Engineering (updated 2024) Flashcards
Name four different types of rotary-wing aircraft. To which general aircraft category do all these aircraft belong? What other kinds of aircraft are possible?
Helicopter, autogyro, gyrodyne, compound helicopter, convertiplane
Category: Heavier-than-air.
Other types: Lighter-than-air (e.g., balloons, airships).
Which rotorcraft requires torque compensation?
Single-rotor aircraft with main rotor shaft driven by engine
How is the torque compensated when a helicopter has more than one main rotor (equal number)?
Achieved by counter-rotating rotors (tandem or coaxial).
Name the SI base units.
Length: Meter (m).
Mass: Kilogram (Kg).
Time: Second (s).
Electric current: Ampere (A).
Temperature: Kelvin (K).
Luminous intensity: Candela (cd).
Amount of substance: Mole (mol).
Combine the base units to derive the units of force, pressure, work, and power.
Force: Newton (N). (mass * acceleration)
Pressure: Pascal (Pa). (Force/Area)
Work: Joule (J). (Force * distance)
Power: Watt (W). (Work/Time)
Convert the given velocity into: knots, ft/min, m/s, km/h.
100kt
5m/s
180ft/min
100knots:
- 10.127 ft/min
- 51,44 m/s
- 185,2 km/h
5m/s:
- 9,72 kt
- 984,25 ft/min
- 18 km/h
180 ft/min:
- 1,78 kt
- 0,914 m/s
- 3,29 km/h
Name and describe the three laws of motion developed by Newton. Give an example of each law.
First law (Inertia): Object in motion stays in motion (e.g., car braking).
Second law (F = ma): Force = mass × acceleration (e.g., pushing a cart).
Third law (Action-Reaction): Equal and opposite reaction (e.g., rocket launch).
Explain Bernoulli’s law.
Ptot = Pdyn + Pstat = constant
Is constant if:
- incompressible fluid
- closed system
Explain the principle of a nozzle and a diffusor.
Nozzle: area decreses, velocity increses
Diffusor: area incresas, velocity decreses
Describe the terms isobaric, isochoric, isothermal, isentropic, polytropic - change of state.
Isobaric: Constant pressure.
Isochoric: Constant volume.
Isothermal: Constant temperature.
Isentropic: Adiabatic process
Polytropic: Realistic change of states
Which are the two main principles of driving the main rotor?
Tip drive.
Shaft drive.
Which are the main consequences arising from these principles?
Tip drive: No torque effect, high fuel consumption.
Shaft drive: Requires torque balancing.
Which anti-torque systems do you know? Name the advantages and disadvantages of these systems.
Conventional tail rotor:
+ work on all helicopter sizes
- Tip vortices (LTE)
NOTAR:
+ No tail drive shaft, really safe
- Can’t be used with heavy helicopters
Shrouded tail rotor (fenestron):
+ No LTE
- Need more pedal input
Explain the terms truss frame design, monocoque design, and semi-monocoque design.
Truss: Framework of supports.
Monocoque: Load supported by the skin.
Semi-monocoque: Combines both.
What are the names of the different axes of orientation for an aircraft? Name the associated movements.
Yaw (vertical)
Roll (longitudinal)
Pitch (lateral).
Which (helicopter) control device does initiate which type of movement?
Cyclic: Pitch and roll.
Collective: Vertical movement.
Pedals: Yaw.
Name and describe the two main assemblies of a swashplate.
Stationary: Transfers pilot inputs to the rotor system.
Rotating: Adjusts blade pitch as it rotates with the rotor.
Which inputs are transferred to the swashplate?
Cyclic and collective
How and where does the coning angle develop?
Develops due to lift and centrifugal force in rotor blades.
Where: between horizontal plane and TPP
How is forward flight initiated with a helicopter? Describe the entire procedure from the pilot’s input on the stick to the resulting movement of the helicopter.
Cyclic input tilts rotor disk forward, generating forward thrust.
Which physical phenomenon calls for the use of lead-lag hinges? Explain this phenomenon using an example from everyday life.
Conservation of angular momentum.
I.E: skater increases rotation by pulling arms towards the body.
Which other effect causes lead-lag of the rotor blades? Where does this effect always occur?
Hooke’s joint effect.
always occur at 3 and 9 o’clock
Explain the lead/lag position of a 4-bladed main rotor during forward flight (counterclockwise rotation).
Advancing blade is leading (3 o’clock)
Retreating blade is lagging (9 o’clock)
Blade at 12 o’clock is lagging
Blade at 6 o’clock is leading
How and by which control input is the pitch angle of the tail rotor blades changed?
Controlled by pedals.
Which components are required for the safe operation of a hydraulic system?
Reservoir
Consumer
Monitoring system
Valve
Pump
Fluid
Lines
Filters
Which helicopter systems are usually operated hydraulically?
Flight controls, landing gear, rotor brake, ramps,
Which hydraulically operated system is of particular importance to a helicopter pilot?
Flight control system.
Which type of reservoir should be used in an aircraft hydraulic system? What is its most important characteristic?
Enclosed system (prevents cavitation).
Which types of pumps are used in hydraulic systems? In what essential respects do these pumps differ from each other?
Gear Pump: Constant flow.
Radial Pump: Low pulsation.
Axial Piston Pump: Variable flow, high volume.
Which type of pump is primarily used for flight control purposes?
Axial piston pump.
Where are the most important hydraulic pumps mounted? And why?
Near main gearbox
WHY: so the pump can be driven by the main rotor during engine failure
Name the different types of rotor configurations! Name one German Army helicopter type each for every type of system.
Fully articulated (e.g., CH-53).
Semi-rigid (e.g., Bell 206).
Rigid (e.g., EC-135).
Which movements must the rotor blades be able to perform?
Flapping, lead-lag, feathering.
How are these movements allowed in the different rotor configurations?
Fully articulated rotor:
Through hinges and bearings
Semi-rigid:
Teetering, hinge and within the blade
Rigid:
Within the blade
Name advantages and disadvantages of the different rotor configurations.
Fully articulated: Smooth ride, complex.
Semi-rigid: Simple, risk of mast bumping.
Rigid: Low maintenance, high stress.
How is a tail rotor provided with a delta 3 hinge affected by flapping? How does this angle come about?
Minimizes flapping so the tail rotor can be moved closer to the fuslage/tail
Why is the conventional tail rotor installed on a pylon?
To counteract the roll
Or,
Increases efficiency and reduces vibrations.
And for safety
What is the purpose of the transmission system?
Transfer or transmit forces
Changing direction of forces
Changing RPM
Name five components of the transmission system.
Main gearbox, tail rotor driveshaft, clutch, freewheeling unit, rotor brake
When is a centrifugal clutch required in a helicopter?
Unloaded start, piston/single shaft gas turbine
or,
It is required for gradual rotor engagement.
Why is a centrifugal clutch unsuitable for autorotation?
Can’t disengage quickly in emergencies.
Which component is suitable for power-off landings? Describe this component’s design/structure and explain how it works.
Freewheeling unit (auto-rotation)
Clamp coupling principle
Placed = between main gearbox and engine
Describe the design/structure of the main drive shaft.
A metal tube between the engine and the main gear box able to transfer/withstand the torque through moveable/flexible couplings.
or,
High-strength alloy, torsion resistant.
How can offset and torsion of the tail rotor drive shaft be compensated for? What causes these offsets?
How: Flexible couplings and bearings
What causes: Gust, hard landings, vibrations and turbulence
How is the main gearbox lubricated?
Wet sump lubrication system
Which information on the lubrication oil circuit can be displayed in the cockpit?
- Pressure
- Temperature
- Chips
How is the final stage of the main gearbox often designed? Why?
Planetary gear system (compact design).
Why: High reduction of RPM
How are forces transmitted from the rotor system to the airframe?
Thrust bearings and dampers.
Rotor mast -》Main Gear Box -》Fuselage
Which auxiliary systems are usually driven by the transmission system?
Hydraulic pump, electrical generator, cooling fans and lubrication
In simple words define the term “stress” and “strain.”
Stress: Force per unit area. F/A = stress
Strain: Change in length divided by the original length.
Which types of stress do you know? State one example for each type!
Bending = Rotor blades
Shearing = Fuselage
Tension = Rotor blades being pulled apart
Compression = Landing gear
Torsion = Drive shaft
Buckling = Fuselage
Name the 3 types of loads a helicopter could be subject to! Also, give an example of how you as a pilot could affect these loads!
Static loads: Weight of fuel or passengers.
Dynamic loads: Hard landings (G-forces).
Cyclic loads: Cyclic inputs
Name the most commonly used materials in aircraft engineering! Give some examples where a specific material is used for a certain part/component of the helicopter (old vs. modern materials, e.g., gearbox is typically made out of…).
Old: Steel, wood, titanium.
Modern: Kevlar, carbon fiber, aluminum.
Example: Gearboxes are typically made of steel or aluminum.
Out of which two parts is a so-called “composite” consisting?
Fiber and Matrix
What is a “sandwich structure”?
A lightweight core material (e.g., foam) sandwiched between two stronger outer layers (e.g., aluminum).
List two advantages as well as disadvantages of modern composite materials!
Advantages: High strength-to-weight ratio, corrosion resistance.
Disadvantages: Expensive, harder to detect damage.
Name the design principles in aircraft engineering! State an example for each principle!
Safe life: Replace parts before failure (e.g., rotor blades).
Fail safe: Multiple wing spars.
Damage tolerance: Structures can carry loads even if damaged.
Crash safety: Crash absorbing seats
List 6 typically used attachment methods in aviation! Explain why so many different methods are required!
Bolts, rivets, welds, adhesives, clamps, pins, screws
Different methods are used to address varying load conditions, materials, and maintenance needs.
You are about to lift off in a helicopter with a counterclockwise rotating main rotor (as seen from above). Where will the aircraft yaw with increasing engine power? Wich countermeasure do you have to take?
It will yaw to the right with increasing power.
Counteract: Push left pedal and thereby increase thrust from the tail roter
You are in a hover flight with a single-rotor helicopter. The rotor is turning counter-clockwise (as seen from above). What will happen if you push the left and the right pedal respectively?
Left pedal: The blade pitch on the tail rotor will increase. Increasing thrust and torque will make the helicopter yaw to the left.
right pedal: The blade pitch on the tail rotor will decrease. Decreasing thrust and torque, will make the helicopter yaw to the right.
Which are the main differences between gas turbines and piston engines with regard to their working cycles (place and time)? What happens to the pressure during the combustion process?
- A piston engine: Same place, different times.
- Pressure increase
- A gas turbine: Different place, same time
- Slight decrease of pressure.
How are the individual strokes of an internal combustion engine called?
Intake - compression - combustion - exhaust.
Name the different types of jet engines!
- Scramjet
- Ramjet
- Turbojet
- Turbofan
- Turboprop
- Propfan
- Rockets
▪ Solid fuel
▪ Liquid fuel
Which main assembly groups does a turboshaft engine consist of?
- Intake
- Compressor
- Combustion chamber
- N1 turbine (compression)
- N2 turbine (free power turbine)
- Exhaust
Which are the main differences between jet engines and turboshaft engines?
- Jet engines produces thrust force.
- Turboshaft engines produces shaft power.
What is the purpose of a turboshaft engine’s compressor?
Increase static pressure to =
- Provide enough air for combustion
- Clear combustion direction
Which main dangers are compressors exposed to? How can these dangers be avoided?
- FOD (Foreign object damage)
o I.e. sand erosion and glassing of the engines -> use filter - Compressor stall or surge – Avoid fast accelerations.
Describe the principal structure/design of a compressor! How do pressure and temperature behave in the different stages?
A compressor consists of rotating blades (rotors) and stationary blades (stators) arranged in stages. Rotors increase air velocity, and stators convert this velocity into pressure.
Pressure: Increases with each stage.
Temperature: Rises due to compression.
Name the different types of combustion chambers! Which type is the most common one used in helicopters? Why?
Types of combustion chambers:
- Annular Combustion Chamber
- Reversed Annular Combustion Chamber
- Tubular Combustion Chamber
- Reversed Tubular Combustion Chamber
- Combination Combustion Chamber
Most common in helicopters: Reversed Annular Combustion Chamber
Why: Compact, save space.
Into which airflows does the airstream split up in the combustion chamber and what is the purpose of these airflows respectively?
Primary air (20-25% of the airflow):
- Ignition for the flame
Secondary air (75-80% of the airflow):
- Centering the flame.
- Provides a cooling “coating” for the flame.
- Flame cut off.
Which turbine types are used in twin turboshaft engines? Which of the two turbines is first passed through by the airstream?
- Compressor turbine (N1)
- Free power turbine (N2)
”N1” is passed through first.
Describe the design/structure of a turbine and explain how pressure and temperature behave within this type of turbine!
Describe the design of the exhaust of turboshaft engines!
Air outlet = exhaust diffusor
- Low thermal detectability
- Pressure decrease
- Noise level
What type of lubrication system is used in turboshaft engines?
Dry sump
