# 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.
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```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.
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```• 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

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```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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