On Sunday, June 10, 2012 1:39:10 PM UTC-4, csonka istvan wrote:
The IGC HC of LS1c-d is 3 points lower than the LS1f (0.98-1.01). Why
is this differnece? The wings are the same, as I know. Does somebody
has any experiences with LS1c-d performance, compared to LS1f, Std.
Cirrus or ASW15? (Assuming more or less the same wingload).

Idaflieg data, as availble in the Thomas book on glider design, supports the difference. This was the subject of review by the US handicap subcommittee a couple of years ago. US handicap difference is 2.4% which reflects maybe a liyyle difference in the analysis. The difference in "opinions" is worth 6 pt/day.
FWIW
UH