A flutter prediction method using a new stability criterion, which is evaluated directly from the coefficients of ARMA model identified from sampled data, is proposed. The method is, therefore, suitable for using with the system identification procedures. The analysis using a two-dimensional wing model shows that the new parameter decreases almost linearly toward zero as the dynamic pressure increases. Moreover, the parameter can be estimated with a small deviation around its true value. As the result of these properties, the proposed method has a good performance for the flutter prediction in comparison with the existing techniques applicable to the discrete-time systems. An analytical consideration reveals that the parameter is approximately equivalent to the flutter margin introduced by Zimmerman and Weissenburger, so that the proposed parameter can be expressed approximately as a quadratic function of dynamic pressure.
The guidance force, which guides an aircraft on the desired trajectory, consists of two parts. One is the force necessary for programming motion and the other is the force to eliminate the guidance errors, which depends significantly on the magnitude of the guidance error correction gains, that is, guidance gains. In this paper, using small perturbation theory, the gains are computed as the functions of the parameters of the dynamics for the autopilot. Finally the simulation results show the effectiveness of the guidance gains computed in this paper.
Hypersonic projectiles, whose speed was beyond the Chapman-Jouguet (C-J) detonation speed, were fired into stoichiometric hydrogen-oxygen premixed gases. The flowfield around the projectile was visualized using a gated CCD camera. Around the projectile, a steady-state detonation wave was generated. With respect to the flow Mach number behind the wave front, the whole detonation-wave was partitioned into four parts; (i) strong overdriven detonation wave, (ii) weak overdriven detonation wave, (iii) quasi C-J detonation wave, and (iv) C-J detonation wave, It has been found that a rarefaction wave delivered from the projectile shoulder has a significant effect on the structure of the detonation wave.
This paper describes the design optimization of a wing for supersonic transport (SST) using Multi-Objective Genetic Algorithm (MOGA). The objective functions are to minimize the drag for transonic cruise, the drag for supersonic cruise and the bending moment at the wing root for supersonic cruise. The wing shape is defined by planform and warp shapes in total of 66 design variables. An Euler code is used to evaluate supersonic performance, and a potential code is used to evaluate transonic performance. To reduce the enormous total calculation time, the CFD calculations are parallelized on NEC SX-4 (32 PE) at Computer Center of Tohoku University. The Pareto optimal solutions are obtained in the three dimensional objective function space by the present approach. The resulting Pareto solutions identify that arrow wing configuration is one of the important factors for the wing performance.
Driver gas contamination in high-enthalpy shock tunnels has been detected using a gasdynamical device composed of a duct and a wedge. The detection technique was developed in the T 5 shock tunnel, and a detector has been newly designed for use in the HEK and HIEST shock tunnels with some modifications. Driver gas in low concentration is satisfactorily detected at the test sections of both shock tunnels. The detector allows the flow visualization of duct internal flow, and a sequence of Schlieren pictures during a shot gives a better understanding of unsteady duct choking phenomena. Futhermore, the useful test time is compared among three shock tunnels and the optimum length-to-diameter ratio of shock tube is discussed.