When a turbo prop aeroplane decelerates during the intial part of the landing roll a constant speed propeller within the beta range ?
Registration > lift > off
Source: Telepilote theorique examen 34
Most high bypass unmixed turbofan engines are equipped with a cold exhaust reverser fan reverser only in order to ?
A booster or LP compressor in a twin spool turbofan ?
The function of swirl vanes round fuel nozzles to 1 increase air pressure at fuel nozzles 2 reduce average axial flow speed in order to stabilise flame front 3 generate a swirl of incoming air to enhance mixing of fuel with air the combination that regroups all of correct statements Rotates at same rotor speed as fan. If engine a twin spool turbofan it highly likely that there will be a hp compressor lp compressor a fan the lp comp the fan will be driven from same turbine on same shaft will therefore be at same speed . 
The take off of a jet aeroplane may be performed with 'reduced thrust' in order to Reduce maintenance costs. If engine a twin spool turbofan it highly likely that there will be a hp compressor lp compressor a fan the lp comp the fan will be driven from same turbine on same shaft will therefore be at same speed . 
In an ignition system during a normal start of a gas turbine engine igniter activation Should commence prior to fuel entering combustion chamber. If engine a twin spool turbofan it highly likely that there will be a hp compressor lp compressor a fan the lp comp the fan will be driven from same turbine on same shaft will therefore be at same speed . 
A gas turbine engine r at ground idle a period of time prior to shutdown to Prevent seizure of rotor blades in their seals. This allows to gas generator the power turbine discs more time to cool than if engines were immediately shut down the danger that rotor will cool (and will shrink) more rapidly than blades they could be seized in their seals. Question 34-8
The purpose of variable pass valves in a high bypass turbofan engine between lp compressor and hp compressor hpc to Prevent fan stall lp compressor stall during engine start low rotor speeds. A bypass valve another name a bleed valve it can also be called a blow off valve anti stall valve or an acceleration valve. Question 34-9
If a gas turbine engine fuel/oil heat exchanger located downstream of hp fuel pump internal leakage of heat exchanger will cause oil level to Prevent fan stall lp compressor stall during engine start low rotor speeds. The oil in fuel/oil heat exchanger (located in tanks) always at a higher pressure than fuel but question states located downstream of hp fuel pump so it a secondary fuel/oil heat exchanger in order to avoid fuel icing in fuel regulation system in this heat exchanger you will have high pressure fuel relatively low pressure oil so any internal leak will transfer fuel to oil system raising indicated oil level. Question 34-10
The compressor pressure ratio of an axial flow compressor primarily determined the Prevent fan stall lp compressor stall during engine start low rotor speeds. The oil in fuel/oil heat exchanger (located in tanks) always at a higher pressure than fuel but question states located downstream of hp fuel pump so it a secondary fuel/oil heat exchanger in order to avoid fuel icing in fuel regulation system in this heat exchanger you will have high pressure fuel relatively low pressure oil so any internal leak will transfer fuel to oil system raising indicated oil level. Question 34-11
In a theoretical gas turbine cycle combustion takes place at constant Prevent fan stall lp compressor stall during engine start low rotor speeds. The oil in fuel/oil heat exchanger (located in tanks) always at a higher pressure than fuel but question states located downstream of hp fuel pump so it a secondary fuel/oil heat exchanger in order to avoid fuel icing in fuel regulation system in this heat exchanger you will have high pressure fuel relatively low pressure oil so any internal leak will transfer fuel to oil system raising indicated oil level. Question 34-12
When a gas turbine engine accelerates from idle to take off thrust and compressor rpm too high in comparison with air inlet velocity this may result in Prevent fan stall lp compressor stall during engine start low rotor speeds. Like stall of a wing compressor stall caused a breakdown of airflow a compressor stall most likely to occur when air flow stagnates in rear stages of compressor a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow when incoming speed low angle of attack will be high when angle of attack gets too high blade stalls so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow) you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question 34-13
Which of following parameters remains constant in a divergent subsonic gas turbine engine intake Prevent fan stall lp compressor stall during engine start low rotor speeds. Like stall of a wing compressor stall caused a breakdown of airflow a compressor stall most likely to occur when air flow stagnates in rear stages of compressor a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow when incoming speed low angle of attack will be high when angle of attack gets too high blade stalls so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow) you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question 34-14
The most favourable conditions to apply flexible take off procedure are 1 high take off mass2 low take off mass3 high outside temperature4 low outside temperature5 high atmospheric pressure6 low atmospheric pressurethe combination grouping all correct answers Prevent fan stall lp compressor stall during engine start low rotor speeds. Like stall of a wing compressor stall caused a breakdown of airflow a compressor stall most likely to occur when air flow stagnates in rear stages of compressor a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow when incoming speed low angle of attack will be high when angle of attack gets too high blade stalls so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow) you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question 34-15
Assuming jet pipe not choked equation to calculate jet engine thrust t with mass flow m airspeed vv and jet velocity vj Prevent fan stall lp compressor stall during engine start low rotor speeds. Like stall of a wing compressor stall caused a breakdown of airflow a compressor stall most likely to occur when air flow stagnates in rear stages of compressor a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow when incoming speed low angle of attack will be high when angle of attack gets too high blade stalls so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow) you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question 34-16
Given p0 = static ambient pressure t0 = static ambient temperaturem = air mass flowvv = true air speedvj = jet efflux exhaust velocitypj = jet efflux exhaust static pressuretj = jet efflux exhaust static temperaturea = exhaust cross sectional areathe thrust t of a jet engine T = m(vj vv ) + a(pj p ). Thrust = air mass flow (jet exhaust velocity true air speed) + exhaust cross sectional area (jet exhaust static pressure static ambient pressure) thrust equal to change in momentum of air entering leaving (it measured the acceleration of air through engine). Question 34-17
The axial compressor of a gas turbine engine usually has more stages than its driving turbine because The power output of a turbine stage higher than power consumption of a compressor stage. Thrust = air mass flow (jet exhaust velocity true air speed) + exhaust cross sectional area (jet exhaust static pressure static ambient pressure) thrust equal to change in momentum of air entering leaving (it measured the acceleration of air through engine). Question 34-18
On a fadec gas turbine engine during normal flight power the fadec's sensors comes from The fadec power source(s) on engine. The fadec has its own independent power supply (generator) which separate from aircraft generator to ensure that fadec system has electrical power as long as engine running regardless of any problems or faults with aircraft system. Question 34-19
In a gas turbine combustion chamber Secondary air required cooling of inner casing. The combustion system's purpose to provide a smooth stream of uniformly heated gas with least loss of pressure the maximum release of heat the combustion chamber made from two tubes one the flame tube which inside air casing between two an air gap through which any air that does not go into combustion chamber passes (secondary air) air enters combustion chamber at around 500 ft/sec is diffused to around 80 ft/sec even at this speed slow flame (at 1/2 ft/sec) would be blown away so a region of low pressure created round it to keep it alright. Question 34-20
If there a single input data failure on a fadec gas turbine engine The engine continues to operate normally. The combustion system's purpose to provide a smooth stream of uniformly heated gas with least loss of pressure the maximum release of heat the combustion chamber made from two tubes one the flame tube which inside air casing between two an air gap through which any air that does not go into combustion chamber passes (secondary air) air enters combustion chamber at around 500 ft/sec is diffused to around 80 ft/sec even at this speed slow flame (at 1/2 ft/sec) would be blown away so a region of low pressure created round it to keep it alright. Question 34-21
Concerning fuel system high pressure shut off valve hpsov of a gas turbine engine Ignition activated before fuel delivered the hpsov to fuel nozzles. The combustion system's purpose to provide a smooth stream of uniformly heated gas with least loss of pressure the maximum release of heat the combustion chamber made from two tubes one the flame tube which inside air casing between two an air gap through which any air that does not go into combustion chamber passes (secondary air) air enters combustion chamber at around 500 ft/sec is diffused to around 80 ft/sec even at this speed slow flame (at 1/2 ft/sec) would be blown away so a region of low pressure created round it to keep it alright. Question 34-22
Derated or reduced take offs save engine life primarily due to Reduced low cycle fatigue damage. Low cycle fatigue where stress high enough deformation to occur this deformation will occur in turbine since it most sensitive to high temperatures. Question 34-23
The diagram shown in annex represents a twin spool turbofan positions before and after air intake are located at numbers 1054 Reduced low cycle fatigue damage. Low cycle fatigue where stress high enough deformation to occur this deformation will occur in turbine since it most sensitive to high temperatures. Question 34-24
What the average compression ratio of a centrifugal compressor Reduced low cycle fatigue damage. axial compressor radial compressor a centrifugal compressor will provide a compression ratio of 5 1 per stage (maximum) which relatively high compared to an axial compressor that achieves a ratio of only 1 2 1 per stage. Question 34-25
If engine compressor air bled off engine anti icing or a similar system turbine temperature Reduced low cycle fatigue damage. Gorny21 the ratio of tertiary airflow around combustion flame tube that cools turbine decreases thus less cooling flow as warm air diverted anti icing so egt will increase as a result. Question 34-26
Increasing frequency of variations in thrust setting during normal operation detrimental to life of hp turbine blades because Low cycle fatigue damage more severe. It commonly known that a metal subjected to repetitive or flunctuating stress will fail at a stress much lower than its ultimate strength failures occuring under cyclic loading are generally termed 'fatigue' the endurance of gas turbine engine to high temperature particularly marked the creep resistance of hp turbine blade alloy in turbine engines low cycle fatigue generally caused repeated loading cycles caused operation (i e starting or takeoff conditions) if a turbine blade goes through one takeoff max power setting it may be fine if it subjected to 8000 of them it may fail due to fatigue. Question 34-27
An axial compressor when operating below its design speed has A tendency to stall in front stages. axial compressor radial compressor the stall of a blade occurs in same way as a wing stalls if angle of attack exceeds a set value blade/wing will stall the first stage of blades on a compressor are rotor blades when it turns air push rearwards increasing velocity onto blades behind but also pressure if horizontal flow low it results in a large angle of attack as this most likely at front of compressor it will tend to stall at front. Question 34-28
The compressor blades in a rotating gas turbine engine are held in position The mountings the resultant of aerodynamic centrifugal forces. axial compressor radial compressor the stall of a blade occurs in same way as a wing stalls if angle of attack exceeds a set value blade/wing will stall the first stage of blades on a compressor are rotor blades when it turns air push rearwards increasing velocity onto blades behind but also pressure if horizontal flow low it results in a large angle of attack as this most likely at front of compressor it will tend to stall at front. Question 34-29
Some gas turbine engines have multiple stages in hp and lp turbines Because one stage does not generate sufficient shaft power. axial compressor radial compressor the stall of a blade occurs in same way as a wing stalls if angle of attack exceeds a set value blade/wing will stall the first stage of blades on a compressor are rotor blades when it turns air push rearwards increasing velocity onto blades behind but also pressure if horizontal flow low it results in a large angle of attack as this most likely at front of compressor it will tend to stall at front. Question 34-30
In which part of a gas turbine engine are high temperature requirements most critical the materials used The combustion chamber front part of hp turbine. Usually titanium alloy the material used the combustion chamber high pressure turbine. Question 34-31
A twin spool engine with an inlet air mass flow of 500 kg/s and a hp compressor mass flow of 250 kg/s has a bypass ratio of The combustion chamber front part of hp turbine. bypass ratio = bypass mass flow / hp compressor mass flow 500 250 = 250 250 / 250 = 1. Question 34-32
A 'fan' stage of a ducted fan turbine engine driven The low pressure turbine. bypass ratio = bypass mass flow / hp compressor mass flow 500 250 = 250 250 / 250 = 1. Question 34-33
The oil supply to gas turbine engine bearings maintained in event of main oil filter becoming clogged Differential pressure opening bypass valve of main oil filter. bypass ratio = bypass mass flow / hp compressor mass flow 500 250 = 250 250 / 250 = 1. Question 34-34
One of purposes of compressor bleed valves to Decrease airflow across rear compressor stages whilst that across early stages increased. Bleed valves are fitted to prevent compressors stalling like stall of a wing compressor stall caused a breakdown of airflow the bleed valve removes excesss volume of air at low compressor speeds to increase flow over front compressor blades reduce flow over latter stages as speed of compressor increases bleed valve closes. Question 34-35
Turbine blade stages may be classed as either 'impulse' or 'reaction' in an impulse blade section pressure i across nozzle guide vanes ii across rotor blades (i) drops (ii) remains constant. nozzle guide vanes = stator the pressure drops across stator blades remains constant across rotor blades. Question 34-36
One advantage of having three instead of two spools in some high bypass turbofan engine that Fewer variable stator vanes variable inlet guide vanes are required to prevent compressor stall at low rotor speeds. Variable inlet guide vanes (v i g v s) are fitted to engines which have a particular problem with inherent compressor stall at low rpm or during engine acceleration or deceleration the vanes are fitted just in front of first rotor stage they can be automatically pivoted around their own axis to vary path of airflow going into compressor so maintaining proper relationship between compressor rotational speed airflow in front compressor stages at low compressor speeds v i g v s are angled to impart greatest amount of swirl to air thereby correcting relative airflow to obtain optimum angle of attack over rotor blades this optimum angle of attack allows a smooth rapid engine acceleration on a three spools high bypass turbofan engine an additional intermediate pressure compressor stage added reduces risk of compressor stall at low rotor speeds. Question 34-37
The compressor surge effect during acceleration prevented the Fuel control unit (f c u ). With modern engines there are various ways to control surge one of them the use of blow off valves (also called compressor bleed valves) on all modern turbine engines with electronic fuel control systems valves are controlled the fuel control unit the end result will be that blow off valve will reduce pressure in compressor to prevent surge. Question 34-38
Creep in a gas turbine engine The permanent increase in length of metal parts due to a combination of tensile stress high temperatures over a prolonged period. With modern engines there are various ways to control surge one of them the use of blow off valves (also called compressor bleed valves) on all modern turbine engines with electronic fuel control systems valves are controlled the fuel control unit the end result will be that blow off valve will reduce pressure in compressor to prevent surge. Question 34-39
About a twin spool compressor The low pressure spool runs at a lower rpm than high pressure spool. With modern engines there are various ways to control surge one of them the use of blow off valves (also called compressor bleed valves) on all modern turbine engines with electronic fuel control systems valves are controlled the fuel control unit the end result will be that blow off valve will reduce pressure in compressor to prevent surge. Question 34-40
In addition to providing 'customer' bleed aeroplane systems air may be bled from compressors of a turbofan engine to increase stall margin The low pressure spool runs at a lower rpm than high pressure spool. During engine starts most turbojet/turbofan engines use engine bleed air to reduce possibility of compressor stalls compressor stall occurs when compressor sucks too much air the turbine wheels to handle excessive pressure then builds aft of compressor the compressor blades stall (also happens with centrifugal type compressor) bleeding air from an engine (air bled just aft of compressor) relieves that excessive pressure the compressor can more easily 'push' sucked air behind him.
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