HOVERING PERFORMANCE
Helicopter performance revolves around whether or not the helicopter can be hovered. More power is required during the hover than in any other flight regime. Obstructions aside, if a hover can be maintained, a takeoff can be made, especially with the additional benefit of translational lift. Hover charts are provided for in ground effect (IGE) hover and out of ground effect (OGE) hover under various conditions of gross weight, altitude, temperature, and power. The “in ground effect” hover ceiling is usually higher than the “out of ground effect” hover ceiling because of the added lift benefit produced by ground effect.
In Ground Effect (IGE) Hover—Hovering close to the surface (usually less than one rotor diameter above the surface) under the influence of ground effect.
Out of Ground Effect (OGE) Hover—Hovering greater than one rotor diameter distance above the surface. Because induced drag is greater while hovering out of ground effect, it takes more power to achieve a hover. See Chapter 3—Aerodynamics of Flight for more details on IGE and OGE hover.
 

As density altitude increases, more power is required to hover. At some point, the power required is equal to the power available. This establishes the hovering ceiling under the existing conditions. Any adjustment to the gross weight by varying fuel, payload, or both, affects the hovering ceiling. The heavier the gross weight, the lower the hovering ceiling. As gross weight is decreased, the hover ceiling increases.
SAMPLE PROBLEM 1
You are to fly a photographer to a remote location to take pictures of the local wildlife. Using figure 8-2, can you safely hover in ground effect at your departure point with the following conditions? 

Pressure Altitude..................................8,000 feet
Temperature...............................................+15°C
Takeoff Gross Weight.....................1,250 pounds
R.P.M..........................................................104%

First enter the chart at 8,000 feet pressure altitude (point A), then move right until reaching a point midway between the +10°C and +20°C lines (point B). From that point, proceed down to find the maximum gross weight where a 2 foot hover can be achieved. In this case, it is approximately 1,280 pounds (point C).
Since the gross weight of your helicopter is less than this, you can safely hover with these conditions.
SAMPLE PROBLEM 2
Once you reach the remote location in the previous problem, you will need to hover out of ground effect for some of the pictures. The pressure altitude at the remote site is 9,000 feet, and you will use 50 pounds of fuel getting there. (The new gross weight is now 1,200 pounds.) The temperature will remain at +15°C. Using figure 8-3, can you accomplish the mission?