The Balance between "% Circling" and "MacCready Speed to Fly"

On Jul 5, 5:33*am, Papa3 wrote:
On Jul 4, 10:06*pm, Nine Bravo Ground wrote:



Overall, you need to set your cruise based on McCready for your
expected ACTUAL climb rate, including centering time and other
considerations such as changes in climb rate at the top or bottom of
the climb (Cochrane explains this pretty well in his papers) -
different pilots estimate this in different ways, some computers give
bottom-to-top averages as well. *The net effect is slower climb rates
than you might otherwise estimate based on staring at you 30-second
averager.

9B

Just a quick note on this point. *I've been informally checking with
pilots for several years after flights on our local DIY contest here
to calibrate the actual conditions against my weather forecasts.
Often times, I'll hear that it was a "great day - I was hitting
5-6kts". * Post flight analysis of several traces reveal that achieved
climbs were more like 3-4kts at best. *It's very clear that we don't
do a great job of accounting for our centering losses and hanging in
for too long once the lift tails off. By the way, * in the good old
days before flight recorders, it seems that lift was a lot stronger.
Maybe it's weight of the FRs that's slowing things down :-)

I think I know where most of the weight changes in my ship have come
from...

This has been discussed before, but bears mentioning in this context:
It is not really worth spending much attention on the speed director
of your vario/computer. It takes a fair amount of attention that is
far better spent on race strategy and tactics. This applies both to
setting the McCready for general speed to fly and chasing the speed
director for localized lift/sink.

I tend to fly three speeds - 80-85 knots for "normal" conditions,
90-95 knots if it is super strong and consistent with clouds and
streeting and 70-75 knots if it is weak, I need a long glide or I am
low (this is all dry - add 5-10 knots for water). This is pretty
consistent for most racing pilots I know. Best L/D for my ship is 60
knots so there is no point in ever flying less than 70 (McCready 1).
There just isn't that much difference in glide angle (L/D of 45
instead of 47 on the factory polar) so slowing down by the additional
15% is just giving speed away. Similarly, the knee in the polar is
somewhere around 85 knots, so it has to be really strong to motivate
me give away altitude at a higher rate.

9B

Andy, you're a Western USA pilot with an ASW-28, aren't you? The OP is
an Eastern USA pilot - he might be better off using 10 kts less for
each condition than you do (adjusting downwards for his ship, too, if
needed). Also, I fly best L/D in the East in my LS8 when things get
desperate, as quite often we're in 0 sink conditions. Flying at
MacCready 1 at 70 kts like you would be a great way to outland, here.

-John

On Jul 5, 12:31 pm, Andy wrote:
I tend to fly three speeds - 80-85 knots for "normal" conditions,
90-95 knots if it is super strong and consistent with clouds and
streeting and 70-75 knots if it is weak, I need a long glide or I am
low (this is all dry - add 5-10 knots for water). This is pretty
consistent for most racing pilots I know. Best L/D for my ship is 60
knots so there is no point in ever flying less than 70 (McCready 1).
There just isn't that much difference in glide angle (L/D of 45
instead of 47 on the factory polar) so slowing down by the additional
15% is just giving speed away. Similarly, the knee in the polar is
somewhere around 85 knots, so it has to be really strong to motivate
me give away altitude at a higher rate.

On Jul 5, 1:09*pm, jcarlyle wrote:
Andy, you're a Western USA pilot with an ASW-28, aren't you? The OP is
an Eastern USA pilot - he might be better off using 10 kts less for
each condition than you do (adjusting downwards for his ship, too, if
needed). Also, I fly best L/D in the East in my LS8 when things get
desperate, as quite often we're in 0 sink conditions. Flying at
MacCready 1 at 70 kts like you would be a great way to outland, here.

-John

On Jul 5, 12:31 pm, Andy wrote:



I tend to fly three speeds - 80-85 knots for "normal" conditions,
90-95 knots if it is super strong and consistent with clouds and
streeting and 70-75 knots if it is weak, I need a long glide or I am
low (this is all dry - add 5-10 knots for water). This is pretty
consistent for most racing pilots I know. Best L/D for my ship is 60
knots so there is no point in ever flying less than 70 (McCready 1).
There just isn't that much difference in glide angle (L/D of 45
instead of 47 on the factory polar) so slowing down by the additional
15% is just giving speed away. Similarly, the knee in the polar is
somewhere around 85 knots, so it has to be really strong to motivate
me give away altitude at a higher rate.

Fair point.

I fly an ASW-27B in the west today, but much of my early career
(1974-85) was flying in the mid-atlantic and northeast.

I agree that if you are flying in 1-2 knot lift in the east you will
cruise slower than for 4-5 knots in the west - for a whole bunch of
reasons. That said, I don't think you gain much flying best L/D (in
my ship at least) versus Mc=1.0. Two points on L/D just isn't worth
the speed loss. And if I'm not mistaken, part of the question was
about flying even slower than best L/D (50 kts was mentioned). I've
come to believe that how you handle "survival mode" is key to doing
well on sketchy days. Part of that is not giving up - keep making
forward progress while you search for the best available lift.

9B

I agree with you that 50 kts is too slow (the OP said he went that
slow sometimes between thermals, and slowed "waaay down" if there were
no landable fields). I also agree that one shouldn't give up, and keep
on making forward progress while searching for lift (I learned that
lesson the hard way, on several occasions).

I fly with a friend who has an ASW-27B, and he does tend to go faster
than I when we're in trouble. He explains it as "the ship just doesn't
like to go slow". It may be that I'm being too conservative - and
since you (and he) have a whole lot more experience than I, perhaps
this is another lesson I should take to heart...

-John


On Jul 5, 8:12 pm, Andy wrote:
Fair point.

I fly an ASW-27B in the west today, but much of my early career
(1974-85) was flying in the mid-atlantic and northeast.

I agree that if you are flying in 1-2 knot lift in the east you will
cruise slower than for 4-5 knots in the west - for a whole bunch of
reasons. That said, I don't think you gain much flying best L/D (in
my ship at least) versus Mc=1.0. Two points on L/D just isn't worth
the speed loss. And if I'm not mistaken, part of the question was
about flying even slower than best L/D (50 kts was mentioned). I've
come to believe that how you handle "survival mode" is key to doing
well on sketchy days. Part of that is not giving up - keep making
forward progress while you search for the best available lift.

On Jul 5, 1:09*pm, jcarlyle wrote:
Andy, you're a Western USA pilot with an ASW-28, aren't you?

No, that's the other Andy (me). We usually sign with our contest
numbers but if we don't you can check the email address.

Another factor related to this discussion is how long to hold onto
water ballast when caught in weak conditions. I tend to dump early to
get up and going again while others tend to hold onto ballast at all
costs in case they need it later.

Andy (GY)

On Jul 11, 6:19*am, Andy wrote:
On Jul 5, 1:09*pm, jcarlyle wrote:

Andy, you're a Western USA pilot with an ASW-28, aren't you?

No, that's the other Andy (me). *We usually sign with our contest
numbers but if we don't you can check the email address.

Another factor related to this discussion is how long to hold onto
water ballast when caught in weak conditions. *I tend to dump early to
get up and going again while others tend to hold onto ballast at all
costs in case they need it later.

Andy (GY)

Other Andy (9B) he

I've done the math on the water ballast question. The interesting
case is a save scenario (which is what I think you are driving at),
otherwise it's simply a wing loading optimization question where less
than 2-3 knots achieved climb wet argues for going dry.

In the save scenario the factors that matter a

1) How strong the save climb is (slower argues for dumping).
2) How high you have to climb in the save to be able to reach the next
"typical" thermal (higher argues for dumping).
3) What the expectation is for climb rate post-save to finish (weaker
argues for dumping).
4) How far it is to the finish (closer argues for dumping).

The decision to hold ballast versus dumping basically involves trading
off the time lost in the save climb versus the time gained with a
faster cross-country speed post-save. If conditions are expected to
be relatively strong later and you are relatively early in a long
flight it is more likely to pay to hold the ballast. If you are
barely gaining altitude in a weak thermal with ballast on board and
you are closer to the finish you are much better off dumping.

In most of the scenarios I've run you have to have 50-75 miles left to
go to make it worth holding your water (keep in mind that on a MAT or
TAT if you have gotten in a hole you may want to extend your flight so
it might not be hard to hit that threshold).

The analysis also assumes no difference in thermal strength for a
ballasted versus dry turn radius (i.e. considering only the inherent
glider turning sink rate difference wet versus dry). If the thermals
are harder to core wet then it becomes nearly impossible to find a
case for holding your water through the save - the lost time getting
back up is just too much to overcome.

9B