Bob Kuykendall wrote:

Going forward, I propose that if we're going to be tossing a lot of
best L/D claims around, that we restrict ourselves to tested, verified
best L/D performance values, for example the idaflieg or Johnson
results. Otherwise I'm just going to have to join the Liar's Dice game
and claim a patently unobtainable 50:1 for the HP-24. And I'd like to
think of myself as a more honest person than that.

How about the L/D ten years later after 1000 hours of exposure in the
sun, 300 assemblys by trained monkeys, blowing dust and sand over the wings,
and repeatedly forcing the canopy and gear up and down?

I think there are more interesting questions than just some L/D figure.
Does polyurethane keep airflow better after years of the conditions
I just described than other finishes? How about wing flexing causing
cracks? Do longer wings inevitably mean more cracks unless they get
another $10k worth of finishing?

Is a side opening canopy going to deform (like our L-13 canopy)
over the course of many years? How heavy/sturdy does a canopy
frame need to be to maintain it's shape (I remember watching Bob
look at the HP canopy frame matching to the body with a careful eye)?

And who sells a glider that has parts that don't fit flush with
the disclaimer "in a year or two the parts will stretch and fit perfectly"?

So I personally don't look too hard at the L/D by itself.
The stall speed, the 80 knot sink speed, the possibility of ballast,
and the tradeoffs of flaps vs. no flaps and how this is integrated,
and retract gear, seem to be better indicators than some number.

A glider with 1000+ hours, no refinish or new parts since manufacture,
and then a flight test, is what I'm talking about. If it beats
350 fpm sink at 80kts, and stalls under 35kts at MGW, then it's
time to move on and ask about other flight characteristics
(stall/spin like SZD 50-3 and tricky takeoffs like PIK-20).

In this sense the World Class concept I think was apt, because
the goal was not L/D (perhaps with the knowledge that
waviness and rough handling would negate the cost put into a
high L/D anyway).

--

------------+
Mark J. Boyd