A proper understanding of weather and how it will affect both your intended flight and aircraft are a huge part of the aeronautical knowledge required to earn a pilot’s certificate. As you progress through your certificate levels and ratings as a pilot you will continually build upon the knowledge required to operate under that certificate level. ASA’s oral exam guides are here to help and include questions and answers written by examiners to allow you to simulate the experience of the oral exam. Today we’ve got some sample questions from our Commercial Pilot Oral Exam Guide related to cold weather.

First, from airplane systems section L on environmental systems, we have questions related to heaters and the problems that can be associated with them:

1. What are the two main types of heater systems commonly found on general aviation aircraft? (FAA-H-8083-25)

Fresh air heaters—Fresh air heaters that pass air over an exhaust shroud into the cabin through ducts are a type of combustion heater commonly used in general aviation aircraft. As the fresh air flows over the hot exhaust shroud, it absorbs the heat from the engine exhaust, significantly increasing its temperature. The heated air is then distributed into the aircraft cabin through a network of ducts. These ducts are strategically placed to ensure proper circulation of warm air throughout the cabin.

Combustion heaters—Combustion heaters, also known as fuel-burning heaters, utilize a combustion process to generate heat. These heaters typically burn aviation fuel, such as Jet-A or avgas, to produce heat that is then distributed throughout the aircraft cabin. Combustion heaters are often equipped with a heat exchanger, which transfers the heat from the combustion chamber to the cabin air. Air circulation fans help distribute the heated air throughout the cabin, providing warmth to occupants. Combustion heaters are commonly found in many piston-engine aircraft and smaller turboprop aircraft.

2. What are the main aeromedical risks associated with cabin heater systems in general aviation aircraft? (FAA-H-8083-25)

Cabin heater systems in general aviation aircraft, while providing comfort and warmth, can pose certain aeromedical risks. The main risks associated with cabin heater systems include:

Carbon monoxide (CO) poisoning—CO is a colorless and odorless gas produced by incomplete combustion of fuels, such as aviation fuel or other hydrocarbons used in the heater system. If there is a leak or malfunction in the heater system, CO can enter the aircraft cabin, leading to CO poisoning. Inhaling high levels of CO can cause symptoms ranging from headaches, dizziness, and nausea to more severe consequences, including loss of consciousness or death. A common cause for carbon monoxide in a cabin is cracked tubing or exhaust shrouds that allow the gas into the cabin.

Oxygen depletion—Another risk associated with cabin heaters is the potential for oxygen depletion. Some combustion-based heater systems consume oxygen during the combustion process. In an inadequately ventilated or sealed cabin, excessive use of a combustion heater can lead to a reduction in the available oxygen levels. This can result in hypoxia, which is a condition characterized by an insufficient supply of oxygen to the body’s tissues and organs. Hypoxia can impair cognitive function, decrease alertness, and potentially lead to a loss of consciousness.

Next, learn how to answer questions on keeping your aircraft free from ice with information from section M on deicing and anti-icing:

1. What is the difference between a deice system and an anti-ice system? (FAA-H-8083-31)

A deice system is used to eliminate ice that has already formed. An anti-ice system is used to prevent the formation of ice.

2. What types of systems are used in the prevention and elimination of airframe ice? (FAA-H-8083-31)

Pneumatic—A deice type of system; consists of inflatable boots attached to the leading edges of the wings and tail surfaces. Compressed air from the pressure side of the engine vacuum pump is cycled through ducts or tubes in the boots causing the boots to inflate. Most systems also incorporate a timer.

Hot air—An anti-ice type system; commonly found on turboprop and turbojet aircraft. Hot air is directed from the engine (compressor) to the leading edges of the wings.

Electrical—Electrical deicing systems in general aviation aircraft use embedded heating elements or wires on critical surfaces like wings, tailplanes, and propellers. Activating the system sends an electrical current through the elements, generating heat to prevent or remove ice buildup. Temperature sensors monitor surface temperatures for optimal deicing. Power is supplied through the aircraft’s electrical system or dedicated sources such as batteries.

Fluid—Liquid deicing systems are used in general aviation aircraft to remove ice and prevent its formation. A liquid deicing system typically involves spraying a specialized deicing fluid onto critical surfaces such as wings, tailplanes, and propellers. This fluid contains anti-icing agents that prevent ice buildup and facilitate ice removal. The deicing fluid is stored in dedicated tanks and distributed through a network of tubing and nozzles. Pilots activate the system to spray the fluid onto the surfaces before or during flight. The fluid coats the surfaces and is intended to provide a protective layer to prevent further ice formation or accumulation.

3. What types of systems are used in the prevention and elimination of propeller ice? (FAA-H-8083-31)

Electrically heated boots—Consist of heating elements incorporated into the boots which are bonded to the propeller. The ice buildup on the propeller is heated from below and then thrown off by centrifugal force.

Fluid system—Consists of an electrically driven pump which, when activated, supplies a fluid, such as alcohol, to a device in the propeller spinner which distributes the fluid along the propeller assisted by centrifugal force.

4. What types of systems are used in the prevention and elimination of windshield ice? (FAA-H-8083-31)

Fluid system—A liquid fluid system, typically driven by an electric pump, can be activated to spray deicing fluid onto the windshield (or other surfaces) of the aircraft to prevent formation of ice. A best practice is to deploy this fluid before ice accumulates and begins to coat surfaces. It is intended to be most effective at stopping ice from bonding to surfaces, not removing it once it has built up.

Electrical system—Heating elements are embedded in the windshield or in a device attached to the windshield which when activated, prevents the formation of ice.

These questions refer to FAA-H-8083-25, the Pilot’s Handbook of Aeronautical Knowledge,  and FAA-H-8083-31, the Aviation Maintenance Technician Handbook—Airframe. You can find this information and more in the eleventh edition of Commercial Pilot Oral Exam Guide.

Featured image by 2happy at stockvault.net.

The post Cold Weather and Aircraft: What a Pilot Needs to Know first appeared on Learn To Fly.

Most aircraft are equipped with either a 14- or a 28-volt direct current (DC) electrical system. A basic aircraft electrical system consists of the following components:

• Alternator/generator
• Battery
• Master/battery switch
• Alternator/generator switch
• Bus bar, fuses, and circuit breakers
• Voltage regulator
• Ammeter/loadmeter
• Associated electrical wiring

Engine-driven alternators or generators supply electric current to the electrical system. They also maintain a sufficient electrical charge in the battery. Electrical energy stored in a battery provides a source of electrical power for starting the engine and a limited supply of electrical power for use in the event the alternator or generator fails. Most DC generators do not produce a sufficient amount of electrical current at low engine rpm to operate the entire electrical system. During operations at low engine rpm, the electrical needs must be drawn from the battery, which can quickly be depleted.

Alternators have several advantages over generators. Alternators produce sufficient current to operate the entire electrical system, even at slower engine speeds, by producing alternating current (AC), which is converted to DC. The electrical output of an alternator is more constant throughout a wide range of engine speeds.

Some aircraft have receptacles to which an external ground power unit (GPU) may be connected to provide electrical energy for starting. These are very useful, especially during cold weather starting. Follow the manufacturer’s recommendations for engine starting using a GPU. The electrical system is turned on or off with a master switch. Turning the master switch to the ON position provides electrical energy to all the electrical equipment circuits except the ignition system. Equipment that commonly uses the electrical system for its source of energy includes:

• Position lights
• Anticollision lights
• Landing lights
• Taxi lights
• Interior cabin lights
• Instrument lights
• Radio equipment
• Turn indicator
• Fuel gauges
• Electric fuel pump
• Stall warning system
• Pitot heat
• Starting motor

Many aircraft are equipped with a battery switch that controls the electrical power to the aircraft in a manner similar to the master switch. In addition, an alternator switch is installed that permits the pilot to exclude the alternator from the electrical system in the event of alternator failure.

With the alternator half of the switch in the OFF position, the entire electrical load is placed on the battery. All nonessential electrical equipment should be turned off to conserve battery power.

A bus bar is used as a terminal in the aircraft electrical system to connect the main electrical system to the equipment using electricity as a source of power. This simplifies the wiring system and provides a common point from which voltage can be distributed throughout the system.

Fuses or circuit breakers are used in the electrical system to protect the circuits and equipment from electrical overload. Spare fuses of the proper amperage limit should be carried in the aircraft to replace defective or blown fuses. Circuit breakers have the same function as a fuse but can be manually reset, rather than replaced, if an overload condition occurs in the electrical system. Placards at the fuse or circuit breaker panel identify the circuit by name and show the amperage limit. An ammeter is used to monitor the performance of the aircraft electrical system. The ammeter shows if the alternator/generator is producing an adequate supply of electrical power. It also indicates whether or not the battery is receiving an electrical charge.

Ammeters are designed with the zero point in the center of the face and a negative or positive indication on either side. When the pointer of the ammeter is on the plus side, it shows the charging rate of the battery. A minus indication means more current is being drawn from the battery than is being replaced. A full-scale minus deflection indicates a malfunction of the alternator/generator. A full-scale positive deflection indicates a malfunction of the regulator. In either case, consult the AFM/POH for appropriate action to be taken.

Not all aircraft are equipped with an ammeter. Some have a warning light that, when lighted, indicates a discharge in the system as a generator/alternator malfunction. Refer to the AFM/POH for appropriate action to be taken.

Another electrical monitoring indicator is a loadmeter. This type of gauge has a scale beginning with zero and shows the load being placed on the alternator/generator. The loadmeter reflects the total percentage of the load placed on the generating capacity of the electrical system by the electrical accessories and battery. When all electrical components are turned off, it reflects only the amount of charging current demanded by the battery.

A voltage regulator controls the rate of charge to the battery by stabilizing the generator or alternator electrical output. The generator/alternator voltage output should be higher than the battery voltage. For example, a 12-volt battery would be fed by a generator/alternator system of approximately 14 volts. The difference in voltage keeps the battery charged.

The post Aircraft Systems: Electrical System first appeared on Learn To Fly.

In a typical pressurization system, the cabin, flight compartment, and baggage compartments are incorporated into a sealed unit capable of containing air under a pressure higher than outside atmospheric pressure. On aircraft powered by turbine engines, bleed air from the engine compressor section is used to pressurize the cabin. Superchargers may be used on older model turbine-powered aircraft to pump air into the sealed fuselage. Piston-powered aircraft may use air supplied from each engine turbocharger through a sonic venturi (flow limiter). Air is released from the fuselage by a device called an outflow valve. By regulating the air exit, the outflow valve allows for a constant inflow of air to the pressurized area.

A cabin pressurization system typically maintains a cabin pressure altitude of approximately 8,000 feet at the maximum designed cruising altitude of an aircraft. This prevents rapid changes of cabin altitude that may be uncomfortable or cause injury to passengers and crew. In addition, the pressurization system permits a reasonably fast exchange of air from the inside to the outside of the cabin. This is necessary to eliminate odors and to remove stale air.

Pressurization of the aircraft cabin is necessary in order to protect occupants against hypoxia. Within a pressurized cabin, occupants can be transported comfortably and safely for long periods of time, particularly if the cabin altitude is maintained at 8,000 feet or below, where the use of oxygen equipment is not required. The flight crew in this type of aircraft must be aware of the danger of accidental loss of cabin pressure and be prepared to deal with such an emergency whenever it occurs.

The following terms will aid in understanding the operating principles of pressurization and air conditioning systems:

• Aircraft altitude—the actual height above sea level at which the aircraft is flying
• Ambient temperature—the temperature in the area immediately surrounding the aircraft
• Ambient pressure—the pressure in the area immediately surrounding the aircraft
• Cabin altitude—cabin pressure in terms of equivalent altitude above sea level
• Differential pressure—the difference in pressure between the pressure acting on one side of a wall and the pressure acting on the other side of the wall. In aircraft air-conditioning and pressurizing systems, it is the difference between cabin pressure and atmospheric pressure.

The cabin pressure control system provides cabin pressure regulation, pressure relief, vacuum relief, and the means for selecting the desired cabin altitude in the isobaric and differential range. In addition, dumping of the cabin pressure is a function of the pressure control system. A cabin pressure regulator, an outflow valve, and a safety valve are used to accomplish these functions.

The cabin pressure regulator controls cabin pressure to a selected value in the isobaric range and limits cabin pressure to a preset differential value in the differential range. When an aircraft reaches the altitude at which the difference between the pressure inside and outside the cabin is equal to the highest differential pressure for which the fuselage structure is designed, a further increase in aircraft altitude will result in a corresponding increase in cabin altitude. Differential control is used to prevent the maximum differential pressure, for which the fuselage was designed, from being exceeded. This differential pressure is determined by the structural strength of the cabin and often by the relationship of the cabin size to the probable areas of rupture, such as window areas and doors.

The cabin air pressure safety valve is a combination pressure relief, vacuum relief, and dump valve. The pressure relief valve prevents cabin pressure from exceeding a predetermined differential pressure above ambient pressure. The vacuum relief prevents ambient pressure from exceeding cabin pressure by allowing external air to enter the cabin when ambient pressure exceeds cabin pressure. The flight deck control switch actuates the dump valve. When this switch is positioned to ram, a solenoid valve opens, causing the valve to dump cabin air into the atmosphere.

The degree of pressurization and the operating altitude of the aircraft are limited by several critical design factors. Primarily, the fuselage is designed to withstand a particular maximum cabin differential pressure.

Several instruments are used in conjunction with the pressurization controller. The cabin differential pressure gauge indicates the difference between inside and outside pressure. This gauge should be monitored to assure that the cabin does not exceed the maximum allowable differential pressure. A cabin altimeter is also provided as a check on the performance of the system. In some cases, these two instruments are combined into one. A third instrument indicates the cabin rate of climb or descent. A cabin rate-of-climb instrument and a cabin altimeter are illustrated in the figure below.

The post Aircraft Systems: Pressurized Aircraft first appeared on Learn To Fly.

Many sophisticated engines have fuel directly metered into the induction manifold and then into the cylinders without using a carburetor. This is known as fuel injection.

A venturi system is still used to create the pressure differential. This is coupled to a fuel control unit (FCU), from which metered fuel is piped to the fuel manifold unit (fuel distributor). From here, a separate fuel line carries fuel to the discharge nozzle in each cylinder head, or into the inlet port prior to the inlet valve. The mixture control in the fuel injection system controls the idle cut-off.

With fuel injection, each individual cylinder is provided with a correct mixture by its own separate fuel line. (This is unlike the carburetor system, which supplies the same fuel/air mixture to all cylinders. This requires a slightly richer-than-ideal mixture to ensure that the leanest-running cylinder does not run too lean.)

The advantages of fuel injection include:

• freedom from fuel ice (no suitable place for it to form);
• more uniform delivery of the fuel/air mixture to each cylinder;
• improved control of fuel/air ratio;
• fewer maintenance problems;
• instant acceleration of the engine after idling with no tendency for it to stall; and
• increased engine efficiency.

Starting an already hot engine that has a fuel injection system may be difficult because of vapor locking in the fuel lines. Electric boost pumps that pressurize the fuel lines can help alleviate this problem. Having very fine fuel lines, fuel injection engines are more susceptible to any contamination in the fuel such as dirt or water. Correct fuel management is imperative! Know the fuel system of your particular airplane. Surplus fuel provided by a fuel injection system will pass through a return line which may be routed to only one of the fuel tanks. If the pilot does not remain aware of where the surplus fuel is being returned to, it may result in uneven fuel loading in the tanks or fuel being vented overboard (thus reducing flight fuel available).

The post Aircraft Systems: Fuel Injection Systems first appeared on Learn To Fly.

When a propeller rotates, the tips travel at a greater speed than the hub. To compensate for the greater speed at the tips, the blades are twisted slightly. The propeller blade angles decrease from the hub to the tips with the greatest angle of incidence, or highest pitch, at the hub and the smallest at the tip. This produces a relatively uniform angle of attack (uniform lift) along the blade’s length in cruise flight.

No propeller is 100% efficient. There is always some loss of power when converting engine output into thrust. This loss is primarily due to propeller slippage. A propeller’s efficiency is the ratio of thrust horsepower (propeller output) to brake horsepower (engine output). A fixed propeller will have a peak (best) efficiency at only one combination of airspeed and RPM.

A constant-speed (controllable-pitch) propeller allows the pilot to select the most efficient propeller blade angle for each phase of flight. In this system, the throttle controls the power output as registered on the manifold pressure gauge, and the propeller control regulates the engine RPM (propeller RPM). The pitch angle of the blades is changed by governor regulated oil pressure which keeps engine speed at a constant selected RPM. A constant-speed propeller allows the pilot to select a small propeller blade angle (flat pitch) and high RPM to develop maximum power and thrust for takeoff.

To reduce the engine output to climb power after takeoff, a pilot should decrease the manifold pressure. The RPM is decreased by increasing the propeller blade angle. When the throttle is advanced (increased) during cruise, the propeller pitch angle will automatically increase to allow engine RPM to remain the same. A pilot should avoid a high manifold pressure setting with low RPM on engines equipped with a constant-speed propeller to prevent placing undue stress on engine components. To avoid high manifold pressure combined with low RPM, the manifold pressure should be reduced before reducing RPM when decreasing power settings, and the RPM increased before increasing the manifold pressure when increasing power settings.

Let’s take a look at these three sample knowledge test questions and see if we can answer them given the information from Monday and todays posts.

1. Which statement best describes the operating principle of a constant-speed propeller?
A—As throttle setting is changed by the pilot, the prop governor causes pitch angle of the propeller blades to remain unchanged.
B—A high blade angle, or increased pitch, reduces the propeller drag and allows more engine power for takeoffs.
C—The propeller control regulates the engine RPM and in turn the propeller RPM.

2. Propeller efficiency is the
A—ratio of thrust horsepower to brake horsepower.
B—actual distance a propeller advances in one revolution.
C—ratio of geometric pitch to effective pitch.

3. A fixed-pitch propeller is designed for best efficiency only at a given combination of
A—altitude and RPM.
B—airspeed and RPM.
C—airspeed and altitude.

Answers in the comments section.

The post CFI Brief: How does a Propeller Work? first appeared on Learn To Fly.

Propeller Principles
The aircraft propeller consists of two or more blades and a central hub to which the blades are attached. Each blade of an aircraft propeller is essentially a rotating wing. As a result of their construction, the propeller blades produce forces that create thrust to pull or push the airplane through the air.

The power needed to rotate the propeller blades is furnished by the engine. The propeller is mounted on a shaft. which may be an extension of the crankshaft on low-horsepower engines; on high-horsepower engines, it is mounted on a propeller shaft which is geared to the engine crankshaft. In either case. the engine rotates the airfoils of the blades through the air at high speeds, and the propeller transforms the rotary motion (power) of the engine into thrust.

The engine supplies brake horsepower through a rotating shaft. and the propeller converts it into thrust horsepower. In this conversion, some power is wasted. For maximum efficiency, the propeller must be designed to keep this waste as small as possible. Since the efficiency of any machine is the ratio of the useful power output to the power input, propeller efficiency is the ratio of thrust horsepower to brake horsepower. The usual symbol for propeller efficiency is the Greek letter η (eta). Propeller efficiency varies from 50% to 87%, depending on how much the propeller “slips.”

THP = BHP × Propeller Efficiency

Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch (see figure 1). Geometric pitch is the distance a propeller should advance in one revolution; effective pitch is the distance it actually advances. Thus, geometric or theoretical pitch is based on no slippage, but actual, or effective pitch, recognizes propeller slippage in the air.

The typical propeller blade can be described as a twisted airfoil of irregular planform. Two views of a propeller blade are shown in figure 2. For purposes of analysis, a blade can be divided into segments, which are located by station numbers in inches from the center of the blade hub. The cross sections of each 6-in. blade segment are shown as airfoils in the right-hand side of figure 2. Also identified in figure 2 are the blade shank and the blade butt. The blade shank is the thick, rounded portion of the propeller blade near the hub, which is designed to give strength to the blade. The blade butt, also called the blade base or root, is the end of the blade that fits in the propeller hub. The blade tip is that part of the propeller blade farthest from the hub, generally defined as the last 6 in. of the blade.

A cross section of a typical propeller blade is shown in figure 3. This section or blade element is an airfoil comparable to a cross section of an aircraft wing. The blade back is the cambered or curved side of the blade, similar to the upper surface of an aircraft wing. The blade face is the flat side of the propeller blade (“facing” the pilot, if the propeller is up front in the tractor position). The chord line is an imaginary line drawn through the blade from the leading edge to the trailing edge. The leading edge is the thick edge of the blade that meets the air as the propeller rotates.

Blade angle, usually measured in degrees, is the angle between the chord line of the blade and the plane of rotation (figure 4). The chord of the propeller blade is determined in about the same manner as the chord of an airfoil. In fact, a propeller blade can be considered as being made up of an infinite number of thin blade elements, each of which is a miniature airfoil section whose chord is the width of the propeller blade at that section. Because most propellers have a flat blade face, pitch is easily measured by finding the angle between a line drawn along the face of the propeller blade and a line scribed by the plane of rotation. Pitch is not the same as blade angle, but, because pitch is largely determined by blade angle, the two terms are often used interchangeably. An increase or decrease in one is usually associated with an increase or decrease in the other.

Forces Acting On The Propeller
A rotating propeller is acted upon by centrifugal, twisting, and bending forces. The principal forces acting on a rotating propeller are illustrated in figure 5.

Centrifugal force (A of figure 5) is a physical force that tends to throw the rotating propeller blades away from the hub. Torque bending force (B of figure 5), in the form of air resistance, tends to bend the propeller blades opposite to the direction of rotation. Thrust bending force (C of figure 5) is the thrust load that tends to bend propeller blades forward as the aircraft is pulled through the air. Aerodynamic twisting force (D of figure 5) creates a rotational force (twisting moment) about the center of pressure, causing the blade to tend to pitch to a lower blade angle (streamline).

At high angles of attack this twisting moment is reduced as the center of lift moves forward. At very high blade angles of attack, the blades may exhibit a weak tendency to pitch toward a greater blade angle.

Centrifugal twisting force also twists the blade to flat pitch (unless the blade is counterweighted so its center of mass is behind the center of rotation). This is a strong force at normal propeller speeds. Imagine a string tied to your finger and to a small weight (see figure 6). If the weight is spinning about your finger, the weight will align itself directly in line with the point on your finger where it is tied (reference the plane scribed by the spinning weight). This same force causes the center of mass of the propeller to align itself with the center of rotation on the spin-plane, causing a strong pitch tendency toward minimum blade pitch angle.

A propeller must be capable of withstanding severe stresses, which are greater near the hub, caused by centrifugal force and thrust. The stresses increase in proportion to the RPM. The blade face is also subjected to tension from the centrifugal force and additional tension from the bending. For these reasons, nicks or scratches on the blade may cause very serious consequences.

A propeller must also be rigid enough to prevent fluttering, a type of vibration in which the ends of the blade twist back and forth at high frequency around an axis perpendicular to the engine crankshaft. Fluttering is accompanied by a distinctive noise often mistaken for exhaust noise. The constant vibration tends to weaken the blade and eventually causes failure.

The post Aircraft Systems: Propeller Principles first appeared on Learn To Fly.

Most light aircraft engines are cooled externally by air. For internal cooling and lubrication, an engine depends on circulating oil. Engine lubricating oil not only prevents direct metal-to-metal contact of moving parts, it also absorbs and dissipates part of the engine heat produced by internal combustion. If the engine oil level is too low, an abnormally high engine oil temperature indication may result.

On the ground or in the air, excessively high engine temperatures can cause excessive oil consumption, loss of power, and possible permanent internal engine damage.

If the engine oil temperature and cylinder head temperature gauges have exceeded their normal operating range, or if the pilot suspects that the engine (with a fixed-pitch propeller) is detonating during climb-out, the pilot may have been operating with either too much power and the mixture set too lean, using fuel of too low a grade, or operating the engine with not enough oil in it. Reducing the rate of climb and increasing airspeed, enriching the fuel mixture, or retarding the throttle will help cool an overheating engine. Also, rapid throttle operation can induce detonation, which may detune the crankshaft.

The most important rule to remember in the event of a power failure after becoming airborne is to maintain safe airspeed. Now let’s go ahead and take a look at some sample knowledge test questions complete with explanations.

Excessively high engine temperatures, either in the air or on the ground, will
A. increase fuel consumption and may increase power due to the increased heat.
B. result in damage to heat-conducting hoses and warping of cylinder cooling fans.
C. cause loss of power, excessive oil consumption, and possible permanent internal engine damage.

High engine temperatures can lead to loss of power, excessive oil consumption, detonation, and serious engine damage.

If the engine oil temperature and cylinder head temperature gauges have exceeded their normal operating range, the pilot may have been operating with
A. the mixture set too rich
B. higher-than-normal oil pressure.
C. too much power and with the mixture set too lean.

Excessively high engine temperatures can result from insufficient cooling caused by too lean a mixture, too low a grade of fuel, low oil, or insufficient airflow over the engine.

Answer (A) is incorrect because a richer fuel mixture will normally cool an engine. Answer (B) is incorrect because high oil pressure does not cause high engine temperatures.

For internal cooling, reciprocating aircraft engines are especially dependent on
A. a properly functioning thermostat.
B. air flowing over the exhaust manifold.
C. the circulation of lubricating oil.

Oil, used primarily to lubricate the moving parts of the engine, also cools the internal parts of the engine as it circulates.

Answer (A) is incorrect because most air-cooled aircraft engines do not have thermostats. Answer (B) is incorrect because, although air-cooling is important, internal cooling is more reliant on oil circulation. Air cools the cylinders, not the exhaust manifold.

An abnormally high engine oil temperature indication may be caused by
A. the oil level being too low.
B. operating with a too high viscosity oil.
C. operating with an excessively rich mixture.

Oil, used primarily to lubricate the moving parts of the engine, also helps reduce engine temperature by removing some of the heat from the cylinders. Therefore, if the oil level is too low, the transfer of heat to less oil would cause the oil temperature to rise.

Answer (B) is incorrect because the higher the viscosity, the better the lubricating and cooling capability of the oil. Answer (C) is incorrect because a rich fuel/air mixture usually decreases engine temperature.

What action can a pilot take to aid in cooling an engine that is overheating during a climb?
A. Reduce rate of climb and increase airspeed.
B. Reduce climb speed and increase RPM.
C. Increase climb speed and increase RPM.

To avoid excessive cylinder head temperatures, a pilot can open the cowl flaps, increase airspeed, enrich the mixture, or reduce power. Any of these procedures will aid in reducing the engine temperature. Establishing a shallower climb (increasing airspeed) increases the airflow through the cooling system, reducing high engine temperatures.

Answer (B) is incorrect because reducing airspeed hinders cooling, and increasing RPM will further increase engine temperature. Answer (C) is incorrect because increasing RPM will increase engine temperature.

The post CFI Brief: It’s Getting Hot in Here. first appeared on Learn To Fly.

The burning fuel within the cylinders produces intense heat, most of which is expelled through the exhaust system. Much of the remaining heat, however, must be removed, or at least dissipated, to prevent the engine from overheating. Otherwise, the extremely high engine temperatures can lead to loss of power, excessive oil consumption, detonation, and serious engine damage.

While the oil system is vital to the internal cooling of the engine, an additional method of cooling is necessary for the engine’s external surface. Most small aircraft are air cooled, although some are liquid cooled.

Air cooling is accomplished by air flowing into the engine compartment through openings in front of the engine cowling. Baffles route this air over fins attached to the engine cylinders, and other parts of the engine, where the air absorbs the engine heat. Expulsion of the hot air takes place through one or more openings in the lower, aft portion of the engine cowling.

The outside air enters the engine compartment through an inlet behind the propeller hub. Baffles direct it to the hottest parts of the engine, primarily the cylinders, which have fins that increase the area exposed to the airflow.

The air cooling system is less effective during ground operations, takeoffs, go-arounds, and other periods of highpower, low-airspeed operation. Conversely, high-speed descents provide excess air and can shock cool the engine, subjecting it to abrupt temperature fluctuations.

Operating the engine at higher than its designed temperature can cause loss of power, excessive oil consumption, and detonation. It will also lead to serious permanent damage, such as scoring the cylinder walls, damaging the pistons and rings, and burning and warping the valves. Monitoring the flight deck engine temperature instruments aids in avoiding high operating temperature.

Under normal operating conditions in aircraft not equipped with cowl flaps, the engine temperature can be controlled by changing the airspeed or the power output of the engine. High engine temperatures can be decreased by increasing the airspeed and/or reducing the power.

The oil temperature gauge gives an indirect and delayed indication of rising engine temperature, but can be used for determining engine temperature if this is the only means available.

Most aircraft are equipped with a cylinder-head temperature gauge that indicates a direct and immediate cylinder temperature change. This instrument is calibrated in degrees Celsius or Fahrenheit and is usually color coded with a green arc to indicate the normal operating range. A red line on the instrument indicates maximum allowable cylinder head temperature.

To avoid excessive cylinder head temperatures, increase airspeed, enrich the fuel-air mixture, and/or reduce power. Any of these procedures help to reduce the engine temperature. On aircraft equipped with cowl flaps, use the cowl flap positions to control the temperature. Cowl flaps are hinged covers that fit over the opening through which the hot air is expelled. If the engine temperature is low, the cowl flaps can be closed, thereby restricting the flow of expelled hot air and increasing engine temperature. If the engine temperature is high, the cowl flaps can be opened to permit a greater flow of air through the system, thereby decreasing the engine temperature.

The post Aircraft Systems: Engine Cooling Systems first appeared on Learn To Fly.

There are two basic types of electricity: static and current. In static electricity, electrons accumulate on a surface and remain here until they build up a pressure high enough to force their way to another surface or device which has fewer electrons. Static electricity is generally a bother, and steps must be taken to prevent its formation and/or to get rid of it.

Current electricity, on the other hand, is the type most often used. There are two types of current electricity, Direct Current (DC), in which the electrons always flow in the same direction, and Alternating Current (AC), in which the electrons periodically reverse their direction of flow.

Static Electricity
When you slide across the plastic seat covers of an automobile, the friction between your clothing and the seat covers causes your clothes to pick up an excess of electrons from the seat. This is exactly the same thing described earlier when a piece of amber was rubbed with sheep’s wool.

If there is no conductor between your body and the car to make a path for these electrons to leak off, your body holds the extra electrons and is said to be charged because there is an electrically unbalanced condition between it and the car. But as soon as you touch or even come close to a bare metal part of the car, the extra electrons leave and jump to the metal in the form of a spark. This accumulation and holding of electrical charges is called static electricity.

Lightning is just a big spark. Friction of the air moving up and down inside the clouds causes water droplets in the clouds to become charged, and when enough electrons have concentrated in a cloud, the electrical pressure they produce forces them to move through the air. These electrons jump between clouds having different charges or from a cloud to the ground. This is the gigantic spark we call lightning.

As mentioned earlier, an object with an excess of electrons is negatively charged, and an object which has lost its electrons and wants to get them back is positively charged. Two positively charged or two negatively charged objects repel each other, while objects having opposite charges attract. When oppositely charged objects touch, the extra electrons travel from the negative object to the one with the positive charge and they become discharged, or electrically neutral. While static electricity has some uses, it is most often thought of as a nuisance. So a path must be provided to allow the electrons to pass harmlessly from one charged object to another before the charges can build up enough pressure to cause a spark to jump.

In addition to producing a mild shock when you touch the metal part of your car, static electricity can cause radio interference and can damage sensitive electronic components. It is possible, on a dry day, that just taking a few steps on a nylon carpet can build up more than 10,000 volts of static electricity on your body. When you have accumulated this much charge and touch some electronic components, they can be destroyed. When working with sensitive electronic equipment, always wear a grounded wrist strap to bleed off any charge on your body before handling the equipment.

Many airplanes have static discharge points or wicks installed on the trailing edges of the control surfaces. These devices allow the static charges that build up on the control surfaces as air flows over them to discharge harmlessly into the air and not cause static interference in the radio equipment.

Static electricity causes a serious fire hazard when aircraft are being fueled or defueled. The flow of gasoline or turbine fuel in the hose produces enough static electricity to cause a spark to jump and ignite explosive fumes.

Current Electricity
Current electricity is the form of electricity that has the most practical applications. A source of electrical energy such as a battery or alternator acts as a pump that forces electrons to flow through conductors. In this study of practical electricity, this flow is called current and because we are considering it to flow from positive to negative, it is positive current.

For current to flow, there must be a complete path from one terminal of the source back to the other terminal. The figure below shows a complete electrical circuit. The battery is the component in which chemical energy is changed into electrical energy, and current is forced out of the positive terminal, through the switch, the control device, to the lamp. The lamp acts as the load, which changes electrical energy into heat and light. The current then returns to the negative terminal of the battery. Current flows as long as the switch is closed, forming a complete path.

The electrical pressure that forces current through the circuit is measured in volts, with the basic unit of electrical pressure being one volt. Electrical current is measured in amperes or, as we more commonly call it, in amps. One amp is the flow of one coulomb per second, and one coulomb is 6.28 billion billion (6.28 x 1018) electrons. All conductors have some resistance which opposes the flow of electrons in much the same way that friction opposes mechanical movement. The basic unit of electrical resistance is the ohm. One volt of electrical pressure will force 1 amp of current to flow through 1 ohm of resistance.

When current flows through a resistor, power is dissipated and voltage is dropped. The voltage across a resistor can be measured with a voltmeter in the same way as the voltage produced by a battery. This voltage is caused by current (I) flowing through the resistor (R), and it is called an IR drop, or a voltage drop. The end of the resistor where the positive current enters is the positive end, and the end where it leaves is the negative end.

When current flows through a resistance, power is used, or dissipated, and voltage is dropped. The voltage dropped across a resistor can be measured with a voltmeter in the same way as the voltage produced across the terminals of a battery.

Electrical pressure caused by changing some other form of energy into electrical energy may be called an electromotive force (EMF) a potential difference, or just a potential. Electrical pressure caused by current flowing through a resistance is not a source of electrical energy; it is a drop in the electrical pressure. This voltage is usually called a voltage drop or an IR drop because the amount of drop may be found by multiplying the current (I) by the resistance (R) through which it flows. These terms for voltage are often used interchangeably, and all of them use the volt as the basic unit of measurement.

The post Aircraft Systems: Types of Electricity first appeared on Learn To Fly.

One of the biggest differences to point out revolves around the way the flight controls are moved. Because of the high air loads, it is very difficult to move the flight control surfaces of jet aircraft with just mechanical and aerodynamic forces. So flight controls are usually moved by hydraulic actuators. Flight controls are divided into primary flight controls and secondary (or auxiliary) flight controls. The primary flight controls are those that maneuver the aircraft in roll, pitch, and yaw. These include the ailerons, elevator, and rudder. Secondary (or auxiliary) flight controls include tabs, trailing-edge flaps, leading-edge flaps, spoilers, and slats.

Roll control of most jet aircraft is accomplished by ailerons and flight spoilers. The exact mix of controls is determined by the aircraft’s flight regime. In low speed flight, all control surfaces operate to provide the desired roll control. As the aircraft moves into higher speed operations, control surface movement is reduced to provide approximately the same roll response to a given input through a wide range of speeds.

Many aircraft have two sets of ailerons—inboard and outboard. The inboard ailerons operate in all flight regimes. The outboard ailerons work only when the wing flaps are extended and are automatically locked out when flaps are retracted. This allows good roll response in low speed flight with the flaps extended and prevents excessive roll and wing bending at high speeds when the flaps are retracted.

Spoilers increase drag and reduce lift on the wing. If raised on only one wing, they aid roll control by causing that wing to drop. If the spoilers rise symmetrically in flight, the aircraft can either be slowed in level flight or can descend rapidly without an increase in airspeed. When the spoilers rise on the ground at high speeds, they destroy the wing’s lift which puts more of the aircraft’s weight on its wheels which in turn makes the brakes more effective.

Often aircraft have both flight and ground spoilers. The flight spoilers are available both in flight and on the ground. However, the ground spoilers can only be raised when the weight of the aircraft is on the landing gear. When the spoilers deploy on the ground, they decrease lift and make the brakes more effective. In flight, a ground-sensing switch on the landing gear prevents deployment of the ground spoilers.

Vortex generators are small (an inch or so high) aerodynamic surfaces located in different places on different airplanes. They prevent undesirable airflow separation from the surface by mixing the boundary airflow with the high energy airflow just above the surface. When located on the upper surface of a wing, the vortex generators prevent shock-induced separation from the wing as the aircraft approaches its critical Mach number. This increases aileron effectiveness at high speeds.

As you progress through the ranks of aviation and begin flying larger aircraft you will start noticing some of these secondary flight controls installed on your aircraft. But many of the training aircraft like the Cessna 172’s, Piper Archers, or piston powered aircraft you might be flying today won’t have secondary controls such as spoilers installed. The majority of the time these aircraft are just not large enough, heavy enough or fast enough that spoilers would be an effective or beneficial flight control. It is however beneficial to gain experience in the knowledge of these flight control systems as it will help you later on in training when you merge your private and professional aerodynamics lessons into practice.

For more advanced information on aerodynamics check out our collegiate level textbook, Aerodynamics for Aviators.

The post CFI Brief: Flight Controls of a typical Commercial Airliner first appeared on Learn To Fly.