Just had a quick look in the sailplane directory to compare the T53/Blanik !
T53b empty wt = 354kg/780lb
Blanket L13 empty wt = 292kg/644lb
I would guess much of the wt difference was in the wing design,big shame and missed opportunity there for slingsby,i think if they could have reduced the empty weight then it could have had sales potential esp usa/australia.
The T53 fuselage design (my opinion LOL) was much superior to the blanik,lets face it - for a fairly tall person the blanik rear seat was not a comfy place to be !!
As to the wing shape,slingsby did a fair bit of research/liason with american manufacturers...the T53 looks pretty much like a 'Hershey bar' type -built for ease of manufacture rather than form.
edit...could not get these links to work earlier,but ok now
http://www.google.co.uk/url?sa=t&sou...crcNauDK6JZoBQ
http://www.google.co.uk/url?sa=t&sou...9HAnSo11vQVOsQ
great cutaway showing why the wing was so heavy (how many ribs ? LOL) and why the airbrakes were so ineffective.
I loved the comment about the airbrakes being as good as a skylark !!...yeah right !! more in the standard libelle class I would say.