Looks to me like an APIS 15 polar is pretty much identical to the LS4. The
APIS 13 has a slightly better L/D at lower speeds and slightly worse in the
60-100 mph range. So the 13 is awfully close, but the cost is not much less
than a 15, i.e. 8% less.

Don't know how the price compares to a new or used LS4 or how the APIS
actually flies, but on paper it looks very good. Polar is waay better than
the SparrowHawk, based on the info I've seen.
Wad.


If you think that a modern 13m design can match the LS4 in
performance, then by all means I think you should go on out there and
develop that glider! I know that it can be done; I'm just somewhat
skeptical that the result would be a viable commercial product.