Lateral CG is often plotted against the longitudinal CG. [Figure 7-11]  In this case, –1.6 is plotted against 93.8, which was the longitudinal CG determined in the previous problem. The intersection of the two lines falls well within the lateral CG envelope.
 
 

Your ability to predict the performance of a helicopter is extremely important. It allows you to determine how much weight the helicopter can carry before takeoff, if your helicopter can safely hover at a specific altitude and temperature, how far it will take to climb above obstacles, and what your maximum climb rate will be. 
 

FACTORS AFFECTING PERFORMANCE
A helicopter’s performance is dependent on the power output of the engine and the lift production of the rotors, whether it is the main rotor(s) or tail rotor. Any factor that affects engine and rotor efficiency affects performance. The three major factors that affect performance are density altitude, weight, and wind.
 
 

DENSITY ALTITUDE
The density of the air directly affects the performance of the helicopter. As the density of the air increases, engine power output, rotor efficiency, and aerodynamic lift all increase. Density altitude is the altitude above mean sea level at which a given atmospheric density occurs in the standard atmosphere. It can also be interpreted as pressure altitude corrected for nonstandard temperature differences.
Pressure altitude is displayed as the height above a standard datum plane, which, in this case, is a theoretical plane where air pressure is equal to 29.92 in. Hg. Pressure altitude is the indicated height value on the altimeter when the altimeter setting is adjusted to
29.92 in. Hg. Pressure altitude, as opposed to true altitude, is an important value for calculating performance as it more accurately represents the air content at a particular level. The difference between true altitude
Density Altitude—Pressure altitude corrected for nonstandard temperature variations. Performance charts for many older aircraft are based on this value.
Standard Atmosphere—At sea level, the standard atmosphere consists of a barometric pressure of 29.92 inches of mercury (in. Hg.) or 1013.2 millibars, and a temperature of 15°C (59°F). Pressure and temperature normally decrease as altitude increases. The standard lapse rate in the lower atmosphere for each 1,000 feet of altitude is approximately 1 in. Hg. and 2°C (3.5°F). For example, the standard pressure and temperature at 3,000 feet mean sea level (MSL) is 26.92 in. Hg. (29.92 – 3) and 9°C (15°C – 6°C).