DGLR-MTR-2000.PDF

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personic Exit Mach Numbers for the blading. This leads to compression shocks including additional shock-boundary layer interactions with the combined complexity and sensitivity to geometrical deviations. Much attention was given therefore to the aerodynamic design. On the other hand the minimisation of necessary airfoil cooling flows and the optimisation of the tip-clearance are important to get the best result with respect to the engine operation line. The compressor turbine design including the interturbine duct was also affected by the mechanical boundary conditions with very high temperature and stress levels for life limiting parts. This shows the excellent interaction between the necessary technical disciplines. Fig. 7 shows the loss contributors in this class of engine size in comparison with a large engine. It is evident that tip clearance and cooling losses are of the same order as aerodynamic losses and have to be taken careful into account. Fig. 7: Thermodynamic losses in the turbine module In Fig. 8 published results of several tip clearance investigations are plotted together with rig and demonstrator engine data from MTU. Fig. 8 Influence of tip clearance variations on stage efficiency As blade height is only 17mm, a tip clearance of 0.1mm results in an efficiency change of 1 point. Fig. 9 highlights the impact of tip clearance on the radial efficiency distribution for 1, 2 and 3 % relative radial gap(s/h). The efficiency is affected down to 50% blade height. Fig. 9: Influence of tip clearance variation on the radial efficiency distribution Therefore, an efficient system was chosen with liner segments hung into a casing of low thermal expansion and controlled by forced cooling. The short and rigid gas generator rotor contributes to the efficient tipclearance control. In order to minimise the cooling air both nozzle and vane are of single crystal material which permits high temperatures. The blade cooling configuration was developed to minimise the amount of air and the detrimental effects of secondary flows re-entering the gas path. 6.4 Power Turbine The power turbine is a two-stage uncooled design. The philosophy behind this module was to ensure ease of maintainability and repair whilst achieving a low cost reduced weight yet reliable design. Several features were key in this achievement. The power turbine is easily replaced in field through the removal of a series of retaining bolts on the power turbine case together with the curvic bolts. The module then simply slides rearwards and clear from the engine. The power turbine bearings and air/oil system are retained within the core engine module. The power turbine can be replaced without the need to re-test the engine. The curvic coupling, mentioned previously, transmits the torque to the engine reduction gearbox. This curvic coupling allows accurate re-assembly of the power turbine, reducing the susceptibility of the module high speed balance to wear at this interface. To ensure Foreign Object Damage (FOD) tolerance a single crystal material and equi-axed material was
chosen for the first and second stages respectively. The materials chosen offer impact resistance at a relatively low density. This is an important consideration with the cantilevered power turbine design when assessing the highly unlikely event of a blade loss and the associated out-of-balance moment that is generated. The power turbine foreign object damage (FOD) tolerance was optimised and demonstrated during the development programme. The power turbine rotates in the reverse direction to the engine core. This reverse rotation minimises the 'turning' required by the PT1 NGV to ensure acceptable entry conditions to the first stage of blade. This contributes to the high overall efficiency of the power turbine. The efficiency is further improved by the absence of an exhaust diffuser and its associated discharge losses. Overall module weight is also reduced. 7. FADEC CONCEPT The engine control system is essentially based on a FADEC (full authority digital engine control) developed from the background acquired over more than 10 years flight experience on other turboshaft engines applications. This concept allows a great simplification in the hydromechanical units most of which are grouped in the accessory gearbox module. It provides carefree engine operation, control and monitoring. It is essentially a single channel with electric manual back up and analogue overspeed protection. The control function provides basically automatic start sequence, rotor run up, and then maintains the Rotor at the nominal value. In flight the engine is protected against limit exceedance, surge and flame out for a minimum of pilot workload. Many other functions are also available like training mode which simulate an engine failure for pilot training and automatic relight in flight in case of flame out. A lot of work has been done including several altitude tests for optimisation of engine transient accelerations and decelerations. The result of this optimisation is one of the key elements enabling TIGER aircraft impressive manoeuvrability. The FADEC also provides maintenance help functions: • Built In Test: monitors the defect of the Control Unit, all the accessories and aircraft interfaces electrically linked to the Control Unit. After a defect is detected the pilot is informed of the consequences if any on the engine operation and complementary localisation information helps the maintenance personal to repair after the flight. • Engine Performance Check: monitors that the minimum specified power is available. • Limit Exceedance Monitoring: records potential limit exceedance duration and peak values of main parameters (torque, turbine temperature, gas generator and power turbine speeds) in order to define the maintenance actions. • Life Usage Monitoring: computes the life consumption of the life limited parts (impellers, disks, …) 8. MODULARITY AND MAINTENANCE The engine consists of four separate, interchangeable modules, including the FADEC can be changed without the need to retest the engines, nor are any special checks or adjustments required on module change. Maintenance time and costs are reduced by „On Condition monitoring“ carried out by the FADEC, with its built in diagnostic aids, pre-clogging and by-pass indicators for the fuel and oil filters and chip detectors in the oil system to monitor bearing condition. The built in test failure detection system also informs the maintenance personal of the location of faults, to minimise maintenance time. A minimised toolkit is required for first line maintenance, consisting of just a few hand tools. All line replaceable units (LRU) can be removed by one operator, in an average time of 15 minutes, and there is no wire locking. 9. TEST EXPERIENCE During the programme, a total 17.700 hours of engine running have been completed. Development bench running of 10200 hours has been accumulated, including 1500 hours of endurance testing and 1.800 hours of AMT. Flight engines have logged up a total 6500 hours, 5800 hours in the Tiger, and 700 hours in the Panther FTB. The engines in the flight programme have proved to be very reliable. In the 6500 flight hours there has been 1 unplanned „in flight“ shutdown, caused by a design problem which has now been corrected and 1 basic unplanned engine removal. Considering this is during the development flight programme, it is an impressive
Page 1 and 2: THE SUCCESSFUL DEVELOPMENT HISTORY
Page 3 and 4: equirements and to release the prod
Page 5: Fig. 4 Flame structure at atmospher

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