Modelling and imulation of the fuel tranfer for CoG poition control in an Aircraft J. M. GIRON-SIERRA., J.F. JIMENEZ, C. C. INSAURRALDE, M. A. SEMINARIO, B. HIGHAM (), R. A. MELVILLE () Dep. Arquitectura de Computadore y Automática Univeridad Complutene de Madrid Av. Complutene S/N, 8 Madrid, Spain SPAIN () Fuel Sytem Engineer - Reearch Airbu UK New Filton Houe, Filton, Britol BS99 7AR UNITED KINGDOM Abtract: - Fuel tranfer are ued in aircraft for the control of the COG poition. Thi i eential for tability and operational performance. Thi paper deal with the modelling and imulation of the fuel tranfer in a generic airplane. The model i etablihed uing Simulink, for an eay adaptation to pecific airplane cae. Simulation are ueful to tudy COG control trategie, and operational reaction to certain contingencie. The paper focu on the COG control in the aeronautical technical context, keeping it inide a region of interet. Key-Word: - Avionic, Aircraft Fuel Sytem, Fuel Ditribution Control, Aircraft tability, CoG Control Introduction Aircraft ue fuel for everal purpoe. It i not only to keep the engine running. A a fluid, the fuel can be moved to optimie the COG poition, or ued for engine cooling. There i a pecific on-board control ytem in charge of fuel management. Thi paper decribe part of an European Community Reearch Project, denoted Smartfuel. The objective of thi project i to develop a new fuel management ytem, baed on the ue of a fieldbu and mart component. The conortium for the project i formed by four companie providing fuel ytem component, two companie making aircraft and which can be uer of the new ytem, and three univeritie providing cientific upport. The purpoe of thi paper i to preent a new imulation environment, for the tudy of fuel management operation and control, focuing on the optimiation of the COG poition. The imulation i baed on a computer model of the fuel management ytem. Expert in aircraft development, partner of the reearch project, gave u the required data for modelling. There are ome book with chapter on aircraft ubytem, including fuel management ytem [][]. Other book and article deal with the effect of the COG on the aircraft performance. [-6]. The order to follow in thi paper i firt to decribe the reearch objective and the fuel ytem, then to preent a computer model of the ytem, then to ue the model for imulation purpoe, focuing on the COG poition control. Finally ome concluion are drawn. Objective of the Reearch The engineer of aircraft fuel management ytem, partner of the project, aked for a new imulation environment. Part of the need i connected with new fuel component and new fuel control trategie, for aircraft performance improvement. Another part i related with what-if tudie. For intance what to do when a flight i reconfigured, or when an aircraft balancing problem appear. In thee cae, ome of the function hould be aumed by the on-board control, and other by the human and/or the external flight upport environment (from airport, etc.). Simulation are baed on model. Conequently, once imulation requirement have been etablihed, the firt effort hould be driven to develop an adequate model of the fuel management ytem. The model hould operate according with the logic of the on-board control ytem, and hould offer information of the variable of interet: fuel quantity and ditribution among tank, COG poition, and tatu of the component. For evident tability reaon, the COG poition mut be kept into a zone. Thi poition i alo important for fuel conumption along the flight.
J B C H N D E Thu, the objective of the reearch are to develop a model, and to make a imulation environment for control and operation tudie, with main focu on COG poition. A generic airplane will be conidered. The model hould be eaily modifiable, to be able to conider more pecific airplane cae. The Fuel Management Sytem Figure how a chematic of a fuel management ytem of a generic airplane. There are three fuel tank in each wing, and one trim tank at the tail. There are enor to gauge the fuel quantity in each tank. The figure $ how only one enor per tank. Thi i a implified view of the ytem. In reality, a many a 6 fuel gauge enor can be ued in a tank, due to the geometry of the tank inide the wing. However, data concentrator are ued, o a et of enor can be een a one enor. The fuel characteritic do change along the flight, o meaurement hould be corrected in real time. Collector Collector Cell Cell P P P P K L M G A F Right Feed Tank Left Feed Tank Right Mid Tank Left Mid Tank Right Outer Tank Left Outer Tank O Trim Tank trim angle. The airplane drag depend on thi angle, and hould be optimied to reach longer ditance. An important operation of the fuel management ytem i refuelling. It hould be fat and afe. Model of the Fuel Management Sytem From the control point of view, the fuel management ytem i a hybrid control ytem. There i a combination of continuou variable, uch fuel quantity, and dicrete variable, due to the ue of on/off valve and pump. The computer model of the fuel management ytem will be developed uing Matlab-Simulink. It offer everal important advantage for the project. It can be eaily edited, o both component characteritic and interaction can be modified, to conider pecific airplane. Simulink ue icon to repreent abtract component. For intance a DC motor can be repreented with an icon correponding to the tranfer function of the motor. The icon are drag into an editing window, and can be connected with arrow following the cacade of caue and effect. Model are imilar to block diagram. There are everal tep in the model development. Firt, modelling of component uing Simulink icon. Second, connection of component. The logic of the ytem (the ytem intelligence) i expreed in part by the component, which can be of logical nature, and in part by the interconnection tructure.. Model of Component Tank are modelled in a imple way. Figure how the Simulink model, and figure how thi model a an icon. In In fig., chematic of the fuel ytem in a generic airplane On/off valve are ued to control the fuel tranfer between tank. Since the wing are inclined, imple gravity tranfer can be done. Notice that the ytem ha alo pump. The pump enure certain function, not only tranfer; for intance, engine cooling. Notice that the ytem embodie ome fuel path redundancie, to guarantee engine upply even when there are component failure. Tranfer between wing can be done. Likewie, tranfer from and to the tail tank can be done. Thi later function i important to obtain a good airplane m Initial m Out In In fig., Tank model
fig., Icon for the right feed tank The engine i modelled a depicted in figure. Figure 5 i the icon for thi model In In >= Relational Operator fc Conumption rate U U(E) E Selector integrator fig., Engine model Out fig.7, Icon for the middle to aft tank pump The aft to fed tank valve i modelled a depicted in figure 8. Thi valve i very important to control the CoG poition. So, it logic i fairly complex. Figure 9 how the icon for thi valve. In In Relay In rf rf8 Switch6 rf rf rf rf Switch7 Switch5 Product rf pfr rf9 pfr rf ctrl rf Multiport Switch In max/min valve opening Switch Out int Out Product attitude head /(f+) qrt rho cte Aircraft attitude head frictional factor Math Function fuel denity fig.8, Model of the aft to fed tank valve. Engine R fig.5, Engine icon Notice that the engine model include ome logic to repreent different conume rate along the flight. Each pump ha a different model ince the particular logic i embodied in the model. For intance figure 6 how the model for the pump linking the middle tank with the aft tank. Figure 7 how the icon for thi model. In rf8 In >= Relational Operator5 pfr rf6 R& R& Controler Trim/fed valve fig.9, Valve icon The grey ymbol in figure 8 repreent a poitional valve. Conventional valve are on/off, however the opening of poitional valve can be controlled in a range from cloed to open. Figure how the model of the controller aociated with the aft to fed tank valve. Figure how the icon of the controller. In top Relay Switch Product Switch int Out In5 Trim tank tate du/dt d rf5 rf5 In em MATLAB Function Control.m Derivative Gain Saturation p Gain Product Out rf Switch control fig.6, Model of the middle to aft tank pump cte In6 Switch i Integrator Gain fig., Model of the controller.
controler fig., Controller icon Some Matlab code ha been developed a Simulink function for the etimation of the CoG poition. Figure how the icon for the CoG poition etimator. 5 Control of the COG Poition The imulation environment depicted in figure i ued to tudy the control of the CoG poition along a typical flight. Figure how the tank weight evolution along the different phae of a typical flight. kg.5 x.5 trim tank fed tank mid tank outer tank.5 -.5.5.5.5 fig., Tank weight evolution during a typical flight fig., CoG poition etimator. Model of the Fuel Management Sytem Once the model of the component have been developed, their icon can be interconected to build a complete model of the fuel management ytem. Figure how a general view of the Simulink model. AIRBUS Engine R AIRBUS Engine L ROT RE.5 ->.5 -> 57.5 LE LOT Right Feed Tank 57.5 Left Feed Tank pump / pump /.5 Right mid tank.5 Left Mid Tank pump ROT/ pump ROT/RTF controller R& R& Right outer tank R_mid/trim pump 789.5 L_mid/trim pump Controler 789.5 Left outer tank Trim/fed valve control valve opening R& TGT -. Trim tank flight Scheduler right tank Right To Workpace R wing tank CoG Left tank Left To Workpace left wing tank fig., Complete model of fuel management ytem. Each icon can be edited to change it parameter. For intance a tank can be edited to have kg of fuel at the beginning of flight. Alo the number of tank can be modified, etc. Along the flight there are everal tranfer, to enure engine upply and a good COG poition. Here i a brief decription of the fuel ytem work during the main phae of the flight: During the take off, the engine conumption i the highet, thi correpond to the line coming downward from the top right of figure. Thi i the content of the fed tank. During thi hort period no fuel tranfer take place among the tank Once the aircraft ha reached a predetermined flight level, tranfer form mid tank to aft tank take place. The content of the aft tank increae a hown by the line coming upward from the bottom left of the figure. The line tarting from near.5 and coming downward i the content of the mid tank. The tranfer continue during the cruie until the aft tank reache a weight of kg. A can be een alo in figure Later during the flight when the fed tank reach a minimum level ( kg) fuel i tranferred from the mid to the fed tank. Notice that before landing there i a line coming downward from kg to kg. Thi i the content of the aft tank. The line ha two part. The firt part decribe the controlled tranfer of fuel from the aft to the fed tank to aure that CoG i alway inide it ecurity region. The econd part happen jut before landing. It i neceary to tranfer the remaining fuel in the aft tank a fat a poible to the fed tank. No
fuel hould remain in the aft tank during landing. Fuel conumption and tranfer caue a motion of the COG. It i important to keep the COG inide a zone. In the airplane engineering context, thi problem i analyzed uing a pecial graphical repreentation. The CoG poition i expreed a a percentage of the Mean Aerodynamic chord (MAC). Depending on the pecific aerodynamic of each aircraft, the CoG hould not urpa certain limit which are alo expreed a a percentage of the MAC. Thee limit depend alo on the total aircraft weight and thu, they change during the flight a fuel i conumed. In conequence, a key experiment to be done in the imulation environment i to reproduce a complete flight and ee the evolution of the COG poition. Figure 5 how the reult. kg. x 5.8.6. with the oberved behaviour on real flight. From the many remark the expert made, it eem that the imulation environment i of clear profeional interet. In the future, a friendly human interface will be developed, for experiment pecification. Alo, certain pecific airplane cae will be tudied, and the imulation ytem will be improved. Acknowledgment: The author thank to the European Community upport, through the Reearch Project Smartfuel. Likewie, the author thank the collaboration of the reearch partner Reference: [] D.A. Lombardo, Advanced Aircraft Sytem, McGraw-Hill, 99 [] I. Moir, A. Seabridge, Aircraft Sytem, AIAA, [] W.A. Mair, D.L. Birdall, Aircraft Performance, Cambridge Univerity Pre, 996 [] G.J.J. Ruijgrok, Element of Airplane Performance, Delft Univerity Pre, 99 [5] N.X. Vihn, Aircraft Performance, Cambridge Univerity Pre, 99 [6] J.W. Burrow, Fuel Optimal Trajectory Computation, AIAA 8-8, Vol.9, No., April, 98. 5 6 7 % MAC Figure 5 Evolution of the CoG during a typical flight. In figure 5 the CoG limit are repreented by an external perimeter formed with traight tretche. The CoG evolution i a curve that i alway inide the perimeter (a hould be). 7 Concluion In thi paper a new control-oriented model of the fuel management ytem of a generic airplane ha been developed. With the model everal imulation can be applied, for the tudy of COG control trategie with new component, and for the what-if analyi of operational contingencie. The model i developed with Simulink, o it can be eaily modified to tudy pecific airplane cae. Simulation have been run under the uperviion of aircraft maker, and they howed good agreement