Store Ejection Simulations on a Rafale Aircraft

摘要

Rafale is a multirole fighter aircraft. Among a wide range of capabilities Rafale can undertake ground attacks and ensure air supremacy. These missions require weapons that vary from cruise missiles to long range air to air missiles or guided bombs. The firing envelope of stores includes high-G manoeuvres and can be cleared thanks to the Ejector Release Unit (ERU) performance. During the firing sequence, pressurized gas is expanded into the ERU pistons which push the weapon downwards away from the aircraft for a wide range of flight conditions (mach, altitude, load factor etc.). The expelling phase is extremely short, around 100 ms, and the thrust applied to the bomb is huge enough to move it constantly away from the aircraft. The effects on the store kinematics (pitch and roll rates) and on the aircraft attitudes are significant. Ejections also induce distortions and constraints in the aircraft structure that can be sizing cases. Therefore numerous and expensive flight and ground tests are required to integrate new under-wing stores or to extend the firing envelope. The development of suitable models giving an accurate prediction of the ejections effects is essential to reduce the number of tests points, prepare suitable test instrumentation and extrapolate the non tested flight points and configurations in order to clear the foreseen firing envelope. The main difficulties are to quantify the store roll and pitch rates taking into account the wing aeroelasticity influence on the ejection efficiency. The present paper describes the main physical parameters driving the ejection: the rigid body motion and the elastic distortion of the plane, the rigid motion of the store, the non-linear effects (contacts, friction) at the store-ejector interface, the unsteady aeroelasticity and finally the ejection thrust. In this paper, the models implemented to reproduce these phenomena are described in the scope of the Rafale project. Modal analysis is used to reduce the models sizes and efficiently perform time simulations. Finite elements models of the store and the aircraft are coupled to a thermodynamic model of the ejector. An aerodynamic field is applied on the aircraft and on the store to take into account rigid body motion aerodynamics effects and aircraft unsteady aeroelasticity. Non-linear effects such as friction and contacts are taken into account through specific routines. Ground and flight ejection tests as well as a ground vibration test performed to validate the models are also presented. The structural and thermodynamic models updating methodology based on the ground tests will be described. The improvements of each modelling step (aeroelasticity, contact, friction etc.) will be highlighted. Based on updated aircraft, store and ERU models, in-flight ejections are computed and compared to flight test data. The computations allow to accurately predict the store kinematics (roll, pitch rates and vertical speed) as well as the aircraft attitude and internal constraints when firing stores while cruising or during a manoeuvre. The suitability of the presented approach has been demonstrated in the scope of the Rafale project.