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. The auxiliary fuel tank release handle (used also for release of the bomb) is located on the lower left-hand side of the main panel just under the ignition switch. (See figure 5.)

b. Before releasing the belly tank, be sure that the selector valve has been turned to one of the wing tanks. Then pull the release control.

The belly tank fuel line will automatically pull out of the retainer inside the tank which holds it in place.


The auxiliary belly tank should always be released before engaging in combat.



(1) Before attempting to operate the SCR-535-A radio set, the detonator circuit should be checked as follows:

(2) The detonator located in the radio receiver (BC-647-A) is set off when a voltage of the required value or higher is placed across its terminals. This will occur if the inertia or crash switch is operated, or the two buttons marked "DANGER" (located on the right-hand side of the radiocontrol panel in the cabin), are both pressed at the same time.

(3) When the airplane is on the ground for any length of time, the detonator plug should be disconnected from the detonator. (The detonator plug attaches to the detonator located in the left-hand side of the radio receiver, which is on the aft cabin deck.)

(4) Always test the detonator circuit to make certain there is no voltage at the plug before attaching it to the detonator. A test lamp, attached to a bracket on the aft left-hand side of the turn-over beam is used to testfor voltage in the detonator circuit. Attach the detonator plug to the test lamp circuit at the male receptacle near the test lamp. If the lamp lights there is voltage at the detonator plug and it should not be attached to the detonator or destruction of the radio receiver will result.

(5) II there is current at the detonator plug, as indicated by a lighted test lamp, it is probably due to the inertia switch being tripped. To rest the inertia switch, proceed as follows:

(a) Remove the small adjustment setting wheel from its storage location on the top of the inertia switch and use it to turn the small square shaft, on the forward left-hand side of the switch, in a clockwise direction until the stop is reached. Then press the button on the top of the inertia switch, remove the adjustment settinp wheel, and then release the pressure on the but^n. (A spring in the inertia switch will rotate the small square shaft in a counterclockwise direction until it is automatically stopped.) The inertia switch is now reset and the test lamp should be out indicating no voltage at the detonator plug.


Reattach the adjustment setting wheel to the top of the inertia switch.

(b) Rap the inertia switch lightly with the knuckles and if correctly set, the switch will not be tripped by this test jarring and the test lamp will remain off.

(6) The detonator may be fired not only by the inertia or crash switch but also by a manual control on the radio control panel in the cabin. This manual control consists of two protected buttons marked "DANGER". To fire the detonator both of these buttons must be pressed at the same time. To make certain this manual detonator control circuit is in operation, attach the detonator plug to test lamp circuit and press both "DANGER" buttons at the same time. This should light the test lamp, indicating that the circuit Is in operation.

(7) If the test lamp does not light when the two "DANGER" buttons are pressed at the same time, either the circuit is not in operation or the test lamp Is burned out or broken. Replace the test lamp with a new one and again test the circuit by pressing the buttons. If the test lamp lights, the system is in operation.

(8) The detonator circuit controlled by the two "DANGER" buttons bypasses the inertia switch and is entirely independent of it. Therefore, pressing the "DANGER" buttons will not trip the inertia switch.

(9) The above tests have indicated that the inertia switch and the push buttons are in working condition and since the inertia switch has been reset and the test lamp is not lighted it is permissible to attach the detonator plug to the detonator at the left-hand side of the radio receiver.

(10) The dptonator plug should not be inserted in the detonator until the airplane is ready to leave on a mission over enemy territory and should be disconnected when the airplane is on the ground for any length of time.


Always test the detonator circuit before attaching the detonator plug, to the radio receiver.

b. The SCR-535-A radio set is a recognition set only and cannot be used for communication.

(1) To start the radio equipment, make certain that the switch on the control box (BC-648-A) located in the ait fuselage is on the "ON" position, then push to "ON" the radio switch on the radio control panel In the cabin.

(2) To stop the equipment, push the radio switch on the radio control panel to the "OFF" position.


(1) To start the radio equipment, push the button "A", "B", "C", or "D" on control box BC-602-A, which is located on the radio control panel. Each button mentioned above selects a different crystal controlled frequency channel. (The commanding officer will give instructions regarding the frequency channel tobe used.) An indicator lamp below each channel-selector button shows the operator which channel is being used. Dimmer masks are provided to prevent glare from the channel-indicator lamps during night operation, Move the dimmer mask lever to the left to cover the channel-indicator lamps.

(2) After pressing the channel-selector button, allow approximately 1 minute for tbe vacuum tubes to warm up before attempting to use the radio.

(3) Place the "T.-R.-V.O." switchinthe "V.O." position for throttle button control of the transmitter.

(4) To transmit, hold in the button on the throttle handle, close the microphone switch (located in the oxygen mask) and speak into the microphone. Always turn off the microphone switch when the radio is not in use. This will prevent the transmission of extraneous noise of engine, machine guns, and side tones, which would be constantly received bythe pilot, tending to jam the radio channel.

(5) Since there is a slight delay in transferring from the receive to the transmit condition, due to relay operation, it is advisable to begin the messages with a meaningless word like "hello" which will actuate the switching mechanism and insure that the message is transmitted in full.

(6) To receive, release the burton on the throttle handle.

(7) To stop the equipment, press the "OFF" button on the "T.-R.-V.O." switch panel.


The operation of this radio equipment Involves the use of high voltages which are dangerous to life. A dangerous potential exists on both the transmitter and receiver whenever the equipment is in either the transmit or receive condition.


(1) The SCR-274-N radio installation Incorporates a control box composed of Individual controls for three separate receiver units of various range; from 3 to 6 megacycles, from 190 to 550 kilocycles and from 6 to 9.1 megacycles. To operate these receivers, move the battery switch from "OFF" to the "CW" (continuous wave)or the "M.C.W." (modulated continuous wave) positions. Place the "TEL" switch to either "a" or "B" to correspond to the jack used for the headset plug. Set the filter switch box control to "RANGE," "VOICE," or "BOTH," as desired. Tuning Is accomplished with the large "tuning" knob while adjusting for suitable volume with the "increase output" control knob.

(2) Two transmitters are installed, only one being used at a time, and are preset with the different frequencies recorded on the "write-in" space on the transmitter control. When transmitting, move the "transmitter selection" switch to the frequency desired. Set the "transmitter power" toggle switch to the "ON." It requires 15 seconds to warm up the transmitter tubes. Set the emission switch to "TONE," "CW," or "VOICE," as required. K the emission switch is on "VOICE" press the "microphone control" button on the throttle control, and talk clearly and distinctly into the microphone. In the "VOICE" position, the transmitting dynamotor will not start until the microphone control button has been closed. Side tone should be heard distinctly whenever transmitting. With the emission switch on "TONE" or "CW, the dynamotor will be running continuously but the transmitter will not be on the air until the transmitter key is pressed.

(3) The "transmitter power" toggle switch should be left "ON" throughout the flight to avoid repetition of the 15-second warm-up period.

(4) To reduce battery drain and increase dynamotor life, the emission selector switch should remain on "VOICE," unless continued use on "TONE" or "CW" is anticipated.


The dynamotor generates 600 volts dc. Before attempting to connect or disconnect a transmitter or power plug, determine that it is not running by touching the dynamotor to note the absence of vibration.

While tuning up the antenna circuit of the transmitter, do NOT touch the antenna when the power Is "ON."