Aircraft Systems 1 Flashcards

Question

Functions of Stringers

Answer 1

*Stabilise and reinforce the skin by accepting some of the flight loading

Answer 2

*Require a robust construction, as local loads can be high, especially on transport aircraft *Composite honeycombs are frequently used in their manufacture *Designed in short sections and supported laterally off the frames *Typically pick-up loads in a longitudinal direction, causing problems when the fuselage bends

Answer 3

*Support the cabin floor and distribute floor loading through the frames

Answer 4

Skin Stringers Erosion Strip Spars Honeycomb Trim Tabs

Answer 5

Air and inertia forces, bending moments and stress directions, and torsion and shear stresses.

Answer 6

Location and direction, reaction to bending moments, stiffening effects for the skin.

Answer 7

Provides protection to the leading edge from dust particles. (some fleets utilise “blade tape”).

Answer 8

Reacts to shear forces (shear stress), The mechanics of the spar box, roving spars.

Answer 9

Construction, maching, deformation (into hexagonal structure), sheet construction, combination with composites (Kevlar), airframe use.

Answer 10

Set during post rotor tune to reduce vibration and fatigue.

Answer 11

Swept Tip Straight Tip BERP Taperd

Answer 12

*Vertical Fin *Horizontal Stabiliser

Answer 13

Tail Rotor

Answer 14

Single Tail Rotor Shrouded Tail Rotor (Fenestron) NOTAR (No Tail Rotor)

Answer 15

The vertical Fin provides additional anti torque force to the fuselage once the aircraft has forward motion and airflow across the lifting surface. The design makes use of forward motion and the resulting airflow to create an anti-torque force to the main fuselage to counter the torque exerted by the main rotor. The tail rotor provides this anti torque while hovering and assists while in forward flight but by aerodynamic action of the tail fin the tail rotors job gets easier the faster the aircraft flies… this allows more energy from the engine to be used by the main rotor for lift and forward flight as the tail rotor does not have to work as hard.

Answer 16

The horizontal stabilizer is used to help hold the fuselage flat or parallel to the ground and make the ride more comfortable for the occupants inside. Because the helicopter achieves forward flight by tilting the rotor disk in the direction the pilot wants to fly… the tendency is for the fuselage to get dragged along under it and parallel to the plane of rotation.

Answer 17

*Longitudinal axis - roll *Lateral axis - pitch

Answer 18

*Normal axis - yaw

Answer 19

Four Stroke Cycle Piston Gas Turbine Cycle

Answer 20

◦Each step of the cycle is separate and distinct ◦Ignition is timed to occur at the optimum point during each cycle ◦Known as the Otto Cycle

Answer 21

◦Phases of power occur simultaneously and continuously ◦Ignition occurs during starting cycle and combustion is continuous ◦Known as the Brayton Cycle

Answer 22

Induction Compression Power Exhaust

Answer 23

In-Line Inverted In-line Flat Opposed V Radial

Answer 24

*RPM: ◦Increased RPM leads to increased stress and therefore increased wear on engine components ◦RPM limitations for each engine type ◦If principle limitation of a main power condition is exceeded, a report must be made after landing *Temperature: ◦High cylinder temperatures lead to a breakdown in cylinder wall lubrication, excessive gas temperatures and distortion ◦High oil temperatures cause failure of cylinder and bearing lubrication ◦Oil shortage, or lubrication system defect, may cause inadequate lubrication and bearing failure ◦Must have minimum oil and/or cylinder head temperatures (CHT) before applying full power (i.e. before take-off) ◦Correct temperatures ensure proper oil circulation and help to prevent engine damage

Answer 25

Turbojet Turbofan Turboprop Turboshaft

Answer 26

Intake Compression Combustion Turbine Exhaust

Answer 27

Intake (air inlet) - Air directed by inlet into compressor Compression - Air is compressed increasing temperature and decreasing volume. Air is brought in through the inlet duct, compressed to a high pressure and delivered to the combustion section (combustion chambers). Combustion - Fuel is added and burned, further increasing temperature and volume *Fuel is injected and ignited by igniter plugs *Not all of the compressed air is used to support combustion. Some of the compressed air bypasses the burner section and circulates within the engine to provide internal cooling *The fuel/air mixture in the combustion chamber is burned in a continuous combustion process and produces a very high temperature *The mixture of hot air and gases expands and is directed to the turbine blades forcing the turbine section to rotate, which in turn drives the compressor by means of a direct shaft *After powering the turbine section, the high velocity exhaust gases exit the tail pipe or exhaust section *Combustion continues until the engine is shut down by turning off the fuel supply Turbine - The gases leaving the combustion system contain a large amount of energy, which needs to be extracted as efficiently as possible to drive the compressor and engine driven accessories. Exhaust - Energy extracted by turbines reducing temperature and pressure *Exhaust gases are used to provide jet thrust as in a turbojet engine *Alternatively, the gases can be directed through an additional turbine to drive the rotors through reduction gearing *Pilot must understand the importance of knowing and observing limits on turbine engines *Turbine engines are extremely heat sensitive. For example, an overtemp or overtorque condition that lasts for more than a few seconds can literally destroy internal engine components *Engine temperatures get hotter during starting than at any other time. Thus, turbine engines have minimum rotational speeds for introducing fuel into the combustion chambers during start-up

Answer 28

The axial compressor is a rotating, aerofoil-based compressor in which the gas or working fluid principally flows parallel to the axis of rotation. Axial flow compressors produce a continuous flow of compressed gas, and have the benefits of high efficiency and large mass flow rate, particularly in relation to their size and cross-section. They require several rows of aerofoils to achieve a large pressure rise, making them complex and relatively expensive when compared to other designs (e.g. centrifugal compressors). They normally have more than one stage which prevents the breakdown of airflow through the engine.

Answer 29

Divergent Duct Energy is neither added nor removed *The gaseous energy is being converted from velocity to pressure and temperature *There is a velocity decrease as air flows from a small inlet to a larger outlet *As velocity decreases, impact pressure (Pi) also decreases *Since no energy is added or subtracted from the system, total pressure (Pt) for the air remains constant and static pressure (Ps) increases *Temperature rises as compression is a heating process

Answer 30

The compressor rotor blades convert mechanical energy into gaseous energy Most of the increase is in the form of velocity (Pi), with a small increase in static pressure (Ps). The stator vanes slow the air by means of their divergent duct shape, converting 'the accelerated velocity (Pi) to higher static pressure (Ps). The vanes are positioned at an angle such that the exiting air is directed into the rotor blades of the next stage at the most efficient angle.

Answer 31

The impeller is rotated at high speed by the turbine, and air entering the intake at atmospheric temperature and pressure passes through the fixed intake guide vanes, which direct the air smoothly into the centre of the impeller. The impeller is designed to admit the air without excessive velocity. The air is then picked up by the rotating guide vanes of the impeller, and centrifugal force causes the air to flow outwards along the vanes to the impeller tip. The air leaves the impeller tip approximately at right angles to its intake direction, and at an increased velocity. On leaving the impeller vane passages, the air acquires a tangential velocity which represents about half the total energy acquired during its passage through the impeller. The air then passes through the diffuser where the passages form divergent nozzles which convert most of the velocity energy into pressure energy. Work is done by the compressor in compressing the air and since the process involves adiabatic (no heat transfer) heating, a rise in air temperature results.

Answer 32

The purpose of the diffuser assembly is to convert energy of the air leaving the compressor to pressure energy before it passes into the combustion chamber: *It consists of a number of vanes formed tangential to the impeller *The vane passages are divergent to convert the velocity energy into pressure energy *The inner edges of the vanes are in line with the direction of the resultant airflow from the impeller

Answer 33

Cheap to Produce Easy to manufacture Low maintainance and running costs Small mass flow rates Large frontal area Air flows radially in the compressor Usually single stage hence low compression ratio (12:1) 86% efficient

Answer 34

Expensive to produce Difficult to manufacture High maintainance and running costs Large mass flow rates Small frontal area Air flows parallel to the axis of the shaft Usually multi stage hence high compression ratio (30:1) 95% efficient

Answer 35

Annular - These have a continuous liner and casing in a ring (annulus) Annular combustors remove the need for separate combustion zones and simply have a continuous liner and casing in a ring (the annulus). There are many advantages to annular combustors, including more uniform combustion, shorter size (therefore lighter), and less surface area. Annular combustors tend to have very uniform exit temperatures. Only 30% of the air entering the chamber is used for combustion. The rest of the air is ducted round the outside of the combustion chamber and is used for cooling and dilution. The purpose of the diffuser is to slow the high speed and highly compressed air from the compressor to a velocity optimal for the combustor. The liner contains the combustion process and introduces the various airflows (intermediate, dilution, and cooling) into the combustion zone. The liner must be designed and built to withstand extended high temperatures.

Answer 36

Annular - These have a continuous liner and casing in a ring (annulus) Annular combustors remove the need for separate combustion zones and simply have a continuous liner and casing in a ring (the annulus). There are many advantages to annular combustors, including more uniform combustion, shorter size (therefore lighter), and less surface area. Annular combustors tend to have very uniform exit temperatures. Only 30% of the air entering the chamber is used for combustion. The rest of the air is ducted round the outside of the combustion chamber and is used for cooling and dilution. The purpose of the diffuser is to slow the high speed and highly compressed air from the compressor to a velocity optimal for the combustor. The liner contains the combustion process and introduces the various airflows (intermediate, dilution, and cooling) into the combustion zone. The liner must be designed and built to withstand extended high temperatures.

Answer 37

Primary Air is highly compressed air from the high-pressure compressor (often decelerated via the diffuser) that is fed through the main channels in the dome of the combustor and the first set of liner holes. This air is then mixed with fuel to allow combustion. Intermediate air is the air injected into the combustion zone through the second set of liner holes (primary air goes through the first set). This air completes the reaction processes, cooling the air and diluting the high concentrations of carbon monoxide and hydrogen. Dilution air is airflow injected through holes in the liner at the end of the combustion chamber to help cool the air before it reaches the turbine stages. The air is used to produce the uniform temperature profile desired in the combustor. As technology improves, allowing turbine blades to withstand higher temperatures the requirement for dilution air is reduced.

Answer 38

Turbines: *Convert the gaseous energy of the air/burned fuel mixture out of the combustor into mechanical energy to drive the compressor, driven accessories and rotors Nozzle Guide Vanes: *Converts gaseous energy into mechanical energy by expanding the hot, high-pressure gases to a lower temperature and pressure *Direct the gases onto the turbine at the optimum angle Power turbine: *On the same shaft as the compressors Free power turbine: *Independent from the main shaft

Answer 39

Energy is neither added nor removed: *The gaseous energy is being converted from pressure and temperature to velocity *There is a velocity increase as air flows from a large inlet to a smaller outlet *As velocity increases, impact pressure (Pi) also increases *Since no energy is added or subtracted from the system, total pressure (Pt) for the air remains constant and static pressure (Ps) decreases *Temperature reduces

Answer 40

*Turbine blades are subjected to very high temperatures and centrifugal loads and tend to lengthen (creep) and ultimately fail if RPM and temperature limits are exceeded

Answer 41

*Rapid changes in temperature causes uneven expansion and contraction in a turbine blade which increases the stress in the blade. Minimising power changes and allowing temperatures to stabilise before shutdown can reduce thermal stress and prolong blade life

Aircraft Systems 1 Flashcards

(66 cards)