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Aerodynamics - Forces in straight and level flight, climbs, descents, and turns - Explained

Outline Overview:

  1. Lift opposes weight. Thrust opposes drag

  2. In level unaccelerated flight, weight equals lift and thrust equals drag.

  3. Acceleration is a change in velocity - speed or direction.

  4. An airplane that is turning is always accelerating - changing direction. A body in motion tends to stay in motion.

  5. Forces in a climb. Lift acts perpendicular to the flight path. There will be a vertical and rearward component. The rearward component is lift acting rearward. This adds essentially to drag. The weight that opposes lift has a rearward component. This rearward component of weight adds to drag. Power must be used to overcome these two forces or the airplane will slow down.

  6. Forces in a descent Lift acts perpendicular to the flight path. Because the lift vector is tilted forward there is a forward component of lift. The weight that opposes lift produces a forward component of weight. Both of these will cause the airplane to gain speed while descending given the same power as used when level.

  7. Forces in a turn. Because the airplane is turning it is always experiencing acceleration. When the airplane is banked, total lift is diverted from the vertical, directly opposing weight, to an angle, which is the bank angle. This lift then contains a vertical and horizontal com-ponent. The horizontal component turns the airplane (centripetal force), and the vertical component directly opposes weight which decreases because the lift is now at an angle. To make up the vertical components loss of lift the angle of attack of the wing must be in-creased. This makes the tilted lift more and this lift must be such that the vertical compo-nent equals the weight of the airplane. So, in a 60 degree bank turn the total lift must be doubled to restore the vertical component to the value that equals weight. The force that op-poses the tilted lift is the weight that opposes lift with is also called Load Factor. It is made up of two forces, weight and centrifugal force. Centrifugal force is the force that opposes the horizontal component of lift (Centripetal force.)

  8. The higher the bank angle the more the load factor. At 60 degrees of bank the load factor is 2g. After that as the bank is increased, load factor increases very quickly with small chang-es in bank. At 75-80 degrees the load factor exceeds the airplanes load limit, approximately 3.8g.

  9. The stall speed also increases with the angle of bank because more angle of attack is need-ed to create the additional lift. More AOA gets the airplane closer to the critical AOA. At 60 degrees of bank the stall speed is increased by over 40%.

  10. When turning, the rudder is used to first eliminate Adverse Yaw and secondly to keep the left turning tendencies from causing a skid or slip. If you feel yourself sliding left or right dur-ing a turn, you are not coordinated. Apply enough rudder to keep you straight up and down in your seat. The ball isn’t the way to correct for uncoordinated flight unless flying without visual reference.

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