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

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