CPL AGK Flashcards
Radial engines have great power to weight ratios, however they….
Have a large frontal area, and thus produce large amounts of drag
Inline inverted engines are designed to
Give the prop clearance from the ground (and also to increase forward visibility)
The more cylinders there are….
the smoother the engine runs (due to more constant power strokes)
Compression ratio=
Total volume of cylinder/clearance volume
What are the units/values for 1 horsepower
33000 foot pounds/minute
550 foot pounds/second
0.746 kW
What is indicated horsepower
Pure power generated from the engine
What is friction horespower
Horsepower loss due to frictional forces inside the engine
HP
BHP=IHP-FHP
volumetric efficiency=
amount of cht of charge (by weight) in cylinder @ standard temperature and pressure arge in cylinder (by weight)/Maximum amoun
What is a typical volumetric efficiency
70%-80%
What is thermal efficiency?
Ratio of power actually delivered by the engine to the power theoretically available in the fuel
What is a typical thermal efficiency value
30%
when the engine is off, what should the manifold pressure read
atmospheric pressure
How are magnetos powered?
Engine driver
What is engine kickback
When the spark occurs too early and causes the crankshaft is pushed in the wrong direction (this is why we need impulse coupling to delay the spark, as this phenomenom often occurs at low rpm)
Why do we only use the left magneto on startup
because only 1 spark plug is required on start up
What does the distributor in an ignition system do
distributes the current to the different spark plugs
What is a “dead-cut check”
A check whereby the magnetos are checked if they are earthing or not
What does the accelerator pump in a carby system provide
Additional mixture when the throttle is opened rapidly in order to avoid power lag.
What does the enrichment valve do
provides additional fuel at <75% power settings to aid in cooling
What is the idling jet for?
Used to provide fuel when the throttle is almost closed at low rpms (is positioned after the throttle bautterfly for this purpose
What are the conditions for carby icing
<50% humidity and around 35 degrees celcius
What is impact ice
Supercooled water droplets in the intake impact on metal surfaces and then freeze
What is fuel icing
Vaporisation of fuel causing a temperature drop which causes water to precipitate which will then freeze onto surfaces
What is throttle icing
Air that accelerates decreases in temperature
In what conditions is throttle icing most likely to occur
greatest at low power settings
-10 to 20 degrees celcius with a high relative humidity
What are some of the advantages of fuel injection systems
No fuel icing
More efficient
Fewer maintenance problems
Faster acceleration response
What are some of the disadvantages of fuel injection systems
Vapour locks
More susceptible to contamination (due to having thin lines)
Fuel that goes through return lines may be vented overboard if the tank it is being delivered to is full
What are the purposes of oil
clean, cool, lubricate, protect, seal
Why is straight mineral oil used for the first 50ish hours of engine life?
Because it allows the surfaces to rub together and create their own fit
Why do we prefer ashless dispersant oil in general use
Because it doesn’t possess the carbon-forming characteristics of mineral oil, and it prevents sludge from forming (therefore less oil blocks)
Why are synthetic oils so good?
Because they have been designed to operate at a large variety of temperatures and altitudes
Can you mix aircraft oil types?
yes (although take caution with mixing of synthetic oils due to lack of data on effects)
Can we use motor oils in planes?
No
How can we tell that an aircraft is burning oil?
Rich blue smoke is coming out of the exhaust
Oil consumption is a good indication of….
engine health
Commercial aviation oil number is what compared to the SAE oil number
2 times
e.g. aviation=80 but SAE=40
What is the approximate specific gravity of piston airplane oil
0.9
Why does oil need to be changed reguarly
oxidation and water absorption
Describe the oil system typical of most light aircraft
Wet-sump
stores oil in a collector tank
gravity dependent (although does have a pump)
Incorporates pressure relieve valve to prevent against excessive pressure
Describe the oil system typical of aerobatic aircraft
Dry-sump
Uses a scavenge pump to attain oil from an external tank
Due to the pump systems, inverted flight is possible
give some reasons as to low oil pressure
low qty
leak in the oil lines/tank
failure of the oil pump
oil pressure relief valve stuck open
Are pressure gauges reliable?
Not all instruments are reliable, and so it is important to crosscheck with other instruments in order to deduce the issue, as using multiple data sources should result in more accurate interpretation
What is supercharging
artificially increasing the pressure available to the intake manifold. the more air=more fuel=bigger boom=more power
Differentiate between a supercharger and a turbocharger
supercharger=compressor is controlled by the mechanical gears of the engine. Turbocharger uses exhaust gases to turn a turbine which turns a compressor.
How does a supercharger increase pressure
Air is forced out from the impeller, gains kinetic energy and flows out through diffuser vanes, this kinetic energy is then converted into an approximate 50% increase in pressure
What are the factors that influence how much pressure a supercharger will develop
RPM
Diameter of impeller
Shape of impeller blades
Shape of diffuser vanes
Where is the carby placed in a supercharger system and why?
Just before the inlet so as to aid in cooling so that the air doesn’t heat up too much
Current superchargers can maintain sea level pressure up to what altitude
10,000ft
Define full throttle height
The maximum height at which a supercharger is able to provide sea level pressure
What happens above full throttle height
Aircraft behaves like a normally aspirated engine, and a decrease in performance occurs as the aircraft climbs higher and higher
Why do we see an INCREASE in the volumetric efficiency as we climb higher?
Because of the reduced pressure differential, exhaust gases are able to flow out more efficiently.
What RPM is full throttle height
Each rpm setting has a corresponding full throttle height
How does the supercharger protect against overboosting
The throttle valve will not open fully unless the aircraft is at or above full throttle height
Give some reasons as to why turbochargers are more efficient that superchargers
Turbos don’t lose power due to the fact that some of the engine power has to go to powering supercharger gears
most turbos have fuel injection systems which are more efficient than carbys, which are fitted on superchargers
What is ground boosting
Turbochargers are capable of providing inlet manifold pressures above sea level pressure on the ground
What is altitude boosting
Turbochargers are capable of maintaining power up to the critical altitude
What is the critical altitude in regards to turbochargers
The altitude where manifold pressure can no longer be maintained
What does the bypass duct in a turbocharger do
controls TURBINE rpm
What does the wastegate doe
Prevents overboosting
Describe the effects of leaks before and after the wastegate
before the wastegate=power loss
After the wastegate=no loss
What does the Absolute Pressure Controller do?
Monitors upper deck pressure and changes the position of the wastegate to maintain this pressure
What is bootstrapping
When the system tries to balance pressure even though is can’t due to the fact that the critical altitude has been reached
Describe the positions in a wastegate on climb and descent
climb=close (increase UDP)
descent=opens (decrease UDP)
How does a fuel tank stop the fuel from sloshing about
By implementing baffles
Why is the top of the fuel tank vented
to maintain atmospheric pressure
Why should the fuel pump be turned on when changing tanks in a carby fitted aircraft
To maintain fuel pressure
Why is it normal to have the electrical fuel pump on in some stages of flight
because critical stages (such as a go around) require the fuel provided by the electric fuel pump if the mechanical pump fails.
What is a rich mixture cut?
Engine failure do to excessively rich mixture
Why is lead added to fuel?
To resist detonation
Is MOGAS octane rated the same as AVGAS?
nope
What is hydraulics
Force transmitted by fluid pressure
Why do we prefer hydraulic systems over mechanical systems
Good power to weight ratio
Why are fluids so good for the transmission of force
Fluids are considered incompressible and therefore any force applied is transferred to the next contact object
Can you mix hydraulic fluids?
No
What are the types of pumps in hydraulic systems
Gear types (classic 2 gear system) Piston type (hand pump, usually used in emergency) Variable displacement (swashplate changes angle in order to move pistons)
What does the accumulator in a hydraulic system do?
Maintains pressure in the system and dampers pressure surges
What does a check valve do
Allow the travel of fluid in one direction only
Where is the Pressure relief valve located in a hydraulic system
Between the pump and the system components
What is the purpose of the Thermal Relief Valve
Allows fluid that has experienced thermal expansion to escape, which prevents lines from rupturing
What does an actuator do?
Converts force produced by fluid pressure into movement
What does the Emergency Extension Valve do?
Relieves system pressure and causes the landing gear to fall down automatically
How does a squat switch work
Detects weight (checks that ac is on the ground) and prevents the gear being retracted
How does an airswitch work
Prevents the undercarriage from being retracted below a certain airspeed
Above what speeds does hydroplaning occur?
9X </PSI for locked wheels
How does a thermocouple work?
Measures difference in temperatures from a ‘hot junction’ and ‘cold junction’
How does a continued loop detector work?
Consist of an inner and outer core separated by a dialetric compound capable of detecting any overheating in the wire.
How does a Fenwal Resistance type fire detector work?
Nickel wire core in a flexible inconel tube. Space between the m is a eutectic salt (has a low melting point). As the salt melts The circuit experiences a current increase, thus activating the alarm. The system is reset when the salt solidifies.
Why is a Graviner Firewire Capacitive detector preferred over Fenwal Resistance types?
Because they measure both resistance and capacitance (rather than just resistance) and so the chances of a false alarm are reduced.
How does a Systron Donner detector work?
Contains helium gas that expands with heat, exerting pressure on a pressure switch, which operates an alarm.
How do carbon monoxide detectors work?
Contains a yellow silica gel that turns yellow when exposed to carbon monoxide. The darker the green, the more severe the exposure.
How do photoelectric cell smoke detectors work?
When light can’t be transmitted onto a diode (due to smoke), tAn alert is produced
What type of fire extinguishing system is used on most light aircraft/ smaller twin engine commercial aircraft
CO2/conventional type
What type of fire extinguishing system is used on most modern commercial aircraft
High-Rate Discharge
What area do extinguishers typically discharge into
Nacelle area (engine housing)
What are the types of agents used in fire extinguishers
Methyl Bromide (MB)
Bromochlorodifloromethane (BCF)
Bromotrifloromethane (BTM)
Why do extinguishers need to be operated in an enclosed area?
Because they take oxygen from the air, and so need to have a finite amount of oxygen present.
Can BCF agents be used in fire extinguishers?
Although they are banned due to environemntal damage, they are exempt on aircraft due to their capability at extinguishing electrical fires
What is the danger associated with operating an extinguisher in an enclosed area
asphyxiation
Define rigidity
tendency for a gyroscope to maintain alignment in space
Rigidity is proportional to….
Inertia X angular velocity
What is precession
Tendency for a force applied to a gyroscope to be displaced 90 degrees in the direction of motion
What is topple in regards to gyroscopes
Movement in the vertical plane
Why are venturi systems used for powering gyroscopes undeesired
Becuase they require forward motion of the aircraft, and can only get the gyroscopes operating properly a few minutes after takeoff. They may also be affected by icing
What disadvantages do suction gyros have to electric gyros
Can be affected by contaminants in the air
Can’t be operated until the engine starts
At high altitudes insufficient suction may occur
Electric gyros have a constant power and are therefore more accurate
Why does the HI need to be realigned in flight every 15 minutes
because it does not seek a magnetic datum like the compass
What is the deviation in HI readings/hour
10 degrees for old aircraft
1 degree for new aircraft
What does a lattitude nut do?
Provides a torque proportional to the rotation of the earth and therefore prevents apparent drift in certain instruments
What is transport error?
Errors in gyroscopic instrument readings due to the aircraft flying east or west (with or against the rotation of the earth), and the instrument can’t compensate for this
The attitude indicator operates off what gyroscopic property
rigidity. Gyroscope stays aligned and the aircraft moves around it
What is the typical gimbal pitch limitation
85 degrees
how long can it take an erection system to level a gyro if it topples?
15 minutes
What do pendulous vanes in an erection system do?
Makes sure the the AI gyro stays level by sensing gravity and precessing the axis
What is a typical acceleration error on the AI
pitch up and to the right
How does a turn indicator work
AC yaws in one direction, gimbal is precessed in the other
The turn coordinator is sensitive to what that the turn indicator isn’t
roll
What is semimonocoque
Frame and skin takes stress
What is monocoque
Only skin takes stress
