Rotor Aerodynamics in

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Chapter 5

• Rotor Aerodynamics in
• Forward Flight

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Glauert (1926 1928)
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Momentum theory
where
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As V 0, V vi
As V , V V
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where vh is the induced velocity in hover at the
same thrust, and
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or
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As V
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Non-uniform inflow
Glauert (1926)
K gt 1 (typical 1.2) r 0, vi (vi)0 y 0, vi
(vi)0 (1 Kr) y 90 or 270, vi (vi)0 y
180, vi (vi)0 (1 - Kr) vi lt 0 represents
upwash
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In forward flight, air passing through the rear
portion of the rotor disk has a greater downwash
angle than air passing through the forward portion
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Induced power
For V gtgt vi,
where w T/A is the disc loading.
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To compensate the non-uniform induced velocity,
k is typically 1.20.
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Wake
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Blade element theory
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In non-dimensional terms,
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UP terms (non-dimensional)
1. Inflow factor
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UP terms (non-dimensional)
2. Component of uR normal to the blade,
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UP terms (non-dimensional)
3. Component resulting from angular motion of
flapping
In non-dimensional term,
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For small angle,
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Thrust
N blades
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Using no-feathering plane (NFP) as the reference
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Thrust coefficient