General Systems (GS)

Water hammer is negligible in hydraulic system pipe installation. 


Water hammer is an important parameters which used to dimensionate pipes.

Hydraulic Pumps generally used in aircraft hydraulic systems are gear type and capable to 
provide roughly same pressure at any flow demand (if below specified max flow demand).

Hydraulic Pumps generally used in aircraft hydraulic systems are piston type and capable to 
provide roughly same pressure at any flow demand (if below specified max flow demand).

Acceleration of fluid is not negligible for the calculation of the necessary pressure of hydraulic pressurized reservoirs.

, the emergency braking system must have differential control.

, consideration shall be given to supplying the nosewheel steering and normal brakes from different hydraulic systems.

when engine driven, are installed in engine gearbox. Its suction line and fire shut-off valve in suction line are fire proof tested

when engine driven, are installed in engine gearbox. Its suction line is fire resistant (5 min) and fire shut-off valve in suction line is fire proof tested (15 min).

Do not need pressurization. Vented type reservoir is sufficient whenever located above the pump.

Utilizes the system pressure, acting on a differential piston, to achieve the required tank pressure.

The pressure required in the reservoir to supply fluid to the pump should be calculated using the guidelines in AIR1922.

This pressure must be sufficient to avoid pump cavitation at Pcrit.

Each reservoir should be equipped with pressure regulating valves and a filter.

No Hydraulic Reservoirs shall be located in a designated fire zone.

Better reliability.

Simpler

Cheaper.

Less volume and weight for for the same power delivered.

Several suppliers able to design and produce them.

Fixed output frequency, with fixed efficiency and capability.

No overvoltage event potentially leading to common failures.

Those required for descent, approach and Landing.

Those required for immediate safety

Those required for continued controlled flight

Increase hydraulic Systems.

Increase Electric Systems.

Increase Pneumatic Systems.

Increase Mechanical Systems.

Reduce electrical power demand.

Decrease the losses in the feeders and distribution wiring.

The electrical consumers.

The interactions of all the electrical generation and supplied equipments.

Less susceptible to abuse conditions.

Less weight for the same power delivered.

Maintenance free and higher service life. This, plus the improved reliability, leads to an important Direct Maintenance Cost (DMC) reduction.

Better control of the SOC. No memory effect.

No mounting restrictions

Higher reliability.

Higher maximum operating temperature.

Power consumption.

Cost.

Navigation lights.

Landing lights.

Turn-Off/Taxi lights.

Logo lights.

Anticolision lights (Beacon & Strobe).

Wing/Engine Scan Lights.

Reduction in temperature.

Reduction of O2 partial pressure.

Lack of oxygen (hypoxia)

40 kft, Mach=0.8.

SL, Mach=0.4.

1.5 kg/min of air.

1 kg/min of air.

0.5 kg/min of air.

Cost.

Temperature range.

Weight.

Efficiency.

Complexity

Sometimes.

Never.

Always.

Thick profile, low speed, small droplets.

Thin profile, low speed, big droplets.

Thin profile, high speed, big droplets.

Low speed, high Outside Ambient Temperature.

Low speed, low Outside Ambient Temperature

High speed, high Outside Ambient Temperature

High speed, low Outside Ambient Temperature

Main Engine Start In Flight at 30 kFt.

On Ground Electrical power demands only.

On Ground Electrical & Pneumatic power demands from the A/C systems

The ECB commands the Bleed Valve to close and the APU electrical generator to absorb more shaft power in order to avoid a Load Compressor over speed.

To command the opening of the Anti-surge Valve and the closure of the Inlet Guide Vanes, to alleviate the bleed pressure raise & reduce the bleed airflow supply.

The command to the aircraft’s fuel system to shut off completely the fuel supply to the APU and stop it to prevent the burst of the aircraft’s bleed piping.

To keep fully open the Bleed Shut-off Valve while correspondingly closing the Load Compressor IGVs.

To automatically shut down the APU in case an oil system overtemperature is sensed by the APU ECB.

To correspondingly close the Load Compressor IGVs to reduce the bleed flow, while keeping constant the fuel flow to maintain a constant L/C speed.

To keep the Surge Valve fully closed while progressively reducing the fuel flow to avoid an APU rotors overspeed condition potentially leading to a rotor burst.

An electrical 12VDC Starter/Generator.

An electrical 28VDC Starter/Generator.

An electrical 28VDC Starter Motor.

An air turbine starter.

The A350 flight test campaign (Honeywell HGT1700) is already showing in 2013, APU in- flight restart reliabilities of around 98%.

The A330 fleet (Honeywell 331-350 APU) has already shown APU in-flight restart reliabilities of 97%or higher.

The APU shall be operative without permanent presence of operator.

The APU in its installed configuration shall have an adequate in- flight start reliability (not less than 95%) throughout the flight envelope taking account of all approved fuel types and temperatures

The APU in its installed configuration shall have an adequate in- flight start reliability (not less than 83%) throughout the flight envelope taking account of all approved fuel types and temperatures

The APU shall be capable to pressurize the aircraft and maintain an adequate cockpit and cabin environment in one-engine inoperative cruise conditions, taking into account one engine operative requirements, up to 30,000 ft.

The A350 shall be capable to start any engines - regardless of engine starting sequence or engine type (RR or GE) - on ground using battery power supply.

Same as in a propulsive power plant, the APU shall be installed in a Fire Compartment.

The APU engine shall be mounted on the A/C structure with a Suspension System designed 
to withstand the corresponding inertial loads.

The APU Air Intake usually has an electrically actuated flap door that is kept closed while the APU is not operating.

The Exhaust Muffler outlet at the very rear end point of the fuselage is the most favorable location for its pressure effect for in-flight APU starts

The Cooling Inlet function is to convey the necessary atmospheric air flow into the APU for both the : Power Unit and Load Compressor

The impacts on the aircraft in case of rotor burst.

The noise projection on the ground.

The in-flight aerodynamic conditions.

The accessibility for ground maintenance operations

The length of fuel supply line, bleed air pipe & electrical cables lengths.

Maintenance tasks and APU replacement are easier.

The noise projection on the ground.

An adequate APU compartment drainage system.

A manual (non-automatic) APU fire detection & extinguishing system for APU ground use.

The use of fireproof titanium firewalls of 0.4 mm thickness.

The installation of the APU in a fire compartment with a fire detection & extinguishing system.

The fire detection & fire extinguishing systems only.

The installation of the APU in the fuselage tailcone area, and the limitation of the APU use 
mostly for ground.

The fireproof design of the APU compartment & components, the ventilation, the drainage, and the fire detection & fire extinguishing systems.

To achieve the certification of the aircraft electrical & pneumatic systems to be supplied by the APU.

To achieve the APU Qualification obtained by the manufacturer for the engine by TSO C77B.

The Compatibility & the Flight Test campaigns.

The APU engine test cells

The Flight Tests aircrafts

The Compatibility Tests rig.

The Icing Tests rig


The duration of the typical A/C’s: Electrical duty cycle + ECS duty cycle – the MES time

Minimum 10 years

6 to 7 years

On Ground Electrical & Pneumatic power demands from the A/C systems 


In-Flight Electrical power demands

Main engine start in flight at 22Kft

The Surge Control Valve ( SCV ) will be commanded to ‘close’ since the L/C operating condition reaches the cracking line. 


The L/C IGVs control logic will command the closing of the SCV to further increase the flow towards the ECS.

The APU lubrication system heat exchanger will remain air cooled by airflow pumped by the APU exhaust eductor or a gearbox driven fan.

The APU Inlet door position regulated by the ECB will be further opened to increase the airflow through the APU Load Compressor.

The surge control logic will command the closing of the SCV to further increase the flow towards the ECS.

Stability augmentation

Thrust setting

Positions aerodynamic control surfaces according to pilot, autopilot or stability augmentation inputs

Provides the pilot with the required force feedback

Flight Envelope Protection

Load alleviation (manoeuvre and gust).

Flutter suppression.

Thrust vectoring.

Abnormal position recovery, including post stall

Artificial feel systems are required to provide good handling qualities in irreversible FCS systems

In an “irreversible” FCS, pilot cannot reconfigure the system after a failure.

In an irreversible FCS aerodynamic loads are not fed back to the pilot inceptor

They require the use of hydraulic systems to provide power to the actuators.

They require a high degree of redundancy.

High development cost and high system clearance effort.

SW development complexity and inherent computing delays.

Safety critical SW certified against Common Mode Failures (testing +
specification).

EMI susceptibility

Evolving regulation.

A mechanical back-up system is required to control the aircraft after a total FBW system failure.

Configuration changes are easy to implement in comparison with mechanically signaled FCS.

May be Active control technology (ACT) or Control configured vehicle (CCV)

Direct mechanical link are replaced by an electrical signalling system

Pilot control aircraft dynamics parameters instead of aircraft surface position


Improve aircraft natural dynamic behaviour


Cockpit layout design flexibility


Reduced maintenance and operational cost


Reduced weight, increased reliability

Requires a careful balance between stick force and control authority at low and high speed.

Provides automatic prevention of stall departure and spinning.

Concurrent and complementary design of the basic airframe together with FCS to achieve performance improvements.

Allows improved aircraft performance and manoeuvrability.

Automatic structural protection and gust alleviation enhancing safety and reduce pilot’s workload.

Require full authority FCS with aircraft response feedback.

Use of the FCS to actively compensate for deficiencies in the aerodynamics of the basic airframe.

If there is a mechanical jamming, control surface remains in the last commanded position.

The mechanical signaling circuit is prone to jamming.

Interface Documents.

Compliance Check List.

Maintenance concept

Technical Direction (Compatibility with A/C Concept and other systems and Target Cost)

Preliminary Design (Control Surface Definition, Space Envelope, Target Weight)

Flight Physics (Functional def., Suf. deflexion, Actuation rate, Trim charact./artificial feel, Failures criticality)

Loads (Hinge moment and Surface deflexion limits)

Regulation (Certification basis and Safety criteria)

Reliability (Failure rate target)

Maintenance (Maintenance Concept and Failure detection level)

Kerosene Type Fuels have higher freezing temperature.

Density of Kerosene Type Fuels is higher.

Kerosene Type Fuels is less flammable than Wide-Cut Fuel Types

Kerosene Type Fuels have lower volatility / Vapor Pressure than Wide- Cut Fuel Types.

Allow fuel thermal expansion inside the tanks without external leakage.

Maintain the fuel tank temperature.

Avoid fuel tank overpressure or under-pressure during climbs and dives.

The fuel reserves are higher than 5% of the fuel tank contents.

The aircraft can be refueled in flight.

The fuel supply of the engines is maintained across all the flight envelope

It allows simultaneous air refuelling of two receiver aircraft.

Reduces the receiver pilot work load when in contact.

None, they are fully compatible between them.

Allows reverse refuelling

.

Possibility to refuel aircrafts with probe.

Higher flow rates and then less time to complete 

refueling.

A tanker with flying boom can be adapted with a probe-adapter



It would allow simultaneous air refuelling of two receiver aircraft.

Normally minimizes the modification of the aircraft and fuel system due to the Air Refueling 
Installation

None, they are fully compatible between them.

Simpler and cheaper design.

Allows A/Cs not originally designed as tanker to be converted.

Allows higher fuel transfer flow rates minimizing the time in contact.

No BOOM operator is needed.

Can be used to refuel helicopters. 



Transferring fuel is always the big safety concern.

Lack of fuel transfer in flight will not allow the receiver to make a safe landing.

AAR operations requires two aircraft flying in close formation.
In addition to the danger of flying in close formation, there are risks associated with the dispense devices.

Coupling detached & Uncontrolled hose movement.

Requires two aircraft flying in close formation

Several aircraft are flying in close proximity, increasing the pilot workload and hence the risk of collision.

In addition to the danger of flying in close formation, there are risks associated with the dispense devices.

To eliminate the possibility of a fire in the aircraft

To sense and indicate the presence of overheat, smoke or fire

To signal presence and locate fire in the aircraft

To extinguish the fire in the aircraft.

They are considered risk substances for human health.

Density of halon is too high compared with new substances considered equivalent for fire 
extinguishing.

When used, or escape to the atmosphere, they are substances that contribute to destroy the ozone layer of the upper atmosphere.

The Montreal Protocol of 1987 identified Halon 1301 and Halon 1211 as two of a number of halogenated agents requiring limitations of use and production.

The avoid fuel tank explosion sealing the tank after projectile impact.

They reduce the risk of fire in hot areas around the fuel tanks by minimizing fuel leakage in case of a thread impact

To conserve inerting performances by keeping the tank sealed.

Colour.

Resistance to fuel exposure.

Conductivity

Civil ones are more demanding than military one. 


There is not any difference.

Military: The objective is to reduce vulnerability and enhance the ability to survive enemy fire into a possibly explosive fuel tank.

Civil: Active protection on center wing or body style tanks reasons of being unused by operators and are prone to be heated due to the usual closeness of heat sources like the air conditioning packs.

The purpose of civil ones is to minimize the risk of tank explosion in case of fuel system failures and military ones is to minimize the risk of tank explosion in case of external military threats.

For military application Limiting Oxygen Concentration LOC =9% and civil LOC=12%.

Test individual elements .

Test all aspects of the complete a/c and of the man/machine interface.

Modeling, simulation, individual elements or the complete a/c are tested as far as possible to find design deviations as soon as possible.

Structural loads tests .

Functional tests

Taxi tests.

Wind Tunnel tests

Simulation tests.

Ground vibration tests.

Gain margin tests.

Weight & Balance.

Propulsion tests.

Brake by wire systems do not use brake order computer control. The command is mechanically transmitted by to the Brake Valve. Only Antiskid computer is used to carry on antiskid function.

Beside non-commanded brake order generated from computer caused by SW error or HW failure at take-off, brake availability at landing could also be critical. A back up brake control (emergency system) torque limited (without antiskid protection) is normally needed.

Radial tyres are normally used because they are lighter than Bias Tyres.

Bias tyres are normally used because sidewall thickness and better retreadability. Sidewall thickness contributes to minimize punches when operating underinflated when sidewall is 
more exposed to ground contamination

Electronic component based on power semiconductors 


Mechanical trip device activated by the heating

Protects 
 installations from short circuits and overloads.

Remote control/monitor capability

High Mean Time Between Failure-MTBF.

Is a wiring protection device as circuit breaker (CB), Arc Fault Circuit Breakers (AFCB), Remote Controlled Circuit Breakers (RCCB).

Ensure a maximum availability of the bus-bars.

Mechanical disconnection (mechanically disconnect it from the engine).

Participate in the connection/disconnection of the power sources.

Ensure the electrical network reconfigurations.

Ensure the protection against short circuit, over voltage, …

Ensure the electrical protections in order to avoid power source paralleling (AC) and propagation of defaults.

They require a high volume.

They are general use devices.

Influenced by ambient temperature.

No monitor capability.

Complex to monitor.

Slow response.

No reset capability.

No arc-fault detection capability.

Electrical disconnection (line contactor opening).

Mechanical disconnection ( generator mechanically disconnected from the engine).

Higher efficiency

Output voltage regulation (thinner range).

No power source rating imposed limit.

Lower ripple.

High hydro-mechanical stiffness and associated high frequency response is relevant for flight control actuation. Additional typical factors are good response time, efficiency, reliability and robustness of hydro-mechanical systems when compared with another systems.

High hydro-mechanical stiffness and associated high frequency response is relevant for flight control actuation. Additional typical factors are response time and efficiency but not reliability and robustness, when compared with another Systems

High Power Transmission vs. System Weight.

High Efficiency.

Robustness & Reliable.

Shared Power Generation System.

The use of EHAs or EMAs for PFC may allow using only two hydraulic systems. This is dependent on having sufficient redundancy within the electrical power generation system.

If there are a large number of services that are powered hydraulically, four independent hydraulic systems may be a design solution in order to reduce the size of pumps.

There is no any aircraft using two hydraulic systems. If any primary flight control is required to be hydraulically powered, definitively three hydraulic systems are required.

Large aircrafts with two engines and three hydraulic systems normally requires a PTU (Power Transfer Unit) to transfer hydraulic power between the hydraulic systems in determined failure cases or for ground taxing with one engine shut down.

In a “direct link” FCS, there is a linear relation between control surface displacement and stick forces.

In a “fly by wire” FCS, pilot controls parameters rather than surface position.

Artificial feel systems are required to provide good handling qualities in irreversible FCS systems

In an “irreversible” FCS, pilot cannot reconfigure the system after a failure.