recommended long-range cruise condition. By this procedure,  the aircraft is capable of its maximum design-operating radius  or can achieve flight distances less than the maximum with  a maximum of fuel reserve at the destination.  A propeller-driven aircraft combines the propeller with the  reciprocating engine for propulsive power. Fuel flow is  determined mainly by the shaft power put into the propeller  rather than thrust. Thus, the fuel flow can be related directly  to the power required to maintain the aircraft in steady, level  flight, and on performance charts power can be substituted  for fuel flow. This fact allows for the determination of range  through analysis of power required versus speed.  If maximum specific range is desired, the flight condition  must provide a maximum of speed per fuel flow. While  the peak value of specific range would provide maximum  range operation, long-range cruise operation is generally  recommended at a slightly higher airspeed. Most long-range  cruise operations are conducted at the flight condition that  provides 99 percent of the absolute maximum specific range.  The advantage of such operation is that one percent of range  is traded for three to five percent higher cruise speed. Since  the higher cruise speed has a great number of advantages, the  small sacrifice of range is a fair bargain. The values of specific  range versus speed are affected by three principal variables:  These are the source of range and endurance operating data  included in the performance section of the AFM/POH.  Cruise control of an aircraft implies that the aircraft is  operated to maintain the recommended long-range cruise  condition throughout the flight. Since fuel is consumed during  cruise, the gross weight of the aircraft varies and optimum  airspeed, altitude, and power setting can also vary. Cruise  control means the control of the optimum airspeed, altitude,  and power setting to maintain the 99 percent maximum  specific range condition. At the beginning of cruise flight, the  relatively high initial weight of the aircraft requires specific  values of airspeed, altitude, and power setting to produce the  recommended cruise condition. As fuel is consumed and the  aircraft’s gross weight decreases, the optimum airspeed and  power setting may decrease, or the optimum altitude may  increase. In addition, the optimum specific range increases.  Therefore, the pilot must provide the proper cruise control  procedure to ensure that optimum conditions are maintained.  Total range is dependent on both fuel available and specific  range. When range and economy of operation are the principal  goals, the pilot must ensure that the aircraft is operated at the  The maximum range condition is obtained at maximum lift/  drag ratio (L/D$_{MAX}$), and it is important to note that for a given  aircraft configuration, the L/D$_{MAX}$ occurs at a particular AOA  and lift coefficient and is unaffected by weight or altitude. A  variation in weight alters the values of airspeed and power  required to obtain the L/D$_{MAX}$.  [Figure 11-12]  Different  theories exist on how to achieve max range when there is a  headwind or tailwind present. Many say that speeding up in  a headwind or slowing down in a tail wind helps to achieve  max range. While this theory may be true in a lot of cases,  it is not always true as there are different variables to every  situation. Each aircraft configuration is different, and there  is not a rule of thumb that encompasses all of them as to how  to achieve the max range.  The maximum endurance condition would be obtained at the  point of minimum power required since this would require the  lowest fuel flow to keep the airplane in steady, level flight.  Maximum range condition would occur where the ratio of  speed to power required is greatest.  [Figure 11-11]   NM specific range = pounds of fuel  NM/hour specific range =  pounds of fuel/hour  knots specific range =  fuel flow  or  or  1. Aircraft gross weight 2. Altitude 3.  The external aerodynamic configuration of the aircraft.  11-10  Figure 11-12.  Effect of weight.  Power required  t  L/ DMAX  e $_{r}$w e i g h t  H i g h i $_{c}$w$_{g}$ i g h e$_{t }$ h B w a s r $_{e}$w e i L o Constant altitude  Speed 