actual flight tests. However, they do not test the hel- icopter under each and every condition shown on a performance chart. Instead, they evaluate specific data and mathematically derive the remaining data.  and tailwinds may require the use of more tail rotor thrust to maintain directional control. This increased tail rotor thrust absorbs power from the engine, which means there is less power available to the main rotor for the production of lift. Some helicopters even have a critical wind azimuth or maximum safe relative wind chart. Operating the helicopter beyond these limits could cause loss of tail rotor effectiveness. Takeoff and climb performance is greatly affected by wind. When taking off into a headwind, effective trans- lational lift is achieved earlier, resulting in more lift and a steeper climb angle. When taking off with a tailwind, more distance is required to accelerate through transla- tion lift. 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 ef fect” hover ceiling is usually higher than the “out of ground effect” hover ceiling because of the added lift benefit produced by ground effect. In developing performance charts, aircraft manufactur- ers make certain assumptions about the condition of the helicopter and the ability of the pilot. It is assumed that the helicopter is in good operating condition and the engine is developing its rated power. The pilot is assumed to be following normal operating procedures and to have average flying abilities. Average means a pilot capable of doing each of the required tasks cor- rectly and at the appropriate times. Using these assumptions, the manufacturer devel- ops performance data for the helicopter based on 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. 8-3 HOVERING PERFORMANCE PERFORMANCE CHARTS Figure 8-1. Density Altitude Chart. 28.0GLYPH<.notdef> 28.1GLYPH<.notdef> 28.2GLYPH<.notdef> 28.3GLYPH<.notdef> 28.4GLYPH<.notdef> 28.5GLYPH<.notdef> 28.6GLYPH<.notdef> 28.7GLYPH<.notdef> 28.8GLYPH<.notdef> 28.9GLYPH<.notdef> 29.0GLYPH<.notdef> 29.1GLYPH<.notdef> 29.2GLYPH<.notdef> 29.3GLYPH<.notdef> 29.4GLYPH<.notdef> 29.5GLYPH<.notdef> 29.6GLYPH<.notdef> 29.7GLYPH<.notdef> 29.8GLYPH<.notdef> 29.9GLYPH<.notdef> 29.92GLYPH<.notdef> 30.0GLYPH<.notdef> 30.1 GLYPH<.notdef> 30.2GLYPH<.notdef> 30.3GLYPH<.notdef> 30.4GLYPH<.notdef> 30.5GLYPH<.notdef> 30.6GLYPH<.notdef> 30.7GLYPH<.notdef> 30.8GLYPH<.notdef> 30.9GLYPH<.notdef> 31.0 1,824GLYPH<.notdef> 1,727GLYPH<.notdef> 1,630GLYPH<.notdef> 1,533GLYPH<.notdef> 1,436GLYPH<.notdef> 1,340GLYPH<.notdef> 1,244GLYPH<.notdef> 1,148GLYPH<.notdef> 1,053GLYPH<.notdef> 957GLYPH<.notdef> 863GLYPH<.notdef> 768GLYPH<.notdef> 673GLYPH<.notdef> 579GLYPH<.notdef> 485GLYPH<.notdef> 392GLYPH<.notdef> 298GLYPH<.notdef> 205GLYPH<.notdef> 112GLYPH<.notdef> 20GLYPH<.notdef> 0 -73GLYPH<.notdef> -165 GLYPH<.notdef> -257GLYPH<.notdef> -348GLYPH<.notdef> -440GLYPH<.notdef> -531GLYPH<.notdef> -622GLYPH<.notdef> -712GLYPH<.notdef> -803GLYPH<.notdef> -893GLYPH<.notdef> -983 AltimeterGLYPH<.notdef> Setting PressureGLYPH<.notdef> AltitudeGLYPH<.notdef> ConversionGLYPH<.notdef> Factor 0 -18 F C -12 10 -7 20 -1 30 4 40 10 50 16 60 21 70 27 80 32 90 Outside Air Temperature Approximate Density Alti t ude – Thousands of Feet 13 12 11 10 9 8 7 6 5 4 3 2 1 SL 1 2 , 0 0 0 1 1 , 0 0 0 1 0 , 0 0 0 9 , 0 0 0 8 , 0 0 0 7 , 0 0 0 6 , 0 0 0 5 , 0 0 0 4 , 0 0 0 3 , 0 0 0 2 , 0 0 0 1 , 0 0 0 - 1 , 0 0 0 P r e s s u r e A l t i t u d e – F e e t S t a n d a r d T e m p e r a t u r e S e a L e v e l