Ex. 8 Hovering

Ground Effect is brought about by the reduction in induced flow through the disc, the air cannot escape as quickly and through a reduction in the inflow angle, the power required to hover is reduced.

Hovering in a wind reduces ground effect, as the downwash is blown downwind.
If the wind is strong enough (say > 12-15kts) the loss of ground effect is partly made up for by the onset of Effective Translational Lift.
The aircraft attitude will affect ground effect as the induced flow will not meet the ground perpendicularly and any benefit will be reduced.
The surface beneath the helicopter affects the ground effect a hard surface like concrete creates more ground effect than a more porous one like grass.

With varying head design comes and varying amount of control power. Teetering head designs have less control power and a more appreciable lag between cyclic movement and disc response. It should be remembered that control in the hover is achieved by a constant set of corrections being applied to the controls to prevent the helicopter from moving. When the pilot notices say a drift to the left, he will apply a right cyclic input, which in turn will tilt the disc to the right, which in turn will translate the helicopter to the right. The airframe attitude lags the input by a longer time on a teetring rotor design because there is on way of directly transmitting the control input to the airframe. The airframe attitude in this instance being a function of C of G, Wind Strength, Cyclic Stick Position.
With this in mind it is not surprising that trainee pilots over control initially by applying to great an input to the cyclic, because of the lag caused by the factors described above. The pilot applies his input, thinks nothing has happened and applies a further cyclic input, just as his first effort has an effect.

When carrying out spot turns in the hover it is important to realise that if a clockwise turn is desired, whilst turning we must keep the disc pointed into the wind. We can achieve this by moving the cyclic in a circle in the opposite direction at the the same angular rate as the spot turn, the magnitude of the movement is dependant upon the wind strength. An anti-clockwise turn will lead to a clockwise input on the cyclic and vice-versa. The airframe will adopt different attitudes dependant upon head design, wind strength

The faster the aircraft moves over the ground the greater the reduction in ground effect. The greatest benefit is when the wind is light and the groundspeed is low.

A hydraulic failure will result in high forces to overcome on the controls. The normally small movements and pressures required to hold ahover will be impossible to maintain. The helicopter is still controllable in the hover, but with a reduced level of accuracy. The best option is normally to land. The action recommended in the Pilots Flight Manual is the one which should be followed.

Hovering at a height roughly equal to the rotor diameter creates the fastest downwash, and consequently will do the most damage.
Care must always be taken to consider where the helicopters downwash will go based upon hover height and wind strength, more than one fixed wing aircraft has been blown over by a taxying helicopter.
Clearly with a fast moving downwash, particulate sufaces like dust and snow will blow about. In these circumstance it is best to keep moving forward at a normal hover height and touchdown immediately on stopping.
Care should be exercised when hovering over unprepared areas (off airfield) as any small light items may be distrubed and cause damage to people, or anything else nearby. These small items may also be sucked into engine air intakes, or damage the helicopter as they are picked up by the downwash.