Figure 3-11

HELICOPTER AERODYNAMICS WORKBOOK

CHAPTER 3

CONING

As the rotor blades turn, centrifugal force is created which pulls the blades outward from the

hub. When lift (or aerodynamic force) is created and combines with centrifugal force coning

occurs (see figure 3-11). Coning increases as lift increases.

Figure 3-11

VORTICES

As the rotor blades rotate and lift is produced, high pressure is formed below the blade and low

pressure above the blade. The sharp trailing edge of the blade keeps the high-pressure air from the

low-pressure area on most of the blade, except for the tip, where nothing prevents the air from

curling up from the bottom of the blade to the top. This air continues to spiral and drops off to

form the trailing tip vortex. This vortex continues to spin, and the velocity drops off with

increasing distance from the origin. In a hover, the vortices of one revolution impinge on the

vortices of the following revolutions, causing an uneven path of the vortices, which eventually

destroy each other. These tip vortices affect the induced velocity through the rotor system, and

due to this impingement and resultant unsteadiness in the flow field, a rotor system in a hover

creates its own gusty air, requiring the pilot to constantly correct to maintain a hover (figure 3-12).

Figure 3-12

HELICOPTER POWERED FLIGHT ANALYSIS 3-11