Correlation Between Engine and Aircraft Loadings for Several Mission Types

Abstract

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.

Comparative Study of a Powerplant Life Consumption Rate When Installed in Two Different Aircraft Variants

“…Through those studies, new engine life consumption rate methodologies were introduced. For instance, the engine loading depending on the mission type was studied for the case of the F-16 (Templalexis et al, 2020) [2] and the same methodology will be applied for other aircrafts as well. The ultimate goal is to make use of results to train a smart algorithm.…”

“…However for this study that would be an oversimplification since it is known that when flying the EMB-145 aircraft version, there are much more throttle adjustments that need to be done. Consequently, the rain flow cycle counting method as applied in (Templalexis et al, 2020) [2] and in (M. Musallam et al, 2012) [13] was applied to the High Pressure (HP) spool, in order to have a more accurate recording of the engine cycles. The stress as a parameter was substituted by the PLA, which is constantly recorded during flight and it is directly proportional to the stress level developed during operation.…”

“…The methodology for the (HPT) blade lifing is presented in (Templalexis et al, 2020) [2]. A brief outline is also given here.…”