PHAK Ch 7 (Aircraft Systems)

Question 1

Cessna 172S Engine

Answer 1

Reciprocating Engine: two types (spark ignition) and (compression ignition)
Both use cylinders and pistons to convert linear motion to the rotary motion of the crank shaft. Differ in the process of igniting the fuel: Spark engines use spark plugs (CESSNA 172S), and compression engines compresses the fuel air mixture raising the temperature of the fuel for automatic ignition.

Question 2

Horizontally Opposed Engine

Answer 2

Horizontal or Flat engine, with equal cylinders on each side that opposes the cylinder on the other side. MINIMIZES DRAG AND LIGHTWEIGHT CRANKCASE

Question 3

Operating Cycle (How many cylinders?)

Answer 3

Main Parts of a Spark Ignition Four Stroke Engine: cylinders, crank case, accessory housing. Intake/exhaust valves, spark plugs, pistons (in the cylinders). Crankshaft and connecting rods (in the crankcase), magnetos (engine accessory housing)

Four Cylinder Engine: the conversion of chemical energy into mechanical energy occurs over a four stroke operating cycle

Intake
Compression
Power
Exhaust

Question 4

Four STAGES of the Four Stroke Operating Cycle

Answer 4

Intake: piston goes down, intake valve opens fuel air mixture is drawn into cylinder
Compression: intake valve closes, piston moves back up, compressing the fuel air mixture
Ignition: Spark plug ignites the fuel air mixture, forcing the piston down and turns the crankshaft
Exhaust: exhaust valve opens and the burned gases are vented out, the cylinder begins to move back up.

FOUR STROKE….. EACH CYLINDER OPERATES ON A DIFFERENT STROKE

Question 5

Propeller (General Information, AirFoil)

Answer 5

A rotating airfoil/ wing (Generates thrust: all based on the shape of the airfoil, AOA, and the RPM of the engine) Twisted from the hub to the tip.

The greatest angle of incidence (AOA) or the highest pitch is at the hub, while the smallest pitch or smallest angle of incidence is at the tip. (The reason for the twist is to produce uniform lift from the hub to the tip, Needed due to the speed difference at the tip and the base of the prop (tip travels faster than the base (more distance))

Two types: fixed pitch or adjustable pitch

Question 6

Fixed Pitch Propeller (CESSNA 172S)

Answer 6

The pitch of the airfoil/propeller is set by the manufacturer, cannot be adjusted in flight, this setting only has the best efficiency at a given combination of airspeed and RPM.

Two types: climb and cruise.
Climb: has a lower pitch, therefore less drag, this results in higher rpm, more horsepower capability. Increases performance during Takeoffs and Climbs.
Cruise: has a higher pitch, therefore more drag, this results in lower rpm and less horsepower capability, which increases performance during Cruising Flight.

Question 7

Crankshaft and Throttle Control (In regards to the Propeller)

Answer 7

The propeller is connected to the crankshaft, engine rpm is the same as the crankshaft rpm.
In fixed pitch tachometer is the indicator of the engine rpm.

The RPM is regulated by the Throttle, which controls the fuel-air-flow to the engine. At a given altitude, the higher the tachometer reading, the higher the power output of the engine.

DENSITY ALTITUDE (HIGH) DECREASES THE POWER OUTPUT OF THE ENGINE, AS ALTITUDE CHANGES THROTTLE MUST BE CHANGED TO MAINTAIN THE SAME RPM

Question 8

Propeller (CESSNA 172S)
NEED TO KNOW SPECS

Answer 8

Fluxed pitch propeller, 76 inches in diameter (needs to be at least 75in)
Aluminum Alloy Propeller

Prop Manufacturer: McCauley Propeller Systems

Question 9

Adjustable Pitch Propeller (NOT CESSNA 172S)
Constant Speed Propeller (NOT CESSNA 172S)

Answer 9

Adjustable Pitch Propeller: The pitch can be adjusted on the ground, cannot be adjusted in flight.

Constant Speed Propeller: where the pitch can be varied automatically in flight, using the throttle and the propeller control. The throttle controls power output and the propeller control regulates engine RPM. MANIFOLD PRESSURE GAUGE, only in constant speed props

Question 10

Induction Systems

Answer 10

It brings air from the outside, mixes it with fuel, delivers the fuel air mixture into the cylinder.
Intakes through the air vent (filtered) at the front of the engine’s cowling.

If the filter becomes clogged, alternate door opens automatically due to suction, 10% engine power loss at full throttle.

Two Types: Carburetor Systems (NOT CESSNA 172S) and Fuel Injection (CESSNA 172S)

Question 11

Carburetors Systems

Answer 11

Float Type: most common outside air flows through an air filter, then flows into carburetor through Venturi, (low pressure force, cause of the smaller space ) ( in the Venturi), the fuel air mixture is then drawn through the intake manifold and into the combustion chambers where it is ignited. Needle meters the amount of fuel entering the carburetor, depending on the position of the float. The flow of the fuel-air mixture to the combustion chambers is regulated by the throttle valve, in the flight deck.

Pressure Type: NOT AS COMMON discharges fuel into the airstream at a pressure well above atmospheric pressure.

Question 12

Carburetor Disadvantages

Answer 12

1) They do not function well with abrupt maneuvers
2) Incomplete vaporization (b/c of low pressure) and difficulty discharging fuel into some supercharged systems
3) Icing tendencies (b/c fuel is released at an area of low pressure in the Venturi throat )( ) this is due to the drop in temperature (due to low pressure area) because of fuel vaporization takes place within the Venturi, ice readily forms in the Venturi and on the throttle valve. CAN ICE AT 70F or 21F with high humidity above 80%

INDICATED BY: ENGINE ROUGHNESS, DECREASE IN ENGINE RPM, (CONSTANT SPEED PITCH PROPELLER SHOWN by DECREASE IN MANIFOLD PRESSURE)

Question 13

Carburetor Heat

Answer 13

Preheats the air before it reaches the carburetor, can be used to melt ice that has already formed in the carburetor, Should be used as a preventative measure should be left in the ON position until the pilot is SURE the ice is removed. Otherwise could aggravate the situation.

Use of carb heat causes a decrease in engine power by 10%, because the hot air is less dense than the outside air. Thus a decrease in rpm (also some engine roughness), follow by a gradual increase in rpm, if no ice then the engine decreases in rpm and remains constant.

Carb Heat should not be used when full power is required (during takeoff) or during normal engine operation.

Question 14

Fuel Injection Systems (CESSNA 172S)

Answer 14

The fuel is injected directly into the cylinders

6 Basic Components:
Engine Driven Fuel Pump
Fuel Air Control Unit
Fuel Manifold/ Fuel Distributor
Discharge Nozzles
Aux Fuel Pump
Fuel Pressure/Flow Indicators

Question 15

Auxiliary and Engine Driven Fuel Pump

Answer 15

Auxiliary: provides fuel UNDER PRESSURE to the fuel-air control unit for engine starting and/or emergency use.
AFTER STARTING…
Engine Driven Fuel Pump: provides fuel UNDER PRESSURE from the fuel tank to the fuel-air control unit.

Question 16

Fuel Air Control Unit

Answer 16

REPLACES THE CARBURETOR

Meters the fuel based on the mixture control settings and it sends it to the fuel manifold valve at a rate controlled by the THROTTLE

Question 17

Fuel Manifold Valve

Answer 17

The fuel is distributed to the individual fuel discharge nozzles.

Question 18

Fuel Discharge Nozzles

Answer 18

Located in each cylinder head, Inject fuel-air mixture directly into each cylinder intake port

Question 19

Fuel Injection (Advantages & Disadvatages)

Answer 19

Advantages:
Less susceptible to icing, (still could have impact icing: ice occurring on the outside of the aircraft, covering important bits)
Better fuel flow
Faster throttle response
Precise mixture control
Fuel Economic
Easier for Cold Weather Starts

Disadvantages:
Difficulty in starting Hot Engine
Vapor locks during ground operations on Hot Days
Problems restarting due to fuel starvation

Question 20

Fuel Quantity Indicators

Answer 20

Fuel Quantity Indicators will detect low fuel conditions and incorrect sensor outputs, when fuel quantity is less than 5 gallons indicated (and remains less than 60secs), will display on the PFD.

Question 21

Fuel Injection “Flow”

Answer 21

From Fuel Tank (gravity fed and fuel vented for better flow)
To Auxiliarly Fuel Pump (During Start) provides fuel under pressure to fuel air control unit
**To Engine Driven Fuel Pump (After Start) Provides fuel under pressure to fuel air control unit

The Fuel Air Control Unit meters fuel (based on the mixture) and air (based on the throttle) and mixes these together at a rate controlled by the throttle. Then sends it off to the fuel manifold valve.
The Fuel Manifold Valve, this distributes fuel into the individual fuel discharge nozzles,
The Fuel Injection Nozzles, inject the fuel-air mixture directly into each cylinder intake port.

General Flow: Starting (Aux fuel Pump) After Start (Engine Driven Fuel Pump), to the Fuel-Air Control Unit (mixes fuel and air using mixture and throttle), Fuel Manifold Valve (Distributed Fuel to Nozzles) Fuel Nozzles (Distributes Fuel to the Cylinders)

Question 22

Naturally Aspirated

Answer 22

The air from the outside is naturally pumped into the cylinder, Which means there are no turbo chargers or super chargers.

Question 23

Engine Specs

Answer 23

Cessna 172S Engine Model Number: I0-360-L2A.
Engine Type: Normally aspirated, direct drive, air-cooled, horizontally opposed, fuel injected, four cylinder engine with 360 cubic inches of displacement.

Question 24

Direct Drive

Answer 24

The Cessna 172S has one gear and dose not have changeable gears

Question 25

Ignition System

Answer 25

Spark Ignition: the ignition system provides the spark (spark plugs) that ignites the fuel-air mixture in the cylinders.

It is made up of spark plugs, magnetos, high-tension leads and ignition switch

Question 26

Magnetos

Answer 26

Uses a permanent magnet to generate an electrical current completely independent from the aircraft’s electrical system.

Two individual magnetos, four spark plugs, with separate sets of wires.
Each magnetos fires one of the two spark plugs in each cylinder.

Using BOTH magnetos improves combustion of the fuel air mixture and results in a slightly higher power output.
Using either the L or R magneto creates a slight decrease in engine power can be expected.

If more than the normal RPM drop is dented at Run Up checklist (do not fly aircraft) could be fouled plugs.

Question 27

Ignition Switch

Answer 27

Following engine shutdown, the engine (even with master and battery off) can fire and turn over is the ignition is left on and the propeller is moved. BECAUSE the magneto requires no outside source of electrical power Or even if the Ignition Switch is left on the OFF position the ground wire is disconnected or broken, the engine can start if the propeller is moved and their is fuel left in the cylinders. MIXTURE should be left in the idle cutoff position

Question 28

Oil Systems

Answer 28

Several Functions: lubrication of the engines moving parts, cooling of the engine (reduces friction), removing heat from the cylinders, providing a seal between the cylinders walls and pistons, carrying away contaminants.

Two different types of systems: wet sump CESSNA 172S or dry sump (oil contained in separate tank)

Wet sump: the oil is located in a sump that is an integral part of the engine. This uses an oil pump which draws oil from the sump and rotates it to the engine, after this oil passes through the engine it RETURNS to the sump.

Question 29

Oil Pressure Gauge
Oil Temperature Gauge

Answer 29

Provides a direct indication of the oil system operation. Pressure in (PSI) of the oil supplied to the engine.

Oil Temperature gauge: provides the temperature of the oil. *oil temperature changes more slowly,
High temp indicator may suggest a blocked oil line, low oil quantity, blocked oil cooler, or deceptive temperature gauge.
*Low temp indication improper viscosity during cold weather operations

Question 30

Engine Cooling System

Answer 30

Burning fuel in the cylinders creates an intense heat, some removed through the exhaust, some of it needs a cooling system to prevent overheating…. Cessna 172S are air cooled through the use of air entering the filtered air inlet vent located under the propeller on the fuselage, BAFFLES route the air over FINS attached to the engines cylinders. Hot air is removed through the aft portion of the engine’s cowling.

Air cooling is less effective during ground operations, takeoffs, go arounds, and other times of high power settings and low-airspeed operations… high speed descents can provide excess air and shock cool the engine; leading to abrupt changes in temperature.

Question 31

Extremely High Engine Temperatures

Answer 31

Can lead to loss of power, excessive oil consumption, detonation, and serious engine damage.
If high engine temperatures are seen a change in the airspeed or the power output of the engine can be decreased by increasing the airspeed and decreasing the engine power.

Question 32

Cylinder Head Temperature Gauge

Answer 32

Indicates a direct and immediate cylinder temperature change, to avoid excessive cylinder head temperatures, increase airspeed, enrichen the fuel mixture, and reduce power.

Question 33

Exhaust System

Answer 33

Engine Exhaust System: vent the burned combustion gases overboard, provides heat to the cabin, and defrost the windscreen.

They have a exhaust piping attached to the cylinders, as well as a muffler and a muffler shroud.

Exhaust gases are pushed out of the cylinder through the exhaust valve and then through the exhaust pipe system into the atmosphere.

Exhaust contains Carbon Monoxide double check the exhaust pipe is in good condition and free of cracks.

Question 34

Cabin Heat

Answer 34

Exhaust gas is outside air that is drawn into the air inlet and is ducted through the shroud around the muffler, the muffler is hot from the exhaust gases, this heats the clean air through the shroud and delivers it into the cabin for heat and defrosting applications.

Question 35

EGT Probe

Answer 35

Exhaust Gas Temperature Prob- measures the temperature of the exhaust gases at the exhaust manifold.

Question 36

EGT Probe

Answer 36

Exhaust Gas Temperature Prob- measures the temperature of the exhaust gases at the exhaust manifold.

Question 37

Starting System

Answer 37

Direct Cranking Electric Starter System: consists of source of electricity, wiring systems, switches and solenoids.

Question 38

Starting System

Answer 38

Direct Cranking Electric Starter System: consists of source of electricity, wiring systems, switches and solenoids.

Question 39

The Starter Process for Cranking the Engine

Answer 39

Starter engages the flywheel, rotating the engine at a speed that allows the engine to start and maintain operation.

Question 40

Detonation vs Pre-ignition

Answer 40

Denotation: is an uncontrolled, explosive ignition of the fuel-air mixture within the cylinder’s combustion chamber, causes engine overheating, roughness or loss of power

Characterized By: high cylinder head temperatures, and high power settings

*use of lower fuel grade than specified
*operating the engine with extremely high manifold pressures with low RPM
*operation of the engine at high power settings with an excessively lean mixture
*extended ground operations or steep climbs that reduce cylinder cooling

Pre-Ignition: occurs when the fuel air mixture ignites prior to the engine’s normal ignition event, causes the engine to lose power and produces high operating temperatures, can severely damage the engine

*caused by residual hot spots in the combustion chamber
*often created by a small carbon deposit on a spark plug
*a cracked spark plug insulator, or other damage in the cylinder… anything that causes heat sufficient enough to ignite the fuel-air mixture

CAN OCCUR SIMULTANEOUSLY ONE MAY CAUSE THE OTHER***

Ways to avoid: always use the recommended grade of fuel and operate the engine within its proper temperature, pressure and rpm ranges.

Question 41

Airframe Systems

Answer 41

Fuel, Electrical, Hydraulic and Oxygen Systems make up the airframe systems

Question 42

Fuel System

Answer 42

The fuel system is designed to provide uninterrupted flow of clean fuel from the fuel tanks to the engine. The fuel MUST be available to the engine under all conditions.

Two types: gravity fed and fuel pump systems

Question 43

Gravity Fed System (CESSNA 172S)

Answer 43

Utilizes the force of gravity, high wing airplanes to the engine from the wings (flow downward), gravity feeds the fuel into the carburetor

Question 44

Fuel Pump System (CESSNA 172S TECHNICALLY)

Answer 44

Aircraft with two fuel pumps, the main fuel pump is engine driven, with an electrically driven auxiliary fuel pump (provided for engine starting and emergency situations) the Auxiliary Pump (also called the boost pump) adds reliability to the system and is controlled by a switch in the flight deck