M14.1 Flashcards
A/C engine supplies:
hydraulic, electric, pneumatic
2 types of engines:
Piston type & Gas turbine
Piston type
Advantages:
-simple in design
-more fuel efficient
Disadvantages:
-performance decrease at higher altitude -can’t be on large A/C (weight to power ratio)
Gas Turbines
Advantages:
-operate at high altitudes & speed
-easily provide thrust, torque, & bleed air -powers either a single fan or a set of a counter-rotating fans via a gearbox
Different types of Gas Turbines
- Turbofan engine
- Turbojet engine
- Turboprop engine
- APU
Turbofan engine
-used on modern aircraft
-high A/C speed is possible w/ good engine efficiency @ high altitude
-developed from turbojet
-usually twin or triple spool engine
-fan is always driven by a turbine via drive shaft
-do not have reduction gear to reduce fan speed
Turbofan engine
-converts large part of gas energy into torque to drive the fan and compressor engine -remaining hot gas from core engine is directly converted into thrust
*Total thrust = core engine + fan
-fan accelerates high airflow, low outlet
velocity
-core engine accelerates small quantity of air, high outlet velocity
-fan can produce 80% of total thrust ;
primarily dependent on bypass ratio
Turbojet engine
-first type of gas turbine used on A/C
-give VERY high A/C speed
-VERY LOUD because of extremely high
exhaust gas velocities
-need too much fuel
-all gas energy is converted into thrust
Turboprop engine
-specially design to produce shaft horsepower only which is to drive a propeller
-installed on small commuter A/C
-achievable A/C speed & fuel efficiency
-produce their thrust by a small acceleration of a large quantity of air with propeller
-driven directly on compressor shaft or by a turbine and a long center drive shaft.
-all gas energy into torque
- always required to reduce
the high gas turbine engine rotation to speeds that can be managed by the propeller
Reduction gear
Auxiliary Power Unit:
-small gas turbine engine
-supply A/C w/ electric & pneumatic power if the engine is not available
-A/C is independent of airport equipment
– propelling force, which is generated in the opposite direction to the flow of mass through the jet nozzle.
Jet Propulsion
- engine which uses jet propulsion.
Reaction Engine
this engine uses Newton’s 3rd law of motion (for every force which acts on a body there is an opposite & equal reaction)
Reaction Engine
F=MxA
To accelerate air, air pressure must increase:
2 ways of doing it:
- mechanically w/ compressor
- thermally by increasing volume of air when a fuel/air mixture is burned/heated
Base for all gas turbine engine:
- Hans Van Ohain, 1937
- Frank Whittle, 1941
centrifugal flow compressor driven by radial turbine
Hans Van Ohain, 1937
centrifugal flow compressor driven by axial turbine; these engines were only possible after the development of materials heat-resistant enough for continuous combustion
Frank Whittle, 1941
– generated by the acceleration of ambient air which is forced through the engine.
Thrust Force
2 parameters of THRUST:
- mass of ambient air which is accelerated
- quantity of acceleration itself
series of changes of state of a working medium which occur periodically
Cyclic Process
– technical processes usually used for converting heat into mechanical work (combustion engines) or for heating & cooling by performing work.
Brayton Cycle
– line of equal pressure
Isobars