Inplane H force

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In-plane H force
Blade velocity
Advancing side, y 90
Retreating side, y 270
Drag is higher in the advancing side than the
retreating side, leaving a net drag force on the
blade, positive in the rearward direction.
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In-plane H force
In the rearward direction
L
f
f
D
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Drag-dependent term
Lift-dependent term
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In non-dimensional terms, for N blades
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One more term to be considered .
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Considering flapping
In the rearward direction
L
f
f
D
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N blades
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Torque and power
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Profile drag term
N blades
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Induced term
Non-dimensional and N blades
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Total torque
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Forces in trimmed level flight
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Power coefficient
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Empirical corrections
(1) A spanwise component of drag (2) A yawed-wing
effect on the profile drag coefficient at azimuth
angles significantly away from 90 and 270 (3)
The reversed region on the retreating side
where k is typically between 4.5 and 4.7.
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Flapping coefficients
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(not a function of y)
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Let the moment of inertia of the blade about its
hinge be
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In non-dimensional terms
N blades
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where
is known as the Lock number.
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The integral on the right-hand-side
include 1. 2. Terms in siny, a1, b1 3.
Terms in cosy, a1, b1
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Since MT is not a function of y, all integrals
involving siny and cosy will end up to be zero.
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Typical numerical values
Rotor solidity s 0.08 Blade lift slope a
5.7 Lock number g 8 Aircraft weight ratio
W/r(WR)2A 0.008 Parasite drag factor f/A
0.016 Parasite drag Dp (1/2) rV2f f is the
equivalent flat plate area
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