Bob Kuykendall wrote:
Earlier, Kay Scott wrote:


Looking at sailplanes. Is a 15m LS6 really any better
than a 15m LS3?


Yes, no doubt about it in my mind.

The biggest difference is that the LS6 actually achieves 40:1, while
the LS3 just claims it.

I have to disagree with this statement. The LS3 certainly achieves 40:1,
my LS3 does and so did the one that Dick Johnson tested:

http://ssa.org/Johnson/25-1978-11.pdf

The interesting thing is that the LS3a and the LS3/17 didn't
seem to be able to achieve the same results.

Obviously the LS6 is better than the LS3 up in the very high speed
range and the LS6 can be flown over a wider range of wing loadings.

Of note, the LS3 uses the old FX67 profiles,
which are quite sensitive to bugs, rain, dust, and other real-world
elements. The LS6, on the other hand, uses FX81-series profiles, which
are more conservative but also more robust. The FX81s tend to maintain
more laminar flow under real-world conditions, and they also have lower
pitching moment and consequently less trim drag.

In practice the LS3 doesn't seem to be as sensitive as other gliders of
this era.
Is this trim drag as much of an issue for flapped gliders?


Earlier models LS6 have manual-connect controls and a somewhat hokey
aileron damper system retrofitted to combat flutter. Later models have
a neat mechanical mass-balance system and auto-connect controls.
However, at least one operator complains that later LS6s have more
aileron friction than earlier ones. This could be due to the switch
from stainless steel to mylar for the lower flaperon seal.

The LS3 autoconnects unlike the later LS3a and LS3/17, which have
separate flaps and ailerons. This feature comes at the expense of a ton
of mass balance lead on the flaperons.



Both are flapped and have 40:1 glide
slopes. In fact why does the LS6
have a better handicap than say a
Discus, when the Discus is 2 points
better in the glide?


My take on that is that it's because the LS6 flaps allow better
profile-to-speed optimization, and that the LS6 has a somewhat thinner
wing in T/C.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24


Greg O'Sullivan