Introduction — Page 1, Lesson 7

Let's start with the very foundation of this whole subject. I want to walk you through what an aeroplane actually is, at its most basic level, and the very first forces we deal with. Think of the primary requirements of an aircraft. Every single one of them has a specific job. First, you need a wing to generate a lift force — that's the upward force we'll talk about in a moment. Second, you need a fuselage to house the payload — that's the cargo, the passengers, the things the aircraft is actually carrying. Third, you need tail surfaces to add stability — keeping the aircraft pointing the right way. Fourth, you need control surfaces to change the direction of flight. And fifth, you need engines to make it go forward. Now, here's a key idea: all aircraft share these features, but the position of them varies from type to type. Why are wing plan shapes different? Why are wings sometimes mounted on top of the fuselage instead of the bottom? Why is the horizontal stabilizer sometimes mounted high on top of the fin rather than on either side of the rear fuselage? The answer is the core philosophy of this entire subject: every feature has a purpose and is never included merely for reasons of style. The designer configures each type of aeroplane in a specific way to obtain the performance required by the operator. Now let's get to the physics. An aeroplane, like all bodies, has mass. When the aircraft is stationary on the ground, it has only one force acting upon it: the force due to the acceleration of gravity. That force is its WEIGHT, and it acts vertically downward at all times. Let me show you that. Before an aeroplane can leave the ground and fly, that downward force of weight must be balanced by a force which acts upwards. That force is called LIFT. And here's the critical relationship: the lift force must be increased until it is the same as the aeroplane's weight. Not more, not less — equal. That's the balance we need for flight. So right now, we have two forces: weight acting down, lift acting up. In the next part of this chapter, we'll add thrust and drag to complete the picture. But for now, hold onto this: weight is always there, acting vertically downward, and lift is the force we generate to balance it.