Blade mean lift coefficient

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Blade mean lift coefficient
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Blade loading
In Chapter 2, we define w T/A as the disc
loading. CT can be viewed as the non-dimensional
disc loading. With CL between 0.3 to 0.6, CT/s
is between 0.05 and 0.1 and CT is between 0.005
and 0.01.
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Power approximation
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• Assumption
• Uniform inflow
• Constant profile drag coefficient

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In the hover,
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• For
• Non-uniform inflow
• Constant profile drag coefficient

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For the hover,
Figure of merit
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Tip Loss
Assume that outboard of a station r BR the
blade section produce drag but no lift. The
typical value of B is 0.97 or 0.98.
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• Assumptions
• a is measured from the no-lift line.
• Stall and compressibility effects can be
  neglected.

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• Assumptions
• The blade has zero twist, i.e., q is constant.
• The induced velocity is uniform , i.e., l is
  constant.

With a typical value of B 0.97 or 0.98, the
thrust is lower between 5 and 10 for a given q.
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• Assume
• the effective disc area is reduced by a factor of
  B2,
• the induced velocity is proportional to the
  square root of disc loading,
• The increase in induced velocity is by a factor
  of 1/B.

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For a given thrust coefficient, CT,
With a typical value of B 0.97 or 0.98, the
induced power is higher between 2 and 3. It
can be incorporated into the constant k.
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Numerical example hover
Blade radius, R 6 m Blade chord (constant), c
0.5 m Blade twist, linear from 12 at root to 6
at tip Number of blades, N 4 Empirical
constant, k 1.13 Blade profile drag coefficient
(constant), 0.010
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