TM 1-1520-240-10            7A-7-1 SECTION  VII.  CRUISE 7A-7-1.  Description. The cruise charts, figures 7A-7-1 through 7A-7-84, pres- ent torque requirements and fuel flow for cruise flight as a function of airspeed and gross weight for various com- binations of pressure altitude and free air temperature. Dot pattern (shaded) area indicates time limited opera- tion 7A-7-2.  Use of Charts. The primary use of charts is illustrated by the example cruise chart (fig. 7A-7-1). To use the charts it is usually necessary  to  know  the  planned  PA,  estimated  FAT, planned cruise TAS, and the GW.  First select the proper chart based on PA and free air temperature.  Enter the chart at the cruise TAS, move right and read IAS, move left to the GW, move down and read torque required, then move up and read associated fuel flow. Maximum perfor- mance conditions are determined by entering the chart where the maximum range line or maximum  endurance and rate of climb (R/C) line intersect the gross weight line: then read airspeed, fuel flow, and torque required. Normally, sufficient accuracy can be obtained by select- ing the chart nearest to the planned cruising altitude and FAT, or move conservatively, by selecting the chart with the next higher  altitude and FAT (example cruise chart, method one).  If greater accuracy is required, interpola- tion between altitudes and/or temperatures is permissi- ble (example cruise chart, method two).  To be conserva- tive, use the GW at the beginning of the cruise flight.  For improved accuracy or long flights, it is preferable to deter- mine  cruise  information  for  several  flight  segments  to allow for decreasing GW. a. Airspeed.  True and indicated airspeeds are pre- sented at opposite sides of each chart.  On any chart, IAS can be directly converted to TAS (or vice versa) by read- ing directly across the chart without regard to other chart information.  Estimated airspeed limits with an operating CGI appear as dashed  lines on each chart.  Airspeed limits with the CGI inoperative are presented in the air- speed limits section of Chapter 5. NOTE Airspeed limitations with an operative cruise guide indicator are per the indicator display. Estimated  values  shown  on  these  cruise charts are for information only, as an aid to pre–flight planning. b. Torque.  Since PA and temperature are defined for each chart, torque required varies only with GW and airspeed.  The torque required per engine as presented on the charts is for dual engine operation.  The torque required for single engine operation is double the dual engine torque value for any given condition.  See cruise chart example 2 for example on torque required.  The torque available limits shown are either transmission or engine torque limits (whichever is least). c. Fuel  Flow.  The  fuel  flow  scales  presented  on each chart opposite the torque scales are for dual engine operation.  Torque may be converted directly to fuel flow on any chart without regard to other chart information. A single engine fuel flow chart is presented in Section X. Torque required for any given condition as obtained  from the preceding cruise charts should be doubled before being used to obtain single engine fuel flow from this chart. d. Maximum Range.  Maximum range lines indicate optimum GW/cruise speed conditions with respect to dis- tance covered per pound of fuel consumed for zero wind condition. e. Maximum Endurance and Rate of Climb.  Maxi- mum endurance and rate of climb lines indicate optimum GW / cruise speed conditions for maximum endurance and maximum rate of climb.  These conditions require minimum fuel flow (maximum endurance) and provide maximum  torque  change  for  climb  (maximum  rate  of climb).  This airspeed also represents the best single engine airspeed. 7A-7-3.  Conditions. The cruise charts are based on 100% RRPM for ambient temperatures of -10_C and above, and 98% and 100% RRPM for ambient temperatures of -20_C and below. 7A-7-4.  Performance Penalties with EAPS. The  engine  performance  loss  with  EAPS  installed  is shown in the table 7A-7-1.  The corrections shown in the table are to be applied to the applicable performance data shown in Chapter 7.