TM 1-1520-238-10Change 107A-15Section V. CRUISE7A.19 DESCRIPTION.The cruise charts (figs 7A-7 thru 7A-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 pressurealtitudes from sea level to 16,000 feet in 2000-foot incre-ments. Free air temperatures range from –50to +60 C in10 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 torquewith change in frontal area information is presented in theupper left corner of each chart.7A.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 theplanned pressure altitude, estimated free air temperature,planned cruise speed, IAS, and gross weight. First, selectthe proper chart on the basis of pressure altitude and FAT.Enter the chart at the cruise airspeed, IAS, move right andread TAS, move left to the gross weight, move down andread 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 rangeline or the maximum endurance and rate-of-climb line in-tersects the gross weight line; then read airspeed, fuelflow, and torque required. Normally, sufficient accuracycan be obtained by selecting the chart nearest theplanned cruising altitude and FAT or, more conservatively,by selecting the chart with the next higher altitude andFAT. If greater accuracy is required, interpolation betweenaltitudes and/or temperatures is permissible. To be con-servative, use the gross weight at the beginning of thecruise 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 grossweight.7A.20.1 Airspeed.True and indicated airspeeds arepresented 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 chartwithout regard for the other chart information. The appli-cable MACH No. or gross weight maximum permissableairspeed limits (V_{NE}) determined from figure 5-2 appearon the appropriate charts.7A.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 requiredand the torque limits shown on these charts are for dual-engine operation. The torque available shown on thesecharts are maximum continuous torque available, andmaximum torque available, 30 minute limit and 10 minutelimit where less than two-engine transmission limit. Thesetorque lines are the maximum torque available for ATF = 1at the TGT limits specified in Chapter 5. Higher torquethan that represented by these lines may be used if it isavailable without exceeding the limitations presented inChapter 5. The limit torque line shown on these charts is for dual engine transmission limit and is defined as100% torque. An increase or decrease in torque requiredbecause of drag area change is calculated by adding orsubtracting the change in torque from the torque change(DQ) curve on the chart, and then reading the new totalfuel flow.7A.20.3 Fuel Flow.Fuel flow scales are provided op-posite the torque scales. On any chart, torque may beconverted directly to fuel flow without regard to other chartinformation. Sea level ground fuel flow at flat pitch and100% N_{P} is approximately 555 pounds per hour.7A.20.4 Maximum Range.The maximum range linesindicate the combinations of gross weight and airspeedthat will produce the greatest flight range per pound of fuelunder zero wind conditions.7A.20.5 Maximum Endurance and Rate ofClimb.The maximum endurance and rate of climb linesindicate the combinations of gross weight and airspeedthat will produce the maximum endurance and the maxi-mum rate of climb. The torque required for level flight atthis condition is a minimum, providing a minimum fuel flow(maximum endurance) and a maximum torque changeavailable for climb (maximum rate of climb).7A.20.6 Change in Frontal Area.Since the cruise in-formation is given for the primary mission configuration,adjustments to torque should be made when operatingwith alternative wing-stores configurations. To determinethe change in torque, first obtain the appropriate multiply-ing factor from the drag chart (fig 7A-18), then enter thecruise chart at the planned cruise speed TAS, move rightto the broken DQ line, and move up and read DQ. MultiplyDQ by the multiplying factor to obtain change in torque,then add or