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
What are the minimum limit load factor requirements of utility AC?
positive: 4.4
negative: -1.8
- What are the minimum limit load factor requirements of acrobatic AC?
- For transport AC?
- positive: 6, negative: -3
- positive: 2.5-3.8, negative: -1
- In straight and level flight the lift is equal to.....
- The shear at the root is equal to...
- ...the AC weight.
- ...one half of the AC weight minus half the wing weight.
The 737-300 has a MTOM of 59194kg, a MZFM of 47628kg and carries 18602kg of usable fuel in the wings. Its CFM-56 engines are installed under wing pylons and have a mass of 2206kg each. The 717-200 (former MD-95) has a lower MTOM (55338kg) and MZFM (45586kg). The usable fuel in the wing tanks is 13382kg. It is equipped with rear fueslage mounted BMW-Rolls Royce BR715-A1-30 turbofans, which have a mass of 2085kg each.
- Not considering the wing structural weight, which AC has the maximum wing root shear in level flight, and at what mass and airspeed?
The shear load at the wing root in level flight is one half of the AC weight minus the weight of the wing, the weight of the fuel contained in the wing tanks and, for the Boeing 737, the weight of one engine. Not considering the wing weight, we have....
- 0.5 AC weight
- engine weight
- 0.5 fuel weight
- wing root shear load
The MD95, although it is a lighter AC, has the highest wing root shear load at maximum zero fuel weight. The advantage of an aerodynamically clean wing, without pylons and engine nacelles, is compensated by a heavier wing structure. Wing shear loads depend on AC mass, fuel mass and load factor and are completely independent from airspeed.
What are the main differences between a hazardous and a catastrophic failure condition?
A hazardous failure condition can cause large reduction in safety margins, physical distress to the crew and serious or fatal injuries to pax.
A catastrophic failure condition can cause multiple fatalities between the occupants, serious or fatal injuries to flight crew members, loss of AC.
An airliner is cruising at 38000ft when one of the cockpit window bursts. A sudden pressurization loss in the cabin follows; one of the pilots suffers minor injuries. The pilots put on their oxygen masks and initiate an emergency descent. The increased noise, the wind pressure and the cold temperature in the cockpit makes the pilots'task much more difficult. However, they manage to land the AC safely after declaring an emergency to air traffic control. No pax is seriously injured although many are in shock and receive first aid at the airport.
How would you categorize the described above?
Describe the three main functions of the AC structure.
- The AC structure contains the crew, the payload, the fuel and all systems and components necessary to perform the AC.
- 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 AC.
Ductile materials:
In normal flying conditions, the wing spar web is mainly subjected to
A static test is successful if the AC structure withstands the ultimate load
In an airliner, the maximum wing root bending moment is usually reached
Explain the concept of aileron reversal speed.
Structural flexibility adversely affects the effectiveness of control surfaces. For example, the downward deflection of an aileron causes a nose down twisting of the wing, which reduces the local incidence and consequently the increase of lift generated by the aileron itself. The aerodynamic twisting moment due to aileron deflection increases with the square of the airspeed, but the elastic restoring moment is constant, since it depends uniquely on the torsional stiffness of the wing structure. Therefore, ailerons become less and less effective as the airspeed increases until, at a particular speed, aileron deflection does not produce any rolling moment at all. This airspeed is called aileron reversal speed; above this speed, the effect of aileron deflection is reversed.
Name at least four functions that can be performed by the hydraulic system of an AC.
- Primary and secondary flight control actuator
- landing gear extension and retraction
- landing gear doors operation
- wheel braking
- nosewheel steering
- cargo door operation
To stop fluid from flowing back from the accumulators to the main system in case of a pump failure, hydraulic circuits are fitted with...
What type of pump is commonly used in AC hydraulic systems?
Describe the basic principle of a Fly-By-Wire flight control system?
The command from the cockpit controls or from the autopilot is converted into an electrical signal and sent to the flight control computer, which also receives information about AC response, servo-valves and actuators positions. The command is processed and sent to the actuators, which move the control surfaces according to a predefined control law to realize the pilot demands.
Which of the following are primary flight controls?
The MCDU (Multipurpose Control and Display Unit) is the input device for
Explain the principle of the electro-hydrostatic actuator (EHA).
The EHA is a modern, efficient form of actuator where significant power is drawn only when a control input is received. An electronically controlled, integrated variable speed electric motor drives a constant displacement hydraulic pump to generate hydraulic power to move a control surface. If no control input is received, the electric motor is stopped and the only power absorbed is that required by the power drive electronics. Its short reaction time makes it suitable to operate primary flight controls. The Airbus A380, the Lockheed Martin F-35 Lightning II and the new Airbus A350 all use EHAs in the flight control system.
How is the ultimate load defined?
The ultimate load is defined as the limit loads multiplied by a safety factor 1.5.
How is the limit load factor defined?
There must be no permanent deformation of the structure at the limit load factor. It is the maximum load factor that can be applied to an AC without deformation.
When is the ultimate load test considered successful?
When the ultimate load factor can be reached for at least 3 seconds without failure of the AC structure. Permanent deformations, however, are allowed.
Which parts of the AC are dependent of airspeed (airflow dynamic pressure q=1/2 rho*v2)?
Aerodynamic loads on the fuselage, doors, windows and access panels; torsion load on the wing; tail plane and other airplane parts exposed to the air stream (antennas, probes, etc.); loads due to control deflection; horizontal tail lift, and hence fuselage bending moment.
What does the pitot tube basically measure?
The dynamic pressure
Why are Mach number limits set for high-speed AC?
To avoid possible negative effects of compressibility (such as the formation of shock waves on the lifting surfaces, that could cause unsteady flow separation phenomena).
What is a maneuvering load envelope?
It is a combination of maneuver load factor and airspeed limitations.
How much is the maneuvering load factor at the stalling speed VS?
At the stalling speed VS, the maximum positive load factor that can be achieved is by definition equal to one.
- What can be reached with VA (maneuvering speed)?
- What can be reached with VG?
VA and VG are both the minimum speeds at which at which the limit positive and negative load factors can be reached.
What does the design cruise speed VC usually indicate on the airspeed indicator?
VC usually corresponds to the "red line" on the airspeed indicator = VNE in piston engine AC and VMO in turbine powered AC.
What is true about the design dive speed VD?
AC flying in the vicinity of thunderstorms or encountering high altitude "clear air turbulence" can be subjected to which load factors?
Load factors due to gusts between -1.5 and 3.5, or even higher.
What happens when an AC encounters a mass of air moving upwards (vertical gust)?
The AC angle of attack suddenly increases.
How can fast AC designed to fly at low altitudes in heavy turbulence rdeuce the load factor increment due to gusts?
Fast aircraft that are designed to fly at low altitude in heavy turbulence have a relatively high wing loading and a short wing span to reduce the load factor increments due to gusts.
The lighter the AC,....
- What is the definition of aeroelasticity?
- By which scheme is this field of study summarised?
- Aeroelasticity is the subject that describes the interaction of aerodynamic, inertia and elastic forces for a flexible structure and the phenomena that can result.
- This field of study is psummarised most clearly by the classical Collar's scheme.
- What effect has the interaction of static or steady state systems of aerodynamic and elastic forces?
- What effect has the interaction of inertia and elastic forces? What are the frequencies dependent of?
- What effect has the interaction of aerodynamic and inertia forces?
- It produces phenomena such as structural divergence and control reversal. These phenomena fall under the category of static aeroelasticity.
- Mechanical vibrations. Frequencies depend on the structural stiffness, mass and moments of inertia, internal damping and on modes of vibration.
- It is the basis of flight mechanics and dynamic stability, which describes the motion of an AC as rigid body.
Which factos will induce oscillations of structural components?
The interaction of unsteady aerodynamic forces, typically caused by atmospheric turbulence, with elastic and inertia forces will induce oscillations of structural components.
If the natural or resonant frequency of the component is in the same region of the frequencies of the unsteady loads, the amplitude of the oscillations may diverge and cause a structural failure. How is this phenomena called? What does it include?
These phenomena fall under the category of dynamic aeroelasticity and include flutter, buffeting and dynamic response.
What happens at low airpseeds when the wing is deformed?
At low airspeeds, the deformation of the wing will increase until a stable equilibrium between the torsional aerodynamic load and the elastic reaction of the wing structure is reached.
What happens with a straight wing at low airspeed?
For a straight wing, the angle of attack of the wing sections towards the tip will increase more than close to the root. This will cause a spanwise redistribution of lift: the center of pressure will move outward and the bending moment at the wing root will increase.
