For internal cooling, reciprocating aircraft engines are especially 
dependent on 





   ANSWER: the circulation of lubricating oil. 

   An engine accomplishes much of its 
   cooling by the flow of oil through the lubrication system. 
   The lubrication system aids in cooling by reducing friction 
   and absorbing heat from internal engine parts. Many 
   airplane engines use an oil cooler, a small radiator device 
   that will cool the oil before it is recirculated through the 
   engine. 

If the engine oil temperature and cylinder head temperature gauges 
have exceeded their normal operating range, the pilot may have 
been operating with 





   ANSWER: too much power and with the mixture set too lean. 

   If the engine oil temperature and 
   cylinder head temperature gauges exceed their normal 
   operating range, it is possible that the power setting is too 
   high and the fuel/air mixture is set excessively lean. These 
   conditions may cause engine overheating. 

What action can a pilot take to aid in cooling an engine that is 
overheating during a climb? 





   ANSWER: Reduce rate of climb and increase airspeed. 

   If an airplane is overheating during a 
   climb, the engine temperature will be decreased if the 
   airspeed is increased. Airspeed will increase if the rate of 
   climb is reduced. 

What is one procedure to aid in cooling an engine that is 
overheating? 





   ANSWER: Enrich the fuel mixture. 

   Enriched fuel mixtures have a cooling 
   effect on an engine. 

One purpose of the dual ignition system on an aircraft engine is to 
provide for 





   ANSWER: improved engine performance. 

   Most airplane engines are equipped 
   with dual ignition systems, which have two magnetos to 
   supply the electrical current to two spark plugs for each 
   combustion chamber. The main advantages of the dual 
   system are increased safety and improved burning and 
   combustion of the mixture, which results in improved 
   performance. 

With regard to carburetor ice, float-type carburetor systems in 
comparison to fuel injection systems are generally considered to be 





   ANSWER: more susceptible to icing. 

   Float-type carburetor systems are 
   generally more susceptible to icing than fuel-injected 
   engines. When there is visible moisture or high humidity 
   and the temperature is between 20°F and 70°F, icing is 
   possible, particularly at low power settings. 

The operating principle of float-type carburetors is based on the 





   ANSWER: difference in air pressure at the venturi throat and the air 
   inlet. 

   In a float-type carburetor, air flows 
   into the carburetor and through a venturi tube (a narrow 
   throat in the carburetor). As the air flows more rapidly 
   through the venturi, a low pressure area is created which 
   draws the fuel from a main fuel jet located at the throat of the 
   carburetor and into the airstream, where it is mixed with 
   flowing air. It is called a float-type carburetor in that a ready 
   supply of gasoline is kept in the float bowl by a float, which 
   activates a fuel inlet valve. 

If an aircraft is equipped with a fixed-pitch propeller and a 
float-type carburetor, the first indication of carburetor ice would 
most likely be 





   ANSWER: loss of RPM. 

   In an airplane equipped with a 
   fixed-pitch propeller and float-type carburetor, the first 
   indication of carburetor ice would be a loss in RPM. 

The presence of carburetor ice in an aircraft equipped with a 
fixed-pitch propeller can be verified by applying carburetor heat 
and noting 





   ANSWER: a decrease in RPM and then a gradual increase in RPM. 

   The presence of carburetor ice in an 
   airplane equipped with a fixed-pitch propeller can be verified 
   by applying carburetor heat and noting a decrease in RPM 
   and then a gradual increase. The decrease in RPM as heat is 
   applied is caused by less dense hot air entering the engine 
   and reducing power output. Also, if ice is present, melting 
   water entering the engine may also cause a loss in 
   performance. As the carburetor ice melts, however, the RPM 
   gradually increases until it stabilizes when the ice is 
   completely removed. 

Which condition is most favorable to the development of 
carburetor icing? 





   ANSWER: Temperature between 20 and 70°F and high humidity. 

   When the temperature is between 
   20°F and 70°F with visible moisture or high humidity, one 
   should be on the alert for carburetor ice. During low or 
   closed throttle settings, an engine is particularly susceptible 
   to carburetor icing. 

The possibility of carburetor icing exists even when the ambient air 
temperature is as 





   ANSWER: high as 70°F and the relative humidity is high. 

   When the temperature is between 
   20°F and 70°F with visible moisture or high humidity, one 
   should be on the alert for carburetor ice. During low or 
   closed throttle settings, an engine is particularly susceptible 
   to carburetor icing. 

Generally speaking, the use of carburetor heat tends to 





   ANSWER: decrease engine performance. 

   Use of carburetor heat tends to 
   decrease the engine performance and also to increase the 
   operating temperature. Warmer air is less dense, and engine 
   performance decreases with density. Thus, carburetor heat 
   should not be used when full power is required (as during 
   takeoff) or during normal engine operation except as a check 
   for the presence or removal of carburetor ice. 

Applying carburetor heat will 





   ANSWER: enrich the fuel/air mixture. 

   Applying carburetor heat will enrich 
   the fuel/air mixture. Warm air is less dense than cold air, 
   hence the application of heat increases the fuel-to-air ratio. 

What change occurs in the fuel/air mixture when carburetor heat is 
applied? 





   ANSWER: The fuel/air mixture becomes richer. 

   When carburetor heat is applied, hot 
   air is introduced into the carburetor. Hot air is less dense 
   than cold air; therefore, the decrease in air density with a 
   constant amount of fuel makes a richer mixture. 

During the run-up at a high-elevation airport, a pilot notes a slight 
engine roughness that is not affected by the magneto check but 
grows worse during the carburetor heat check. Under these 
circumstances, what would be the most logical initial action? 





   ANSWER: Check the results obtained with a leaner setting of the 
   mixture. 

   If, during a run-up at a high-elevation 
   airport, you notice a slight roughness that is not affected by 
   a magneto check but grows worse during the carburetor heat 
   check, you should check the results obtained with a leaner 
   setting of the mixture control. At a high-elevation field, the 
   air is less dense and the application of carburetor heat 
   increases the already too rich fuel-to-air mixture. By leaning 
   the mixture during the run-up, the condition should improve. 

The basic purpose of adjusting the fuel/air mixture at altitude is to 





   ANSWER: decrease the fuel flow in order to compensate for 
   decreased air density. 

   At higher altitudes the air density is 
   decreased. Thus the mixture control must be adjusted to 
   decrease the fuel flow in order to maintain a constant fuel/air 
   ratio. 

While cruising at 9,500 feet MSL, the fuel/air mixture is properly 
adjusted. What will occur if a descent to 4,500 feet MSL is made 
without readjusting the mixture? 





   ANSWER: The fuel/air mixture may become excessively lean. 

   At 9,500 ft., the mixture control is 
   adjusted to provide the proper fuel/air ratio. As the airplane 
   descends, the density of the air increases and there will be 
   less fuel to air in the ratio, causing a leaner running engine. 
   This excessively lean mixture will create higher cylinder 
   temperature and may cause detonation. 

Detonation occurs in a reciprocating aircraft engine when 





   ANSWER: the unburned charge in the cylinders explodes instead of 
   burning normally. 

   Detonation occurs when the fuel/air 
   mixture in the cylinders explodes instead of burning 
   normally. This more rapid force slams the piston down 
   instead of pushing it. 

If a pilot suspects that the engine (with a fixed-pitch propeller) is 
detonating during climb-out after takeoff, the initial corrective 
action to take would be to 





   ANSWER: lower the nose slightly to increase airspeed. 

   If you suspect engine detonation 
   during climb-out after takeoff, you would normally decrease 
   the pitch to increase airspeed (more cooling) and decrease 
   the load on the engine. Detonation is usually caused by a 
   poor grade of fuel or an excessive engine temperature. 

If the grade of fuel used in an aircraft engine is lower than specified 
for the engine, it will most likely cause 





   ANSWER: detonation. 

   If the grade of fuel used in an airplane 
   engine is lower than specified for the engine, it will probably 
   cause detonation. Lower grades of fuel ignite at lower 
   temperatures. A higher temperature engine (which should 
   use a higher grade of fuel) may cause lower grade fuel to 
   explode (detonate) rather than burn evenly. 

The uncontrolled firing of the fuel/air charge in advance of normal 
spark ignition is known as 





   ANSWER: pre-ignition. 

   Pre-ignition is the ignition of the fuel 
   prior to normal ignition or ignition before the electrical arcing 
   occurs at the spark plug. Pre-ignition may be caused by 
   excessively hot exhaust valves, carbon particles, or spark 
   plugs and electrodes heated to an incandescent, or glowing, 
   state. These hot spots are usually caused by high 
   temperatures encountered during detonation. A significant 
   difference between pre-ignition and detonation is that if the 
   conditions for detonation exist in one cylinder they usually 
   exist in all cylinders, but pre-ignition often takes place in 
   only one or two cylinders. 

What type fuel can be substituted for an aircraft if the 
recommended octane is not available? 





   ANSWER: The next higher octane aviation gas. 

   If the recommended octane is not 
   available for an airplane, the next higher octane aviation gas 
   should be used. 

Filling the fuel tanks after the last flight of the day is considered a 
good operating procedure because this will 





   ANSWER: prevent moisture condensation by eliminating airspace in 
   the tanks. 

   Filling the fuel tanks after the last 
   flight of the day is considered good operating practice 
   because it prevents moisture condensation by eliminating 
   airspace in the tanks. Humid air may result in condensation 
   at night when the airplane cools. 

On aircraft equipped with fuel pumps, when is the auxiliary electric 
driven pump used? 





   ANSWER: In the event engine-driven fuel pump fails. 

   In a fuel pump system, two fuel 
   pumps are used on most airplanes. The main fuel pump is 
   engine-driven and an auxiliary electric-driven pump is 
   provided for use in the event the engine pump fails. 

Which would most likely cause the cylinder head temperature and 
engine oil temperature gauges to exceed their normal operating 
ranges? 





   ANSWER: Using fuel that has a lower-than-specified fuel rating. 

   Use of fuel with lower-than-specified 
   fuel ratings, e.g., 80 octane instead of 100, can cause many 
   problems, including higher operating temperatures, 
   detonation, etc. 


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