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Powerplant
Turbine Engines
| Question | Answer |
|---|---|
| Shrouded turbine blades have what advantages over traditional blades? | -Reduced vibration -Improved airflow characteristics |
| What design feature do some turbine blades have to reduce vibration and improve airflow? | They are shrouded |
| In a Dual-Spool Compressor, at what speed does the Low-Speed compressor operate? | It seeks its own best operating speed (The High pressure rotor is governed for speed) -Altitude increases, load decreases, low-pressure rotor increases speed. |
| What variables affect the inlet air density on a turbine engine? | -Speed of aircraft -Altitude -Ambient Temp. |
| Aircraft speed, Altitude, and ambient temperature will all affect the Inlet Air _ of a turbine engine. | Inlet Air Density |
| What does a Dump Valve do, and why? | It cuts off fuel to the nozzles, and drains the manifolds. -Prevents fuel boiling off from residual engine heat. |
| What does "Field Cleaning" an engine mean? | Procedure for removing accumulated dirt/deposits on compressor blades. |
| The procedure for removing accumulated dirt deposits on compressor blades is called? | Field Cleaning |
| What are 3 Types of Turbine Blades (not how they're mounted). | Impulse, Reaction & Impulse-Reaction. |
| What is the purpose of an Automatic Bleed Valve? | Vents some of the high-pressure air overboard to prevent a compressor stall/Surge. -Otherwise, air could "pile up" in high pressure stages and inhibit airflow through engine. |
| What is one function of the Nozzle Diaphragm in a turbine engine? | It directs/deflects the gases to a specific angle in the direction of turbine rotation. -Gases will hit the turbine blades @ desired angle. |
| Main advantage of an Axial-Flow compressor vs. Centrifugal. | Higher peak efficiency. |
| Should, and how would you blend a Turbine blade? | It is possible, if: -Parallel to the Length of the blade -Use Smooth contours to minimize stress points. |
| What does an Inlet Guide Vane assembly do for an Axial-Flow compressor? | Directs (Guides*) air into 1st Stage rotor at the proper angle. |
| The airfoils that DO NOT rotate in an Axial-Flow compressor are called _? | Stator Vanes |
| Stator Vanes (Move/Do Not move) in a turbine engine? | Do Not move (Think "Stationary" |
| Continued/Excessive heat, and Centrifugal Force on rotor blades will likely cause what? | Creep (Permanent Elongation of blades) |
| What is Blade Creep? What causes it? | Permanent Elongation of turbine blades, caused by continued/excessive heat and Centrifugal Force. |
| Hot Section inspections are normally required when? | On a Time/Cycle basis. |
| What factors affect a Turbine engine's Thermal Efficiency? | -Turbine Inlet Temp -Compression Ratio -Turbine & Compressor Efficiency |
| Turbine Inlet temp, Compression Ratio and Turbine/Compressor Efficiency all affect the _ _ of a Turbine Engine? | Thermal Efficiency -*Think: Temp that goes in, how much it compresses (heat generated), and how efficiently it does so. |
| Which has higher Pressure Ratios? (Axial/Centrifugal) flow compressors. | Axial, with better efficiency. |
| One advantage of Centrifugal-flow Compressors is a High _ _ -per-stage. | Pressure Rise (The pressure rises higher per stage). |
| What is the primary function of the Turbine Assembly in a Turbojet Engine? | Turns the Compressor -Ignited gases spin the turbine, which drives the compressor up front, making the engine self-sustaining. |
| What is Standard Atmosphere? (Temperature F/C) | 15 deg. C 59 deg. F |
| What is Standard Pressure? | 29.92 in/mercury |
| What is Standard Pressure/Atmosphere used in for Turbine Engines? | Calculating the power of an engine. |
| When an engine with multiple-stage compressors is operated @ high altitudes, the low pressure rotor will (Increase/Decrease) in speed as the compressor load (increases/decreases) | Increases, Decreases |
| The Low-Pressure rotor in a split compressor will increase speed when the compressor load _? | Increases |
| Stator Vanes serve what purpose in an Axial-flow compressor section? | The decrease the velocity/prevent swirling |
| Stator Vanes convert the Velocity from the Rotors into what kind of energy? | Pressure (Think: Rotors speed it up, Stators raise the pressure) |
| Which turbine engine offers the greatest advantages for starting flexibility, and improved high-altitude performance? | Split-Spool, Axial-flow |
| The Fan on a Dual-Axial Compressor, Forward-Fan engine is connected to ? | The Low-Pressure compressor -*The fan is big enough that some of the air passes through the outside of the engine casing |
| If the fuel/air mixture on a turbine is too weak (assuming normal airflow), the result may be_? | A Lean Die-out |
| Turbine engine Main Bearing Oil Seals are usually what type? | Labyrinth and/or Carbon Rubbing |
| Labyrinth or Carbon Rubbing seals are usually used where in a Turbine Engine? | Main Bearing Oil Seals |
| If a turbine engine can't reach T/O EPR before the EGT limit is reached, this could indicate _? | The compressor may be contaminated or damaged. |
| What is the proper starting sequence for a turbojet engine? | Starter, Ignition, Fuel |
| What areas of a turbine engine are susceptible to dirt? | Casings, Inlet guide vanes, compressor blades *Extreme heat tends to prevent coating on the turbine blades. |
| Engine driven propellers impart a (large/small) amount of acceleration to a (large/.small) mass of air. | Small acceleration to a large mass of air. *As opposed to a Turbojet/fan engine, which imparts a large acceleration to a small mass of air. |
| What is "Galling" | The transfer of metal from one surface to another. |
| Severe rubbing of turbine engine compressor blades will usually cause what? | Galling |
| Who establishes mandatory replacement times for critical engine components? | Engine Manufacturer |
| What type of combustion chamber Case & Liner are removed/installed as ONE unit? | Can-Type (Outer case/housing with perforated stainless combustion chamber/liner inside) |
| When subsonic air flows through a Convergent Nozzle, the velocity _? | Increases, for subsonic airflow. (Bernoulli's Principle) *Area decreases, velocity increases, pressure decreases* |
| When subsonic air flows through a Divergent Nozzle, the velocity _? | Decreases, for subsonic airflow. (Bernoulli's Principle) *Area Increases, Velocity decreases, pressure increases* |
| When Supersonic air flows through a Divergent Nozzle, the velocity _? | Increases (Opposite of subsonic air, where Increasing area increases pressure/decreases velocity.) |
| Possible cause of Turbine Engine High oil temp, with no change in power setting parameters? | Main bearing distress *Bearing is overheating, and heat is transferring to the oil* |
| Two basic parts of a Centrifugal Compressor? | Impeller and Diffuser Impeller-speeds up the air/adds energy Diffuser-Slows the air/increases pressure |
| The majority of the air passing through the combustion chamber of a turbine engine is used for what? | -Support combustion -Cool the engine |
| A Turbine Hot Section is most susceptible to what kind of damage? | Cracking, from extreme temps and vibrations |
| During low-thrust ops, what can help stabilize compressor airflow? | Variable guide vanes and/or compressor bleed valves. |
| What do Variable guide vanes and compressor bleed valves help prevent? | Compressor stalls @ low thrust. |
| Explain Variable Guide Vanes purpose/operation. | Prevent compressor stalls @ low thrust. -Compressor RPM high relative to air flowing through, compressor blade AOA will become too high and surge/stall can occur. They adjust to the proper angle. |
| Explain how Automatic Compressor Bleed valves prevent compressor stalls. | Bleed air valves (connected to fuel control) open to reduce back-pressure, letting more air into the engine |
| At what stage in a turbine engine are gas pressures the greatest? | At the compressor outlet. |
| The compression ratio of an Axial-flow compressor is a function of the _? | Number of compressor stages. |
| What is the advantage of a Dual Axial-Flow compressor? | Higher compression ratios |
| What is the primary function of a Turbine Engine Exhaust cone? | Straightens/collects exhaust gases into a solid exhaust jet. |
| The "Brayton cycle" is also known as the constant _ cycle. | Constant Pressure |
| Explain the Brayton Cycle principle. | Cycle of energy used by a turbine engine. -Energy added to air by burning the fuel -Volume of air increases -Pressure remains relatively constant. |
| In a turbine engine, combustion occurs at a constant (volume/pressure/density) | Pressure (Brayton Cycle) |
| Why are lead/wax/grease markings not used on Turbine engine hot sections? | They contain carbon, which when exposed to high temperatures, will cause granular embrittlement and lead to cracking. |
| In turbine hot sections, what are safe ways to mark components? | Layout dye, Felt tip markers, Chalk |
| What does Newton's Second "Law of Momentum" State? | Acceleration of an object depends on the Force acting on it, and it's mass. (Remember: the 1st Inertia law covers objects in motion/at rest). |
| If ball/roller bearings are found to have any magnetism, what must be done? | They must be degaussed before using them again. (They would attract ferrous particles and be damaged) |
| What are two methods of removing dirt deposits on a turbine engine? | Fluid wash Abrasive grit blast |
| What 3 main sections make up a gas turbine engine? | Compressor, Combustor and Turbine |
| A compressor stall is caused by a (low/high) angle of attack through the first compressor stages. | High |
| What two factors affect the AOA of an axial-flow compressor blade? | Velocity of the air through the engine RPM of the compressor |
| What is the purpose of a diffuser in a turbine engine? | In a Centrifugal-flow engine, the diffuser acts like the Stators. -The Impeller accelerates the air (velocity) -Diffuser converts velocity to pressure. |
| After a Fuel Control Unit has been replaced on an engine, what must be done? | Re-Trim the engine |
| Why are turbine blades more susceptible to damage than compressor blades? | Exposure to high operating temperatures |
| What are the 3 basic types of Combustion sections used on turbine engines? | Multiple Can, Annular, Can-Annular |
| The purpose of the turbine section is to drive the _ section. | Compressor Section |
| First-Stage turbine blades are found to have stress rupture cracks on the leading edges. This is a sign of a _ condition. | Overtemperature condition. |
| What is the most |
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avandermey
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