The vast majority of helicopters in use is equipped with a turbine engine. Compared to the piston engine know that it has advantages in terms of power to weight ratio, reduction of vibration and behavior at high altitude.
In the family of turbine engines, we can distinguish two main categories:
- Free turbine engines;
- Turbine engines tied up.
The free turbine engines are the category most popular and modern, in fact, tied the turbine is characteristic only of a few engines (for example, the Turbomeca Artouste II and III) and this type of engine has marked disadvantages than advantages: the benefit is time Fast response and simple construction, the disadvantages are that the engine has no chance of assembling "building blocks" (ie having only a tree on which all components are seated have many limitations in terms of maintenance practices ) and a chance to use envelope rather limited.
Then analyze how a turbine engine is free on a helicopter, taking as example a very common pattern: The PT6 Pratt & Whithey
In the family of turbine engines, we can distinguish two main categories:
- Free turbine engines;
- Turbine engines tied up.
The free turbine engines are the category most popular and modern, in fact, tied the turbine is characteristic only of a few engines (for example, the Turbomeca Artouste II and III) and this type of engine has marked disadvantages than advantages: the benefit is time Fast response and simple construction, the disadvantages are that the engine has no chance of assembling "building blocks" (ie having only a tree on which all components are seated have many limitations in terms of maintenance practices ) and a chance to use envelope rather limited.
Then analyze how a turbine engine is free on a helicopter, taking as example a very common pattern: The PT6 Pratt & Whithey
This type of engine (figure shows the PT6A) is essentially two parts: the first goes from the first stage of axial compressor to the turbine power of the compressor (N1), and the second part is the free power turbine up to the output shaft (N2).
Using a rotary engine in the wing is essential to consider the basic rule according to which the speed of the rotor must remain nearly constant. We know that in the case of piston engine maintaining the rotor speed is assigned to manual control by the pilot or the aircraft it is fitted by the automated system known as the "governor".
In the case of turbine-powered (and always in the case of PT6, particularly PT6C-67C installed sull'Agusta Westland AW-139) power control is obtained by two main components: The EEC (Electronic Engine Control) and FMM (Fuel Management Module). The EEC is basically an electronic box that contains all the necessary components for automatic control of engine speed and consequently those of the rotors (main and tail). The FMM (in Figure 1 is the first component from the right, in front of the accessory box) all'EEC work together to control the dosage of the fuel usage throughout the engine. The way to use "automatic" motor is therefore through a network of sensors to detect deal with the speed of two shafts (N1 and N2) of the main rotor (Nr) of torque on the output shaft (Q) the engine temperature (in this case is going to ITT Interstage Turbine Temperature, ie the temperature difference between the two turbines) and the outside temperature (OAT). The mass of information coming from these sensors, coupled with the transducers of the collective pitch lever, converge in the EEC, which processes them and transmits them as impulses to the mechanical components of the FMM. In case of failure of the automatic pilot can govern the EEC manually using switches located on the FMM of the collective pitch lever, then the channel of "backup" of this type of equipment is always represented by human intervention.
Always talking about the engine, we face a problem that is easy to put on, and that is what happens when the engine is affected by a disaster.
In the case of a helicopter equipped with two engines, if flight conditions permit you are not forced to land but you can continue with the remaining engine. In the case of a helicopter equipped with one engine we will proceed with an operation called "autorotation". The particularly interesting from the point of view of the engine is that in the general case of a malfunction, the engine does not drag with it the transmission, but through a component called "free wheel" enables the transmission to disengage from the main motor. Basically it works like the freewheel of the bicycle: the pedals in a forward direction motion, another free themselves automaticamente.Senza this device would in fact have a direct link between engine and transmission, in case of mechanical blockage of the latter thereby blocks the entire transmission dll'elicottero, with easy to understand consequences.
Using a rotary engine in the wing is essential to consider the basic rule according to which the speed of the rotor must remain nearly constant. We know that in the case of piston engine maintaining the rotor speed is assigned to manual control by the pilot or the aircraft it is fitted by the automated system known as the "governor".
In the case of turbine-powered (and always in the case of PT6, particularly PT6C-67C installed sull'Agusta Westland AW-139) power control is obtained by two main components: The EEC (Electronic Engine Control) and FMM (Fuel Management Module). The EEC is basically an electronic box that contains all the necessary components for automatic control of engine speed and consequently those of the rotors (main and tail). The FMM (in Figure 1 is the first component from the right, in front of the accessory box) all'EEC work together to control the dosage of the fuel usage throughout the engine. The way to use "automatic" motor is therefore through a network of sensors to detect deal with the speed of two shafts (N1 and N2) of the main rotor (Nr) of torque on the output shaft (Q) the engine temperature (in this case is going to ITT Interstage Turbine Temperature, ie the temperature difference between the two turbines) and the outside temperature (OAT). The mass of information coming from these sensors, coupled with the transducers of the collective pitch lever, converge in the EEC, which processes them and transmits them as impulses to the mechanical components of the FMM. In case of failure of the automatic pilot can govern the EEC manually using switches located on the FMM of the collective pitch lever, then the channel of "backup" of this type of equipment is always represented by human intervention.
Always talking about the engine, we face a problem that is easy to put on, and that is what happens when the engine is affected by a disaster.
In the case of a helicopter equipped with two engines, if flight conditions permit you are not forced to land but you can continue with the remaining engine. In the case of a helicopter equipped with one engine we will proceed with an operation called "autorotation". The particularly interesting from the point of view of the engine is that in the general case of a malfunction, the engine does not drag with it the transmission, but through a component called "free wheel" enables the transmission to disengage from the main motor. Basically it works like the freewheel of the bicycle: the pedals in a forward direction motion, another free themselves automaticamente.Senza this device would in fact have a direct link between engine and transmission, in case of mechanical blockage of the latter thereby blocks the entire transmission dll'elicottero, with easy to understand consequences.
