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Engineering Flashcards

1
Q

Name four different types of rotary-wing aircrafts. To which general category do all these aircrafts belong, and what other kinds of aircrafts are possible?

A

Autogyro
Gyrodyne
Compound helicopter
Convertiplane
Helicopter

All are heavier than air, which also includes rockets and fixed-wing.

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2
Q

Which rotorcraft requires torque compensation?

A

All single-rotor with a drive shaft

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3
Q

Name the base units

A

Length ; meter ; m
Mass ; kilogram ; kg
Time ; seconds ; s
Current ; ampere ; A
Temperature ; kelvin ; K
Luminous intensity ; candela ; cd
Amount of substance ; mol ; mol

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4
Q

What is the units of force, pressure, work and power?

A

Force = m*a
mass times acceleration (newton)

Pressure = f/a
force over area (pascal)

Work = f*s
force times displacement (joule)

Power = W/t
work over time (watt)

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5
Q

Name the three laws of newton

A
  1. Law of inertia
  2. Law of acceleration
  3. Law of action and reaction
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6
Q

Explain Bernoulli’s law

A

total pressure = dynamic pressure + static pressure = constant, for a closed system and incompressible airflow

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7
Q

Describe the thermodynamic terms

A

Isobaric = constant pressure
Isochoric = constant volume
Isothermal = constant temperature

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8
Q

The two main principles of driving the main motor?

A

Tip drive / shaft drive

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9
Q

Which anti-torque systems do you know

A

Conventional tail rotor
Fenestron
NOTAR

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10
Q

Explain truss frame design, monocoque design and semi-monocoque design

A

Truss frame:
Steel tubes welded together, main tubes and diagonal struts, sometimes covered with fabric. Oldest design.

Monocoque:
Consists of skin, former and bulkheads. The skin must carry the primary stresses and keep the fuselage rigid. Often used with fiber reinforced plastics to create complicated and aerodynamically shaped designs.

Semi-monocoque:
Primary structure forms the load carrying structure, light metals, longerons and stringers.
Secondary structure creates the skin and is for aerodynamic streamlining, consists of fiber reinforced plastic.

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11
Q

What are the names of the different axes of orientation for an aircraft? Name the associated movements about these axes.

A

Longitudinal axis = roll
Lateral axis = pitch
Vertical axis = yaw

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12
Q

Which control devices does initiate which type of movement?

A

Movement around vertical axis = pedals
Movement lateral axis = cyclic
Movement longitudinal axis = cyclic
Movement along the vertical axis = collective lever

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13
Q

Name and describe the two main assemblies of a swashplate

A

Rotating part = transmits control inputs to the rotor blades via pitch links
Stationary part = receives control inputs and transmits them to the rotating part, is connected to the rotating part via bearings
Swashplate = 4 degrees of freedom

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14
Q

Which inputs are transferred to the swashplate?

A

Inputs from cyclic stick
Inputs from collective lever

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15
Q

How and where does the coning angle develop?

A

Angle between TPP and rotor blade axis.
Lift created by the rotor blades leads to a flapping motion upward, kept in balance by centrifugal forces (rotor RPM)

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16
Q

How is forward flight initiated

A

Control input (cyclic stick)
Tilting of stationary part of swashplate
Tilting of rotational part of swashplate
Cyclic change of angle by pitch control rods
Cyclic change of lift, cyclic flapping of rotor blades 90 degrees later
Tilting of the TPP
Tilting of the thrust vector

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17
Q

Which physical phenomenon calls for the use of lead/lag hinges?

A

Conservation of angular momentum: if the distance to the axis of rotation is decreased the rotational velocity increases; if the distance is getting bigger, the rotational velocity decreases
Example: figure skating (piruette)

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18
Q

Which other effect causes lead/lag of the rotor blades? Where does this effect always occur?

A

Hooke’s joint effect.
At 3 o’clock and 9 o’clock positions of the rotor blades.

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19
Q

Explain the lead/lag position of a 4-bladed main rotor during forward flight

A

3 o’clock blade leads (hooke’s joint)
6 o’clock blade leads (conservation of angular momentum)
9 o’clock blade lags (hooke’s joint)
12 o’clock blade lags (conservation of angular momentum)

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20
Q

How and by which control input is the pitch angle of the tail rotor blades changed?

A

Collectively by the pedals

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21
Q

Which components are required for the safe operation of a hydraulic system?

A

Reservoir
Lines, hoses
Fluid
Consumers
Valves
Pumps
Monitoring system

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22
Q

Which helicopter systems are usually operated hydraulically?

A

Landing gear
Flight control system
Ramps, doors
Brakes

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23
Q

Which hydraulically operated system is of particular importance to a helicopter pilot?

A

Flight control system

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24
Q

Which type of reservoir should be used in an aircraft hydraulic system? What is its most important characteristic?

A

Pressurized reservoir (closed reservoir).
Prevents cavitation.

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25
Which types of pumps are used in hydraulic systems?
Gear pumps (constant volume displacement) Axial piston pumps (variable displacement) Gerotor pumps Radial pumps
26
Which type of pump is primarily used for flight control purposes?
Axial piston pumps
27
Where are the most important hydraulic pumps mounted? And why?
At the main gear box, because in case of engine failure, we can still use hydraulic support to control the helicopter
28
Name the different types of rotor configurations. Name a helicopter type for each configuration.
Fully articulated = CH-53 Semi rigid = Bell 206 Rigid hingeless = BO105 Rigid hinge- and bearingless = EC135 Spheriflex = NH90 Starflex = Tiger
29
Which movements must the rotor blades be able to perform?
Flapping, lead/lag, feathering
30
How are rotor blade movements allowed in different configurations?
Fully articulated = hinges and bearing Semi-rigid = one central flapping hinge, feathering bearing Hingeless = Feathering bearing, blades do flapping and lead/lag Hinge- and bearingless = blade angle changed by control cuff, flapping and lead/lag carried by rotor blade
31
Advantages and disadvantages of different rotor configurations
Fully articulated: + simple, for all types of helicopters - many parts, bearings and hinges needs maintenance and lubrication Semi rigid: + cheap, easy construction, less parts - less reactive, no negative g tolerance due to mast bumping Rigid: + less maintenance because of no flapping or lead/lag hinges, very reactive - high loads on rotor blades, mast moment
32
How is a tail rotor provided with a delta 3 hinge affected by flapping? How does this angle come about?
It reduces flapping of rotor blades, and therefore it is possible to mount the tailrotor closer to the tailboom without hitting it. The connection of flapping hinge and control rods is 30 degrees shifted.
33
What is the purpose of the transmission system?
Transmitting forces Changing direction of forces Changing RPM
34
Name five components of the transmission system
Main gear box Drive shaft Freewheeling unit Rotor mast Tailrotor drive Clutch Rotor brake
35
When is a centrifugal clutch required in a helictoper?
A helicopter with a piston engine or single shaft gas turbine, to ensure unloaded engine start
36
Why is a centrifugal clutch unsuitable for autorotation?
A clutch wouldn't disengage fast enough
37
Which component is suitable for power-off landings?
Freewheeling unit. Connects the inner shaft (main gear box) with the outer shaft (engine) with the clamp coupling principle.
38
Describe the design/structure of the main drive shaft
Usually metal tube, it ensures a moveable coupling to provide flexibility because of the vibrations. It has welded plates near the end of the shaft to compensate linear deformation and angular deviation.
39
How can offset and torsion of the tail rotor drive shaft be compensated for? What causes these offsets?
Compensation via elastic couplings, no vibrations are transmitted. High RPM to reduce torque.
40
How is the main gearbox lubricated?
Wet sump lubrication
41
Which information on the lubrication oil circuit can be displayed in the cockpit?
Oil pressure, oil temperature, oil pressure warning light, oil chip detection
42
How is the final stage of the main gearbox often designed?
Planetary gear. Low weight, small in size, high reduction ratio and high transfer of torque.
43
How are forces transmitted from the rotor system to the airframe?
Rotor mast --> transmission --> via struts to the transmission deck --> fuselage
44
Which auxiliary systems are usually driven by the transmission system?
Hydraulic pumps, oil pumps, tachometer generator, oil cooler fan
45
Which are the main differences between gas turbines and piston engines?
Piston engine = 4 strokes, only one stroke delivers power Gas turbines = mechanical power is delivered constantly
46
How are the individual strokes of an internal combustion engine called?
Intake, compression, expansion, exhaust
47
Name different types of jet engines
Ramjet Turbojet Turbofan Turboprop Propfan Turboshaft
48
Which main assembly groups does a turboshaft engine consist of?
Inlet Compressor Combustion chamber Compressor turbine (N1) Free power turbine (N2) Drive shaft Exhaust
49
Which are the main differences between jet engines and turboshaft engines?
Turboshaft generates no thrust from exhaust gases, energy is only to drive shaft 1st turbine stage is used to drive the compressor, while the 2nd stage is needed to run the drive shaft. Turbojets doesn't need a 2nd stage.
50
What is the purpose of a turboshaft engine's compressor?
Provide air Clear combustion direction
51
Which main dangers are compressors exposed to?
Compressor stall (reduce collective / shut down engine)
52
Name the different types of combustion chambers. Which are the most common?
Annular (mostly used, with reverse flow) Tubular Combined
53
Into which airflows does the airstream split up in the combustion chamber and what is the purpose of these airflow respectively?
Primary air (20-25%): mixed with fuel and used for combustion Secondary air: (75-80%): used for cooling and directing the flame
54
What type of lubrication system is used in turboshaft engines?
Dry sump lubrication
55
Describe the design/structure of a reaction turbine and explain how pressure and temperature behave within this type of turbine.
Stator increases velocity of airflow by reducing static pressure, rotor uses energy of the airflow and decreases total pressure by reducing static and dynamic pressure
56
Describe the design of the exhaust of turboshaft engines
Exhaust functions as a diffusor to reduce noise, infrared detectability (temp signature)
57
58
Name the design principles in engineering, and an example.
Safe life = maintenance / changing parts Fail safe = having two engines, back up instruments etc Crash safe = skids break outwards, seats are dampened, fuselage buckles etc Damage tolerant = being tolerant enough to withstand a crack without breaking completely
59
What is a sandwich structure?
Consists of a core material and an outer skin of wood, glass-fiber reinforced plastic or metal bonded to both sides
60
Which two parts is a so called "composite" made of?
Fiber + matrix
61
Name the three types of loads a helicopter could be subject to
Static load Dynamic load Cyclic load
62
Which types of stresses do you know? Give an example too
Tension = rotor blades during flight Torsion = a shaft Compression = landing gear Shearing = every rivet or bolt Bending = rotor blades when not turning Buckling = landing gear and fuselage during very hard landings
63

Engineering (2 decks)

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