Development and Conception of a test bench to help the reparation of Thrust Reversers Miguel Filipe Vieira Batista [email protected] Instituto Superior Técnico, Universidade de Lisboa, Portugal November 2016 Abstract This thesis aims to design and develop a test bench to the reparation of the Thrust Reversers of the CFM56-5B engine. Currently, the Thrust Reverser is fixed in the engine workshop and its operation is only tested when it is mounted on the wing, because it was considered that the repair made at the workshop was sufficient. The maintenance and checking on the wing are made through the AMM. It was found, however, that this type of maintenance was not sufficient. Having seen the potential that the maintenance of Thrust Reversers presents, TAP decided to invest in the development of equipment for reparation and test of Thrust Reversers. Keywords: Thrust Reverser, test bench, TAP 1. Introduction 2. Aerostructures This paper is on the The turbojet and turbofan aircraft development and conception of a test type have a fuselage, wings, tail, bench to help the reparation of Thrust propulsion system, braking system and Reversers. monitoring systems. Since the TR is a The aircraft is one of the most component that embraces the engine, important means of transport in one will present the components that existence. One of the components of the make up this system (nacelle), shown in aircraft is the Thrust Reverser which is figure 1. used to brake, besides the brakes and spoilers. Due to its frequent use, the components wear, which leads to the need for repair and maintenance. In order to ensure the proper functioning of this system, it is necessary to make verification testing and validation of components in order to guarantee security in the various stages of use. TAP Engine Maintenance workshop carries out the repair and maintenance of Figure 1 – Nacelle components. [1] engines and Thrust Reversers of the aircraft fleet of TAP. The pylon is the component that connects the assembly to the airplane wing. The structure consists of the cowl inlet (rollover that allows air to enter), the cowl fan (rollover protecting the fan), TR which involves the engine and deflects 1 the air bypass and exhaust (nozzle and transmitting movement to the High cone). Pressure Compressor (HPC) making use of an outer shaft (rotational speed N2) The Jet propulsion is a direct surrounding the inner shaft. application of Newton's 3rd Law which states that “for every force acting on a The remaining air, which represents body, there is an opposing force in the the remaining 80% of the total flow is same direction and intensity”, that is, for called secondary air flow or bypass. The all forces there is always a reaction force. bypass ratio is the relationship between In the case of propulsion, the "body" of the secondary flow that bypasses the which are being exerted forces is the air core and the primary flow passing passing through the reactor, resulting in through the core. In the case of the its acceleration. The force needed to CFM56-5B engine, the bypass ratio is cause the air acceleration has, therefore, 5.5:1 to 6:1, the secondary air flow is 5.5 a direction opposite reaction force that to 6 times higher than the flow rate of will be responsible for the movement, this primary air. Currently relationships can force is called thrust. be achieved up to 11 to 1. In a turbofan, the engine core is The turbofan increases its made of a fan, a low pressure momentum by increasing the mass flow compressor (booster) upstream and an rate through the bypass. Moreover, this additional turbine downstream. The secondary flow is used to cool gases impulse is then achieved by combining leaving the turbine, reducing the thermal the high exhaust velocity, from burning differential output and reduced noise of fuel with a flow in a duct after the fan, the aircraft. shown in figure 2. 3. Breaking systems / Reverse Thrust After crossing a certain distance, the aircraft needs to land. The complete landing of an aircraft is to land, lead the aircraft to a low speed (taxi speed) and its complete stop. However, most of the Figure 2 – Turbofan engine scheme. [1] commercial jet engines continue to produce forward thrust even when they Of the air flow which is admitted to are inactive, acting contrary to the the fan, a small portion proceeds to the deceleration of the aircraft. The landing core (≈20%), primary flow, providing brakes and the spoilers of modern oxygen for combustion to occur, which is aircraft are sufficient under normal responsible for generating thermal circumstances, but for safety reasons, power, and supplying air to the cooling and to reduce tensions on the brakes, circuits of the reactor. another deceleration method is needed: The turbines are responsible for the Thrust Reverser. performing the conversion of the thermal 4. Thrust Reverser power to mechanical power, so that the compressors and the fan can move. In On an aircraft with a jet engine, a the particular case of a turbofan shaft, simple and efficient method of braking is double Low Pressure Turbine (LPT) to reverse the direction of engine exhaust moves the fan and the low pressure flow jet and use the engine power to slow compressor via an inner shaft (N1 itself. There is a set of rotational speed) and the High Pressure Thrust Reversers on each engine A320. Turbine (LPT) is then responsible for 2 Each set consists of two halves The Thrust Reverser is designed to be which are hinged at the top of the pylon used only on the ground and works in and locked together on top of the split four modes: stow, deploy, disabled and line. Moreover, the assembly is also manual. In stow mode, the reversing embedded in the end of the fan structure. system acts as an aerodynamic structure This system works only together, that is, to store and secure the aircraft engine it cannot deflect the air only from one and its components. The reverser also side. Thus, the Thrust Reverser is a acts as a conduit that provides a temporary deviation in the engine streamlined flow path and an outlet of the exhaust system of an aircraft so that the engine fan to the exhaust gas system. In produced exhaust gases are directed the deploy mode, the reverser changes forward instead of going backward. This the direction of the exhaust air flow to the acts contrary to the displacement forward engine to obtain the thrust inversion. This of the aircraft, providing deceleration. reverse of thrust causes a braking effect Ideally, the reversed exhaust flow should which slows the aircraft. be directed to the straight ahead. In order to actuate the Thrust However, for aerodynamic reasons, this Reverser one must meet the following is not possible, and an angle of 45° is requirements: all wheels must be on the used, resulting in a less efficient solution, ground to ensure the touchdown, all shown in figures 3 and 4. wheels must be spinning fast enough to keep up with the aircraft, the aircraft must be moving slowly enough and throttles must be in the correct position. The initial deceleration provided by the reverse pulse may reduce the braking force and landing distance of a quarter or more. However, the regulations require that an aircraft must be able to land on a runway without the Figure 3 – TR closed. [1] use of Thrust Reverser. Once the aircraft's speed has slowed down, the Thrust Reverser is turned off to prevent that the reverse air current throws debris into the intake air in the front of the engine and causes damage by external objects. The need to use the Thrust Reverser is most evident in scenarios involving bad weather, where factors such as snow or rain on the track Figure 4 – TR open. [1] reduces the efficiency of the brakes and in emergencies such as canceled takeoffs. The Thrust Reverser is triggered The amount of generated thrust and manually. First the engine controls power are proportional to the speed of (throttle) are put in idle, the TR command the aircraft, making thrust reverse more (throttle) is pushed up and, when all efficient at high speeds. For maximum necessary conditions for landing are efficiency, it must operate quickly after satisfied, the throttle is placed at the landing. Figure 5 shows the maximum, so the engine produces the percentage of reverse thrust (in % of maximum thrust in order to brake. impulse created) due to engine power (% of power level in rpm) for a target bucket 3 Thrust Reverser type. It is important to the conduits normal output, so that the notice that the higher inversion pulse (at thrust is directed forward. In a turbojet about 60% of the momentum created) is engines, this system is less efficient than made at the maximum engine power the Target Bucket system, since the (100%), it is not possible to use all the Clam-Shell system only uses the flow of engine power for braking. air from the turbine which is not as hot as the exhaust gases, shown in figure 7. 5. Types of Thrust Reversers Figure 7 – Clam-Shell system (closed and open). [3] In the Coldstream systems, ports in the bypass duct are used to redirect air which is accelerated by the fan section, Figure 5 – Reverse Thrust due to engine power. [3] but does not pass through the combustion chamber (called air bypass) There are five Thrust Reverser providing reverse thrust. The cold stream systems in common use: Target Bucket, system can be activated electrically, Clam-Shell, Coldstream Pneumatic pneumatically or hydraulically, shown in (Translating Cowl), Coldstream figure 8.