Ground Effect

 Save everyone big $$ when working a helicopter by ensuring that you organise a flat and solid helipad so that the helicopter can take advantage of Ground Effect.

Combine that with a take off or landing path which does not require an immediate climb and the helicopter will be able to utilise the maximum load or the lowest takeoff or landing power (it uses less fuel) for the local ambient conditions and be more cost effective. As well, like any machine, the less power used to make it work - the longer it lasts before components wear out.

Here's how it works:

The helicopter manufacturer makes allowance for the ground cushion caused by the rotor pushing air downwards faster than it can escape. This cushion of higher pressure air is very noticeable and can be used by an experienced pilot to improve the helicopter's operational performance.

The manufacturer, through their test flight program for certification, produces 2 sets of performance charts for their helicopters.

In Ground Effect (IGE) Hover

Definition:  hovering a helicopter at a given weight and Density Altitude on a calm day at less than 2 ft above a smooth hard surface. This configuration uses much less engine power than OGE.

When hovering as per the above definition, the air passing down thru the rotor disc cannot escape quickly and for simplicity can be envisaged as cushion of air building up similar in fashion to a hovercraft. This cushion means that the rotor blades do not require as much angle of attack and therefore less engine power is used for the gross weight at that moment in time to maintain height above the ground.

This translates into a number of benefits such as a greater capacity to carry more useful load or better fuel consumption etc.

The surface above which the machine is hovering is critical to the smooth flow of air.

For many helicopters, the “In Ground Effect” hover (IGE) performance chart is legal only up to 2 ft above a smooth, hard, level surface such as a concrete helipad. At this height above this type of surface, when the helicopter is in Ground Effect, the air flowing down from the rotor disc cannot escape quickly. As a surface gets rougher or less level, the ground cushion is reduced and the IGE hover is also proportionally reduced to the point it may not exist.

Hovering low above such things as water, long grass, sloping ground, rough ground, creek beds etc hinder the ground cushion build up and a consequence increase in power is required.

Out Of Ground Effect (OGE) Hover

Definition: hovering at a height more than 2 ft above a smooth hard surface on a calm day at a given weight. This configuration eats up available engine power and in many situations is not possible.

The helicopter cannot contain the OGE ground cushion as effectively or, because it is so high above the terrain - may not have any ground cushion at all, and therefore it needs either more engine power or a reduction in it's gross weight so that less power is required to maintain the hover. If these conditions aren't available when the helicopter is hovering very low above the landing site, it will sink back to less than 2 ft and probably need to run its skids along the ground to get some extra forward speed to assist the take off or landing.

On other words: If a pilot tries to make a machine hover OGE without sufficient engine power available, the helicopter must sink down. The trick at very low height above the terrain is to have a clear area beneath and in front so that if the helicopter starts to sink the pilot can regain regain airspeed and fly away.  If there are obstructions which reduce the opportunity to make an actual ground contact landing - such as a slope or trees - a damaging landing is the usual outcome. The subsequent heavy landing will severely damage some part of the machine such as the skid gear or tail rotor!!

A similar problem arises if a pilot tries to high hover out of ground effect at any altitude - with the intention of not actually landing. The lack of power or too much weight may cause it to sink rapidly towards the terrain.

The pilot can enable an OGE hover by reducing payload or fuel load. This is detrimental to some commercial work as it puts up the cost by increasing flight time. Careful planning can maximise load carrying capabilities