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Weather (Voss) > Engines > Flashcards

Engines Flashcards

1
Q

EXPLAIN Bernoulli’s Equation

A

-states that as any incomp. (subsonic) fluid passes through a convergent opening, its velocity increases and pressure decreases

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2
Q

DESCRIBE the behavior of airflow in a nozzle

A
  • the shape of the opening increases the airflow’s velocity and decreases the airflow’s pressure
  • convergent for subsonic
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3
Q

DESCRIBE the behavior of airflow in a diffuser

A
  • pressure is increased and velocity is decreased

- divergent for subsonic

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4
Q

DESCRIBE the Brayton Cycle

A

-four simultaneous events: intake, compression, combustion, and exhaust

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5
Q

DESCRIBE a gas generator

A
  • produces high energy airflow necessary for thrust
  • minimally include: compressor, combustion chamber, and turbine
  • on turboprop/shaft/fan, will include fan, properller, , or rotor blades
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6
Q

DESCRIBE how airflow properties change through each section of a gas turbine engine

A

I C D B T E
Temp / / _ / \ \
Pres / / / \ \ \
Velo \ / \ / / /

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7
Q

DESCRIBE engine thrust

A

-a combination of velocity of exhaust gas and inlet velocity

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8
Q

DESCRIBE the effects of airflow properties on thrust in a gas turbine engine

A
  • density^: Th^
  • Temp^: less Th, vary as much as 20%
  • pressure^: ^Th
  • altitude^: less Th, faster in isothermal
  • AS^: less Th
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9
Q

EXPLAIN ram effect in a gas turbine engine

A

-thrust decrease with increase in airspeed offset by compressibility of air near supersonic which actually causes thrust neutral or increase

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10
Q

DESCRIBE the cockpit thrust measuring devices

A
  • for gas turbine: Engine Pressure Ratio (EPR) gauge, it measures the ratio between inlet and exhaust pressures
  • for prop or rotor driven: torquemeter, indicates shaft HP available
  • tach: indication of engine speed
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11
Q

DESCRIBE inlet ducts

A
  • designed to provide proper amt of hi pressure, turbulence free air to compressor
  • broad range of operating cond.
  • diffuser
  • single or divided entrance
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12
Q

DESCRIBE compressors

A
  • supply enough air to satisfy req. of combustion section
  • increases pressure of air and directs it to the burners
  • supply compressor bleed air to operate various comp.
  • not closed system
  • increase V without decrease in P thanks to drive shaft energy input
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13
Q

DESCRIBE the burner section of a gas turbine engine

A
  • contains comb. chamber and provides means for proper fuel air mixing
  • 25% primary air for F/A mix
  • 75% secondary air flows around for cooling and flame control
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14
Q

DESCRIBE combustion chambers

A
  • three types: can, annular, and can-annular
  • can: older, centrifugal compressor engines, stronger, durable, poor use of space, P loss, uneven heat distro.
  • annular: uniform heat distro., good use of space, better F/A mixing, cannot be removed easily, structural problems
  • can-annular: in large hi perf. aircraft, combines easy manintenance with excellent thermodynamics of each
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15
Q

DESCRIBE the turbine section of a gas turbine engine

A
  • drives the compressor and the accesories
  • designed to increase airflow velocity
  • 75% of energy used to spin turbine
  • 25% used for thrust
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16
Q

DESCRIBE the phenomenon of creep in a gas turbine engine

A
  • rotor blades undergo elongation
  • cumulative process
  • deformed blades not efficient and may fail catastrophically
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17
Q

DESCRIBE the exhaust section of a gas turbine engine

A
  • direct flow of hot gases rearward to cause a high exit velocity and prevent turb.
  • exhaust outer duct, exhaust inner core, and three or four raidal hollow struts
  • fixed convergent type for subsonic
  • variable C-D type for supersonic
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18
Q

DESCRIBE the afterburner section of a gas turbine engine

A
  • aka thrust augmentation
  • used in turbojets and turbofans
  • increase maximum Thrust available by 50% or more
  • huge fuel usage
  • consists of spray bars, flame holders, screech liner, and variable exhaust nozzle
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19
Q

DESCRIBE the angle of attack of compressor blades

A
  • angle btwn RW and rotor blade’s chordline

- can stall compressor if rotor blades spinning at wrong speed for inlet airapeed

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20
Q

DESCRIBE a compressor stall

A
  • still an airfoil, spinning rotors encounter different AOA depending on speed
  • anything that decreases inlet airflow or increases compressor RPM could stall
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21
Q

DESCRIBE four mechanical malfunctions that can lead to a compressor stall

A

1) variable inlet guide vane and stator vane: failure to change AOA
2) fuel control unit (FCU): wrong amounts of fuel can cause back-flow or flame out
3) foreign object damage: deformation of blade changes aero prop.
4) variable exhaust nozzle: if fails to open, extra back pressure could cause failure

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22
Q

DESCRIBE appropriate actions a pilot can take regarding compressor stalls

A
  • avoid erratic/abrupt PCL changes esp. at high AOA or low AS
  • fly min. AS and avoid abrupt changes in AC attitude
  • avoid flt thru svr wx and turb
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23
Q

DESCRIBE four engine design features that can be incorporated into a gas turbine engine
design to minimize the potential for a compressor stal

A
  • variable inlet guide vane and stator vane: changes AOA at low engine spd
  • dual/twin/split-spool compressor: front rotor turns slower
  • bleed valves: increase airflow in the front of the compressor @ low RPM
  • variable exhaust nozzle: unload pressure during afterburner operation
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24
Q

DESCRIBE a turbojet engine

A
  • simplest gas turbine engine
  • inlet and exhaust section + basic gas generator
  • thrust from highly accelerating small mass of air
  • all air thru inlet goes thru GG
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25
Q

DESCRIBE the characteristics of a turbojet engine

A
  • lightest specific weight
  • higher and faster
  • low propulsive efficiency at fwd speeds
  • high TSFC at low alt and AS
  • long T/O roll
26
Q

DESCRIBE a turbofan engine

A
  • cross btween TJ and TP
  • gas from GG plus ducted fan
  • fan accelerates farily large mass of air around GG (bypass.ducted air)
  • bypass air = 30-60% of thrust
  • better thrust/fuel than turbojet
27
Q

DESCRIBE the characteristics of a turbofan engine

A
  • higher Th at low AS
  • lower TSFC
  • shorter T/O distance
  • noise reduction
  • higher specific weight
  • larger frontal area
  • inefficient at higher alts.
28
Q

DEFINE thrust specific fuel consumption

A

amount of fuel required to produce one pound of thrust

29
Q

COMPARE the thrust specific fuel consumption of turbojet engines

A
  • turbojet worse than turbofan

- high at low AS and altitude

30
Q

COMPARE the thrust specific fuel consumption of turbofan engines

A
  • better than turbojet
  • higher bypass ratio better
  • high at low AS and altitude
31
Q

COMPARE the propulsive efficiency of airplane engines

A
  • turboprop best at low AS but drops off rapidly after 350 mph
  • turbofan best at middle-hi speeds
  • turbojet best at hi speeds
32
Q

DESCRIBE the effect of bypass ratio on turbofan engine performance

A
  • hi BPR most efficient
  • airliner/cargo higher
  • fighter lower for smaller frontal area and better high speed performance
33
Q

DESCRIBE a turboprop engine, to include the propeller assembly

A
  • GG plus reduction gearbox and prop
  • best qualities of GG with PE of propeller
  • prop provides majority of thrust by imparting small accel. to large mass of air
34
Q

DESCRIBE the operation of the reduction gear box of a turboprop engine

A
  • basically one speed tranny’-prevents prop from reaching supersonic speeds
  • converts high rmp and low torque of GG to low rpm and high torque for prop
  • in T-6B 30000 to 2000 RPM
35
Q

COMPARE the propulsive efficiency of airplane engines

A

as TP climbs to higher alt. mass of air being accel. by prop decreases due to decreased density

36
Q

DESCRIBE the torquemeter assembly of a turboprop engine

A
  • set of shafts located btwn the GG and the RGB
  • used on some TP engined to transmit and measure power output from GG to RGB
  • displays twisting on instrument panel in in-lbs of torque or SHP
37
Q

DESCRIBE operations of the propeller of a turboprop engine

A
  • TP accelerates large mass of air with prop to moderate speed
  • prop. maintains constant 100% RPM
  • changes blade pitch to maintain RPM
  • alpha range: PCL btween idle and full, FCU works with prop governor to ensure constant RPM
  • beta range: ground ops, idle to max reverse, PCL mechanically connected to pitch change assembly as well as FCU
38
Q

DESCRIBE a turboshaft engine

A
  • turboprop but spins helicopter rotor etc vice prop
  • used to drive ships, tanks, trains, etc.
  • GG + free/power turbine
39
Q

DESCRIBE the operation of the free/power turbine of a turboshaft engine

A
  • mechanically indepenedent from GG
  • exhaust from GG turbine drive power turbine
  • power turbine connected to main transmission thru coaxial main drive shaft
40
Q

EXPLAIN how Pascal’s Law governs the forces and pressures associated with a confined
liquid

A

pressure applied to a confined liquid is transmitted equally in all directions without loss of pressure and acts with equal force on equal surfaces

41
Q

EXPLAIN the relationship between linear displacement and the change in force between
the input and output pistons of a closed hydraulic system

A
  • linear displacement is exchanged for change in force

- a 10 inch input displacement with 10 lbs acting over 2in^2 can push 200 lbs i inch with a 20in^2 surface area

42
Q

DESCRIBE a basic aircraft hydraulic system

A
  • main purpose is to multiply force
  • power system: fluid supply, pump, selector valves, etc.
  • near 3000 psi
  • 2 systems, one for flight controls and one for utility systems + flight controls
43
Q

DESCRIBE AC/DC electrical systems, to include their relative advantages

A
  • AC reverses directions, used in homes
  • DC flows in one direction, used in cars, boats, small electronic devices
  • Aircraft usually use AC
  • AC uses less current, smaller a/c wiring, less weight, lighter, reliable, simple
44
Q

DESCRIBE a basic aircraft electrical system

A

engine powers accesory gearbox=>constant speed drive=>AC generator/alternator which powers the buses

engine powers accesory gearbox=>dc starter/generator=>buses and battery

four buses:

  • essential bus: flight safety (att. gyro)
  • primary bus: mission (radar)
  • monitor/seconday bus: convenience circuits (lighting)
  • starter bus: routes power to start a/c engines
45
Q

DEFINE volatility

A

measurement of a liquid’s ability to convert to a vaporous state

46
Q

DEFINE flashpoint

A

lowest temp. of a combustible substance that would ignite with a momentary application of a flame

47
Q

DESCRIBE how temperature affects flashpoint

A

???

48
Q

STATE the characteristics of common military aviation fuels

A
  • JP4: previously most common, highly volatile, low FP (-35dgFP), easier starting, slower acceleration, lower operating temps, hi vapor lock tend., and shorter range
  • JP5: Navy, MC, and CG primary fuel, thermally stable, high heat content, low volatility, high FP (140dgFP), safe on ships
  • JP8: better fuel handling and operation safety, lower FP than JP5 (100dgF), AF uses this
49
Q

DESCRIBE a basic aircraft fuel system

A
  • must provide clean, vapor-free fuel at proper pressure and flow rates in all conditions
  • fuel tank holds it, boost pump pumps it, emerg. shutoff valve, pressure gauge, fuel filter, engine driven pump, FCU controls flow, flow gauge, cooler/heat xchanger, manifolds, P&D valves, afterburner
50
Q

DESCRIBE rated thrust

A
  • maximum value of thrust based on TIT/ITT (turbine inlet temp)
  • normal rated (NRT): trust at max cont. TIT with no time limitation (cruising)
  • military rated thrust (MRT): thrust at max TIT for limited (30 mins) time
  • combat rated (CRT): thrust with afterburner in operation
51
Q

DESCRIBE the functions of lubricants

A

-primary: reduce friction caused by metal-to-metal contact

52
Q

DESCRIBE the characteristics of synthetic lubricants

A
  • don’t mix oils from different manuf. or used in same engine
  • not compatible with mineral or petrol based oils and must never be mixed
  • lower tendency to leave coking deposits, stronger chemical stability at high temps
  • very corrosive
  • short shelf life
53
Q

DEFINE viscosity

A
  • property of a fluid that resists the force tending to cause the fluid to flow
  • oil gets thinner when hot
54
Q

DESCRIBE a basic aircraft lubrication system

A
  • wet pump: when limited supply of oil and cooling needed, limited to sump capa., hard to cool oil, not adaptable to extended unusual attitudes (inversion)
  • dry sump: oil in tank located in airframe or on engine, larger supply, better temp regulation, streamlined, self contained, pressure and scavenger subsystem
55
Q

DESCRIBE the types of accessories used on aircraft

A
  • two types: air driven or mechanical
  • air: A/C, cockpit pressurization, engine anti-ice, heating units
  • mech: tach, hydraulic pumps, generators, alternators, etc.
56
Q

DESCRIBE how accessories are driven

A
  • air driven: compressor discharge air at hi P and T is bled from engine through ports or valves at intervals along comp. case and at end of the diffuser
  • mechanical: geared drive taken directly from the main shaft connecting the turbine to the comp.
57
Q

DEFINE interstage bleed air

A

-air ducted overboard to prevent comp. stall during certain periods of low thrust operation

58
Q

DESCRIBE the starting sequence for a gas turbine engine

A
  • starter accelerates compressor
  • sufficient air established thru engine
  • ingition activated
  • fuel added
  • starter continues until idle RPM attained
59
Q

DESCRIBE abnormal starts of a gas turbine engine

A
  • hot start: exceeding max allow. temp
  • hung start: temp. in turb. section continues to rise and comp. rpm stabilizes below normal
  • false start: comp. rpm stabilizes below normal and turb. temp. reamins within limits
  • wet start: F/A mix does not light initially but has capa. to eventually ignite
60
Q

DESCRIBE a DC electric starter

A
  • most common
  • mechanically connected to comp. and mounted on either engine acc. gear box or front frame of engine
  • battery, APU, or external electrical source may power it
61
Q

DESCRIBE an air turbine starter

A
  • aka pneumatic starters
  • most common on large gas turnines
  • small geared air turbine motor attached to the engine
  • air is directed to the air turbine which accelerates the compressor
  • air supplied by ground cart or APU
62
Q

DESCRIBE a basic aircraft ignition system

A
  • hi energy capacitor type ignition normally used
  • high voltage and hot spark
  • works at even high alts.
  • minimal fouling
  • two ignitor plugs (spark ignitors)
  • spark only needed for engine starting

Weather (Voss) (3 decks)

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