Or, to put it another way:
Thrust = 1
Weight = 4
Drag = 1/12th of 4, or 1/3
T - D = 2/3
Climb Angle = 2/3 divided by 4, = 1.67radians, or 16.7gradient
Dick W
For the mathematically minded this uses two approximations, that Cos of small angles is 1 and that the tangent of small angles is the same as the angle itself in radians.