On Monday, October 22, 2012 3:12:22 PM UTC-7, Bob Kuykendall wrote:
On Oct 22, 12:15*pm, Bob Whelan wrote:



This being RAS, take a look back at Dick Schreder's original HP-15...a failed

attempt to utilize extremely high aspect ratio to maximize performance. It

likely ran afoul of structural and aerodynamic considerations, mostly the

latter, I'd guess. The small chord almost certainly meant its airfoil (even if

laminarly executed) was operating outside the theoretical laminar bucket at

slow (thermalling) speeds due to Reynolds number effects, even without

considering profile accuracy. What's the most effective way to hurt average XC

speed?



Bob, I don't think that there were any particular structural issues

with the HP-15. As I understand it, Dick built it while he was in a

phase of experimenting with honeycomb cores. So it had thick skins for

bending stiffness and milled honeycomb core to give it shape--but no

wing ribs or discrete spar caps. The carrythrough consisted of a set

of knuckles bolted or riveted to the skin that joined to their

counterparts on the opposite wing.



As I recall, you are spot-on regarding its performance

characteristics. It went like stink in a straight line, but had huge

sink rates when slowed down and compelled to circle.



Thanks, Bob K.

Dick was years ahead of his time on the HP-15. I did a quick comparison to the Duckhawk.

Wing Area: HP-15 75 sq.ft.
Duckhawk 80 sq.ft.

Aspect Ratio: HP-15 33
Duckhawk 30

Empty Wt. HP-15 330 lb.
Duckhawk 390 lb.

Gross Wt. HP-15 600 lb.
Duckhawk 960 lb.

I suspect the airfoil was a significant part of the problem for the HP-15. I don't have any information on the percentage thickness of the profile, but given the materials it's likely to have been thicker than the Duckhawk.

Dick did some amazing things during a time without sophisticated CFD and carbon fiber.

Cheers,
Craig