Page 141 - Aeronautical Engineer Data Book
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116 Aeronautical Engineer’s Data Book
Vector diagram for a blade element of a propeller
O' A'
Projection of
axis of rotation
B
α w b
φ V o
β
A c
O u = ωr = 2πrn a
Aerodynamic forces acting on a blade element
Projection of axis Chord line
of rotation O'
–w
d
dD α
dL
b a
φ dF
dR
γ
90˚
c
dQ O
e
A
Fig. 8.1 Propeller blade elements
The value of which makes b a maximum is
termed the optimum advance angle opt .
Maximum blade efficiency is given by:
2 – 1 2(L/D) – 1
( b ) max = =
2 + 1 2(L/D) + 1
8.1.2 Performance characteristics
The pitch and angle have different values at
different radii along a propeller blade. It is
common to refer to all parameters determining
the overall characteristics of a propeller to their
values at either 0.7r or 0.75r.
Lift coefficient C L is a linear function of the
angle of attack ( ) up to the point where the
