Aviation of WWII
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Pilot`s Notes Airacobra Pilot`s Notes

Pilot`s flight operating instructions for ARMY MODEL P-39Q-1 AIRPLANE


a. WITH AIRPLANE IGNITION SWITCH "OFF" turn propeller over two or three complete revolutions by hand.

b. Turn battery switch (figure 5) "ON."

c. Check fuel supply of right and left tanks.

d. Turn ignition switch on (figure 5) to "BOTH." The"fuel quantity gage, the carburetor air, and the coolant give readings upon operation of the ignition switch. (The coolant will not register il Its temperature is below 50°C (122°F).)

e. Turn fuel selector valve (figure 8) to "RES TANK."


Selection of the reserve tank is recommended as it provides sufficient fuel for both "WARM-UP" and "TAKE-OFF."

f. Set the mixture control lever (figure 5) to the "IDLE CUT-OFF" range.

g. Crack the throttle (figure 5) open approximately 1 inch.

h. Turn electric booster fuel pump switch "ON" and~prime engine. Priming completed, TURN ELECTRIC BOOSTER FUEL PUMP SWITCH "OFF."

i. Give the primer (figure 5) two or three full strokes when engine is cold and one-half or one full stroke when engine Is warm.

i. Energize the starter by pressing the starter pedal (figure 7) downward with the heel and hold until the inertia flywheel at the starter sounds as though it has reached maximum rpm. Then engage the starter by tipping the starter pedal forward with the toe. Hold pedal until the engine fires regularly, then release. WHEN THE ENGINE STARTS, PUSH MIXTURE CONTROL HANDLE (figure 5) FORWARD TO "AUTOMATIC RICH."


Should engine stop, return the mixture control to "IDLE CUT-OFF" position immediately to avoid flooding the engine with fuel, as the fuel pressure will build to normal operating pressure of 16 pounds per square inch when engine starts firing.

If engine is not overloaded, another start can be made using the same procedure. In case of overloading, the next start should be attempted without priming.


a. The engine should be warmed up at a speed that is free from vibration, under 1400 rpm. During engine warm-up test-operate the flaps by placing the flap switch (figure 5) in the "DOWN" position until the indicator on the top surface of the left-hand outer wing panel at the flap shows fully down. Then place the flap switch In the "UP" position until the indicator shows fully up.

b. Operation is assured for flight when the OIL TEMPERATURE GAGE (figure 5) shows a temperature of not less than 30°C (86°F> and the COOLANT TEMPERATURE GAGE (figure 5 (shows a temperature of not less than 85°C (185°F). The oil pressure gage may fluctuate during warm-up, but this should subside when the' oil temperature increases, eventually becoming practically steady.

If the oil pressure is not established within approximately 15 to 30 seconds after starting, STOP THE ENGINE by setting manual mixture control in "IDLE CUT-OFF" and investigate the trouble.

c. Allowable engine operation for take-off as follows:

(1) Maximum rpm 3000 at sea level manifold pressure, fuel, Specification No. AN-W-F-781 amendment 5. 50.5 Inches Hg (5 minutes operation only),


(2) Maximum rpm 3000 at sea level manifold pressure, fuel, Specification No. AN-W-F-781 amendment 5. 57 inches Hg (5 minutes operation only).

(3) Oil pressure 55 pounds minimum, 85 pounds maximum.

(4) Oil temperature: Grade 1100, oil 85°C (185° F). Grade 1120, oil 95°C (203°F).

(5) Coolant temperature: 125°C (257°F) maximum, 85°C (185°F) minimum.

(6) Reduction gear oil pressure: 190 pounds maximum, 70 pounds minimum.

(7) Fuel pressure: 15-16 pounds. When using amendment 4 fuel, reduce engine operation and performance 10 percent.


a. Magnetos should be tested individually when the engine is warm to check for lossof engine revolutions and manifold pressure.

Single magneto checks should be made at an engine speed of 2300 rpm with the propeller control lever set at "TAKE-OFF" (full low pitch)and mixture control lever in "AUTOMATIC RICH" position.

It is normal for the right magneto (exhaust) to decrease 80 rpm and the left magneto (intake) to decrease 60 rpm.

Loss of speed in excess of 100 rpm generally indicates faulty ignition or spark plugs.

b. PROPELLER. - To assure efficient operation of the Aero Products propeller, move the propeller pitch control lever, located on the engine control quadrant (figure 5), back and forth from 1400 rpm to 2300 rpm several times to free the oil in the hydraulic system; then push forward to take off.
CAUTION   Do not make single magneto checks over 2300 rpm and 30 inches Hg manifold pressure. The checking of the ignition switch for proper "ground" when in "OFF" position should be accomplished at "idling" speed only.


a. Release the parking brakes by depressing both brake pedals.

b. From a standing start it is not possible to start a sharp turn in one direction if the airplane has been stopped with the nose wheel pointed in the opposite direction. Get the airplane moving and then apply brakes in direction of the desired turn.

c. Clear the engine by a "burst" of throttle and taxi down the runway for take-off position. It is recommended that the oil and coolant shutters be open when taxying. When the throttle is applied quickly there Is a tendency for the airplane to swing to the left. This is due to engine and propeller torque and may be easily corrected by application of "full right rudder" or a combination of "right rudder" and "right brake."


WARNING   a. Both cabin doors must be tightly closed and the auxiliary latch (figure 5) above each door securely fastened. This latch prevents the door from opening at high speeds. In case of an emergency rest assured that the cabin doors can be immediately released as the emergency release handles (figure 5) break all door fastenings.

b. Set mixture control to "FULL RICH."

c. It is recommended that the trim tabs be set for the take-off as follows:

Rudder trim tab - 4 graduations "Right Rudder." Elevator trim tab - 3 or 4 graduations "Nose Up." Aileron trim tabs - "Zero" setting.



d. The coolant shutter control (figure 9) and the oil shutter control (figure 9) must be adjusted prior to take-off to suit prevailing climatic conditions. Further adjustment must also be made in flight to maintain the necessary operating temperatures.

e. It is recommended that a mechanical take-off be made. If flaps are desired for take-off do not lower over one-fourth. Because of the tricycle landing gear, it is a good practice to ease the ship from the ground when an indicated air speed of 100 mph is attained. A tendency to pull to the left will be noticed but can be corrected by application of right rudder. The tendency to pull to the left will disappear as the airplane gains speed.

i. After reasonable altitude has been gained, turn the~landinggear switch (figure 5) to "UP," raising the landing gear.

g. Turn the flap switch (figure5) to "UP" (assuming the flaps have been used in take-off).

h. Place the landing gear and flap switches to the "OFF" position.

i. Now throttle down to a manifold pressure of approximately 37.5 inches Hg, reducing the engine speed to about 2600 rpm.