AC-SYS
AC-SYSTEMS, Manfriani: AC-Structure, the Landing Gear, Propulsion System (Propellers, Piston Engines, Turbine Engines),....
AC-SYSTEMS, Manfriani: AC-Structure, the Landing Gear, Propulsion System (Propellers, Piston Engines, Turbine Engines),....
In a tension test, what does the constant E mean?
E is the normal modulus of elasticity or Young's modulus.
In an AC wing, the cross sectional area of the web carry all the
The web carries most of the
The torsion loading on a trapezoidal wing section with no sweepback is maximum at
The local aerodynamic heating at stagnation point is
The hottes part of an AC flying at supersonic speed is
At low speeds the load factor is limited by
At high speed, the limit is set by
- What are the load factor limits for the Pilatus-21 turboprop trainer?
- For the Lockheed Martin F-22 Raptor jet fighter?
- +8/-4
- +9.5/-3.5
- How is the load factor increment when encountering vertical gust defined?
- What does this equation tell us?
- \(delta n=delta L/(m*g)=Kg*(rho*U*V*CLalpha)/(2*m*g/S)\)
- The AC sensitivity to gust is a function of wing loading (2 m g/S), lift curve slope (cL alpha-->depends on wing aspect ration), flight altitude and airspeed.
How do AC actually react to vertical gust?
They accelerate upwards, so the net gust velocity is reduced.
How do Airworthiness specifications define the gust velocities to determine load factors due to turbulence?
They define the standard gust velocities (in equivalent airspeed).
The AC weight influences loads on the AC structure. What kind of loads are these?
- Fuselage bending
- Wing bending
- Shear loads
- Tailplane loads
How do airworthiness regulations limit the minimum MLW for the PC-12?
95% of the MTOW--> the AC must be able to land immediately in case of engine failure and cannot dump fuel in emergency.
For multi engine AC equipped with a fuel jettison system, a lower MLW can be specified.
- What is the MZFW critical for?
- What is the MRW critical for?
- The MZFW is critical for wing bending and shear at the limit load factor-> fuel weight alleviates these loads
- The MRW is critical for rolling, towing, braking loads on ground
- What weight does the MZFW limit?
- What does it mean to keep the MZFW balanced with the MTOW?
- The payload weight that can be carried. The MZFW should be as high as possible, while staying in balance with the MTOW.
- This means that the wing bending and shear at the limit load factor should be approximately the same at MTOW (with full tanks) and at MZFW.
What defines the zoning system in the ATA-100 specification?
The zoning system is specified to simplify the location of parts in modern large transport AC.
How many hierarchies of AC zones are defined?
3: Major zones, Intermediate zones, Minor zones
- What do odd numbers in the AC zoning system indicate?
- What do even numbers indicate?
- Odd numbers mark the zones of the left side
- Even numbers zones on the right side of the AC, as seen by the pilot.
What can the skin of the AC's fuselage be made of?
Fabric, plywood (Sperrholz), thin metal sheet or synthetic materials.
Layout of a tricycle undercarriage:
How much should the pitch angle Θ be at which the tail touches the ground?
10-15°
How much should the roll angle be for large transport AC and for light AC?
- at least 8° for large transport AC
- 15° for light AC
Which two limit angles define the required length of the main landing gear legs?
Ground pitch and roll angles
What loads should be on the nosewheel of the AC?
8-15% of the AC weight
For a general aviation or commuter AC, what maximum value of lift can be assumed for design and testing?
2/3 of the AC weight
On which value does the vertical speed at touchdown depend?
On the efficiency of the shock absorber.
What is the safety margin of a stroke?
2.5cm
What is a typical value for the internal gas pressure p0 of AC oleo shock absorbers under static load?
1800psi (12.5 MPa)
What is shimmy and why can it occur?
Shimmy is high speed vibration of the nose wheel and can occur because of the wheel imbalance, tire wear or free play in the wheel suspension mechanism. A hydraulic damper (shimmy damper) must be fitted.
What is the typical lifetime of a wheel?
300-400 landings
Propeller efficiency:
A short take off AC with a low cruise speed will certainly benefit from a...
...large propeller providing high efficiency and high thrusts at low speeds.
For a fast AC,....
....a smaller propeller diameter will be more suitable.
Which peak efficiencies reach modern variable pitch propellers?
0.85-0.9
What describes feathering?
In the event of an engine failure, propeller pitch must be set to a value that reduces drag to a minimum. (90°)
Fuel Systems:
Fuel tanks:
How much weighs the fuel mass in an AC (except for small general aviation AC)?
25-50% of the MTOM
Fuel pumps:
What are transfer pumps?
Transfer pumps move fuel between tanks to maintain mass balance and to supply fuel to the collector ranks from where fuel is drawn to feed the engines.
What are booster pumps?
Also called engine feed pumps. They are used to boost (antreiben) the fuel pressure in the engine feed lines.
Another reason is to prevent cavitation (vapour bubbles) at high levels.
Valves:
What is the function of shut-off valves?
Shutting off fuel when required, preventing fuel transfer from one rank to another.
What are the functions of refuel and defuel valves?
Filling the tanks to allow flow from the refueling gallery to the fuel tanks, or from the tanks to the refueling gallery during defueling (emptying the tanks for maintenance)
Cross-feed valves?
Shifting fuel from one side of the AC to the other side.
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Flashcards
Which different meanings can the sentence "Inability to perform a function as intended" have? Give also examples.
The function is not provided when required (e. g., the loss of an electrical generator)
The function is incorrectly provided (e. g., a wrong altitude indication in the cockpit)
The function is provided when not required (e. g., a false indication of engine fire)
To which considerations can severities of failure conditions be evaluated?
- Effects on the airplane: reduction in safety margins, degradations in performance, loss of capability to conduct certain flight operations, potential or consequential effects on structural integrity.
- Effects on the crew members: increases above normal workload that would affect their ability to cope with adverse operational and environmental conditions or subsequent failures.
- Effects on the occupants: discomfort or injuries to the passengers.
What are the probabilities of...
- probable?
- remote?
- extremely remote?
- extremely improbable?
- 10-5 and 10-3
- 10-7 and 10-5
- 10-7 and 10-9
- 10-9
To which probability corresponds extremely improbable for a light general aviation AC (piston singles < 2700kg mass)?
< 10-6 (1/1'000'000)
What are the definitions of...
- Safe-Life?
- Fail-Safe?
- Fault-Tolerant?
- Systems or components will survive a specific design life with no failures. The structure is designed with enough reserves to withstand all the possible loads during a minimum design life, with no catastrophic failures.
- A failure will cause no (or minimum) harm to other parts and systems or danger to personnel. Catastrophic failures during the design life of an AC cannot occur, because the structure is designed in such a way that in case of failure of a component the remaining structure can still carry the design loads.
- A system can continue operating in the event of the failure of one or more of its components.
Which three main functions does the airframe perform?
- It contains the crew, payload, fuel and all systems and components necessary to perform the AC missions;
- It carries the flight and ground loads within the operational limitations of the AC during all its design life;
- It maintains, without excessive or permanent deformations, the aerodynamic shape of the aircraft, so that lift, trim and control forces can be correctly generated and movable parts can properly operate.
Which three load categories are carried by an AC structure?
- Flight loads: all loads in steady flight and due to manoeuvring, gusts, including engine loads, dynamic effects
- Ground loads: all loads during movement or transportation on ground (jacking, hoisting, towing, taxiing, TO and landing loads)
- Pressurization loads: In pressurised aircraft, the fuselage must withstand the hydrostatic loads due to the pressure difference between the cabin and the atmosphere.
In order to do load analysis what value has to be defined whenever an AC is accelerated, or a part of it?
The fictitious inertial load (D'Alembert's principle)
How are aerodynamic forces generated?
Aerodynamic forces are the resultant of the pressure distribution and (to a much smaller extent) of viscous skin friction over the aircraft skin.
How is...
- lift,
- stabilisation and control forces provided?
- Lift is generated by the wings
- Stabilising and control forces are generated by the tail surfaces.
What is the name of the point where resultant force (integration of the pressure distribution over the airfoil) is split into a lift component (perpendicular to the flow direction) and a drag component (parallel to the flow direction)?
Centre of pressure (c.p.)
- What is the aerodynamical centre (a.c.) independent of?
- How is the aerodynamic moment indicated?
- The aerodynamical moment (about a point called a.c.) is practically independent of the angle of attack for a given dynamic pressure q.
- M0
Where is the a.c. located?
Approximately 25% of the aerofoil chord c from the leading edge.
- The pitching moment coefficient referred to the a.c. is usually negative. What does that mean?
- What does that mean for symmetrical aerfoils?
- This means that for positive lift the centre of pressure lies behind the aerodynamic centre (a.c.).
- For symmetrical aerofoils it is equal to zero.
- Where does the a.c. move when compressibility effects become important (Mach 0.5~0.6)?
- Where is the a.c. in supersonic flow?
- The a.c. moves backwards, slowly at first, then quite rapidly when zones of supersonic flow appear on the aerofoil (transonic regime).
- It tends to 50% of the chord
A major AC system failure...
The wing chordwise pressure distribution defines...
The spanwise distribution defines...
In a tension test to measure elasticity and strength of a material, the yield stress is...
Gust loads can be reduced by design if...
The shock absorbing efficiency of a spring type landing gear is typically...
In which conditions does a constant speed propeller have the maximum efficiency?
How much lateral loads must engine mounts withstand according to airworthiness regulations?
Engine mounts must be sised to withstand a lateral load equal to one third of the vertical design load.
- How much is the vertical speed at maximum landing weight specified by airworthiness regulations?
- How much at maximum TO weight?
- 3.05m/s (10ft/s), for civil AC
- 1.83 m/s (6ft/s)
How much must the loads during accelaration and landing speed at least be?
Airworthiness regulations specify that these loads must be assumed to be at least 25% of the maximum vertical ground reaction.
- How much ground loads is expected on the nose gear?
- How much on the main gear?
- The nose gear is subjected to a higher vertical load (a vertical load factor of 1.2)
- Main gear experiences drag loads equal to the vertical load on each leg multiplied by the braking friction coefficient (the maximum value to be considered is 0.8)
The maximum load that the test specimen can withstand is known as...
In a tension test to measure elasticity and strength of a material, the fracture stress is...
In reality, although the load in Newton drops slightly just before fracture, the stress value increases, because of the reduction in cross section. This phenomenon is known as...
necking, from the “neck” that the tensile test specimen forms when subjected to high strain.
In which two components can the local stress in any point of a body be resolved?
Normal to an arbitrarily defined section plane (tension or compression) and tangential (shear).
How is the vertical location in a beam where the normal stress is zero called?
Neutral axis
- On a section plane, where is the shear stress highest?
- Where are the tension and compression stresses highest?
- The shear stress is highest at the neutral axis.
- The tension and compression stresses, as in the bending loading condition, are highest at the upper and lower ends of the section.
How are the effective shear and bending moment distribution obtained?
By integration of the lift and weight loads over the wing span.
- The shear at a given wing section is equal to...
- The bending moment is given by...
- ...the sum of the vertical loads outboard of that section.
- ...the sum of the moments of the equivalent concentrated loads outboard of the wing section being considered.
Why has the engine weight a beneficial effect?
Because is reduces the shear and the bending loads inboard of its location.
At low angles of attack, the pitching moment coefficient about the aerodynamic centre cm0 is approximately constant. If the wing is built on cambered profiles, its value is....
...negative (for positive lift the centre of pressure lies behind the aerodynamic centre).
What is the main structure of the fuselage sised by?
Mostly by the lift of the wing and the horizontal tail, and by the side force of the vertical tail.
What is the principal parameter in structural analysis?
The normal load factor: nz:Fz/(m*g)
What is the normal load factor if the AC is parked on the tarmac?
The normal load factor is then equal to one.
What are the minimum limit load factor requirements of normal and commuter AC?
positive: 2.9-3.8
negative: -1.2 to -1.6
