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References to Aeronautical Concepts
Presented in Countdown to Flight!

Page(s)	Aeronautical Concept(s) Presented
18	Lilienthal's research used wing with slight bulge on the top front of the wing, curving gently toward the back controlled glider by shifting body weight to move the center of gravity and keep in balance
15 - 20	Brief history of flight that discusses the knowledge that had been acquired up until 1897. This was some of the information that the Wright Brothers received.
22	The brothers' solution to balance the wing lift was to construct a smaller, flat, horizontal control surface that could be raised or lowered in front of the wings. It was called a "horizontal rudder" and worked like an elevator. Its purpose was to control the pressure of air as it moved along the wings. This would help maintain the front-to-back equilibrium. To maintain the side-to-side equilibrium, the brothers decided on "wing warping" in which the wingtips would be twisted, one up and the other down, to counterbalance any change in the air pressure.
29 - 30	Changed the way the wings were mounted on the fuselage--not straight out so that they formed a "V" shape. Problem with the rapidly changing center of air pressure under the wings. Using a flat wing, the center of pressure moves forward as its angle to the wind is decreased. When the wing is horizontal and parallel to the airflow, the center of air pressure is on the leading edge. When the wing is curved, the center of air pressure moves forward as the wing angle decreases until it reaches a critical point, then it starts to move backwards. When the center of air pressure moves behind the aircraft's center of gravity, the aircraft nose-dives.
29 - 30	They improved wind resistance by placing the pilot in a prone position.
36	The discovery of the stalling angle. As the speed of the glider slowed, the pilot increased the wing angle to compensate and maintain lift. However, at a critical point when the wing angle was very steep, the airflow was insufficient for lift.
38 - 39	Conducted wind tunnel tests to determine optimum curvature of the wing as it relates to lift.
45	One movable, vertical rudder at the rear of the aircraft would give improved control during turns.
50	Propeller Work Propeller blades are airfoils. A turning propeller blade creates an increase in the air pressure behind it. This pushes the propeller toward the lower air pressure area. As the speed of the propeller's forward movement accelerates, the difference between air pressure in front and behind decreases. This decreases the thrust. They needed to be able to maintain the thrust to keep the aircraft airborne.