The angle between the thrust vector and the positive x axis is α,
The drag: D = -|D|i +0j. The angle between the weight vector and the positive x axis is (270 - γ);
W = |W|(-isin γ- j cos γ).
The equilibrium conditions are
Substitute and collect like terms
Solve the equations for the terms in γ:
Take the ratio of the two equations
Divide top and bottom on the right by |D|.