TM 1-1520-238-10 7-2 Change 3 7.3 USE OF PERFORMANCE CHARTS. 7.3.1 Chart Explanation. The first page of each sec- tion describes the chart or charts in that section, and ex- plains how each chart is used. 7.3.2 Reading the Charts. The primary use of each chart is given in an example. The use of a straight edge (ruler or page edge) and a hard fine-point pencil is recom- mended to avoid cumulative errors. The majority of the charts provide a standard pattern for use as follows: Enter first variable on top left scale, move right to second vari- able, deflect down at right angles to third variable, deflect left at right angles to fourth variable, and deflect down, etc, until final variable is read out on final scale. In addition to the primary use, other uses of each chart are explained in the text accompanying each set of performance charts. Abbreviations and symbols used in the charts are listed in Appendix B. NOTE An example of an auxiliary use of the perfor- mance charts follows: Although the hover chart is primarily arranged to find torque re- quired to hover, maximum wheel height for hover can also be found by entering torque available as torque required. In general, any single variable can be found if all others are known. Also, the tradeoffs between two vari- ables can be found. For example, at a given pressure altitude and wheel height you can find the maximum gross weight capability as free air temperature changes. 7.3.3 Data Basis. The type of data used is indicated at the bottom of each performance chart under DATA BA- SIS. The applicable report and date are also given. The data provided generally is based on one of the following categories. a. Flight Test Data. Data obtained by flight test of the aircraft at precisely known conditions using sensitive calibrated instruments. b. Calculated Data. Data based on test, but not on flight test of the complete aircraft. c. Estimated Data. Data based on estimates using aerodynamic theory or other means but not verified by flight test. 7.4 PERFORMANCE SPECIFIC CONDITIONS. The data presented is accurate only for specific conditions listed under the title of each chart. Variables for which data is not presented, but which may affect that phase of per- formance, are discussed in the text. Where data is avail- able or reasonable estimates can be made, the amount that each variable affects performance is given. 7.5 PERFORMANCE GENERAL CONDITIONS. In addition to the specific conditions, the following general conditions are applicable to the performance data: 7.5.1 Rigging. All airframe and engine controls are as- sumed to be rigged within allowable tolerances. 7.5.2 Pilot Technique. Normal pilot technique is as- sumed. Control movements should be smooth and contin- uous. 7.5.3 Aircraft Variation. Variations in performance be- tween individual helicopters are known to exist; they are considered small, however, and cannot be individually ac- counted for. 7.5.4 Instrument Variation. The data shown in the per- formance charts does not account for instrument inaccu- racies or malfunctions. 7.5.5 Configurations. Except as otherwise noted, all data is for the primary mission configuration consisting of the basic helicopter plus a pylon and a fully loaded Hell- fire missile launcher on each inboard stores station, no py- lons or stores on outboard stations. 7.5.6 Types of Fuel. All flight performance data is based on JP–4 fuel. The change in fuel flow and torque avail- able, when using approved alternate fuels (table 2–8), is insignificant. 7.6 PERFORMANCE DISCREPANCIES. Regular use of this chapter will also allow monitoring in- struments and other helicopter systems for malfunction, by comparing actual performance with planned perfor- mance. Knowledge will also be gained concerning the af- fects of variables for which data is not provided, thereby increasing the accuracy of performance predictions. 7.7 TEMPERATURE CONVERSION. A temperature conversion chart (fig 7-1) is included in this section for the purpose of converting Fahrenheit tempera- tures to Celsius.