On 4/26/2012 8:39 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.






If I'm accurately understanding what you're pondering, I think you're asking
if there is (are) any physical reason(s) to expect that increasing wing
loading for a given glider will ultimately 'uncover' any presently 'generally
unconsidered' gotchas that will result in 'something like a laminar airfoil's
drag bucket effect' on the glider's polar.

My short answer: "Yes."

Two aerodynamic possibilities: 1) Reynolds number effects (which, arguably,
make laminar flow airfoils possible in the first place...and would eventually
- because of increasing glide speed necessary to support the increasing weight
- result in breakdown of presently-existing laminar flow runs), and 2) mach
effects.

The former might appear as a glider-based (as distinct from a
wing-profile-based) drag increase, while the latter would take us back to
polar-detectable Chuck Yeager days. The time for swept wing sailplanes may be
at hand!

Bob W.

P.S. The operational Me-163B (arguably a non-laminar glider optimised for
assisted climb/speed over thermalling had operational wing loadings varying
from ~20-psf empty to 45-psf full-up; its operational max speeds ranged from
515 mph at sea level to ~600 mph between 10,000 and 40,000 feet. No
thermalling pireps in any of my sources...