Introduction of jet aircraft

Introduction of jet aircraft


At low speed air is considered incompressible, small changes in its pressure do not lead to variations in its density. However when we increase the speed (Mach <0.5, depending on the temperature), the effects of the shock waves appear that is a discontinuity, a sudden jump (not continuous), in the values ​​of pressure, density and temperature Which increase sharply and the speed also decreases abruptly.
Operation of a jet engine: based on Newton's second and third law ( Check : Newton´s Laws ).
We define thrust as follows: the amount of mass of air per second by the variation of gas velocity.
• The parameters that the cabin crew has to measure the thrust developed by the engine can be:
- low rotor RPM (N1)
- high rotor RPM (N2)
- EPR, engine preassure ratio, ratio of total output pressures and engine input, therefore the EPR is proportional to the thrust and is always greater than one.
• The manufacturer of any jet engine establishes operating margins based on the temperature reached by the engine (ITT: Interstage turbine temperature, intraturbine temperature, or EGT: Exhaust Gas Temperature).
The maximum motor settings are time-limited:
- Take off thrust (TO): 5 min
- Go-around thrust (GA): matches the time and temperature constraint as above.
- Maximum continuous thrust (MCT): Maximum thrust adjustment for continuous use (motor failure)
- Maximum climb thrust (MCL): ascent and acceleration in cruise
- Maximum cruise thrust (MCR): maximum setting recommended by the manufacturer

Considerations of thrust

T= G(Vs-Ve)

T: Thrust

G :  air mass/ time

Vs: velocity of  the outflow air

Ve : velocity of the inlet flow

They are divided into two:
- Factors unrelated of the crew (all those that make a variation of the air mass that enters to the engine, G.):
            Pressure ↓: P ↓ ρ ↓ G ↓ E ↓
            PA ↑: P ↓ ρ ↓ G ↓ E ↓
            DA ↑: ρ ↓ G ↓ E ↓
            Temperature: is the most important interest T ↓  T ↑ ρ ↓ G ↓ E ↓
            Altitude ↑: ρ ↓ G ↓ E ↓ (in the tropopause T = cte the pressure ↓↓)
            Humidity: Very little importance the manufacturer already takes into account
                                When it finds the temperature
            Speed: Mach <= 0,57 constante constant thrust with speed
                                                 0.57 <Mach  compressible air, ρ ↑, E ↑
- Controllable factors from cockpit:
                               Influence RPM: RPM ↑ E ↑
                               Injection of water: E ↑
                               Bleeding air from engine: E ↓
                               Fuel temperature: E ↓


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