On Apr 26, 8:58*am, John Cochrane
wrote:
On Apr 26, 9:39*am, "Dan Marotta" wrote:





Thanks, Tim,

I know all these things. *This is sort of a mind exercise so let me try a
different approach... *I was curious if there's a point analagous to the
drag bucket where the L/D for a given speed would take a sudden dip given
higher wing loading. *I'm visualizing the polar curve taking a sudden trip
downward past a certain weight.

Yeah, I know... *When the wings break off!

I'm really having trouble putting my thoughts into words...

"Tim Taylor" wrote in message

....
On Apr 25, 7:38 pm, "Dan Marotta" wrote:

Is there a practical limit to wing loading?

I'm looking for aero dynamic information, not statements about max gross
weight. Can you load your glider up to the point that, even with strong
and
reliable lift, you're at a disadvantage to lighter ships?

I was just thinking of the old days when I read that some contest pilots
tried, or considered, using salt water for ballast because it's heavier.

For every condition there is an optimum wing loading. More is very
often not better. There are weight optimums just like speed optimums
for given thermal strength, thermal width, cloud streeting, and ridge
or wave conditions. Too often I have seen pilots put on too much water
because they falsely believe the old statements that more is better.

You can create models for the correct amount of water if you can
account for all the above factors. Simple models can look at just
thermal strength but the larger circling diameter can make a big
difference on achieved climb rates.

The more you can fly straight the more water is useful. If you are
flying classic thermals without streets then often less is better.

If you need maneuverability to work near ridges less is better also.

My view: For given conditions, performance is a smooth function of
wing loading. No sharp curves, drag buckets, or discontinuities. If
you add 1 lb/ft^2 you glide a few knots faster, but give up a few
hundred feet in the next thermal.

The biggest question is how much you can fly straight. There is a
discontinuity in the advantage of ballast when you can fly straight
without thermaling.

There is a maximum desirable wing loading. If the wings let you fly at
50 lbs / ft^2 you wound not want to fill up. *Designers make modern
gliders so that they carry enough water to win strong days at world
contests in strong conditions. Most of the time that is far more water
than you need.

Most pilots fly with too much water. They are hoping conditions get
better ahead. But they pay a price until it does, and it often
doesn't.

I've been in several contest flights with me empty, a gaggle full and
3 knot thermals. The water made no difference at all.

Filling up with water and flying too slowly removes much of the
advantage of water. If the gaggle is flying at 65 knots because nobody
wants to be first, then trying to climb at 3 knots with full water,
you will outfly them empty.

Where water really hurts is if you get low and have to core tight
thermals. Even if they are strong, you can waste a huge amount of time
here, then finally dump and magically core the lift. One more reason
that water is not as beneficial for isolated thermals as it is with
streets.

John Cochrane

As XX once said.......

"" its hard to find a garden hose at 3,000 agl and put more water
in!!!""

We do have dump valves! Its better to have and dump, than wish you
had more.

Now when to dump and what to dump to, will bring alot of hoop laaaa's
around the fireside chat that goes on and on and on.

# 711.