Design Question: Drag, Re, Cl, etc

[green66]

Hi All,

Design / setup question:

I'd like to ensure that my glider flies fast enough to ensure that its Re is above the point where the drag bucket starts falling apart, or where the polars rapidly shift rightward (increasing drag) with decreasing Re.

The plane isn't designed yet, so I'm open to "anything."

If the plane is very lightly-loaded (assume that it can't fly fast enough unballasted), would a preferred approach be to:

1) Add ballast until the plane does fly fast enough, above minimum desired Re, or
2) Increase speed by reducing Cl (provided flight is still within the drag bucket) by lowering the angle of attack via trim or decalage / incidence adjustment, or
3) Use an airfoil having a lower Cl in the middle of its drag bucket?, or at the tangent point representing best L/D?, or
4) Turbulate the wing with trip strips, zigzags, etc. to mitigate or delay separation, and don't worry about flying too slowly, or
5) Some combination of above, or another concept altogether?

Any advice is appreciated and, of course, some supporting rationale would be helpful.

TIA

[Ollie]

Select the airfoil(s) to perform at the size and minimum weight you have in mind. The PC Soar program will allow you to compare performance of your candidate design(s) with other configurations. See:
http://my.athenet.net/~atkron95/pcsoar.htm

Design the structure to be able to take the loads associated with the maximum ballasted wing loading and airspeeds you have in mind.

Dr. Mark Drela has designed airfoils whose performance are taylored to the requirements of the local chord and minimum airspeed of a number of lightly loaded models from mosquito hand launch to 130 inch span. These airfoils and wing designs are the pinacle of the designers art and science. The structural designs have the best strength to weight ratios I know of. You should study his designs and incorporate them into your own efforts. See:
http://www.charlesriverrc.org/articles.htm

There are links to the Yahoo discussion group for the Allegro Lite and many other of Dr. Drela's designs. Join the group and read Dr. Drela's archived messages to the group. This constitutes the best technical information available to modelers.