On Jan 3, 9:00*am, Eric Greenwell wrote:
Darryl Ramm wrote:
On Jan 2, 10:52 pm, Allan wrote:
Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
just what you need for those high-speed wave flights!
But whats the L/D at 160 & 200 Knots? 10 & 5 ?

Allan

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've never had a Vne issue in thermal
soaring, even at 18,000', though I have been occasionally concerned
about it in strong lift approaching cloudbase. Even a great
cloudstreet is unlikely to have sustained lift that strong so if you
are keeping decent clearance from cloudbase you can usually let your
altitude vary rather than running up the airspeed. I could easily
imagine it being more of an issue in wave, particularly for those
folks running wave under IFR above 18,000'.

Wouldn't the 200 kt Vne be from sea level up to some limited altitude?
If so, you probably don't need to figure the L/D at 200 kts IAS for
wave flying - you'll be flying no faster than Va in wave above the
upper teens to low twenties (depending on how high the 200 kts is good
for), so 8 kts of up will be the strongest lift in which you'll be
able to hold altitude (versus 6-7 kts for, say, an ASW-27).

I will need to get used to the idea of flying that fast in a glider
that weighs 300 lbs empty.

9B