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


Two controls for operation of the filter and heater (figure 8) are located in the cockpit at the left of the pilot's seat on the turn-over beam. These controls operate dampers in the air ducts. The first control selects the desired amount of cold rammed unflitered air which is led directly to the carburetor through a duct leading from the air scoop located on the top cowling directly over the carburetor. The second control permits the selection of hot unflltered or cold filtered air to the carburetor.

It is recommended that under extreme frigid conditions, and when the plane is kept In outside air, that a cover be placed over the carburetor air scoop to prevent snow or ice from forming on the scoop or entering the carburetor. In case a cover is not placed over the air scoop, it is necessary to thaw out the carburetor and scoop before flight. The heat of the engine alone should not be relied upon for thawing ice from these units because the extreme warm-up required to completely thaw these units would overheat the engine.

A carburetor air thermometer is installed on the main instrument panel in the cockpit to calibrate the temperature of carburetor air at all times.


To facilitate starting of the engine in low temperatures, the following units are included with the starter system. A small access door is located on the trailing edge section of the left-hand wing fillet and affords ac. I cess to a plug (figure 16) which can be connected to an outside battery to aid in energizing and engaging the starter in rough weather.


A hand-operated engine primer pump Is Incorporated with the airplane to aid in cold weather starting. The primer pump is located on the lower right-hand side of the radio control panel (figure 5) in the cockpit, and draws engine fuel from the Lunkenheimer strainer, and injects the fuel Into the engine Intake manifold system. Two or three strokes of the primer pump are sufficient In extremely cold temperatures. Avoid overprinting as this will aggravate starting conditions.

A propane induction system is Installed in the airplane to aid in cold weather starting. A fitting and cap are located In the fuselage skin just aft of the trailing edge of the left wing. A tube leads from the bulkhead fitting to the engine supercharger mixture intake elbow. The propane Is Injected into the line by removing the cap from the fitting and attaching an external hose.


The use of oil dilution is recommended when outside temperature is below 0°C (32°F). Dilution of the oil is accomplished prior to stopping the engine by placing the oil dilution valve switch (figure 6) in the "ON" position for approximately 4 minutes with the engine running at about 800 rpm. This period of operation is recommended as it has given most satisfactory dilution when oil and coolant temperatures have not been too high. When coolant and oil temperatures are high (over 100°C (212°F) for coolant and 40°C (104°F) for oil) it will be necessary to shut off the engine and allow to cool; then start the engine and proceed as outlined above.


One quart of gasoline enters the oil system per each minute of operation at the switch at about 800 rpm. Dilution will vary at different rpm's but there is very little danger of over-dilution. Opening the oil dilution valve Injects a quantity of engine fuel Into the oil lines thus diluting the oil. Diluted oil is gradually circulated to the engine oil tank where it is deposited in a hopper compartment Inside the tank. As the engine is started, the diluted oil moves into the oil system. As the diluted oil circulates through the engine, it is heated and carried back to the hopper compartment. Heat from the oil in this compartment gradually warms the oil in the tank outside the compartment and causes it to flow into the lines. Continuous heat in the engine crankcase eventually vaporizes fuel in the oil and exhausts the vapor through the engine breather line.


The oil system incorporates a bypass surge valve (figure 10) that guides the oil flow through or around the oil coolers. When the airplane has been Idle for any length of time In cold weather the oil in the coolers congeals and would ordinarily cause damage from oil pump pressure when the engine is started. If the oil pressure exceeds 60 pounds per square Inch the surge valve opens releasing the pressure in the coolers and sends the majority of oil flow directly to the engine oil tank from the engine. When the seepage of warm oil loosens the congealed oil in the coolers, the valve closes allowing the oil to flow normally through the coolers again.


If nofixed anchorage is available and the ground is frozen too solid to use the mooring arrows provided In the D-l mooring kit, the following procedure may be used: Dig holes in the ground 8 inches deep and 8 inches square. Dig the holes below or adjacent to the mooring points of the airplane. Coil as much manila rope as possible in each hole; or lean deeply notched stakes cornerwise in the hole, so the top of the stake will be as nearly as possible at right angles to the line of mooring, and so the notches will hold firmly when frozen in ice; or tie a short stake crosswise on the mooring rope and place it flat from corner to corner In the hole. The free ends of the rope should be of sufficient length to reach the mooring points of the airplane. Fill the holes with water, and after the water has frozen, attach the free ends of the ropes to the mooring points of the airplane.


When the ground is frozen to such an extent that it is impossible to drive the mooring pins, or to dig suitable holes, first prepare the ground by building fires over the desired mooring points or using a hand-operated portable heater to thaw the ground sufficiently to permit placement of the mooring pins or equipment.


In parking the airplane on snow or ice, if possible, provide a layer of fabric, grass, straw, green boughs, or other insulating material under the wheels to prevent their freezing into the surface. Lack of such precautions frequently result in tearing off large chunks of rubber from the tires when the airplane is again moved. Never leave parking brakes applied for any period of time. Apply foot brakes several times just prior to take-off and in flight just before landing to insure operation.


Operate all oxygen valves carefully in cold weather, opening and closing them slowly. A rapid opening may cause a sudden surge of pressure which may result In an explosion.


The hand microphone is unsatisfactory for use in cold weather, as moisture collects and freezes in the small holes of the microphone mouthpiece. Throat-type microphones should be used for all cold weather operation. All antennae will be cleaned of ice, moisture and snow before each flight. Icing Is prevalent on all types of antenna. In transmitters, frequency shift occurs with wide changes in temperature. Consequently, the transmitter must be returned and checked until a relatively stable temperature is reached.


When operating under extreme cold weather conditions, all safety latches, emergency exit and entrance door latches will be carefully checked for freedom of operation prior to take-off. In cold weather when washing down the airplane or cleaning with steam, water or moisture may enter latches causing them to freeze. Check and free any that are found inoperative.


a. The procedure to starting is largely dependent upon the extent of the cold weather steps which were taken after the previous landing, and upon the outside air temperatures encountered. In temperatures down to -23°C (-10°F) no special procedures are required. When the temperature is at -23°C (-10°F) or below, it is necessary to preheat the engine and accessory compartment prior to attempting a start.

b. To preheat the engine, the oil temperature regulators, air ducts and shutters should be closed and the heat applied through the openings in the engine and at the accessory compartment. At least 2 hours are required to heat an engine at extremely low temperatures. If a 6-8 minute oil dilution has not been performed, it may be necessary to heat the oil system and the lines from the engine accessory compartment to the openings in the wings to assure satisfactory operation. If the engine oil has been drained, it Is necessary to preheat It to 93°C (200°F) before pouring it back Into the tank. This should be done a few minutes prior to the actual starting of the engines. If the electric heaters have been used at the oil tanks, it is assumed that the oil system will be sufficiently warm to permit a start.

c. Do not permit excessively hot air to blast against Ignition harness, flexible hose, self-sealing tanks, or other rubberized or fabric materials. The blast will be too hot unless the hand can be comfortably held for 1 minute in the same position as the part In question.

d. The cockpit and battery compartments should be heated, utilizing the openings provided in the bottom of the fuselage.


If Ice, frost, or snow is present on the airplane wings, or flight surfaces, it must be removed by brushing or flushing prior to take-off.

e. Operate all ailerons, elevators, rudders and all trim tabs through their complete travels three or four times, noting the forces required. If forces are excessive, check system for cause.

f. When it is necessary to remove frost or ice from areas of the airplane, melt a small area of the ice covered surface at a time, using hot water or heat from a portable ground heater; then flush this area with denatured alcohol before the hot water freezes. Pay particular attention to the hinges and controls.

g. The two heater controls on the floor control the air entering the cockpit through two ducts under the pilot's seat. A volume of air is constantly flowing through these ducts and the two controls only control the mixing of hot and cold air. No shut-off is provided. The air that enters the cockpit through these ducts travels through outlets in the rudder pedal wells to the guns and cannons. This air is then drawn forward and expelled overboard by means of four external louvres.