Figure 3-14

HELICOPTER AERODYNAMICS WORKBOOK

CHAPTER 3

Figure 3-14

GROUND VORTEX

During transition to forward flight the pilot will encounter several phenomena exclusive to

helicopter flight which, although encountered almost simultaneously, are discussed separately in

the following sections. The first is ground vortex.

As the helicopter accelerates from a hover in ground effect to forward flight, benefits of

ground effect can be lost at an altitude of less than rotor diameter and airspeed between 5 and

20 knots. This is called ground vortex. As the helicopter moves forward, the rotor downwash

mixes with increased relative wind to create a rotating vortex, which eventually causes an

increased downwash through the rotor system. This simulates a climbing situation, increasing

power required. Eventually this vortex is overrun at a higher speed. These flow patterns are

better described in figure 3-15.

HELICOPTER POWERED FLIGHT ANALYSIS 3-13