That's me, aged 15, with an own-design glider which I named "Black Magic".

      I had devoured Ron Warring's book "Model Gliders" from cover to cover. One chapter showed how to determine angle of attack for minimum sinking speed. This calculation kept me occupied for a week, using my newly-acquired slide-rule. Several pages of work produced the unsurprising result of 3 degrees for the RAF32 wing section.

      The book said not-one word about how to ensure that the wing actually flew at this A of A.  There seemed to be a naive assumption that the direction of flight was always parallel to the horizontal datum line drawn on the plan. Sixty years later this misconception is still met with.