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CPL Helicopter AGK > Carburettors/Carby Heat > Flashcards

Carburettors/Carby Heat Flashcards

1
Q

Carburettors:

Total Pressure = ______ + ______

A

Total Pressure = Static pressure + Dynamic pressure

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2
Q

What is a float chamber?

What does it do?

A
  • Vented reservoir

- Holds fuel from the tank using a float & amp valve

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3
Q

What is a venturi ?

A
  • Narrowing section

- Creates a suction

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4
Q

List the pros of carburettors

A
  • Simple (no moving parts)
  • Cheap
  • Reliable
  • Efficient for small engines
  • Mixture control –> controls fuel into main jet
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5
Q

List the cons of carburettors

A
  • Prone to carburettor icing
  • unable to operate in __ altitudes
  • Unable to deliver same amount of fuel to each cylinder
  • Inefficient in high performance
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6
Q

What does the accelerator pump do?

A
  • Sends surge of fuel –> discharge nozzel as throttle opened rapidly to overcome power lag
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7
Q

What is impact ice?

A
  • Water turns to ice on impact

- Components are below 0 degrees C

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8
Q

Fuel evaporation:

  • What does it cause?
  • What is is caused by?
A

Causes:

  • Throttle ice inside carburettor
  • Increased when throttle partly open/closed

Caused by:

  • Temp drop of ____ fuel (adiabatic cooling)
  • 3-4 degree drop in temp
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9
Q

What are the symptoms of carby ice?

A
  • Drop in manifold pressure
  • Rough running
  • Back firing
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10
Q

What are the conditions most likely to cause carby ice?

What combination of temp and humidity = serious risk?

A
  • < 20 degrees C
  • 80% humidity
  • Decent = low power settings
  • Clouds (closer = more risk)

Serious risk = 10 degreesC & 70-80% humidity

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11
Q

Describe carby heat

A
  • Hot air = less dense –> mixture becomes richer
  • test should drop rmp when open
  • can supply alternate air supply in emergency
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12
Q

Fuel injection systems: PROS

A
  • not gravity sensitive = operate in unusual altitudes
  • allows more precise over mixture strength @ each cylinder
  • Free from icing
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13
Q

Fuel injection systems: CONS

A
  • More complex
  • More expensive
  • Many fuel lines = prone to air locks
  • Fuel pump driven by engine gear
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14
Q

Fuel air control unit - what does it do?

A
  • senses amount air flowing to engine

- metres & sends amount fuel to manifold valve (gear driven)

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15
Q

Fuel manifold valve:
Where situated
What does

A
  • Situation top of engine

- Distributes metered fuel to discharge nozzles

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16
Q

Fuel discharge nozzles - what they do?

A
  • Injects fuel into inlet port where it mixes with air
17
Q

Fuel pressure/flow gauge:

A
  • Measured before fuel manifold valve (gallons/hr)

- Susceptible to misreadings

18
Q

Specific ground range = _____ divided by _____

A

Specific ground range = ground speed / fuel flow

eg. 140 knts / 12 gallons

19
Q

Superchargers/Gear Driven

  • What does it do?
  • Used to overcome?
  • Types?
A
  • Forces more air into manifold –> achieve more torque (higher altitude)
  • used to overcome low air density at height
  • Internal or External
20
Q

Internal Supercharger

A
  • Location: btwn carburettor & inlet valve

- Fuel & air goes through compressor

21
Q

External Supercharger

A
  • Location: before carburettor or fuel control unit (air only goes through)
  • Used in fuel injection systems
22
Q

Rated boost

A
  • Highest manifold pressure engine can tolerate without danger of detonation
23
Q

Full throttle height

A
  • ___ height where max permitted manifold pressure can be obtained
24
Q

Disadvantages of gear driven superchargers:

A
  • Lack of control over speed of impeller
  • Geared @ 10 + 01 (impeller spins 10 times speed of engine)
  • too much pressure –> detonation & engine damage
  • Only prevention to overboost is to reduce throttle which is inefficient
25
Q

Turbocharging (Turbine)

  • What does it give us?
  • How does it work?
A
  • Better control or impeller speed
  • Turbine placed in exhaust & exiting gases –> spin
  • Waste gate in exhaust decides how much gas sent out or to the turbine drive
  • Runs off exhaust gas pressure
26
Q

Waste Gate Control:

Fixed Waste Gate

A
  • Set by engineer
  • Fixed amount of gas goes over turbine all time
  • Requires throttle control to prevent overboosting
  • Cheap, not efficient
27
Q

Waste Gate Control:

Cockpit Adjustable Waste Gate

A
  • Adjusted by pilot

- Another worry for pilot

28
Q

Waste Gate Control:

Throttle operated waste gate

A
  • Adjusted by throttle position
29
Q

Automatic waste gates

A
  • Controlled by:
    > Density & differential pressure controllers
  • Spring controlled with oil pressured waste gates
  • Upper deck (intake)
30
Q

Critical altitude is:

A
  • btwn 20,000 & 25,000 ft in general aviation _____

- Height above which a particular, nominated manifold pressure can no longer be maintained

CPL Helicopter AGK (2 decks)

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