The Prediction of Helicopter Rotor Hover Performance using a ...

where
r is
is the blade twist in degrees. The tip vortex radial coordinate
r = 0.78 + 0.22e -Xif;
with A = 0.145 + 27 Cr
The vortex sheet vertical displacement varies linearly with radius and
can be imagined as part of a line extending from the axis of rotation r = 0 ,
to a cylinder whose radius is equal to the rotor radius, r = 1 . The vertical
displacement at the ends of the imaginary line is
Z r"=0 =
Z r=\
where K = 6 /l28 (0.459 + 18)/c~72
Kn = - 2.2 Jc~j2
K21 = - 2.7 /c^/2 .
0 0 < ij; < TT/2
K200j, - TT/2) r{, > TT/2
KH* 0 < \\) < ik
K ll*b +K 21 ( *~ V *>*b
The radial displacement r of a point on the vortex sheet originating
from a point r say, on the blade is found by evaluating the vertical displace­
ment of the sheet using the expressions above, then
r =
r,rm
A T
R
where r is the radial location of the tip vortex at the point at which it
has the same vertical displacement as the point on the vortex sheet.
The generalised wake coefficients generate a wake on the form shown in
cross section in Fig.2. This figure shows one revolution of the wake for a six
bladed rotor at a moderate thrust coefficient.