Mission segment division of the whole aeroengine loading spectrum based on flight actions

Yu JIN ,Zhigng SUN,b,* ,Yingdong SONG,b,c ,Xin LIN ,Xuming NIU ,Junjie DING

a Jiangsu Province Key Laboratory of Aerospace Power System,College of Energy and Power Engineering,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China

b Key Laboratory of Aero-engine Thermal Environment and Structure,Ministry of Industry and Information Technology,Nanjing 210016,China

c State Key Laboratory of Mechanics and Control Mechanical Structures,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China

KEYWORDS Aircraft engine;Flight mission segment;Mission segment division;Rotor speed mission segment;Spectrum analysis

Abstract This paper studies on a division method of the whole aeroengine loading spectrum flight mission segment and rotor speed mission segment,which is based on the actual flight actions and related to the flight operations of aeroengine and is suitable for the variable-speed aeroengines such as turbojet and turbofan.Through the research,the aeroengine loading spectrum operation-related mission segments can be divided,which can provide important data basis for the life research on the structures which are sensitive to flight maneuver (such as the main shaft,large gearbox and installation section),lay a foundation for the simulation,compilation and prediction of the whole aeroengine loading spectrum.Firstly,based on the summary of basic flight actions in actual flight,the division of flight mission segment was realized by programming.Moreover,the aeroengine rotor speed mission segments,associated with flight actions and missions,were divided based on the flight mission segment division results.Besides,the efficiency and accuracy of the mission segment division results were verified by adopting measured loading spectrum data.Finally,the characteristics of speed mission segment division results were compared and analyzed in tables and figures.The comparison results show that the characteristics of similar speed mission segments are similar,while the characteristics of different speed mission segments are different.And the shapes of similar mission segments vary to the change of flight actions and operations,which can reflect the operation-related feature of the segments.

1.Introduction

The division of the aeroengine loading spectrum mission segment related to practical operation has not been solved well up to now.Aeroengine technology is a key technology that the world military powers preferentially develop,highly monopolize,and tightly block,as well as an important mark of military equipment level,science and industry strength and comprehensive national strength of the country.The national military standard GJB241-2010,the US military standard MIL-E-5007Dand the structural integrity program MIL-STD-1783show that the aeroengine loading spectrum is the basis of stress analysis,structural design criteria,durability test and life analysis of aeroengine parts.Whether aeroengine loading spectrum can truly reflect the actual use of the aeroengine directly affects the evaluation results of engine life and poses a threat to the safety of the engine.As the smallest basic unit of aeroengine loading spectrum,mission segment is the most real and concrete reflection of the actual flight information and service status when the engine performs different tasks,and it is an important basis for the simulation,prediction,and compilation of aeroengine loading spectrum.Due to the randomness of maneuverability and different flying habits of pilots in actual flight,the actual working conditions of aeroengines,especially military aeroengines,vary greatly.The aeroengine loading spectrum is complex and diverse,and the number of mission segments is numerous and disorderly,which makes the division of engine mission segments difficult.

The research on aeroengine loading spectrum began in the 1960s.The U.S.military,NASA,NATO countries,as well as most aircraft companies and engine companies,carried out systematic and thorough research work,implemented a number of large-scale loading spectrum and structural life test evaluation special research plans(including ENSIP,LUCID,TURBISTAN,Flight-by-flight etc.,formed the corresponding specifications and standards which was widely used in the development and use of military and civil aeroengines.In the 1980 s,the division method of the operation-related loading spectrum mission segment was first proposed in the standard loading spectrum program TURBISTANjointly carried out by European countries.In the method,the typical flight mission profile was divided into the initial segment,the middle segment,and the end segment.Moreover,the initial segment was subdivided into ground operation segment and take-off climb segment,and the end segment was subdivided into descending landing stage and ground taxiing stage.According to the load variation amplitude,the middle section was also subdivided into the air cruise section (load variation was less than 4%),the low maneuvering section (load variation was more than 4% and less than 10%) and the high maneuvering section(load variation was more than 10%).Based on the mission segment division method,the standard loading spectrum plan counted statistics and established mission segment database as the compilation data foundation of the standard load spectrum.However,this division method is rather rough,and only the influence of load variation amplitude on the intermediate maneuvering flight process is considered in this mission segment division method,which fails to truly reflect the property of mission segment that should be related to the actual operation.After that,the United States proposed the aeroengine flight-by-flight spectrum and the modeling method of operation-related loading spectrum.However,due to the sensitivity and the technical blockade of western countries,there is no published literature on the study of aeroengine flight-by-flight spectrum.In the mid-1970s,the load data of turbojet,turboprop,turboshaft,and other engines were investigated,measured,and counted domestically.The flight loading spectrum of the second and third generation engines(WP6,WP7,AL31F,etc.) were measured.Many useful information about mission profile and mission mixing was obtained,and the loading spectrum statistical analysis software was developed.Furthermore,the prediction and compilation of aeroengine loading spectrum and the research and application of accelerated mission test technology were carried out combined with the aeroengine model development.In 2005,Song PC and Song YD first proposed an extraction method of maneuver-load mission segments.In their study,all maneuver-load mission segments were classified as‘‘mission segment”.And a maneuver-load mission profile was simulated based on their establishment of the mission segment database.In 2019,Lu Q proposed a division method of typical maneuver-load mission segment.In their method,five kinds of typical mission segments were divided according to whether the mission segment shape was consistent and whether the damage caused to the aeroengine by the duration and amount of the mission segment were close.Although the mission segment division results obtained by this method which is based on the load mathematical characteristics’analysis of the loading spectrum can reflect the fatigue damage information in some way,they do not give expression to the practical significance of the mission segments.Up to now,domestic aeroengine loading spectrum studies mostly adopt the mission profile as research unit.However,the load history of any single mission profile is very complex,and the representativeness of typical mission profiles is very limited.When the typical mission profile is used for load spectrum modeling or compilation,the confidence is far less than 50%.The typical profile method cannot accurately count the mathematical characteristics and damage characteristics of the loading spectrum,and it is difficult to consider the load randomness caused by the operation-related flight actions,which leads to the low accuracy of the modeling,compilation and prediction of the aeroengine loading spectrum.Reducing the research scope and taking the mission segment as the research unit can improve the accuracy of load characteristics analysis and consider the load randomness effectively.However,a method which can accurately and effectively divide the operation-related aeroengine loading spectrum mission segment has not been proposed in China.

This paper proposes a whole aeroengine loading spectrum mission segment division method based on flight action.The mission segment is defined as the process of aeroengine performing a complete flight action.The flight segments of aeroengine measured loading spectrum which represent the actual flight action were divided.Based on the flight segment division results,the mission segments of aeroengine rotor speed spectrum were divided.In addition,the speed spectrum mission segment division results corresponding to various flight tasks were counted and analyzed.The aeroengine loading spectrum mission segments obtained from this division method not only have typical load characteristics,but also have practical operation-related significance,which can provide an important basis for the life analysis of the whole aeroengine and the aeroengine components sensitive to flight maneuver (such as main shaft,large gearbox,mounting joint and so on).Additionally,based on the division of the mission segments of aeroengine rotor speed spectrum,the load characteristics statistical analysis of various mission segments can be carried out,and the modeling,compilation and prediction of aeroengine loading spectrum can be studied,which will provide an important basis for the research of aeroengine loading spectrum.

2.Division of aeroengine loading spectrum flight mission segment based on flight action

2.1.Summary of basic flight actions and identification parameters

According to the aircraft flight training syllabus and flight teaching model,16 basic flight actions were summarized in this paper,including uniform flat flight,accelerated flat flight,decelerated flat flight,climbing,jumping,gliding,dive,horizontal left turn,horizontal right turn,horizontal roll,vertical roll,airplane pitching,ascending left turn,ascending right turn,descending left turn,descending right turn.Additionally,by considering what could be obtained from the finite flight loading spectrum parameters,6 flight characteristic parameters which could describe the 16 basic flight actions were summarized and determined in this paper as well,which were barometric altitude,barometric altitude change rate,velocity,path angle,bank angle and pitch angle respectively.By analyzing the flight characteristic parameters’ variation rule during aircraft completing different basic flight actions,and combining with a large number of actual flight data for verification,the variation rule of the 6 flight characteristic parameters corresponding to the 16 basic flight actions is summarized as shown in Table 1.

As shown in Table 1,the sign‘‘↑”indicates an increase,the sign ‘‘↓”indicates a decrease,the sign ‘‘≈” indicates basically unchanged.

2.2.Preprocessing of measured aeroengine loading spectrum

In this study,the flight mission segment division was based on the measured loading spectrum of five flight characteristic parameters,namely barometric altitude,velocity,path angle,bank angle and pitch angle.The first step of preprocessing was to filter the five flight parameters’ loading spectrum using rain flow filtering method.

Screen the peak-valley values of each parameter’s loading spectrum successively.Judging from the first peak-valley point,whether the rise or fall of the adjacent peak-valley point met the set threshold value.Keep points that were less than the threshold and remove those that were greater than the threshold value.Judge whether the value of the last point and the first point of the rain flow filtering spectrum is the same.If different,add a point with the same value of the original loading spectrum’s last point to get the initial rain flow filtering spectrum.Obtain the final rain flow filtering spectrum by adding some points of the original load spectrum.And the added points satisfied that the ones added on the ascending side were only allowed to rise,and the ones added on the descending side were only allowed to fall.The rain flow filtering threshold was set according to the formula:

where Δ% is the rain flow filtering threshold,andis the maximum amplitude in load history,is the minimum amplitude in load history.

The takeoff segment and landing segment in mission profile were divided by the barometric altitude and Mach number loading spectrum.The time points at which the Mach number and barometric altitude reached the maximum value for the first time and began to descend from the maximum value were determined respectively at first.Then the smaller time value of the two points was defined as the separation point of the takeoff segment and intermediate maneuver flight segment.Similarly,determine the time points at which the Mach number and barometric altitude began to decrease from a certain value and did not rise obviously.Define the larger time value of the two points as the separation point of the landing segment and intermediate maneuver flight segment.After the division of the takeoff segment and landing segment,by defining the time point with no significant change in altitude as the separation point of the ground taxiing segment in the takeoff segment,the takeoff segment was further subdivided into the ground taxiing segment and the takeoff climbing segment using the barometric altitude loading spectrum.In the same way,the landing segment was subdivided into the descent landing segment and the ground taxiing segment.Fig.1 shows the division results of the takeoff segment and landing segment in a measured loading spectrum mission profile.

Fig.1 Division of takeoff segment and landing segment in a measured loading spectrum mission profile.

2.3.Division of measured loading spectrum flight mission segment

After preprocessing,the flight mission segments representing the basic flight actions were divided by programming according to Table 1.Fig.2 shows the basic flight mission segment division result of a measured loading spectrum mission profile without ground taxiing segment.

The meanings of the marks which represent the flight mission segments are shown in Table 2.

Table 1 Summary of basic flight actions and identification parameters.

Table 2 Mark of flight mission segment.

Table 3 Rotor speed mission segment division result of air-to-surface stitched profile.

Based on the division result of flight mission segment representing basic flight actions,the complex flight action flight mission segment composed of basic flight actions could be furtherdivided by considering the cumulative variation and range of flight parameters (such as barometric altitude,path angle,bank angle) and judging the composition structure and time sequence of basic flight actions.For example,if the path angle of a horizontal turn varies by 360° accumulatively,it can be judged that the turn is a hover.If the path angle of an ascending turn changes 180°accumulatively,the action can be judged as a combat turn.If an action of a section is composed of two actions,one is roll and the bank angle changes 180°accumulatively,the other is descending and the path angle changes 180°rapidly,then it can be judged that the action of this section is half roll back.If a certain movement is composed of rising and then falling,and the path angle rapidly changes 360° at the same time,it can be judged that the movement is a somersault,etc.Using this method to analyze the basic flight mission segment division results given in Fig.2,the complex flight mission segments in the intermediate maneuver flight segment can be obtained,including horizontal turn 90°,horizontal turn 180°,horizontal turn 200°,horizontal turn 270°,descending turn 180°,combat turn,turning dive and so on.

Fig.2 Division of flight mission segment in a measured loading spectrum mission profile.

In addition,different-type measured loading spectrum flight mission profile data were brought into the division method for the division and analysis of flight mission segments.The division results showed that the method realized complete recognition of basic flight mission segments,that is,no data points in the mission profile could not be recognized as basic flight mission segment.

3.Division of aeroengine rotor speed spectrum mission segment

3.1.Selection of mission profile and flight mission segment division of selected mission profile

According to the clustering method of typical flight mission profiles in reference,five typical flight mission profiles of an aeroengine,high-altitude cruising profile,medium-altitude cruising profile,air-to-surface profile,throttle level profile and air-to-air profile,were selected to divide the loading spectrum mission segments.Cruising profile refers to the profile where the aircraft cruises after taking off and entering the predetermined route,and the aircraft lands after cruising.When the aircraft cruises,the flight state tends to be stable,and the flight altitude,speed and Mach number only change in the takeoff and landing segment.The high-altitude cruising profiles refer to the profiles where the aircraft cruises at an altitude of more than 10000 m,and the medium-altitude cruising profiles refer to the profiles where the aircraft cruises at an altitude of about 7000 m.Throttle lever profile refers to the profile where the aircraft performs many maneuvers and there is no afterburner in the intermediate maneuvering flight,that is,the duration time of the throttle lever rotation angle greater than 90 ° in the intermediate maneuvering phase is 0.Air-toair profile is a kind of flight mission profile in which the aircraft performs a large number of maneuvers during the maneuvering flight segment,and the flight altitude,flight Mach number,rotation speed and normal overload all have great fluctuations.Air-to-surface profile is a kind of flight mission profile used by combat aircraft to attack enemy land and sea targets with a variety of airborne weapons in order to achieve air support,neutralizing air defense operations,strategic air interception and strategic bombing.Its flight history can be summarized as follows:firstly,it rises to high altitude quickly in a short time,then it dives from high altitude quickly,and completes a series of maneuvers after reaching a certain altitude,and finally lands.

Three profiles were extracted from each typical mission profile and stitched.Use the method described in Section 2 to divide flight mission segments in the three stitched spectrums.According to the division results,various flight actions and missions in various profiles were obtained.

As shown in Figs.3 and 4,the flight mission segment division results of high-altitude cruising stitched profile and medium-altitude cruising stitched profile are shown respectively.It can be seen that the flight actions in the intermediate maneuver flight segment of these two types of cruising profiles are simple,mainly including uniform flat flight,slow horizontal turn,horizontal roll and other basic flight actions.

Fig.5 shows the flight mission segment division results of an air-to-surface stitched profile.It can be seen that the basic flight actions in the intermediate maneuver flight segment of the air-to-surface section mainly include gliding,horizontal turn,descending turn,dive and ascending turn,etc.By analyzing various basic flight actions and complex flight actions in the air-to-surface stitched profile with the method in Section 2.3,it can be obtained that there are 6 typical intermediate maneuver flight missions in the three air-to-surface profiles,which are air-to-surface dive,horizontal turn 180°,horizontal turn 540°,gliding,descending turn 180° with a change in altitude of 1500 m and then ascending turn 180°,turning dive 180°with a change in altitude of 1500 m and then ascending turn 180°,respectively.

Fig.3 Division of flight mission segment in a high-altitude cruising profile.

Fig.4 Division of flight mission segment in a medium-altitude cruising profile.

Fig.5 Division of flight mission segment in an air-to-surface stitched profile.

Similarly,as shown in Fig.6,there are 5 typical intermediate maneuver flight missions in the three throttle lever profiles,which are horizontal turn 180 °,hover,descending turn 180°with a change in altitude of 1000 m and then ascending turn 180°,descending turn 180° with a change in altitude of 2000 m and then ascending turn 180°,turning dive 180° with a change in altitude of 2000 m and then ascending turn 180°,respectively.

Fig.6 Division of flight mission segment in a throttle level stitched profile.

As shown in Fig.7,there are 12 typical intermediate maneuver flight missions in the three air-to-air profiles,which are horizontal turn 180 °,hover,detour,descending turn 180°with a change in altitude of 1000 m and then ascending turn 180°,descending turn 180° with a change in altitude of 2000 m and then ascending turn 180°,turning dive 180° with a change in altitude of 2000 m and then ascending turn 180°,rolling dive with a change in altitude of 2000 m and then climbing,rolling dive with a change in altitude of 2000 m and then ascending turn,W mission with a change in altitude of 2000 m,turning dive 2000 and ascending turn 2500 m and then turning dive 500 m,ascending turn 1000 m and turning dive 3000 m and then ascending turn 2000 m,respectively.

Fig.7 Division of flight mission segment in an air-to-air stitched profile.

3.2.Division of rotor speed mission segment

According to the method introduced in Section 2.2.1,filter the speed stitched spectrums of the three typical mission profiles firstly.Based on the flight mission segment division and analysis results obtained in Section 3.1,the speed mission segments corresponding to various typical intermediate maneuver flight actions were divided.

The black solid line in Fig.8 represents the intermediate maneuver segment speed stitched filtering spectrums of the medium-altitude cruising profile.The blue dotted line in Fig.9 represents the intermediate maneuver segment speed stitched filtering spectrums the high-altitude cruising profile.According to the flight mission segment division results shown in Figs.3 and 4,it can be seen that in the cruising profiles when the aircraft is flying at a constant speed or turning at a slow horizontal speed,the aeroengine rotor speed is basically unchanged,and a small amount of speed fluctuation is random fluctuation.In addition,according to the comparison between the high-altitude and the medium-altitude cruising rotor speed in Figs.8 and 9,the altitude has little effect on the cruising rotor speed,mainly because the flight actions in the cruising profiles are simple and the flight state is very stable.For the complicated maneuvering profiles,with the increase of flight altitude,the air density decreases and the air intake of aeroengine decreases.When the aeroengine performs high maneuvering actions,the rotor speed may be different due to the change of air intake.

Fig.8 Intermediate maneuver segment speed stitched filtering spectrums of the medium-altitude cruising profile.

Fig.9 Intermediate maneuver segment speed stitched filtering spectrums of the high-altitude cruising profile.

Table 3 shows the six division results of rotor speed mission segment in air-to-surface profile.It can be seen that the extracted speed mission segments corresponding to each kind of flight mission are similar in shape,which means that rotor speed basically has the same or similar variation rules while doing the same flight mission.

As for the flight mission,descending turn 180° with a change in altitude of 1500 m and then ascending turn 180°,the two extracted speed mission segments of this flight mission are slightly different in morphology,but their overall variation trend is the same.The second mission segment has more small loads,which may be caused by the filtering threshold selection of speed spectrum.The consistent filtering threshold of the three segments leads to different filtering effects,and the number of small loads of the speed profile with larger load fluctuation is more after filtering.

Table 4 shows the five division results of rotor speed mission segment in throttle level profile.By comparing with the results in Table 3,it can be seen that the speed segments for the same flight mission in two kinds of profiles,such as horizontal turn 180°,have roughly the same shape.Furthermore,by comparing the two flight missions,descending turn 180°then ascending turn 180°and turning dive 180°then ascending turn 180°,it can be seen that the speed segment is more slender when the altitude varies greatly,which means that the change in speed is more drastic when completing similar missions with greater altitude variation.

Table 5 shows the twelve division results of rotor speed mission segment in air-to-air profile.By comparing with the results in Tables 3 and 4,it can be seen that the speed segments for the same flight mission in different kinds of profiles have roughly the same shape.In addition,by comparing the flight missions with different turning angles,it can be seen that the speed segment is simpler when the turning angle is smaller,which means that the change in aeroengine rotor speed is more drastic when completing similar missions with larger turning angle.

Table 4 Rotor speed mission segment division result of throttle level stitched profile.

Table 5 Rotor speed mission segment division result of air-to-air stitched profile.

Table 5 (continued)

3.3.Analysis and summary of the rotor speed mission segment division results

According to the flight mission segment division results of the five typical mission profiles,the rotor speed mission segments division results were obtained.The research results are as follows:

(1) When the aircraft is flying at a constant speed or turning at a slow horizontal speed,the aeroengine speed is basically unchanged;

(2) There are obvious different characteristics between the rotor speed mission segments representing different flight actions;

(3) The shapes and characteristics of speed mission segments representing the same flight action are similar,but the selection of speed filtering value has some impacts on its characteristics;

(4) In several kinds of mission profiles selected in this paper,the rotor speed mission segments representing the same flight action has roughly the same shape and characteristics;

(5) The rotor speed mission segments obtained by division has characteristics related to actual flight actions and actual flight operations.When the altitude change range or the angle change range is different,the characteristics of the speed mission segments representing the same kind of flight action are also different.When the aeroengine completes the same kind of flight mission with greater altitude/ angle change,the speed changes more intensely,the shape of the speed mission segment is slenderer,and the characteristics are more complex.

The division and analysis of the loading spectrum mission segment related to flight maneuver can provide an important basis for the fatigue life analysis of the main shaft,large gearbox and other aeroengine components which are sensitive to flight maneuver.Moreover,based on the speed mission segment division results of the whole aeroengine loading spectrum,the statistical analysis and research on the load characteristics of various mission segments can be carried out.Taking the mission segments as each unit,the modeling,compilation and prediction of the whole aeroengine loading spectrum can be studied,so as to study the whole aeroenginelife.Therefore,the division results of the aeroengine loading spectrum speed mission segment obtained in this paper are of great significance to the strength analysis of the whole aeroengine and its components(such as the main shaft,large gearbox and installation section),the compilation of the whole aeroengine loading spectrum and the prediction of the whole aeroengine design loading spectrum.

4.Conclusions

16 basic flight actions and 6 identification flight parameters are summarized in this paper.By analyzing the variation rule of identification parameters,the division of flight mission segment representing basic flight action is realized by programming.The division method is accurate and effective,and the division results are clear and comprehensive.

This paper presents a method to divide the mission segments of complex flight actions.Based on the flight mission segment division results of basic flight actions,complex flight actions are obtained by considering the variation of flight parameters and judging the composition of basic flight actions.By dividing and analyzing the flight mission segments in middle maneuverable flight segments of five kinds of typical mission profiles,it is proved that the division method is universal,simple and accurate.

A method of dividing the whole aeroengine rotor speed mission segment based on flight mission segment is proposed in this paper.Every kind of rotor speed mission segment is corresponding to every kind of typical intermediate maneuver flight mission.By dividing and analyzing the measured loading spectrum data of five kinds of typical mission profiles,it can be seen that the speed mission segments representing the same action are similar in shape,and the speed mission segments representing different actions are obviously different.The shapes and characteristics of the speed mission segments are different according to the altitude change range or angle change range,which reflects the flight-operation-related and flight-actionrelated characteristics of the speed mission segments,and proves the effectiveness and accuracy of the division method.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The author would like to express her thanks and appreciation to the anonymous reviewers whose substantial and constructive comment significantly improved the paper.This study was co-supported by the Foundation of graduate innovation base of Nanjing University of Aeronautics and Astronautics,China (Nos.kfjj20190206 and kfjj20200218) and the National Science and Technology Major Project,China (No.J2019-V-0009-0103).Especially,Thank Ding Junjie for his contribution to this study.