TM 1-1520-238-10 Change 10 7-13 Section V. CRUISE 7.19 DESCRIPTION. The cruise charts (figs 7-7 thru 7-17) present the level- flight torque required and total fuel flow at various condi- tions of airspeed, pressure altitude, free air temperature, and gross weight. Cruise charts are provided for pressure altitudes from sea level to 16,000 feet in 2000-foot incre- ments. Free air temperatures range from –50 to +60 in 10 C increments. In addition to basic cruise information, the charts show speed for maximum range, maximum en- durance, and maximum rate of climb. Change in torque with change in frontal area information is presented in the upper left corner of each chart. 7.20 USE OF CHARTS. The primary uses of the charts are illustrated by the exam- ples. To use the charts, it is usually necessary to know the planned pressure altitude, estimated free air temperature, planned cruise speed, IAS, and gross weight. First, select the proper chart on the basis of pressure altitude and FAT. Enter the chart at the cruise airspeed, IAS, move right and read TAS, move left to the gross weight, move down and read torque required, and then move up and read associ- ated fuel flow. Maximum performance conditions are de- termined by entering the chart where the maximum range line or the maximum endurance and rate-of-climb line in- tersects the gross weight line; then read airspeed, fuel flow, and torque required. Normally, sufficient accuracy can be obtained by selecting the chart nearest the planned cruising altitude and FAT or, more conservatively, by selecting the chart with the next higher altitude and FAT. If greater accuracy is required, interpolation between altitudes and/or temperatures is permissible. To be con- servative, use the gross weight at the beginning of the cruise flight. For greater accuracy on long flights, howev- er, it is preferable to determine cruise information for sev- eral flight segments to allow for the decreasing gross weight. 7.20.1 Airspeed. True and indicated airspeeds are pre- sented at opposite sides of each chart. On any chart, indicated airspeed can be directly converted to true air- speed (or vice versa) by reading directly across the chart without regard for the other chart information. The appli- cable MACH No. or gross weight maximum permissable airspeed limits (V_NE) determined from figure 5-2 appear on the appropriate charts. 7.20.2 Torque. Since pressure altitude and tempera- ture are fixed for each chart, torque required varies ac- cording to gross weight and airspeed. The torque required and the torque limits shown on these charts are for dual engine operation. The torque available shown on these charts are maximum continuous torque available and maximum torque available, 30 minute limit, where less than the maximum torque-two-engine transmission limit. These torque lines are the maximum torque available for ATF = 1 at the TGT specified in Chapter 5. Higher torque than that represented by these lines may be used if it is available without exceeding the limitations presented in Chapter 5. The limit torque line shown on these charts is for dual engine transmission limit and is defined as 100% torque. An increase or decrease in torque required be- cause of drag area change is calculated by adding or sub- tracting the change in torque from the torque change (DQ) curve on the chart, and then reading the new total fuel flow. 7.20.3 Fuel Flow. Fuel flow scales are provided oppo- site the torque scales. On any chart, torque may be con- verted directly to fuel flow without regard to other chart in- formation. Sea level ground fuel flow at flat pitch and 100% N_P is approximately 550 pounds per hour. 7.20.4 Maximum Range. The maximum range lines in- dicate the combinations of gross weight and airspeed that will produce the greatest flight range per pound of fuel un- der zero wind conditions. 7.20.5 Maximum Endurance and Rate of Climb. The maximum endurance and rate of climb lines indicate the combinations of gross weight and airspeed that will pro- duce the maximum endurance and the maximum rate of climb. The torque required for level flight at this condition is a minimum, providing a minimum fuel flow (maximum endurance) and a maximum torque change available for climb (maximum rate of climb). 7.20.6 Change in Frontal Area. Since the cruise infor- mation is given for the primary mission configuration, ad- justments to torque should be made when operating with alternative wing-stores configurations. To determine the change in torque, first obtain the appropriate multiplying factor from the drag chart (fig 7-18), then enter the cruise chart at the planned cruise speed TAS, move right to the broken DQ line, and move up and read DQ. Multiply DQ by the multiplying factor to obtain change in torque, then add or subtract change