Blade Mean Lift Coefficient

Characteristics of a rotor obviously depend on the lift coefficient at which the blades are operating and it is useful to have a simple approximate indication of this. The blade mean lift coefficient provides such an indication. As the name implies, the mean lift is that which, applied uniformly along the blade span, would give the same total thrust as the actual blade. Writing the

mean lift coefficient as Cl we have, from Equation 3.18:

A

Подпись: CTПодпись: sClx2 dx

Подпись: A x2 dx 0 Подпись: = sC L Подпись: (3.44)

0

3sc l

Подпись: C L Подпись: 3CT s Подпись: (3.45)

from which:

The parameter CT/s has been previously discussed and this gives another reason for the preference some workers have for using it as the definition of thrust coefficient instead of CT.

Blades usually operate in the CL range 0.3-0.6, so typical values of CT/s are between 0.1 and 0.2. Typical values of CT are an order of 10 smaller as solidity values are in the region of 0.1.

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