On Wednesday, November 29, 2017 at 10:35:10 AM UTC-8, Charlie M. (UH & 002 owner/pilot) wrote:

You want a 20' job, or an "aerodynamic" job?

Well now, there's a topic that can go on and on. In my direct experience, stuff that looks gawdawful at the 20-foot or even 10-foot level can perform great at the 0.004" level where it really counts for laminar flow. I've seen gliders where the reflection off the wing looked like some crazy funhouse mirror, where the leading edge waved fore and aft. But down in the boundary layer it is smooth and wave-free in the streamwise direction, and plenty close enough to the desired profile and camber line, and it works just fine..

And a lot of stuff that looks fantastic at the 10- and 20-foot level is actually disruptive at the .004" level. A good example of this is the crisp planform breaks on the latest generation of polyhedral gliders. They do look sharp and precise, but they can't be good for spanwise flow (air trying to sneak out and get all 420 with the tip vortex).

In order of importance, for most gliders I'd rank:

* Control surface seals (mylar, curtain, or combo)

* Wing waviness below 0.004" on top back to 60% chord, on bottom back to hinge line

* Cockpit exhaust provisions (keep cockpit below ambient so canopy leaks come inside, not outside)

* Leading edge contour for the forward 10% of chord

* Canopy fit on forward 1/3 of length

* Wing profile aft of 10% chord