1. Determining Gross Weight

Refer to the WEIGHT AND BALANCE CHART in this section and check the listed basic and alternate tabulated items against those loaded in the airplane. If the airplane is loaded in accordance with the "Basic Load Items" whose weights are entered in the "Pounds" column, and the "Alternate Items' P whose weights are entered under four loading conditions in the "Alternate Loading (Pounds)" column, the gross weight will be found listed at the bottom of the chart. If any items tabulated in the "Pounds" columns are omitted in the loading of the airplane, deduct the weight of the missing items from the "Gross Weight," and the resulting figure will be the correct gross weight as the airplane is actually loaded.

2. Flight Planning.

a. General.

(1) A series of the charts on the following pages is provided to aid in selecting the proper power and altitude to be used for obtaining optimum range of the airplane. A chart is provided for each airplane configuration with its probable range of gross weight.

(2) If the flight plan calls for a continuous flight where the desired cruising power and air speed are reasonably constant after take-off and climb and the external load items are the same throughout the flight, the fuel required and flight time may be computed as a "single section flight. If this is not the case, the flight should be broken up into sections, and each leg of the flight planned separately since dropping of external bombs or tanks causes considerable changes in range and the air speed for given power. (Within the limits of the airplane, the fuel required and flying time for a given mission depend largely upon the speed desired. With all other factors remaining equal in an airplane, speed is obtained at a sacrifice of range, and range is obtained at a sacrifice of speed.)

b. Use of Charts.

(1) Although instructions for their use are shown on the FLIGHT OPERATION INSTRUCTION CHARTS, the following expanded information on proper use of the charts may be helpful.

(2) Select the FLIGHT OPERATION INSTRUCTION CHART f or the model airplane, gross weight, and external loading to be used at take-off. The amount of gasoline available for flight planning purposes depends upon the reserve required and the amount required for starting and warm-up. The fuel required for warm-up is set forth on the chart. Reserve should., be based on the type of mission, terrain over which the flight is to be made, and weather conditions. The fuel required for climb and time to climb to various altitudes is shown on the TAKE -OFF, CLIMB, AND LANDING CHART. Fuel remaining after subtracting reserve, warm-up, and climb fuel from total amount available is the amount to be used for flight planning.

(3) Select a figure in the fuel column in the upper section of the chart equal to, or the next entry less than, the amount of fuel available for flight planning. Move horizontally to the right or left and select a figure equal to, or the next entry greater than, the distance (with no wind) to be flown. Operating values contained in the lower section of the column number in which this figure appears, represent the highest cruising speeds possible at the range desired. It will be noted that the ranges listed in column I under 91 Maximum Continuous Power" are correct only at the altitude shown by the note on the chart for this column. The ranges shown in column 11 and other columns to the right of column H can be obtained at any of the altitudes listed in the "Density Altitude" column. All of the power settings listed in a column will give approximately the same number of miles per gallon if each is used at the altitude shown on the same horizontal line with it. Note that the time required for the flight may be shortened by selection of the higher altitudes. In long range cruising it is important that altitude, air speed, and rpm be held constant. The manifold pressure should be changed as required to hold the above values reasonably constant.

(4) In order to obtain the flight duration, pilot's indicated air speed must be converted to true air speed and this true air speed divided into the air miles to be flown. True air speed may be obtained first by correcting pilot's indicated air speed for position error to obtain an approximate calibrated indicated air speed, then apply the pertinent altitude correction factor to this calibrated indicated air speed. (The air-speed indicator on the P-40 series airplanes reads about two miles per hour slow at 150 miles per hour and about 10 miles per hour slow at 300 miles per hour.) The following table shows the approximate true air speed corresponding to pilot's indicated air speed on the P-40 series airplanes.

(5) The flight plan may be readily changed at any time en route, and the chart will show the balance of range available at various cruising powers by following the INSTRUCTIONS FOR USING CHART printed on each chart.

IMPORTANT: The above instructions and following charts do not take into account the effect of wind. Adjustments to range values and flight duration to allow for wind may be made by any method familiar to the pilot such as by the use of a flight calculator or a navigator's triangle of velocities.

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