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.
-
- 1 / 498
-
Lernkarten
For a swept forward wing, bending has a .... effect.
destabilizing
How is flutter defined?
Flutter can be defined as the dynamic instability of an elastic structure in an airflow and is excited by aerodynamic forces which result from the deflection of the structure.
How is the flutter speed defined?
The flutter speed is defined as the lowest airspeed at which an aircraft structure, or part of it, will sustain a vibrational mode indefinitely (with no damping).
What happens above the flutter speed with the structure?
Above the flutter speed, structural vibrations will diverge and cause a potentially catastrophic structural failure.
What is the inertia axis?
Wing inertia axis is the line which connects the centers of gravity of all wing sections.
Why are the engines of a commercial jet AC hanging in front of the wing? How is this process called?
If the inertia axis is aft of the flexural axis, the inertia forces tend to amplify the twisting oscillation.
The position of the inertia axis may be adjusted by redistributing the wing weight with a process known as mass balancing.
Name three other important aeroelastic phenomena.
- Aileron Buzz: this is a form of flutter associated with shock waves oscillating back and forth on the upper and lower wing surfaces and interacting with the boundary layer. The sharp changes in pressure distribution cause a high frequency oscillation of the aileron.
- Buffeting: the most common form of buffeting is that of the tail, which can experience severe vibrations when it is invested by the turbulent wake of the stalled wing.
- Dynamic response: an elastic aircraft in an accelerated flight condition may experience loads which are much greater than those predicted assuming a perfectly rigid structure. External loads, such as gust and landing loads, excite oscillations of the structure. The additional inertia forces associated with these oscillations can produce dynamic load overshoots.
In which parts is the structure of an AC, or airframe subdivided?
- Fuselage
- Wing
- Empennage
- Controls
- Landing gear
What are the main functions of the fuselage?
The main functions of the fuselage are:
- to provide space for the payload, the flight crew and part of the equipment,
- to provide a safe and comfortable environment for the occupants,
- to connect wing and empennage, carrying the loads introduced by these elements,
- in some designs, to integrate fuel tanks, landing gear and engines.
What are the main loads acting on the fuselage?
- forces and moments transmitted by the wing and empennage,
- inertial forces and moments relative to the payload, flight crew, equipment and (depending on the configuration) fuel and engines,
- for some designs, ground loads transmitted by the landing gear,
- aerodynamic forces on the external surface,
- pressurization loads.
Name the four main components of the fuselage.
- Front fuselage
- Mid fuselage
- Rear fuselage
- Tail cone
What are the main functions of the wing?
- To provide lift and roll control,
- For most civil aircraft designs, to carry part or all of the fuel,
- For most civil aircraft designs, to carry the landing gear and the engines.
The main loads acting on the wing are.....
- Aerodynamic loads (lift, drag, pitching moment)
- Inertial forces and moments relative to the structure, equipment and (depending on the configuration) fuel and engines,
- For most civil aircraft designs, ground loads transmitted by the landing gear.
- What parts belong to the main structure of the wing?
- Which to the auxiliary structure?
- Which parts do the controls comprise?
- Front, mid and rear spar connected by the ribs
- Fixed parts of the leading edge, attached to the front spar, the trailing edge which provides an aerodynamic transition to the flaps and controls, the removable wing tips or winglets and the flap tracks.
- Slats, flaps, ailerons and spoilers.
The Failure Hazard Analysis (FHA) identifies....
Honeywell recommends inspecting its 36-100 APUs at regular intervals. If the APU does not meet the inspection requirements, corrective actions are taken. If it passes the inspection, the unit is approved for flight until the next inspection.
This maintenance concept is known as...
In a static load test, the wing is progressively loaded up to the ultimate load.
(a) Define the concept of load factor.
The load factor is defined as the ratio of lift (L) to the mass (m) times gravity acceleration (g) of an AC.The load factor shows how much more strain is put on the AC compared to straight and level flight.
(b) Explain the difference between limit and ultimate load factor.
The limit load factor is the maximum load factor that can be applied to the AC structure without any permanent deformation or damage.
The maximum load that the test specimen can withstand is known as ultimate load.
(c) For a commercial airplane, what kind of flying condition is likely to cause the highest positive load factors? Quote a typical value.
At high speed, the limit is set by design to a fixed value, according to the operational requirements of the aircraft. This practice is as old as aviation itself: the Wright brothers designed their Flyer to a maximum positive load factor of 5, which is still a reasonable value today for many aircraft types.
Typical values: 2.5 - 3.8 for transport AC, negative: -1
There is also the possibility of vertical gust: The highest positive load factor can be reached if an AC with low mass encounters gust or clear air turbulence (load factors: -1 to 3.5).
In an airliner, the maximum wing root bending moment is usually reached...
Explain the concept of structural divergence.
Under particular conditions, depending on the flexibility of the structure, the interaction of static or steady state systems of aerodynamic and elastic forces does not result in a condition of equilibrium and produces phenomena such as structural divergence and control reversal. These phenomena fall under the category of static aeroelasticity.
Explain fail safe concept for structures.
A failure will cause no (or minimum) harm to other parts and systems or danger to personnel. In the context of structures, fail safe means that if one structure fails other structural parts are not affected or failing. Other structures can withstand and compensate the failure of the structure.
What is the purpose of a hydraulic power tranfer unit, and how does it work?
The power transfer unit (PTU) is basically a hydraulic motor driving a hydraulic pump. Through a PTU, pressure can be transferred form one system to another without the exchange of fluid between systems.
The PTU is used when, for example, there is right hydraulic system pressure but no left hydraulic system pressure.
The fly-by-wire system controls directy...
The system "AC" can be subdivided into...
- Airframe: Fuselage, Wing, Empennage, Control surface,...
- Air vehicle systems: Landing gear, Flight control, Propulsion, Hydraulics, Electrics,...
- Avionic systems: Navigation, Displays, Flight Management, Communications,...
- Mission systems: Sensors, Mission computer, Weapons, Passive defence,...
What is the difference between failure and failure condition?
A failure is the inability of a system, subsystem or component to perform a function as intended.
A failure condition is a condition with an effect on an AC and its occupants caused by one or more failures, considering the relevant operational and environmental conditions.
On February 24, 1989 a United Airline B747 took off from Honolulu bound for Sydney, Australia. As the AC was climbing, between 22000 and 23000 ft, explosive decompression was experienced. The captain declared an emergency, initated a 180° left turn to avoid a thunderstorm and returned to Honolulu.
A portion of the cabin fuselage was teared off and nine pax were ejected. The starboard side engines were damaged and had to be shut down. Parts of the leading and trailing edge flaps where also damaged and the crew decided to use only 10 degrees trailing edge flaps for landing (a non-normal configuration). This resulted in the AC having to land at a higher speed.
The AC landed in Honolulu, stopped at the end of the RWY and an emergency evacuation was executed.
How would you categorize the failure described above.
Briefly describe the three main categories of AC structural loads.
- Flight loads: all loads encountered by an AC in steady flight and due to maneuvering and gusts, including engine loads.
- Ground loads: all loads applied to the AC during movement or transportation on the ground (jacking, towing, taxiing, rolling)
- Pressurization loads: In pressurized AC, the fuselage must withstand the loads due to the pressure differences between cabin and atmosphere.
In a tension test to measure the strength of a material, the ultimate stress is...
In normal flying conditions, the upper wing spar cap is mainly subjected to...
In a static test, the AC structure must withstand the limit load...
In an acrobatic AC, the maximum wing root bending moment is usually reached...
Explain the concept of flutter speed and its relationship with design diving speed VD.
The flutter speed is defined as the lowest airspeed at which an aircraft structure, or part of it, will sustain a vibrational mode indefinitely (with no damping). Above the flutter speed, structural vibrations will diverge and cause a potentially catastrophic structural failure.
Airplanes must be designed so that the flutter speed is at least 15% higher than the design dive speed VD.
Name at least four advantages of hydraulic systems.
- excellent power to weight ratio;
- high power transmission efficiency;
- flexibility in installation;
- resitance (Widerstand) to overload conditions;
- high reliability;
- fast response;
- precise position and load control.
In case of pressure loss in the normal hydraulic system, critical actuators can be powered by an emergency system. The switch between the normal and emergency system is operated:
What type of pump is commonly used in AC hydraulic systems?
Describe the basic principles of control feel in an hydraulically powered system.
Without such an hydraulically powered control system, the pilot could command full control deflection at high speed with virtually no force feedback. This would make precise and safe flying almost impossible.
The spring feel units provide a necessary feedback to the pilot, although the control forces returned by a spring package are obviously independent from airspeed. For the rudder, it is necessary to increase the control forces with airspeed to avoid overstressing the airframe. The ‘q’ unit returns a force feedback proportional to the dynamic pressure q so that applying full rudder deflection at high airspeeds would require extremely high pedal forces.
For the tailplane, an inertia weight (also called bob weight) returns a control force feedback proportional to the load factor. This gives the pilots a feeling of how hard they are maneuvering in pitch.
Which of the following are secondary flight controls?
The FCU (Flight Control Unit) is the input device for...
Explain the principle of the electro-mechanical actuator (EMA).
In the EMA, power drive electronics drives a brushless DC motor operating a reduction gear that drives a screwjack to extend or retract according to input demands. It is mostly used for secondary controls (flaps, slats, trim surfaces).
