In classical aircraft engineering, an aircraft is subdivided in which three groups?
airframe, engine and systems
What are the three system groups of an A/C?
Structure, vehicle system, avionic system
What is the function of the airframe?
- complex and integrated set of structural components
- supports the mass of systems and PAX
- carries loads and stresses
- also known as the “platform”
What is the function of the vehicle system?
- also known as general or utility system
- enables the A/C to fly safely
- provides an adequate environment for crew and PAX
What is the function of the avionic system?
provides information, control and communication functions that enable the aircraft to fulfil its operational role
What is the Flight control system?
- nowadays usually a Fly-by-Wire (FBW) system
- pilot control input is elaborated on the basis of air data, A/C attitude etc. to issue the proper control surface deflections that will effect the desired aircraft motion
What is the Engine control system?
in most recent aircraft a Full Authority Digital Engine Control (FADEC) system
What is the Air data system?
provides airspeed, altitude, air temperature, rate of climb or descent information
What is the Attitude system?
provides information on pitch, yaw and roll angles, rates and accelerations
What is the Electrical system?
provides electrical power for flight and engine control computers, air data system, attitude systems, hydraulic servo-valves and (on some A/C) electrically driven hydraulic pumps
What is the Hydraulic system?
provides motive power for the actuators that move the flight control surfaces, or the engine thrust reversers
What are essential functions?
The functions whose loss would reduce the capability of the A/C or its crew to cope with adverse operating and environmental conditions (i.e. loss of cabin pressurization or loss of the anti-icing system)
What are critical functions?
Functions which could cause the loss of the aircraft or fatal injuries to the occupants (i.e. a complete loss of engine power)
How does the severity of a failure condition relate to its probability?
The severity of a failure condition must be inversely proportional to ist probability
What must be considered to evaluate the severity of a failure condition?
- Effects on the airplane
- Effects on the crew members
- Effects on the occupants
What are the four probability terms and how are they defined?
1. Probable: occur one or more times during the entire operational life of each A/C
2. Remote: may occur several times when considering the total operational life of a number of airplanes of this type
3. Extremely Remote: may occur a few times when considering the total operational life of all airplanes of this type
4. Extremely Improbable: not anticipated to occur during the entire operational life of all airplanes of one type
What are the probability ranges for commuter and transport aircraft?
Probable: 10-5 to 10-3
Remote: 10-7 to 10-5
Extremely remote: 10-9 to 10-7
Extremely Improbable: lower than 10-9
Which main design concepts are applied in aviation?
Explain the concept "Safe-Life"
systems or components will survive a specific design life with no failures
Explain the concept "Fail-Safe"
a failure will cause no (or minimum) harm to other parts and systems or danger to personnel
Explain the concept "Fault-Tolerant"
a system can continue operating in the event of the failure of one or more of its components
Aerodynamic loads result mainly from a pressure distribution over the external surfaces. What does this pressure distribution depend on?
- the angle of incidence
- the aerofoil shape
- (where present) the deflection of control or lift augmentation surfaces (such as ailerons, spoilers, flaps or slats)
Where is the point of application of the lift and drag component?
At the centre of pressure (c.p.)
Explain the pitching moment coefficient (cm0) of a cambered aerofoil
For a cambered aerofoil, cm0 is usually negative (which means that for positive lift the centre of pressure lies behind the aerodynamic centre)
What happens to the compressibility and the a.c. at Mach numbers above 0.5 - 0.6?
- compressibility effects become important
- a.c. starts to move backwards, slowly at first, then quite rapidly when zones of supersonic flow appear on the aerofoil (transonic regime). In supersonic flow, the position of the a.c. tends to 50% of the chord.
Explain "Ground loads"
- for taxiing, take off ground roll, landing
- through landing gear (reduce loads to a level that can be absorbed without damage)
What parts of the A/C do the ground load conditions influence?
- design of the landing gear
- structure of the A/C
- attachment points
List some of the main load conditions to be considered according to airworthiness regulations.
- level landing condition
- lateral drift landing condition
- one-gear landing condition
- side load condition
- braked roll conditions
- forward acting horizontal load (during towing)
Explain "ultimate load"
The maximum load that the test specimen can withstand before the material fails.