364 FORMS Ol' KNKRG\' 6. What is the real significance of the various records which pilots have made? 7. Prepare a brief summary of the advances made by aviation since 1940, obtaining >c)ur material from the current literature. 8. Why is there such a lag between fundamental research and its practical application? 9. Discuss the relative merits of biplanes and monoplanes. 10. What are the advantages and disadvantages of rotary-wing airplanes? 11. In what respects have the huge expenditures on military aviation benefited civil aviation? 12. What are the possible advantages of liquid-cooled engines as compared with air-cooled engines? What type of engine is preferred today, and why? 13. W'hy should automobile engines be warmed up before starting the automobile? 14. What are airplane-engine superchargers, and what is their purpose? 15. What are the advantages and disadvantages of high-altitude flying? 16. Discuss the contribution of plastics to modern airplanes. 17. What are the advantages of neoprene gasoline tanks? 18. How may one become a member of the "Caterpillar Club"? 19. Discuss the various applications of parachutes.
UNIT V SECTION 8 FLYING AN AIRPLANE CONSISTS OF PROPERLY CON- TROLLING THE FORCES OF THRUST, DRAG, LIFT, AND GRAVITY Introduction. Aerodynamics is the study of the forces produced by the relative motion between the air and a soUd body. An airplane is a mechanically driven heavier-than-air craft, fitted with wings which support it in flight by the dynamic action of the air which results from the forward motion of the airplane relative to the air. The forward motion of the airplane is the result of a force, called the thrust, which is produced by the airplane propeller. The dynamic action of the air resulting from the forward motion of the airplane may be resolved into two forces, the lift and the drag. The force of gravity is a static force, i.e., it acts without any motion of the airplane. It is the purpose of this Section to study how the forces of thrust, drag, lift, and gravity are controlled so as to enable one to fly. The Thrust Is the Force Which Propels the Airplane. Birds use their wings to attain forward motion in the air as well as to maintain their position in the air. In the airplane these functions are separated; and the propeller, which is really a specialized wing, is used to maintain forward motion. In the helicopter, however, the propeller has the dual action of the wings of a bird. The propeller produces the force called the thrust in accordance with Newton's third law of motion, which states that to every action there is always an equal and opposite reaction. A rocket is propelled through the air by the thrust which the escaping jet of gases produces against the rocket. The backward force of a propeller against the air is what forces it forward. The propeller may be placed in front of the engine or behind it. In the first case the airplane is called a tractor, and in the second case it is called a pusher. 365