CFI Exam 3 - Systems and Airspace

Horizontally Opposed (Boxer) Engine Advantages

• Perfect primary balance (no balance shafts drawing power) 

• Less vibration 

• Thrust line is where we want it 

What is the typical engine of cars?

In line (first picture) or V engine (second picture)

Piston

• Moves up and down in a cylinder (permanent assembly) 

• Pushed by combustion gases 

• Airtight seal is created by piston rings and oil 

Piston Rings

• Compression Ring – create airtight seal 

• Scraper Ring – scrapes oil back down 

Connecting Rod

• Connects piston and crankshaft 

• Small end is the piston end and connects using a “wrist pin” (aka piston pin, gudgeon pin)

• Larger end connects to the crankshaft using a “crank pin”

  • the end of the rod is split into two halves (rod and cap) which are bolted around the crank pin (aka crankshaft journal)

Crankshaft

• Big, heavy, forged then machined 

• Crankshaft journal  

  • the part the piston rod connects to in order to spin the crankshaft, because crank pins are specific journals on the crankshaft

• Rides on main bearing  

• Turns the propellor (direct drive) 

Transmission means

A lot of GA airplanes have a transmission or gearbox (non-direct drive) 

Camshaft

• Controls the valve opening and closing and is geared to the crankshaft

• ROTATES AT ½ SPEED OF CRANKSHAFT

  • because four stroke engine requires TWO revolutions for ONE CYCLE, the camshaft turns at ½ speed to open and close the valves ONCE per cycle

Crankcase

• Holds the engine block 

• “Splitting the case” - much more expensive repair if the crankcase has to be split 

• Cylinders individually attach to it (each cylinder can be independently removed) 

Cylinder

• have cooling fins

• bolted to crankcase so can be removed individually

• have intake and exhaust valve

4 Stroke Engine

1. Intake

2. Compression

3. Power

4. Exhaust

Cylinder valves

• controlled by the camshaft

• If engine feels like it wants to shake itself apart -> PROBABLY HAVE A STUCK VALVE -> probably going to make it back to the airport -> most common failure mode of GA aircraft engines (one cylinder is not firing) 

  • Probably won’t see anomalies in engine temp and pressure except a really cold cylinder temp if it isn’t firing 

• Sealing is done by the valve face. This means the Exhaust valve can stick open because it must defeat the spring to close. 

Camshaft rocker arm, push rod, and spring

• As the cam rotates, the shape of the metal pushes the push rod upwards which then tilts the rocker arm, compressing the spring and pushing the valve downwards to close and vice versa

• Sealing is done by the valve face (the plunger part of the valve)

• Because the SPRING MUST BE DEFEATED to close the valve, the valve CAN GET STUCK OPEN

If the engine feels like it wants to shake itself apart, this could mean

• you have a stuck valve

• you will probably make it back to the airport

  • one cylinder not firing is the MOST COMMON FAILURE MODE OF GA ENGINES

• You will probably NOT anomalies in engine temp or pressure, except for a really cold cylinder if the temp isn’t firing

Poppet - type valve

• aka mushroom valve - the shape creates a seal (valve face)

• valve used by camshaft to control intake and exhaust

What planes at OSU are carbureted

Seminoles, some 172s, 150 and 152 are carbureted at OSU 

Stoichiometric Ratio

• All the fuel and oxygen atoms burn without excess

• Fuel to Air is usually 12:1

An atom has a

nucleus with proton, neutron, and tiny electron on outside spinning around it (valence ring) 

Electricity

Electron flow through a conductor (anything can be a conductor)

What causes electron flow?

• electromotive force

  • Flow from a surplus to a deficiency (positively ionized atom to a negatively ionized atom) 

  • More electrons – negatively ionized 

  • Less electrons – positively ionized 

• Excessive electron flow can cause heat and damage

Resistor

• Holds electrons tightly 

  • ex: AIR

• Electron flow -> heat -> melts insulator -> short circuit. As a result, need resistor to REDUCE AMPERAGE 

• Can also be used as an insulator

• Measured in OHMS (unit of measure for electrical resistance)

Conductor

• does NOT hold electrons tightly (allows them to flow)

Voltage

Voltage (V) 

• “The force that makes the electron flow” 

• The water behind the damn (electromotive force) 

• High voltage can cause objects to become ionized by creating an electric field

Amperage (I)

• The actual current flow  

  • ex: Water moving through the dam hole 

  • 6.28*10^18 electrons must flow past one point per second to equal a singular amp  

  • Finite number of electrons flowing through a point in circuit 

• Means you can have a lot of voltage and 0 amperage 

• Too much amperage -> too much heat -> damages conductor-> need resistor 

OHMS (R)

• Measure of resistance (refers to a material that hold electrons tightly) 

• Quantifiable  

Voltage equation

• V = I * R

  • For example, if you have a finite voltage, then you can decrease resistance to increase amperage

Mechanical Generator

• has stator, rotor, and commutator

• permanent magnets/residual magnetism to start

What current is used in electrical systems

• DC - direct current

Rotor

• rotating part of the generator that creates magnetic field when it moves through the stationary stator

• usually shaft (Ferrus/Iron) and coils of wire

Stator

• stationary part of generator

• magnets aligned in a circle

Commutator

• converts AC to DC

• uses split rings which are rotated by the force (slip rings if an AC generator)

Electrical Switch

• Open – leaves gap in circuit 

• Closed – completes circuit allowing energy to flow 

Fuse

• Burns up when amperage is too high, creating a gap in the circuit 

  • “calibrated conductor” - RATED IN AMPS 

  • Looks like a horizontal S in the line 

  • Disadvantage because must be replaced to restore electricity to the circuit 

Circuit Breaker 

• Current creates lines of flux around a conductor 

• Induced magnetism pulls on a soft metal core, opening the circuit 

• Advantage is that you can simply push back in to reset the circuit 

• Looks like a hump/upside down U in diagram 

Starter

• Requires significant amperage - more than used in the airplane’s normal electrical circuit 

  • uses relay/contactor/solenoid and separate, high amp circuit 

Relay/Solenoid/Contactor 

• Current flows through resistor and coil 

  • When switch is flipped, a higher amperage circuit is completed by another switch (see textbook) 

  • Looks like a T BAR 

Single Pole/ Throw Switch

See diagram

Ground Symbol

• Means circuit is complete 

• LOOK UP SYMBOL (look like tornado) 

Alternator

• Uses electromagnet

• Requires “Flashing the field” - restoring residual magnetism after long periods of inactivity/replacement - REQUIRES BATTERY CURRENT TO DO SO, UNLIKE GENERATOR

• uses “Rectifier” to convert AC to DC (not a commutator)

ADVANTAGES

• smaller

• lighter

• produce higher power at lower engine RPMs

Magnetos

• Is its own (engine driven) mini generator, uses IMPULSE COUPLER to get enough charge at low RPMs to ignite fuel-air mixture

• Ferrus metal moves relative to conductor with ferrus metal 

  • Around the conductor is wire coil wrapped in a secondary coil 

• Once current on primary is stopped, current transfers to secondary coil (research transformer) 

• LOTS OF VOLTS created, Not a lot of amps 

Transformer

Transforms quantity of voltage 

Spark Plug 

• Nothing electrical 

• Voltage from the magneto ignites electrons in the air, creating a visible spark at the right time (ignition timing) 

Bus Bar

Conductor w/ holes where you can connect things 

Starter

Most modern training airplanes have electric battery powered starter which then activates the solenoid switch, cranking the crankshaft which moves the engine and allows the engine driven magnetos to activate

Wet Sump Oil System

• Engine Case has oil below it in the engine block and sump below it 

• Most GA aircraft use this

• Can be pressurized if have fuel pump

What 6 main functions does oil perform?

• Lubricates​

• Cools​

• Absorbs Heat​

• Cushions​

• Seals​

• Cleans (Carries away abrasives)

Viscosity

• thickness of oil (resistance to flow)

• usually 0 or 5W20 based on SAE scale

• Bigger number → more viscous oil

Lubricity

slipperiness of oil

What oils do we use at OSU

• mineral oil

• multi vis ashless dispersant

Pressurized oil system

• EVERY ENGINE WITH A PRESSURIZED SYSTEM HAS AN OIL PUMP 

• Has pressure relief valve to allow oil to go back to the sump (around 115 PSI) 

• An oil pump “picks up” oil from sump, pumps oil through galleys to critical engine components.​

• Typical oil pressure 60-90 psi.​

• Minimum oil pressure 25 psi.​

• Maximum oil pressure 115 psi​

• Loss of oil pressure may indicate pending engine failure.

Plain Bearings

• Used at critical points (crankshaft main bearings, connecting rod bearings, camshaft bearings, etc.).

  • Film of oil “separates” inner and outer race of bearings, oil supplied by pressurized oil via galleys.​

  • Plain bearings have no rotating surfaces.

• Other types of bearings use rotating surface: ball bearings, roller bearings, etc.

Plain Bearing Failure

Dropping oil pressure -> increased oil temp and failure is imminent 

• Bearings are weld themselves together (causing galling) which can “throw a rod” and stop the engine -> orbit that field and prepare to land 

  • Differs from stuck valve because you won’t see the dropping pressure and temp with stuck valve with stuck valve

  • With stuck valve you can try to find the nearest airport instead of orbiting the immediate field to land 

How is oil cooled?

Oil Cooled by passing through oil cooler en route to sump.

Dry Sump Oil System

• Has oil in separate tank 

• Transported by transfer pump or scavenge pump 

GA aircraft typically use

• air cooled engines

• 1/3 as efficient as liquid cooled but more reliable

  • No coolant, hoses, fittings, or water pump to fail.​

  • Operating temperature range greater with correspondingly greater internal tolerances, lower power output, higher oil consumption.

Cooling Fins

Increase surface area of head/cylinder with correspondingly greater dissipation of heat to contacting air.

Baffles

Sheet metal/fiber material inside cowling that directs ram air flow to cooling fins/ignition leads/hot spots

Ram Air

Relative wind created by moving airplane and channeled to different areas for various applications.

Cowl Flaps

Variable vent in cowl area to control ram air.

Oil Cooler

• used to cool internal engine oil (oil assists in cooling engine).

Total Fuel

• Total quantity of aircraft system (26 gallons in C-152)

• 172 - 56 total, 53 usable due to standpipe at bottom of tank 

Sump

• point at which fuel may be sampled

Fuel Valve

• Valve used to isolate fuel tank (or tanks) from engine, or to modify fuel flow source or route.

Primer

• Device used to inject fuel into cylinder to enrichen mixture and aid starting.

C-172 Fuel System

• 56 total, 53 usable due to standpipe at bottom of tank 

• Fuel reservoir is a one-gallon tank 

• One mechanical (engine driven) and one electric fuel pump 

• Know sump locations (5 each wing, 3 on the nose - placed anywhere there could be contaminants lodged)

• Mark states that gravity is “pretty reliable” so the tanks will probably not starve just bc of an extended bank 

Fuel Injection

• Turn on pump to pressure up system until you have about the right amount 

• Every time an exhaust valve open, the excess fuel goes somewhere else 

• Mechanical/Pneumatic 

C-172 Fuel System

L and R tank → fuel selector (has fuel selector drain valve) → reservoir→ (has drain valve) → Aux fuel pump → Fuel Shutoff → Strainer (has drain valve) → engine driven fuel pump → Fuel/Air control unit (which connects to fuel return line) → Fuel Distribution → EAU

Vapor Lock

• Pressure changes enough that fuel goes from liquid to gas 

Fuel

• 100LL – Blue  

Tetraethyl Led

• oily, poisonous substance put in fuel to increase resistance to detonation 

Compression Ratio

• When piston is at TDC, what is the displacement area compared to BDC 

  • Typical ratio is 8:1 (Cars?) 

• Octane Rating (doesnt add power, etc, just makes fuel less susceptible to detonation) 

Iso Octane

• better engine performance, emissions, efficiency

Octane Rating

• (doesnt add power, etc, just makes fuel less susceptible to detonation) 

Know avgas colors and octane ratings 

red - 80

green - 100

Blue - 100LL

Colorless or Straw - Jet A

Can use modern car gas with an STC (Supp Type Cert) bc red is basically car gas anyways 

note

Oil Scales

• SAE

• Commercial Aviation Grade (2x SAE) 

  • Ex: 100 CAG is 50 SAE 

Total Oil Quantity 172

• Total (like if you just topped it off) is about 9 Quarts (8 in the thing you measure, 1 in the sump) 

• No direct correlation between oil pressure and oil quantity because sump is on the bottom of the engine block so it will work normally until below pickup then DROP OFF A CLIFF 

• There IS a direct correlation between oil temperature and oil quantity 

Mineral Oil

• Less refined – used in newer engines or engines with new cylinders bc they have jagged edges from production – used to break in an engine 

• ONLY USE IF CALLED FOR (we use a dispatch book) 

Carburetor Operation

• Airflow through venturi increases in velocity and decreases in pressure.​

• Decrease in pressure draws fuel from float bowl through fuel discharge nozzle into airflow en route to combustion chamber. ​

• Constrictions (jets) and circuits of correct dimension, and throttle valve opening, provide fuel and air at combustible air/fuel ratio at different throttle settings.

Is the battery involved in the ignition system?

• NO

• Ignition timing generated and controlled by mechanical action (magnet moving in proximity of ferrous metal) of magneto.​

• No battery or alternator involved! Battery and alternator components of electrical, not ignition, system.​

What is the point of a dual ignition system?

• commonly employed for (1) redundancy, and (2) enhanced performance.​

• All major components duplicated: Magnetos, Wires, Spark Plugs, etc.​

Short

• Alternate route current uses to “shortcut” entire circuit.

When did the U.S. switch to ICAO standards?

1993