Fighter aircraft constitutes a well-defined class of aircraft. Their extensive use on a daily basis by operators stands as a strong motive behind studies that concern their rate of “exhaustion ”. For an aircraft operator either civil or military, it is very important at any point in time to have a clear view of the engines’ and the aircrafts’ operating condition. This is valuable information in order to foresee undesired incidences and in order to schedule missions in accordance to the actual and anticipated maintenance needs. For the latter, the operator would also need to know the rate of the engine and the aircraft life consumption per mission. The current study concerns the F-16 Block 52M aircraft, powered by the Pratt and Whitney F100-PW-229 engine. Aircraft is continuously subjected to crack growth mechanisms while flying. On the other hand, engines also go through Low Cycle Fatigue (LCF) cycles and creep prominent conditions while being in operation. The engine and the aircraft structural condition are continuously monitored, based on real time data recordings. To the extent of the authors’ knowledge, that is a common practice for most F-16 users. However, what was found to be missing from the international literature was a study to quantify any potential correlation between the aircraft loading and the engine loading for all typical mission types an aircraft of this type undertakes. For users that have already installed an aircraft loading monitoring system like “Aircraft Structural Integrity Program” (ASIP) it would be very useful to set a “rule of thumb” aside regarding the degree of correlation between aircraft and engine loading. Engine life consumption rate was estimated based on the creep and LCF failure mechanisms applied on the most critical engine section, the turbine. Engine recordings were picked from an arbitrary sample of 200 flights of a certain aircraft, wherein most typical mission types could be found. Turbine and subsequently blade temperature as well as blade stress were calculated using a very narrow time step. These data along with blade material data were fed in the Larson Miller model, to set an algorithm for estimating life consumption due to creep. Engine Total Accumulated Cycles (TACs) which account for LCF loading, are directly measured by the engine recorder, based on an embedded algorithm. Aircraft loading is calculated based on the accelerations the aircraft structures encounter during flight. These are also recorded under a very narrow time step. Last step was the correlation of the engine life consumption against the aircrafts’ loading for typical mission types. Scatter diagrams and statistical measures were used, in order to define the degree of correlation between them.
The Hellenic Air Force (HAF) operates both EMB-145 and EMB-135 LR versions of Embraer aircraft, used in surveillance and civil missions respectively. These aircraft are equipped with the same version of Rolls Royce, AE 3007 turbofan engine. This study aims to quantify and compare the life consumption rate of this engine when installed in each of the two aircraft variants. Two typical missions, one for each variant, were constructed based on mission profile data dictated by the aircraft commanders. For each mission profile segment, corresponding engine data were matched out of the engine recordings archives held by the Hellenic Air Force. The life consumption rate was based on the Low Cycle Fatigue (LCF) and creep cumulative detrimental effect on the rotor blades of the 1st High-Pressure Turbine stage. For the LCF, the rainflow method was used to determine the respective loading cycles, whereas the Larson - Miller parameter method was used to determine the consumed life fractions due to creep. The main conclusion of the study was that the engine when installed in the EMB-145 military variant, is much more loaded. Despite the fact absolute life consumption values could hide a great level of uncertainty, the comparative outcomes wherein errors are, to a certain extent, cancelled out, could be used as a rule of thumb when monitoring engine life consumption rates.
Gas turbine engines exhibit very high maintenance costs. Moreover, in the case of aero applications an in-flight engine incidence, shall, by all means, be avoided, a condition that drives total maintenance costs even higher. A measure in favor of balancing these costs is to monitor continuously the variation of engine performance data recorded during flight, establish methods to deduce useful information regarding the engine “health” status and, as a result, take appropriate actions to maintain a good engine operating condition. The current work presents such a method tailored on the “F100-PW-229” engine that is operated by the ellenic Air Force as the propulsion system of the “F-16 block 52M” aircraft [3]. CEDATS and MS Excel were the computational tools used for the current engine performance study. CEDATS is a software developed for the engine users. It provides basic data trend monitoring functions and engine fault warnings. It is well known that there is always space for improvement for such health monitoring tools since there are cases where engine operating faults are not captured. Within the frame of the current work, a data post – processing method on the engine performance data time series was applied using MS Excel, in order to raise early warnings of an uncaptured compressor operating fault.
The life consumption rate of the aircraft engine is a vital input for aircraft operators who aim to an efficient fleet management. T6 aircraft, propelled by the PT6 turboprop engine, is operated by the Hellenic Air Force, both for training and aerobatic purposes. The current study focuses on quantifying and comparatively assessing the engine life consumption rate for the following missions: i) An “aerobatic” mission which is a typical high intensity maneuver flight and ii) a “training for patrol” mission, representing a typical low intensity maneuver flight. Missions were selected with the criterion of setting the lowest and the highest possible engine loading during a certain mission. In other words, the goal of the study is to define the extent of the loading the engine can encounter as a propulsion system of the T-6 aircraft during a certain mission. This is the first step before proceeding in setting up a methodology for continuously monitoring the engine life consumption rate in support of the squadron flight management plan. The study was based on real time data recorded during the respective flights. An engine model built using “GasTurb” gas turbine simulation software was used to fill in engine operating data at stations where recordings have not been taken. Engine life consumption was based on creep and low cycle fatigue failure mechanisms of the first gas generator turbine stage. Creep life fractions were calculated based on the Larson-Miller parameter curves and the fatigue cycles were counted using the rainflow method. The study showed that the life consumption is about 10 times lower when the aircraft is operated at a low loading mode as opposed to a high loading mode.
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