On 10/22/2012 5:25 PM, Craig Funston wrote:
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

Bob

I goofed including the "structural" comment...but at least I tried to "mostly"
lay the blame on the "aerodynamic" part! And thanks for the structural
methodology fill-in...all completely unknown to me, prior. (Sounds like an
amazingly simple wing, in structural terms, too. As I'm sure you well know,
it's relatively easy to design/engineer complex things...more difficult to
keep things simple.)

I agree with Craig's assessment of Dick Schreder's doing "some amazing
things...". IMO he was one of those "once in a generation" geniuses, blessed
with an amazing mind, far-ranging mechanical competence/expertise, and obvious
piloting skills, not to mention excellent business skills. Truly a renaissance
man, in our field!

As a former owner of an HP-14, I never had any qualms about its structural
integrity, and the ship remains airworthy today (though not regularly flown in
the past few years). More generally, I know of only 3 HP's that fell prey to
structurally-based problems: the one-off HP-7; the original HP-12; and an
Australian-registered HP-14. In my mind, none of the accidents can be
attributed to any fundamental structural design issue. In short, I think
Schreder's design body of work as measured by the record of the large fleet of
homebuilts he helped create have a heckuvan impressive structural safety
record. Just wanna be clear on this point...

Bob - apologies for contributing to thread creep - W.