Relating to the named dudes
What are the parts to a gas generator?
Compressor, burner, turbine
What is gross thrust (...not to be confused with clean thrust)
Measurement of thrust derived solely from velocity of exhaust gases. Measured at standard day conditions (29.92 F/15C)
Describe inlet ducts as well as the different types.
Provide proper amount of high pressure, turbulence free air to compressor. Single inlet ducts: simple & effective. Divided Inlet duct: pilot sits lower and reduces friction loss due to length
Describe the combustion/burner section.
Primary air: 25% (has fuel for ignition), Secondary air: 75% (helps cool walls and control flame). Burner section: contains combustion chamber, proper mixing of fuel and air. Minimize pressure decrease through burner, combustion efficiency remains high, flame cannot blow out, all burning must be done before gases enter turbine section.
Drives the compressor and accessories, and designed to increase airflow velocity. Consists of a stator element, turbine rotor section, and can be single or multi-stage. Turbine section is most highly stressed part of the engine!
You OTTO know this one...Describe the Otto Cycle.
A reciprocating engine's cycle (like a car). Intake compression, combustion, exhaust (or, suck-squeeze-bang-blow). Occurs SEQUENTIALLY, not simultaneously (generally in a single piston)
You won't find this net anywhere on a court. Describe net thrust and it's relationship to gross thrust.
m x (Vfinal - Vinitial)/t. Thrust that corrects for the effect of inlet airflow velocity (while moving). Net & Gross are equal when aircraft is static and in SDC.
Describe subsonic inlets, supersonic inlets, and variable geometry inlet.
Subsonic: Divergent shape, increases airflow pressure while decreasing velocity. Supersonic Inlet: Convergent/Divergent. Starts off in convergent shape (high P low V,) but then changes to divergent so airflow can get to the compressor. Variable Geometry inlet: Use ramps, wedges, or cones to change shape of duct as airspeed changes between subsonic to supersonic
List the 3 types of combustion chambers.
Can, annular, can annular.
Describe the exhaust section.
Must direct the flow of hot gases rearward to cause high exit velocity to gases while preventing turbulence. Located directly behind turbine section. Consists of exhaust outer ducts, exhaust inner duct, exhaust inner core, and 3 or 4 radial hollow struts.
Engines may be BRAYTON my heart...but you don't wanna break this cycle in the skies. Walk us through the Brayton cycle.
Gas turbine engine cycle. Intake, compression, combustion, and exhaust. Occurs SIMULTANEOUSLY in a gas generator.
RAM...but not the GDO-antiterrorism kind. Describe the relationship between ram effect and airspeed.
Airspeed increase without ram effect decreases thrust. Airspeed increases with ram effect keeps thrust relatively constant at subsonic speeds and increases thrust at supersonic speeds. Allows for high altitude performance for fighter aircraft despite low air density.
Describe purpose of inlet and exit guide vanes.
They redirect airflow. Inlet guide vanes impart swirling motion to the air entering compressor in direction of engine rotation, reducing drag on first stage rotor blades. Exit guide vanes straighten airflow for diffuser to reduce turbulence after rotation movement of compressor.
Describe annular combustion chamber.
Describe the 2 types of exhaust nozzles
Convergent and Convergent-Divergent. Convergent: slow subsonic air and accelerates them through convergent section (increasing velocity). Convergent-Divergent: works like a supersonic inlet.
BerWHOlli? Explain Bernoulli's principle.
PT = Ps + (1/2)pV^2. This is true for subsonic, closed systems. As velocity increases, pressure (static) decreases.
Explain the effects altitude has on thrust.
As altitude increases, thrust descreases because the effects of pressure is greater than the increase temperature has on thrust. At 36,000ft, thrust decreases more rapidly due to temp stabilization. 36,000ft is optimal cruise level.
Role of the compressor
Supply enough air to satisfy requirements of the combustion section and improves burner efficiency.
Describe the can combustion chamber.
Each burner has own fuel nozzle, burner liner, and casing. Advantages: strength, durability, ease of maintenance. Disadvantages: poor use of space, greater pressure loss, uneven heat distribution, malfunction can lead to turbine damage.
Describe the afterburner section
Method used in turbojets and turbofans to increase max thrust available from an engine by 50% or more, but fuel consumption increases by 300%. Used when added thrust is required for short periods (takeoff, increasing rate of climb, etc.)
What is a nozzle? What is a diffuser? How do they change in supersonic vs subsonic speeds?
Nozzle: Shape of the opening increases airflow velocity and decreases airflow pressure. Diffuser: Pressure increased while velocity is decreased. Subsonic nozzle and supersonic diffuser are convergent, while subsonic diffuser and supersonic nozzle are divergent.
How do air density, temperature, and pressure affect thrust?
Density: As density increases, thrust will increase. Temperature: As temperature increases, thrust will decrease (& vice versa). Pressure: As pressure increases, thrust will increase. Hint: Mass affects thrust, and the mass of air is density. What affects density will also affect thrust.
3 types of compressors and their advantages/disadvantages
Centrifugal: low cost, good power over range of RPM, high pressure increase per stage BUT large front area increases drag & impractical for multiple stages
Axial: less drag, high peak efficiency and combustion, straight through airflow BUT compressor stalls more likely at low speed, expensive, good for small range RPM
Axial Centrifugal:large pressure increase for engine size BUT not good for supersonic airflow
Describe can annular combustion chamber.
Used in high performance engines. Combines ease of maintenance of can combustion with good thermodynamics of annular combustion. Greater structural stability and lower pressure loss.
Name the 4 parts of the afterburner section.
Spray bars, flame holders, screech liner, and variable exhaust nozzle.