BB, Ramy and your comments. Everything depends on where
you are flying and the strength and variability of the conditions.
Out west at Logan or Parowan you can risk going faster and lower
beneath the cloud streets, at Uvalde I learned the hard way not to
drop more than 2000 feet below the clouds or risk not getting back up
or if you do very slowly (I had one save from 400 feet agl). The best
lift was within 1000 feet of cloudbase on most streets.

I will work on refining the model when I get time so I can run more
scenarios easily. The general things to take aways from the exercise
is that slowing to minimum sink is not usually a good idea unless you
really need to climb, best l/d or slightly faster is much better.
That being slightly conservative costs very little on potential speed
and reduces the risk factor of not finding that next big thermal. The
difference of flying at MC 4 to MC 7 is very little and you lose much
less altitude at the lower MC to stay in the stonger lift and
connected to the clouds.

Tim Taylor wrote:
On May 27, 8:25 am, Nine Bravo Ground wrote:
On May 27, 4:28 am, Nine Bravo Ground wrote:





On May 26, 2:16 pm, Tim Taylor wrote:
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
Nice job Tim. At what speed do you get to top of lift before you
reach the 10-knotter?
The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not.
I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.
My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.
9B
Just as a hypothetical, I figured out how much "centering loss" you
might experience rolling into a 10-knot thermal. If I assume 1/3 of
the time you get 10 knots from the first turn, 1/3 of the time you
spend a turn at 2 knots and a turn at 5 knots before centering and 1/3
of the time you burn a circle on a thermal that turns out not to be
there, then the expected centering loss is the equivalent of 40
seconds circling at zero sink.

9B

Andy,

I agree with BB, Ramy and your comments. Everything depends on where
you are flying and the strength and variability of the conditions.
Out west at Logan or Parowan you can risk going faster and lower
beneath the cloud streets, at Uvalde I learned the hard way not to
drop more than 2000 feet below the clouds or risk not getting back up
or if you do very slowly (I had one save from 400 feet agl). The best
lift was within 1000 feet of cloudbase on most streets.

I will work on refining the model when I get time so I can run more
scenarios easily. The general things to take aways from the exercise
is that slowing to minimum sink is not usually a good idea unless you
really need to climb, best l/d or slightly faster is much better.
That being slightly conservative costs very little on potential speed
and reduces the risk factor of not finding that next big thermal. The
difference of flying at MC 4 to MC 7 is very little and you lose much
less altitude at the lower MC to stay in the stonger lift and
connected to the clouds.



I made a summary of Reichmann for the simple-minded (i.e. me) a few
years ago.

MC 0 = Bad, unless you're struggling to stay airborne.

The penalty for flying MC 1, as opposed to what your flight computer
says, is pretty small, and the gains in range are big in comparison.

As a rule of thumb, flying 1/2 the MC recommended by the theory/computer
is a good strategy.

This was for individual thermals, not streets, but the calculations
above suggest it works for streets as well.

On May 27, 3:25*pm, Tim Taylor wrote:
On May 27, 8:25*am, Nine Bravo Ground wrote:





On May 27, 4:28*am, Nine Bravo Ground wrote:

On May 26, 2:16*pm, Tim Taylor wrote:

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

Nice job Tim. *At what speed do you get to top of lift before you
reach the 10-knotter?

The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not.

I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.

My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.

9B

Just as a hypothetical, I figured out how much "centering loss" you
might experience rolling into a 10-knot thermal. *If I assume 1/3 of
the time you get 10 knots from the first turn, 1/3 of the time you
spend a turn at 2 knots and a turn at 5 knots before centering and 1/3
of the time you burn a circle on a thermal that turns out not to be
there, then the expected centering loss is the equivalent of 40
seconds circling at zero sink.

9B

Andy,

I agree with BB, Ramy and your comments. *Everything depends on where
you are flying and the strength and variability of the conditions.
Out west at Logan or Parowan you can risk going faster and lower
beneath the cloud streets, at Uvalde I learned the hard way not to
drop more than 2000 feet below the clouds or risk not getting back up
or if you do very slowly (I had one save from 400 feet agl). *The best
lift was within 1000 feet of cloudbase on most streets.

I will work on refining the model when I get time so I can run more
scenarios easily. *The general things to take aways from the exercise
is that slowing to minimum sink is not usually a good idea unless you
really need to climb, best l/d or slightly faster is much better.
That being slightly conservative costs very little on potential speed
and reduces the risk factor of not finding that next big thermal. *The
difference of flying at MC 4 to MC 7 is very little and you lose much
less altitude at the lower MC to stay in the stonger lift and
connected to the clouds.

Yup,

It was a little while back that I realized that speed in soaring
contests mostly has to do with the pilot's ability to estimate
probabilities. How fast or slow you fly in cruise matters little
within a broad range. How well you thermal matters only a bit. The
thing that takes you to the next level is being able to answer a
simple question over and over again "if I fly straight ahead on course
right now instead of circling, will I find a better thermal before I
get desperate?" The great pilots know when to press on and when to
stop and climb.

9B

On May 28, 2:42*am, Andy wrote:
On May 27, 3:25*pm, Tim Taylor wrote:





On May 27, 8:25*am, Nine Bravo Ground wrote:

On May 27, 4:28*am, Nine Bravo Ground wrote:

On May 26, 2:16*pm, Tim Taylor wrote:

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

Nice job Tim. *At what speed do you get to top of lift before you
reach the 10-knotter?

The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not.

I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.

My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.

9B

Just as a hypothetical, I figured out how much "centering loss" you
might experience rolling into a 10-knot thermal. *If I assume 1/3 of
the time you get 10 knots from the first turn, 1/3 of the time you
spend a turn at 2 knots and a turn at 5 knots before centering and 1/3
of the time you burn a circle on a thermal that turns out not to be
there, then the expected centering loss is the equivalent of 40
seconds circling at zero sink.

9B

Andy,

I agree with BB, Ramy and your comments. *Everything depends on where
you are flying and the strength and variability of the conditions.
Out west at Logan or Parowan you can risk going faster and lower
beneath the cloud streets, at Uvalde I learned the hard way not to
drop more than 2000 feet below the clouds or risk not getting back up
or if you do very slowly (I had one save from 400 feet agl). *The best
lift was within 1000 feet of cloudbase on most streets.

I will work on refining the model when I get time so I can run more
scenarios easily. *The general things to take aways from the exercise
is that slowing to minimum sink is not usually a good idea unless you
really need to climb, best l/d or slightly faster is much better.
That being slightly conservative costs very little on potential speed
and reduces the risk factor of not finding that next big thermal. *The
difference of flying at MC 4 to MC 7 is very little and you lose much
less altitude at the lower MC to stay in the stonger lift and
connected to the clouds.

Yup,

It was a little while back that I realized that speed in soaring
contests mostly has to do with the pilot's ability to estimate
probabilities. How fast or slow you fly in cruise matters little
within a broad range. How well you thermal matters only a bit. The
thing that takes you to the next level is being able to answer a
simple question over and over again "if I fly straight ahead on course
right now instead of circling, will I find a better thermal before I
get desperate?" The great pilots know when to press on and when to
stop and climb.

9B- Hide quoted text -

- Show quoted text -

Expanding on your thought.
Right and left decisions are much more important than speed to fly
because of energy lines as well as improving the probability of
reduced sink and hopefully, that great circling climb.
I don't hear very many pilots I consider to be really good worrying
about how fast to fly, but they ALL pay attention to where to fly.
UH

If anyone has a lot of time on their hands, the data from the recent
Mifflin Contest day 4 would make for some fascinating empirical
review. There was a single cloudstreet (super highway) running from
about the SW end of Nittany Mountain up to about Nisbet. Some guys
took a slower climb at the beginning of the street to climb all the
way up to cloudbase. Others "bumped up". Still others ran then
circled. I strongly believe that the biggest two determinants of the
speed in that section we

a. Which part of the street you followed (i.e. the lateral decisions)
b. Which climb you took to get connected.

Link to the raw files is he
http://www.ssa.org/members/contestre...-05-21-ALL.zip

If someone wants to crunch the numbers, I can help by giving you some
sample flights to show the area/time in question.

P3




On May 28, 7:56*am, wrote:
On May 28, 2:42*am, Andy wrote:





On May 27, 3:25*pm, Tim Taylor wrote:

On May 27, 8:25*am, Nine Bravo Ground wrote:

On May 27, 4:28*am, Nine Bravo Ground wrote:

On May 26, 2:16*pm, Tim Taylor wrote:

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

Nice job Tim. *At what speed do you get to top of lift before you
reach the 10-knotter?

The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not..

I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.

My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.

On May 28, 4:56*am, wrote:
On May 28, 2:42*am, Andy wrote:





On May 27, 3:25*pm, Tim Taylor wrote:

On May 27, 8:25*am, Nine Bravo Ground wrote:

On May 27, 4:28*am, Nine Bravo Ground wrote:

On May 26, 2:16*pm, Tim Taylor wrote:

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

Nice job Tim. *At what speed do you get to top of lift before you
reach the 10-knotter?

The curves are pretty flat on the slow end down to just above best L/D
speed (say Mc=1). Also notice that once you get to 3 knots on the
McCready there is only 13 seconds of difference between the best and
worst times up to Mc=9. That means you MUST center a thermal on the
first circle to make it worthwhile to stop. Your 20% higher sink for
circling flight is about right for 25-30 degrees of bank - at 45
degrees the sink rate is around 70% higher, so the thermals would have
to be fat AND easy to core. More typically I find that around 1/3 of
the time when I turn in a thermal I wish I hadn't and another 1/3 of
the time it takes me a few turns to center it - that's on a good day.
I don't know if that nets out to a 20 second expected loss or not..

I'm normally pickier about stopping to circle at the beginning of the
street versus when I'm getting towards the end - though I am now
reconsidering this view. Higher TAS with altitude and likely stronger
lift closer to cloudbase would argue for climbing up early rather than
late.

My -27 is a little better on the run than my old LS-4 which I think
biases the optimal a bit more to straight ahead climbing over
circling. My flying style has certainly migrated in that direction.

As a rule of thumb, flying 1/2 the MC recommended by the theory/
computer
is a good strategy.

If flying 1/2 the Mc recommended by "theory" is right, that means you
have the wrong theory! Understanding a correct theory is even
better.

Lowering the Mc setting to account for centering time, bottom to top
average rather than best surge of lift, need to stay connected to the
clouds, character of sky ahead, altitude remaining, number of options
left, etc. etc. is all part of good theory.

This does not mean it ever makes sense to cruise at a setting lower
than the weakest lift you would currently take, which is a common
mistake. If you're cruising at Mc 1, but rejecting smooth easy to core
3 knot (bottom to top) thermals while waiting for the 5 knotter, you
would do better by cruising at Mc 2 and taking the occasional 3
knotter, but not going too high in it.

As UH emphasizes, all this is third order. Flying in the right place
and altitude band is the key decision!

John Cochrane
BB

John Cochrane wrote:
As a rule of thumb, flying 1/2 the MC recommended by the theory/
computer
is a good strategy.

If flying 1/2 the Mc recommended by "theory" is right, that means you
have the wrong theory! Understanding a correct theory is even
better.

Lowering the Mc setting to account for centering time, bottom to top
average rather than best surge of lift, need to stay connected to the
clouds, character of sky ahead, altitude remaining, number of options
left, etc. etc. is all part of good theory.

This does not mean it ever makes sense to cruise at a setting lower
than the weakest lift you would currently take, which is a common
mistake. If you're cruising at Mc 1, but rejecting smooth easy to core
3 knot (bottom to top) thermals while waiting for the 5 knotter, you
would do better by cruising at Mc 2 and taking the occasional 3
knotter, but not going too high in it.

As UH emphasizes, all this is third order. Flying in the right place
and altitude band is the key decision!

John Cochrane
BB

I don't think I made it clear that I was translating into a rule of
thumb for the average pilot (say, me). I've read your paper, and am
convinced, but translating that into my own flying requires a precision
that I just don't have.

So for my purposes I have two options:

Blindly follow the PDA. This would work if I did it, I guess, but
distractions (ooh, shiny!), inattention, picking the wrong route, etc
mean I don't.

Work out a (an?) heuristic which approximates the theory. For me, that's
to take the general reading on my averager during the last thermal
(well. more accurately the next thermal I would accept, but if that part
of the day is consistent the last thermal will do), and then estimate
the relevant MC to fly to the next thermal.

My achieved climb is probably 2/3 of what I see on the averager (UK,
lower cloudbases than many places), so I could choose that as my MC
figure. However, I also know from reading the theory that the difference
in achieved speed over the ground from flying a little faster or slower
is a few percent (2-5).

Thus if I fly half what I saw on the averager, I'm close to (though
below) the optimum speed, but have extended my range. Or, to put it
another way, I'm flying less than 5% slower than someone who can fly to
the theory, but giving myself a larger margin to compensate for the
errors I know I will make.

This is not a strategy for winning contests, but it works quite well for
completing the task. It's also pretty simple in the UK because a day
when I see 6kt consistently on the averager is execptional. Thus I only
need to memorise four speeds to fly (MC 0-3) and remember how to divide
by 2.