Power Over the Forces

Power Over the Forces

In level cruise flight, the force of thrust is equal to the force of drag and the force of lift is equal to the force of weight (gravity). The plane is in a state of equilibrium, sort of like an aerodynamic cruise control. In order to go up or down the balance of the forces must be momentarily unbalanced. To go up, the plane must be pointed up. But increasing the up angle of the wing adds drag, which means that thrust must be added to balance the forces. Just like a car climbing a hill, a plane must get more power or it will slow to a stop. The plane must be pointed down to go down. Decreasing the wing angle also decreases drag, and power must be reduced to rebalance the forces. Just like your car, your plane will exceed the speed limit if you don’t let off the accelerator (called a throttle on a plane) during descent. Once you establish a steady climb or a steady decent, the forces are balanced again.

Summary of Climbing and Descending

  • To go higher, raise the nose (increase the wing angle) and add power.
  • To go lower, lower the nose (decrease the wing angle) and reduce power.

In order to go faster or slower the forces must, once again, be rebalanced. Adding thrust causes you plane to speed up but it also increases lift. This means that if you want to go faster in level flight (hold altitude), the nose must be lowered slightly (the wing angle must be decreased) to reduce the increased lift. Reducing thrust causes your plane to slow down. Lift is reduced when your plane slows, which means the nose must be raised (the wing angle must be increased) to prevent an altitude loss. Remember our old nemesis, drag? The slower we go the more drag we get. So, thrust will have to be added again after you have slowed to the desired speed.

Summary of Going Faster and Slower

  • To go faster, add thrust and lower the nose (decrease the wing angle).
  • To go slower, reduce power and raise the nose (increase the wing angle) and then add thrust when the desired speed is obtained.