Wind-tunnel tests of wing flaps suitable for direct control of glide-path angle
This is a 1936 NACA technical report of wind-tunnel tests on wing flaps for controlling glide-path angle, a serious engineering document issued by the NASA Technical Reports Server for aeronautical researchers and aircraft designers. Its pictures are plotted graphs and a diagram: lift against drag curves for several flap deflections, pitching moment against angle of attack, and a small contour map of values across a grid, all in plain black linework that a designer could use for chart styling or technical diagram reference.
