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AF 202. Advanced Systems. Objectives. Oxygen Systems Cabin Pressurization Systems Turbocharger/Superchargers Controllable-Pitch Propeller Retractable Landing Gear. Oxygen Systems. Oxygen Systems. Oxygen is required per the FARs for high altitude aircraft

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Af 202 l.jpg

AF 202

Advanced Systems


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Objectives

  • Oxygen Systems

  • Cabin Pressurization Systems

  • Turbocharger/Superchargers

  • Controllable-Pitch Propeller

  • Retractable Landing Gear


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Oxygen Systems


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Oxygen Systems

  • Oxygen is required per the FARs for high altitude aircraft

  • Whether the system is permanently installed or portable, only aviation oxygen (100% oxygen) should be used to fill tanks.


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Oxygen Systems

  • Oxygen systems consist of a mask and regulator

  • Certain masks (cannulas) are not approved above 18,000 ft

  • Special regulators must be used above 40,000 ft


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Oxygen Systems

  • Due to the fact that aviation oxygen is 100% oxygen, the potential for fire is much greater

  • Inspecting for cracks or faults in the oxygen system is important for preflight (besides checking to make sure there is oxygen in the system)


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Oxygen Systems

  • Diluter-Demand

    • Supplies oxygen only when the user inhales through the mask

    • A good seal around the mask is important for diluter demand masks to work

    • Approved for use up to 40,000ft


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Oxygen systems

  • Pressure-Demand

    • Oxygen is supplied to the mask under pressure above altitudes of 34,000 feet

    • This way the users lungs are always pressurized with oxygen

    • Approved for use above 40,000 feet


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Oxygen Systems

  • Continuous-flow

    • Usually provided for passengers

    • Mask usually contains a reservoir bag which collects oxygen until inhaled

  • Pulse-Demand

    • On portable systems

    • Detects when pilot inhalation and provides oxygen

    • Prevents waste of oxygen


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Pressurized Aircraft


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Pressurized Aircraft

  • A pressurized cabin allows aircraft to be flown at higher altitudes without requiring the use of supplemental oxygen for crew and passengers

  • Pressurization systems begins with having a cabin area able to hold air under pressure (higher than external air)


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Pressurized Aircraft

  • In turbine powered aircraft, the cabin is pressurized using bleed air from the engine compressor

  • On a reciprocating engine, air supplied from the turbo/supercharger is used to pressurize the aircraft


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Pressurized Aircraft

  • Air is released from the cabin by the outflow valve

  • The outflow valve allows air to exit for the purpose of circulation


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Pressurized Aircraft

  • Controls allow the pilot to select the cruise altitude which is paired with a corresponding cabin altitude

  • Typically 8,000 feet is the chose cabin altitude for the aircraft’s maximum cruising altitude

  • Pilots can read cabin VSI and Altitude along with pressure


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Pressurized Aircraft

  • Cabin pressure regulator controls the cabin pressure to the selected value

  • If an aircraft climbs and the maximum fuselage structural pressure differential, then pressure will be released and the cabin altitude will climb

  • The pressure relief valve accomplishes this


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Manifold Pressure


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Manifold Pressure

  • Manifold pressure measures the ‘Manifold Absolute Pressure’ (MAP).

  • A direct representation of the amount of power being suppliedto the engine


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Manifold Pressure

  • On a turbo/supercharged aircraft, MAP is directly responsive to throttle, along with supercharger speed controls or turbocharger waste gate controls

  • On a variable pitch propeller aircraft, MAP is directly adjusted with the throttle


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Turbocharger/Supercharger


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Turbo/Superchargers

  • Engine power is dependent on the ratio of fuel to air

  • As aircraft climb, air pressure decreases and changes the fuel to air ratio decreasing power of the engine

  • The maximum ceiling an aircraft can climb based on power output is the service ceiling


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Superchargers

  • A supercharger is an engine driven air pump or compressor.

  • It increases the pressure of the induction air so that the engine can produce additional power

  • This will give an aircraft a higher service ceiling


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Supercharger

  • A supercharger can be one speed, two speed, or variable speed

  • Two speed super charges can be switch at higher altitudes to a higher speed for additional power

  • These engines are called altitude engines


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Turbochargers

  • Turbochargers are more efficient than engine driven super chargers

  • Engine exhaust gas is used to drive the compressor.

  • Why is this more efficient?


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Turbochargers

  • While superchargers add power, some must be used to power itself

  • Turbochargers don’t ‘steal’ some engine power to work

  • A downside to turbochargers, however, is the delayed response compared with superchargers


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Turbochargers

  • Another advantage to superchargers is that there is a greater ability to maintain an engine’s rated sea-level horsepower

  • A turbocharged engine will not lose any power until it reaches the critical altitude

  • After the critical altitude, the engine will lose power like it is normally aspirated


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Turbochargers

  • A waste-gate controls how much exhaust gas is used to drive the compressor

  • Most waste-gates are automatic, however there are some manual ones

  • Monitoring manifold pressure is a must to avoid over boosting.


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Turbochargers


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Controllable-Pitch Propeller


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Controllable-Pitch Propeller

  • A controllable-pitch propeller is a propeller whose blade angle can be adjusted in flight

  • Adjustable-pitch propellers are their old ancestors which can only change blade angle before flight


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Controllable-Pitch Propeller

  • A constant-speed propeller is a controllable-pitch propeller whose pitch is automatically varied in flight by a governor set to maintain a certain RPM

  • Two controls are used in this system.

    • Throttle for manifold pressure (power)

    • Propeller control for RPM (blade angle)


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Controllable-Pitch Propeller

  • Once a specific RPM is chosen, the governor continuously adjusts the blade angle to maintain that RPM

  • This can be done to a limit as there are blade angle stops, or limitations, for each aircraft


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Controllable-Pitch Propeller

  • To understand how blade angle changes regulate RPM, one must remember aerodynamics

  • The greater the blade angle, the greater the drag and the harder it is to move

  • Given the same power, an increase in blade angle will slow down the RPM


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Controllable-Pitch Propeller

  • Example:

    Power: 22” Hg

    RPM: 2300

    change to…..

    Power: 22” MP

    RPM: 1700

    What happened to the blade angle?

    The governor INCREASED blade angle


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Controllable-Pitch Propeller

  • Example

    Power: 18” Hg

    RPM: 2200

    change to…

    Power: 22” MP

    RPM: 2200

    Though power increases, RPM stays same?

    The governor INCREASED blade angle


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Controllable-Pitch Propeller

  • Example:

    Power: 22” Hg

    RPM: 2200

    change to…

    Power: 17” Hg

    RPM: 2200

    Why does RPM remain unchanged?

    The governor DECREASED blade angle


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Controllable-Pitch Propeller

  • Though RPM does not change when you reduce throttle, blade angle decreases and so thrust is still decreased

  • Though RPM does not change with an increase of throttle, blade angle increases which will increase thrust


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Controllable-Pitch Propeller

  • Understanding climbs and descents can be tricky

    • When you pitch up, typically engine RPM decreases

    • With a constant-speed propeller, blade angle is just decreased

    • When you pitch down, typically engine RPM increases

    • With a constant-speed propeller, blade angle is just increased


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The Governor

  • So how does this governor work?


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The Governor

  • Propeller control is connected to the governor controlwhich adjusts thetension in the speeder spring

  • Speeder springplaces pressure onthe fly weights


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The Governor

  • The flyweights are L shaped pieces of metal that spin with the RPM speed.

  • The base of the L presses against the speeder springs and lifts the plunger valve which controls oil flow to/from the propeller hub


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The Governor

  • The centripetal force of the flyweights tries to counter the speeder spring.

  • If the flyweights have more force than the speederspring, the valvewill be lifted


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The Governor

  • Engine RPM will determine how much force the flyweights can hold up

  • Whether lifting the valve allows oil in or out depends on the aircraft.

  • None-the-less, oil is used to actuate a cylinder in the propeller hub which adjusts the blade angle


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The Governor

  • In a C-172RG adding oil to the propeller will increase blade angle (and slow down the RPM)

  • Thus an overspeed condition which raises the plunger valve will allow oil in


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The Governor

  • Throttle Examples:

    Let’s say your RPM is set and you increase or decrease throttle.

    Naturally the RPM will want to increase or decrease respectively, but what happens in the governor that prevents is?


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The Governor

The additional power makes the engine want to speed up, thus an overspeed condition exists

The valve is lifted, oil flows in,and then the blade angle isincreased returning theflyweights to normal


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The Governor

The loss of power will cause the engine to want to slow down, thus an underspeed condition occurs.

The valve is lowered allowingoil to leave the propeller huband decrease the blade anglewhich returns the flyweightsto normal


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The Governor

  • RPM Examples:

    Let’s say that your throttle stays the same, what do changes in your propeller control do?

    Remember that the propeller control directly sets the tension on the speeder spring


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The Governor

When you lower RPM, you lower tension on the speeder spring meaning the flyweights will overpower them causing an overspeed condition

Oil enters, blade angle isincreased, RPM decreases,and flyweights spin slowerand match the spring force


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The governor

When you increase RPM, you increase tension on the speeder spring meaning the flyweights will be overpowered causing an underspeed condition

Oil exits, blade angle isdecreased, RPM increases,and flyweights spin fasterand match the spring force


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The Governor

  • The key is the relationship between the force of the speeder spring and the opposing force of the flyweights which are directly related to engine speed


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Retractable Landing Gear


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Retractable Landing Gear

  • The landing gear is retracted using some mechanical help

    • Hydraulic Gear system

    • Electric Gear system


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Retractable Landing Gear

  • Landing gear components contain variations of:

    • Gear selector switch

    • Landing gear position indicators

    • Safety switches

    • Emergency gear extension


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Retractable Landing Gear

  • The gear selector switch varies between hydraulic and electric systems

  • In an electric system is it simply an electric switch

  • In a hydraulic system it is a valve that re-routes the flow of hydraulic fluid


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Retractable Landing Gear

  • Landing Gear indicator lights may also vary

    • Light for each wheel (simply on or off)

    • All gear down light/All gear up light

    • Gear unsafe light (no lights when up)


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Retractable Landing Gear

  • Many safety switches are included

    • Gear up/down switches

    • Squat switches

    • Throttle/flap switches

    • Pressure switches


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Retractable Landing Gear

  • Emergency Gear Extensions

    • In an electrical system, often a hand crank is used to move the mechanical components manually

    • With a hydraulic system a hand pump is utilized, however this is useless if you’ve lost hydraulic fluid…


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Retractable Landing Gear

  • C-172RG Example

    • Squat Switch on nose gear

    • Hydraulic power pack – to 1500 PSI

    • Pressure switch on at 1000 PSI

  • When the gear selector selects a different position, the Pressure switch recognizes 0 PSI and turns on the power pack.


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Retractable Landing Gear

  • If you forget to extend your gear there are 2 warning switches if gear is not extended

    • If your throttle decreases to around 12” MP then you will get a warning horn

    • If flaps extend past 20 degrees you will get a warning horn


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