Tech - Aircraft Engineering 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?
- Autogyro
- Gyrodyne
- Compound helicopter
- Convertiplane
- Helicopter
They belong in the general aircraft category “Heavier-than-air Aircraft”, subdivision “Rotary-wing Aircraft”. Other subdivisions are “Fixed-wing Aircrafts” and “Rockets”
The other general aircraft category is “Lighter-than-air Aircraft” I.e:
- Ballon
- Airship.
Which rotorcraft requires torque compensation?
All rotorcraft with a single shaft driven rotor.
Name the SI base units!
- Length, Meter (l,d)
- Mass, Kilogram (m)
- Time, Second (t)
- Current, Ampére (I)
- Temperature, Kelvin (T)
- Luminous intensity, Candela (lv)
- Amount of substance, Mol (n)
Combine the base units to derive the units of force, pressure, work and power.
- Force (Newton): mass * acceleration
kg * m/s2= N
- Pressure (Pascal): force / area
N/m2=Pa
- Work (Joule): force * length
1 Nm = 1 Joule - Power (Watt): work / time
Nm/s = Watt
Convert the given velocity into: knots, ft/min, m/s, km/h!
100kt = 10 124 ft/min 51,4 m/s 185,2 km/h
5 m/s = 984 ft/min 9,72 kn 18 km/h
180 ft/min = 0,9 m/s 1,78 kn 3,3 km/h
Name and describe the three laws of motion developed by Newton! Give an example of each law!
Newton’s first law (“law of inertia”):
“Each body remains in its state, rest or uniform straight movement, as long as no external force is applied to it. Only if an external force is applied to it, the body will be accelerated.” Sum of all forces = equal.
- I.e. Apple hanging in a tree.
Newton’s second law (“Law of acceleration”):
“Force = mass * acceleration.”
Force is directly proportional to the net force applied, and inversely proportional to the mass of the object.
- I.e. Apple falling from the tree towards the ground.
Newton’s third law (“Law of equality of action and reaction”):
“For every action, there is an equal and opposite reaction.”
Apply force on an object, object will react with the same amount of force in the opposite direction.
- I.e. Apple hitting the ground.
Explain Bernoulli’s law!
The total pressure of a horizontal flow, i.e.
the sum of static and dynamic pressure, remains constant.
P total = P stat + P dyn = constant.
I.e. If dynamic pressure increases, static pressure decreases and vice versa.
Explain the principle of a nozzle and a diffusor!
Nozzle (Flow from bigger to smaller area):
Velocity increases (dynamic pressure increases, static pressure decreases).
Diffusor (Flow from smaller area to bigger area):
Velocity decreases (dynamic pressure decreases, static pressure increases).
Describe the terms isobaric- / isochoric- / isothermal- / isentropic- / polytropic- change of state!
Universal gas law=(p * V)/T
- Isobaric change of state:
Pressure remains constant. Volume and temperature changes.
I.e. Piston rises (volume increases) when heat is applied (temperature increase).
- Isochoric change of state:
Volume remains constant. Pressure and temperature changes.
I.e. Pressure cooker. Heat is applied (temperature increases), Pressure increase.
- Isothermal change of state:
Temperature remains constant. Pressure and volume changes.
I.e. Bike pump. Volume decreases, pressure increases, temperature (heat) is transferred to the surrounding. Happens slowly.
- Isentropic change of state:
Adiabatic change of state which means the change occurs without any heat exchange with the environment, i.e. in complete thermal insulation (and is therefore possible in theory only). - Polytropic change of state:
Between the borderline cases of isothermal and adiabatic changes of state that cannot be achieved technically, where heat can be partially exchanged with the environment.
Which are the two main principles of driving the main rotor?
- Tip drives.
- Shaft drives.
Which are the main consequences arising from these principles?
Tip drives:
- No torque effect on the helicopter airframe = torque balancing not needed = tail rotor not required = weight reduction.
- Have no gearbox for power transmission = weight reduction.
- High fuel consumption.
- High noise levels.
- Low propeller efficiency and insufficient lubrication due to centrifugal forces
(blade propeller drives)
Shaft drives:
- If the helicopter has only a single rotor driven by the engine via a shaft, the rotor shaft generates an equal, but opposite reaction moment that acts on the helicopter airframe. Torque balancing needed. .
Which anti-torque systems do you know? Name the advantages and disadvantages of these systems!
Conventional tail rotor:
+ Easy to construct
+ Cheap
+ Easy maintenence
+ Common
+ Can be used on bigger helicopters
- Exposed. Can hit people and obstacles
- High noise levels
Shrouded tail rotor:
+ Covered. Safer for people and for not hitting obstacles.
+ Quieter. (High frequency).
- Complex maintenance = Expensive.
- Heavy. Not suited for heavy aircraft.
- Less efficient. Needs more power.
NOTAR (No tail rotor):
+ Safe (hitting people and obstacles)
+ Quieter
+ Low operating cost - Lower vibration
- Only suited for light helicopters
- Hard to control autorotation after touchdown
Example of other rotor system:
Tandem rotors:
+ All engine power goes to rotor thrust. No power sacrificed for a tail rotor.
- Mechanically complex. A lot of work.
- Take up a lot of space for landing.
Coaxial rotors:
+ All engine power goes to rotor thrust.
- Difficult design.
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? Which countermeasure do you have to take?
The helicopter will want to yaw to the right with increasing engine power. To counter it, you will have to push left pedal to increase the thrust from the tail rotor.
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, making the helicopter yaw to the left.
Right pedal:
The blade pitch on the tail rotor will decrease, decreasing thrust and torque, making the helicopter yaw to the right.
Which types of stress do you know? State an example for each type!
Bending - Rotor blades.
Shearing - Bolts for main rotor blades, rivets.
Compression - Landing gear / skids, shock absorbers.
Tension - Rotor blades being pulled apart.
Torsion - Drive shaft.
Buckling - Landing gear / skids.
MEMO: Come To The Shining Beautiful Bückeburg
Describe the most commonly used materials in aircraft engineering! (fuselage old & modern, gearbox, rotor blade)
- Fuselage old:
Wood or steel covered with fabric. Later on, steel titanium and light metals (I.e. aluminium). - Fuselage modern:
Composite fiber designs (plastic, glass- and carbon fiber reinforced plastics). Sandwich structures. - Gearbox: Cast iron, steel and aluminium.
- Rotor blade: Composite fiber materials, titanium, steel, aluminium.
Describe the term “sandwich structure”!
- Lightweight core material (wood, hard foam or a metal/plastic honeycomb core)
- Outer thin and stiff skin of wood, glass-fiber reinforced plastic or metal, bonded to both sides.
This provides protection from different types of stress, while at the same time keeping the weight down.
Name the design principles in aircraft engineering! State an example for each principle!
Safe life (maintenance):
Ensuring throughout the service life of an aircraft that no damage occurs in any component relevant to the safety of the aircraft structure.
(maintenance, replacing parts after x amount of hours).
I.e. ???
Fail safe (redundancy):
Designing the aircraft so that damage in, or failure of individual components do not result in failure of the aircraft. (redundancy, I.e. two hydraulic systems, stringers and formers).
I.e. tailboom fuselage.
Crash safety (compression):
Energy absorbing cell structures allowing compression.
I.e. Load absorbing landing gear, Compressible landing skids, crash dampening seats.
Explain the terms truss frame design, monocoque design and semi-monocoque design!
Truss frame design:
Primary structure in the form of a frame, with no additional shell.
Primary structure takes all the load. Frame is made of wood or metal. Mostly consist of four main steel tubes with three or four diagonal struts. The connecting points are welded.
+ Simple, easy to build
+ Easy to repair
+ Cheap
+ Stable
- Heavy
- Reduced interior space
Monocoque design:
One shell that absorbs the entire load. No inner frame. Allows for aerodynamic shape.
- Prone to buckling and compression.
Semi-monocoque design:
Primary structure in the form of a frame (formers and stringers) for load carrying. Secondary structure (outer shell) for aerodynamics.
+ Fail safe (redundancy)
+ Lightweight
- Expensive/more complicated
What are the names of the different axes of orientation for an aircraft? Name the associated movements about these axes!
Roll - Longitudinal axis
Yaw - Vertical axis
Pitch - Lateral axis
MEMO: Roll – Andra bokstaven samma, d.v.s. O.
Yaw – Y ser nästan ut som ett V.
Which (helicopter) control device does initiate which type of movement?
- The cyclic stick to operate the cyclic pitch control.
- The collective pitch lever to operate the collective pitch control
- Pedals for directional control
Extended answer, see below…
Cyclic stick:
- Pitch along the lateral axis
- Roll along the longitudinal axis
Collective:
- Lift along the vertical axis
Pedals:
- Yaw about the vertical axis
Name and describe the two main assemblies of a swashplate (Which movements does it have to fulfill)
Rotating and stationary part. The motion of the swashplate moves the control rods resulting in changes of the mechanical angle (angle of incidence).
SVARET KAN BEHÖVA UTVECKLAS.
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!
- Control input via the cyclic stick
- Tilting of the stationary swashplate by control linkage
- Tilting of the rotating swashplate
- Cyclic change of angle of incidence (by push rod (control rod))
- Cyclic change of lift
- Cyclic flapping of rotor blades
- Tilting of tip-path plane
- Tilting of thrust vector and resulting motion of the helicopter
How and where does the coning angle develop?
Creating a coning angle between the horizontal plane and the rotor tips.
If more collective is pulled, more angle of attack on rotor blades, more force (lift) is generated, and the rotor starts to shape a cone. The angle between the tips of the blades are called tip path plane. The flapping hinges allows the blades to form the coning angle. When the lift force is higher than the weight, the rotor blades bends
upward .
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!
- Control input via the cyclic stick
- Tilting of the stationary swashplate by control linkage
- Tilting of the rotating swashplate
- Cyclic change of angle of incidence (by push rod (control rod))
- Cyclic change of lift
- Cyclic flapping of rotor blades
- Tilting of tip-path plane
- Tilting of thrust vector and resulting motion of the helicopter
Alternative answer:
- Forward input via the cyclic stick
- Stationary and rotating part of swashplate tilts
- Maximum blade pitch angle and lift at 9 o’clock by control rods.
- Blade reaches highest position 90° later.
- Change of lift occurs.
- Flapping of rotor blades (tip-path plane tilting forward).
- Lift is tilted forward, helicopter moves forward.
- (Increased collective and torque compensation with pedals as a result of increased collective needed as well).
Which physical phenomenon calls for the use of lead-lag hinges? Explain this phenomenon using an example from everyday life!
Conservation of angular momentum.
Higher velocity is caused to the blade flapping upwards due to its closer proximity to the center of rotation. (Rotor blade center of gravity is shifted closer to the axis of rotation). This requires the blade to be able to “lead”.
I.e. Figure skater increasing his/hers rotation by pulling arm inwards toward the body.
