Eric Greenwell wrote:
Greg Arnold wrote:

L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
headwind and you've got +5 knots of up in wave you won't care...
I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.

Darryl has it right - the limit for high speed wave flights is Vne, not
L/D. But, extrapolating from an ASW 27 B polar gives ~20:1 at 160
knots.
Attempting to extrapolate to 200 knots is pointless, so we'll have to
wait for Windward Performance to publish a curve.

Just to finish the thought - you only need 8 knots of lift to maintain
altitude at 20:1 and 160 kts.

I am skeptical about 20:1 at 160 knots. I think the best Dick Johnson
flight test was the ASH-26 at 9 pounds wing loading, and it was below
20:1 at 120 knots. A more realistic figure might be 10:1 at 160
knots, which would require 16 knots of lift to maintain altitude.

You can get the ASW 27 B curve from Schleicher's site and draw your own
line.


I am skeptical about the accuracy of that curve! Didn't they claim best
L/D of 48?




It's guess, because the curve only goes to 210 kph, but the curve
I drew "looks right", using the 55.6 kg/m2 line as the starting point.


Can you extrapolate that way? Just as unflapped ships suffer a
noticeable fall off in performance above 80 to 85 knots, flapped ships
must have a similar speed at which their wings aren't working very well
(120 knots?).


I'm sure it's not 10:1, but certainly between than 15:1 and 20:1.


When the Duckhawk comes out, we will put you 15 to 20 nm out over the
ocean at 6,000', and see if you want to fly at 160 knots towards the coast!


The
ASH 26 is not a good choice for comparison because it has the same
aspect ratio as the 27, and only goes to 45 kg/m2 (the 9 pounds you
mentioned).


It is the best data point we have, I believe.