Proceso de constitución de Agrupamientos Escolares

As has been made clear in this research, the maintenance activities relating to every piece of equipment on an aircraft are predefined at a high level. This is because the manufacturer creates a maintenance planning document for the particular aircraft, and also for the engines with which it is fitted. However, the main disadvantage of this maintenance plan is that it can only be efficiently applied if the engine is performing within the given performance conditions. In fact this is very difficult to achieve, and hence the maintenance plan could be inaccurate. This research focuses on the variations of the remaining useful life of the turbine blade regarding the operating conditions, and consequently to the relevant losses that the operator could incur when maintenance actions and replacements are undertaken at less than optimum intervals, thus sacrificing the remaining useful life of the component. The method in use refer to the design lifing approach hence, the results taken could optimize the maintenance planning before the aircraft appears in service. However the same method could apply after the aircraft is in service and in combination with more accurate and detailed data to provide further optimization from the design lifing approach.

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Take-off is a crucial stage of flight, and its affection on the engine’s life will be investigated in the particular research. The recommended maintenance actions usually refer to when the aircraft is performing take-off with the engines at maximum thrust. However, these maintenance actions could be optimized further if the operator were able to constantly monitor the engine in combination with health management operations implementation, such reduced thrust at the take-off segment by exploiting a larger runway, or if the aircraft were to have a smaller gross weight. Before any results are presented, it would seem logical that the life of the engine would be seriously affected by the given thrust at the take-off segment as there is a direct link with the TET, and any increase in the TET increases the rate of creep failure.

For the present research, the maximum thrust of the engine refers to the calculated nominal value of achievable thrust provided by the manufacturer for the specific engine model, but is not concerned with throttle lever angles and other pure engine performance conditions. Therefore the reductions in thrust that will be performed later are based on the calculated reduced percentage of the given nominal maximum value. In order to investigate the reduced take-off thrust scenario in the present case study, an imaginary flight plan has been created.

According to this flight plan, an aircraft which is equipped with the engine detailed above constantly performs one particular route between city 1 and city 2. However, when it performs take-off from both cities it has the ability of reducing the thrust by taking advantage of the long runway. It could be expected that the loads on the engine would be lowered as the thrust reduces, and so the development of creep failure rate would also be lowered. Therefore, if the operator is to perform the health management operation of reducing the take-off thrust combined with condition monitoring of the engines for maintenance reasons, the benefits would be multiplied.

Specifically, the flight plan is divided into take-off, climb, cruise, descent and finally landing/reverse thrust. The first scenario that will be used in order to compare it with the rest will be as follows: take-off with 100% thrust, climb and descent at normal performance conditions, cruise at 30000ft and speed of 0, 8 Mach, and landing/reverse thrust with 0. 8 of the max thrust. The simulations and calculations for the climb and descent will be performed at the average altitude for both segments. For every segment of the initial plan there will be no deviation from the ISA conditions. The comparison will be achieved by changing just the take-off segment, while the others will remain constant for all the times and will be added after every different take-off condition in order to have a complete flight. The different take- off scenarios refer to 100%, 90%, 80%, and 75% of the max thrust. Furthermore, the

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previous thrusts will be matched for different ISA conditions at each time, which will be specifically -15, -10, -5, 0, 5, 10, 15, 22, 26, 32 ISA deviation. Finally, the last factor under investigation is the time the aircraft spends at take-off. Each of the above conditions will be matched for three different take-off durations of 1 min, 1.5 min, and 2 min. The following table 4.2 provides a general view of the concept that will be followed were the different each time take-off is matched with the other constant flight segments.

Table 4-2: indicative methodology of creation of the investigated flight profiles (Source: Author)

Case example 1. 100% take-off with ISA Dev. of -15 + climb + cruise + descent + landing Case example 2. 100% take-offwith ISA Dev. of -10 + climb + cruise + descent + landing

Case example 3. 100% take-offwith ISA Dev. of -5 + climb + cruise + descent + landing

Case example 4. 100% take-offwith ISA Dev. of 0 + climb + cruise + descent + landing

However, it is important here to define a number of crucial issues relating to the flight segments. Even though definitions of each are provided by the relevant authorities,it is very difficult in practice to isolate one flight segment from another. For example, as the relevant legislation indicates, the take-off segment ends when the distance from the ground is 35 feet, and after that the aircraft starts to climb. However the aircraft is still flying with the take- off thrust and it changes gradually to the maximum climb thrust after a specific time, rather than the distance shown above. In addition, sometimes some segments will be omitted in practice. An example of that would be a flight with a constant climb at a low rate and the opposite descent, omitting the segment of cruise. Therefore, for the present study the flight segments will be divided according the nominal thrust that is provided by the manufacturer for every flight segment. Therefore, essentially they are thrust segments that apply for the flight segments.

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