True airspeed - mph Autorotation, 471 Rotor rpm 2,400 2,200 2,000 1,800 1,600 1,400 20 30 40 50 60 70 80 90 Rate of descent - ft/min  Figure 7-3.  An autorotation curve for the S-300 shows the various combinations of horizontal and vertical speeds that supply the required  energy to keep the rotor turning at a constant 471 rpm. gross weight, altitude, temperature, and power. The IGE  hover ceiling is usually higher than the OGE hover ceiling  because of the added lift benefit produced by ground effect.  See Chapter 2, Aerodynamics of Flight, for more details on  IGE and OGE hover. A pilot should always plan an OGE  hover when landing in an area that is uncertain or unverified. 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. 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. Once you reach the remote location in the previous problem,  you will need to hover OGE 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 7-5 , can you accomplish the mission? Enter the chart at 9,000 feet (point A) and proceed to point  B (+15 °C). From there, determine that the maximum gross  You are to fly a photographer to a remote location to take  pictures of the local wildlife. Using  Figure 7-4 , can you  safely hover in ground effect at your departure point with  the following conditions? Sample Hover Problem 2 Sample Hover Problem 1 A. Pressure Altitude................................8,000 feet B. Temperature..........................................+15 °C C. Takeoff Gross Weight.........................1,250 lb rpm..............................................104 percent 7-5