National Geographic : 1943 Sep
They Sustain the Wings 347 U. S. Army Air Forces, Official Ten Men at a Time Study Compass Work in a Classroom on Wheels This contraption at Sheppard Field, Texas, never leaves the ground. In fact, minus an engine, it looks more like a stage plane of melodrama days. But to glider students it's highly useful, to show how flight control instruments are installed. Also, with it they learn how to compensate for compass errors. U. S. Army Air Forces, Official For Maximum Efficiency Propellers Must Be Free of Dents and Scratches Aided by his magnifying glass, a corporal at Chanute Field, Illinois, inspects a "prop." Nicks and dents are etched out. Bullets fired through the propeller blades give the mechanic practice in smoothing off jagged edges. Besides microscopes, a magnetic method of finding invisible interior cracks is also used (page 341).