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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Cartes-fiches
How many different classes of cargo compartments with respect to fire protection are defined in the CS25?
Five classes:
- Class A: the presence of fire would be easily discovered by a crew member and accessible in flight.
- Class B: Cargo or baggage compartment, sufficient access in flight to extinguish a fire. Separate approved smoke detector or fire detector system.
- Class C: cargo or baggage compartment not meeting the requirements for either Class A or B compartment. With separate approves smoke detector or fire detector system, Approved built-in fire extinguishing or suppression system controllable from the cockpit.
- Class D: Cargo or baggage compartment which confines (eingrenzen) fire and does not endanger the dafety of the AC or its occupants.
- Class E: cargo compartment which is reserved, separate approved smoke or fire detector system, shut of ventilation, exclude hazardous quantities of smoke, exit under any cargo loading condition.
- What class are the cargo bays in the Airbus A320?
- What class are the avionic bays of the same AC?
- Class C compartment. So, they are equipped with smoke detection and extinguishing systems.
- Class B compartment. It is easily accessed to put out a fire with a hand fire extinguisher and is equipped only with a smoke detection system.
The PC-12 aileron control system is designed to provide an aileron differential of approximately 2:1. What does that mean?
To reduce the adverse yaw effect the deflection of the upgoing aileron is twice as large than that of the downgoing aileron. Moreover, there is an aileron-rudder interconnect system to improve lateral stability and turn coordination.
In which compartments in the AC are usually smoke detection systems installed?
Smoke detection systems are usually installed in cargo compartments, avionic bays and toilets (detect cigarette smoke).
Fire would generate a lot of smoke before the temperature would rise sufficiently to activate a classic fire detection system based on temeperature monitoring.
Which two main types of smoke detectors do exist?
Ionisation and optical (photoelectric).
How does an ionisation smoke detector work?
The alpha particles from the americium ionise (separate electrons from) the oxygen and nitrogen of the air in the chamber. The negative and positive electrons are attracted to different voltages (positive and negative). Thus a small electrical current flows.
If smoke enters the chamber, the current is disrupted because the smoke particles attach to the ions and neutralise them. The sensors detect this drop in current between the plates and sets off the alarm.
How do optical smoke detectors work?
Optical smoke detectors incorporate a pulsing infra-red LED located in a chamber within the housing of the detector. There is also a photo-diode which normally does not register the column of light emitted by the LED. If smoke enters the chamber the light pulse from the LED will be scattered and hence registered by the photo-diode. After "seeing" smoke on the two following pulses the alarm will go on.
Where are photoelectric smoke detectors used in the AC? Why?
In cargo bays or avionic compartments because they are quick in detecting slow burning and smoky fires.
When does the SDCU (Smoke Detection Control Unit) issue a smoke warning?
- If both smoke detectors in a cavity detect the presence of smoke (AND logic, to reduce the probability of false warnings)
- one smoke detector is faulty and the other detects smoke.
What do advanced smoke detection systems consist of?
They are based on multiple sensors that detect carbon monoxide, carbon dioxide and smoke particles. A microprocessor compares the sensor outputs for consistency before giving a fire warning.-->reduce the probability of a false alarm.
Where in the AC are handheld fire extinguishers used for fire fighting?
All AC areas that are easily accessible to personnel: Cockpit, pax cabin, toilets, avionic bays and in general class A, B and E baggage and cargo compartments.
How many fire extinguishers must be present on board of a transport AC?
- One in the cockpit
- one in each galley
- at least one in each class A, B or E cargo compartments
- one or more in the cabin, depending on pax capacity
What kind of fire extinguishing system must be installed in class C fire compartments?
A remotely operated fire extinguishing system. I.e. forward and aft cargo compartments of an A320.
How long does 10 litres of Halon last for fire suppression?
For 60 min.
Where must a fire extinguisher be installed in an AC when carrying more than 20 pax?
In the waste bin compartment in each lavatory. Automatically discharged when the temperature within the waste bin exceeds a preset value (normally 70°C).
How are engines, APUs and any combustion devices isolated from the rest of the AC?
Isolated by firewalls designed to withstand open flames and temperatures of up to 1,100°C for at least 15 minutes.
What must be installed in all FAR25/CS25 or FAR23/CS23 aircraft in the commuter category concerning fire extinguishing systems?
Must be equipped with fire extinguishing systems for the engines and the APU, if the AC has one.
How many pressurised fire extinguisher bottles equipped with electrically operated squibs (Zündkerzen) are there for each turbofan?
Two. For APU only one fire extinguisher bottle, which discharges automatically.
AC certified to operate above which altitude must have oxygen available for the occupants?
Above 15'000ft.
AC certified to operate at which altitudes must have an emergency oxygen supply system available for the occupants?
At 25'000ft and more. To cope with possible rapid loss of cabin pressurisation.
What does the demand oxygen system in the cockpit of the A320 consist of?
- A high-pressure cylinder, in the left-hand lower fuselage, with sufficient oxygen to sustain the flight crew for the complete duration of the flight.
- A pressure regulator, connected directly to the cylinder that delivers oxygen, at a pressure suitable for the users.
- two overpessure safety systems to vent oxygen overboard, through a safety port, if the pressure gets too high
- a supply solenoid valve that allows the crew to shut off the distribution system
- three or four full-face quick-donning masks, stowed in readily accessible boxes adjacent to the crew members' seats (one at each seat).
How long can the generators installed on the A320 produce a continuous flow of oxygen?
For approximately 12 min (minimum requirement is 10min).
Which items must be on board and in operable condition before a flight can start according operational requirements (JAR-OPS 1, Subpart K)?
- crash axes or crowbars
- emergency torches, one on the flight deck, one at each cabin crew station, and one at each normal or emergency exit
- first-aid kits (at least one for up to 99 pax seats, two for up to 199, three for up to 299, four for 300 and more)
- emergency medical kits
- first aid oxygen (for AC operating above 25,000ft)
- ...
For all aircraft capable of carrying more than 44 passengers within which time must the evacuation be completed?
In less than 90 sec.
In aviation, safety is intended as "....".
In aviation, safety is intended as "The state in which risk is acceptable".
For all air vehicle systems, where are safety requirements defined?
In paragraph 1309 of the airworthiness regulation (FAR2x.1309 and CS-2x.1309).
What is the most important point concerning the relation between severity of a failure condition and its probability?
They must be inversely proportional. The more severe a failure is the smaller must be its probability.
How can AC acceleration be generated?
Aircraft accelerations can be the effect of manoeuvring (turning, rolling, yawing, pitching, etc.) or of atmospheric turbulence.
- When the AC rolls, what kind of loads experience the engines or generally equipment installed or attached to wings?
- What kind of loads do rotating parts on the AC such as propellers, or jet engine compressors and turbines experience if the AC yaws?
- Centrifugal inertia loads.
- Gyroscopic loads (Change the direction of their rotational axis).
- How is AC weight equilibrated during steady horizontal flight?
- How is the pitching moment about the centre of gravity equilibrated?
- How is the drag equilibrated?
- Aircraft weight is equilibrated by wing lift (minus the negative lift on the tail).
- The pitching moment about the centre of gravity is equilibrated by the moment generated by the downlift on the horizontal tail.
- Drag is equilibrated by the engine thrust.
- How is the yawing moment (due to asymmetries of the airframe, or to the propeller effect) equilibrated?
- In a finer flight load analysis, how are aerodynamic in-plane forces and moments generated?
- How is engine torque compensated?
- By the side force on the vertical tail.
- by the propeller whenever it is exposed to a slightly oblique (schief) airflow.
- By small control surface deflections (ailerons).
What is lift carry-over?
When the fuselage is also producing some lift.
In general, by which factors are flight loads affected?
- maneuvering
- air turbulence (gust)
- interaction between AC components
- dynamic effects
What is most severe when there are vibrations?
A severe unbalance in abnormal conditions (a dramatic example is the deformation or loss of compressor blades in a turbine engine due to bird strike)
What does spin-up mean?
drag components due to the forces required to accelerate the tires and wheels up to the landing speed-->spin-up
What is spring back?
forward acting horizontal loads resulting from the rapid reduction of the spin-up drag loads (spring back).
In a lateral drift landing condition,
- How much vertical load in percent of the maximum ground reaction in level landing
- plus how much drag and
- side load of that vertical load must be considered?
- 75% vertical load
- 40% drag
- 25% side load
When can side load conditions be present?
During landing roll because of crosswind or steering.
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
