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An aeroplane is flying with an airspeed of 295 kt and CL is equal to 0.6. Due to turbulence, the pilot decreases the speed to 250 kt. The new CL is…

  • A

    0.84

  • B

    0.43

  • C

    0.38

  • D

    0.90

The aerodynamic force of lift results from the pressure differential between the top and bottom surfaces of the wing.

This lift force can be defined by the following equation:

L = 1/2 x ρ x V2 x CL x S

The lift formula can be used to consider the relationship between speed and angle of attack at a constant altitude (air density). As speed is changed, angle of attack must be adjusted to keep lift constant:

- If speed is decreased, angle of attack must be increased, and vice versa (if speed is doubled, angle of attack must be decreased to make CL four times its previous value).

To solve this exercise you can use the following formula:

New CL x (New Speed)2 = Old CL x (Old Speed)2

New CL x 2502 = 0.6 x 2952
New CL = (0.6 x 2952) / 2502

New CL = 0.835

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