Lower-case "d" equals distance flown. Lower case "h" equals change in height. Capital "D" equals drag. L equals lift. a equals glide angle
From Trigonometry: tangent a equls h over lower case d.
From balance of forces: L cosine a plus capital D sine a equals W.
L sine a equals capital D cosine a.
Measure: height (h), distance (d), and weight (W).
Solve 3 equations in 3 unknowns for lift, drag, and glide angle.