On 2018/06/01 09:28, wrote:
Should be better than 45 after reprofiling, my 17m DG200, same airfoil is 45 factory, the 17m kestrel was 43, and the 19m was 44.

Hi Mike

Unfortunately when they built the 19m they did not understand
aerodynamics so well I suspect. So they added a metre of thick draggy
wing at the root, and left the relatively high lift wingtips in place.

So - what you get is lots of extra profile drag. Best I could get off
GPS traces on long final glides in winter when the air is nice and still
- a little under 1:46... Maybe it is that she is 40+years old (1971 was
a LOOONG time ago). Maybe I am pessimistic. With properly profiled
airfoil but without additional mylar seals on the flaps - only internal
seals. I can honestly claim 1:45 is an achievable glide ratio. On a good
day it is maybe 1 better. But I never counted on that. The single piece
canopy may improve the sealing enough to make a difference there - the
amount of noise the canopy generates indicates that it is a source of
significant drag.

Keith modified a T59D by reprofiling the entire wing, and removing the
outboard 1.5m on each side, and reprofiling that part with thinner,
lower incidence airfoil and polyhedral plus a winglet. That got the
owner more like 1:51 - but the cost to do it commercially would be
prohibitive.