Momentum Theory: Hover

1
Momentum Theory Hover
p
Disc
vi
Dp
v
p
Flow field
Pressure
Velocity
2
Bernoulis Equation
3
Thrust
4
w Disc loading
vi Induced velocity or downwash
5
Induced Power
Non-dimensional Variables
Thrust CT T/rA(WR)2 Power CP
P/rA(WR)3 Induced velocity li vi/ WR
6
Figure of Merit
Po Profile power
Cpo Po/rA(WR)3
7
Momentum Theory Vertical Climb
Vc
Vcvi
Vcv
Flow field
8
Bernoulis Equation
9
Thrust
10
Compared with Hover
vh Induced velocity in hover at the same thrust
11
Induced Power
12
Induced Power
13
Vertical Descent

• Vc vi/2 Vortex Ring State
• Vc vi Turbulent Wake State
• Vc 2vi Windmill Brake State

14
Induced Velocity
15
(No Transcript)
16
Vortex Ring
17
Ground Effect
Ground effect is a condition of improved
performance encountered when operating near
(within 1/2 rotor diameter) of the ground. It is
due to the interference of the surface with the
airflow pattern of the rotor system, and it is
more pronounced the nearer the ground is
approached. Increased blade efficiency while
operating in ground effect is due to two separate
and distinct phenomena.
18
Reduction induced airflow velocity
19
Reduction of the rotor tip vortex
20
(No Transcript)
21
(No Transcript)
22
Ground Effect Formula
At Z D/2 R,