Page 142 - Aeronautical Engineer Data Book

Principles of propulsion 117
1.00
30
20
10
0.80
Blading efficiency, η s 0.60 L = 2 4 3
8
6
0.40
0.20 D

0
0 10 20 30 40 50 60 70 80 90
Pitch angle, φ
Fig. 8.2 Propeller parameter relationship

blade stalls whilst drag coefficient C D is
quadratic function of . Figure 8.2 shows broad
relationships between blading efficiency, pitch
angle and L/D ratio.

8.1.3 Propeller coefficients
It can be shown, neglecting the compressibility
of the air, that:
, n, d , , F) = 0
f(V 0 p
Using dimensional analysis, the following
coefficients are obtained for expressing the
performances of propellers having the same
geometry:
2 4
3 5
2 5
F = n d C F Q = n d C Q P = n d C p
p
p
p
C , C and C are termed the thrust, torque,
Q
P
F
and power coefficients. These are normally
expressed in USCS units, i.e.:
F
=
Thrust coefficient C F 2 4
n d
Q
=
Torque coefficient C Q 2 5
n d
P
=
Power coefficient C P 3 4
n d