Estimation Of Stability Derivatives Research Articles

Estimation of Stability Derivatives in Newtonian Limit for Oscillating Cone

Stability derivatives in Newtonian limit for an oscillating cone are obtained. Stiffness derivative decreases with pivot position for the entire range of cone angles. For cone angles in the range 20 to 30 degrees there is substantial increase in the stiffness derivative. Damping derivative decreases with pivot position for various cone angles and attains a minima at h = 0.75 and then again with increase in pivot position there is non-linear increment in damping derivatives. There is considerable change in the magnitude, for higher cone angles in the range of 20 degrees and above as the centre of pressure has further moved towards the trailing edge of the cone at pivot position around h = 0.88. Stiffness derivative increases with cone angle for various pivot positions. Damping derivative with cone angle for various fixed pivot positions is seen to increase linearly with cone angle, it is also observed that this trend of linear increment tend to become non-linear for cone angles in the range 20 degrees and beyond. Damping derivative decreases with pivot position h = 0.8 for the entire range of cone angles, however, for pivot position h = 1.0, shows almost constant values up to cone angle of 20 degrees. For cone angle 30 degrees value of damping derivative coincides irrespective of pivot position being at h = 0.8 or 1.0 and this trend is attributed to the 3-D effect of the flow field.

Estimation of Stability Derivatives in Pitch for an Oscillating Wedge in Hypersonic Flow

A similitude has been obtained for an oscillating two-dimensional wedge in pitch with attached shock at high angle of incidence in hypersonic flow. A strip theory, in which flow at infinite span wise location is two dimensional and independent of each other is being used. Further this unites the similitude with piston theory to give one dimensional piston theory with large flow deflection. Closed form solution is obtained for stiffness and damping derivatives in pitch. The present theory is valid when the shock wave is attached with the nose of the wedge. With the increase in semi vertex angle of the wedge the stiffness and the damping derivatives are found to increase progressively, and with the increase in the Mach number both stiffness and damping derivatives are found to decrease then with increase in Mach number it becomes independent of Mach number. From the amalgamation of theory developed, we can evaluate the stiffness and damping derivatives for in pitch for a wide range of Mach numbers, for various pivot positions, and angle of attack. Significantly the same results are being validated with the analytical results of Liu and Hui [4] and Lighthill’s [3] theory for some cases.

Estimation of Stability Derivatives for a Planar Wedge in the Newtonian Limit

The present work contains an analytical method derived using Ghosh’s Hypersonic similitude to predict the aerodynamic stability derivatives of a Planar Wedge in the Newtonian limit. It uses the strip theory developed by Ghosh’s where span wise strips are independent of each other, to obtain the expressions for stiffness and damping derivatives in pitch for a planar wedge in the Newtonian limit. The present theory predicts the stability derivatives of a planar wedge for a wide range of geometrical and flow parameters. The knowledge of these stability derivatives is essential to freeze and arrive at the geometrical as well as the kinematic similarity parameters before we go for exhaustive computations and experimental studies. The present method predicts the stability derivatives in pitch for a planar wedge with remarkable computational ease, which is very handy at the design stage. The expressions derived for stability derivatives become exact in the Newtonian limit. It is found that stiffness derivative linearly varies with the pivot position. It is also observed that the centre of pressure moves towards the trailing edge and this shift is quite high at high angles of attack. Hence, this behavior could be utilized to stabilize the aerospace vehicle from the static stability point of view. In the case of damping derivative since the expression for the damping derivative is non-linear and the same has been reflected in the results. However, the behavior remains linear till angle of attack fifteen degrees, later the trend is non-linear.

Application of a Pendulum Support Test Rig for Aircraft Stability Derivative Estimation

This paper presents a novel technique for extracting longitudinal stability derivative information from an actively controlled wind-tunnel test model. The technique, designated as the pendulum support rig, uses a test model mounted inverted and suspended from the wind-tunnel roof via a supporting strut and a single-degree-of-freedom gimbal providing model motion in heave and forward translation. An additional single-degree-of-freedom gimbal connecting the model to the support strut was also used to allow model rotation in pitch. Overall, the technique was found to perform well at predicting the dominant longitudinal stability and control derivatives. This was assessed primarily against the results from an existing established technique obtained by an independent source and from results obtained by the author in a previous investigation, using a different technique.

Evaluation of a Three Degree of Freedom Test Rig for Stability Derivative Estimation

This paper details a quantitative investigation into a cost-effective, three degree-of-freedom test rig to determine aircraft static and dynamic stability derivatives. The technique used a specifically designed three degree-of-freedom gimbaled mechanism to connect an actively controlled model to a vertical support strut. The support strut was also mounted on a six-component piezoelectric balance to obtain aerodynamic force and moment data simultaneously with the model motion. With only minor modifications to the overall setup, a comprehensive set of static and dynamic stability derivatives were obtained which showed reasonable to good agreement with other, independently obtained, data.

223 複数のオブザーバによる航空機の安定微係数の推定(宇宙構造物・飛翔体の制御I)(OS 宇宙構造物・飛翔体の制御)

We consider estimation of stability derivatives of aircrafts from flight data. An estimation scheme which utilizes multiple observers is applied. The multiple observers are designed for representative models derived by rewriting the state equation of the system. Under a certain condition, the output signal is described by output estimates generated by the multiple observers. Using this property, the estimates can be computed from input and output data.

On-line aircraft state and stability derivative estimation using themodified-gain extended Kalman filter

A new on-line state and parameter identification algorithm called the modified-gain extended Kalman filter (MGEKF) is applied to the problem of on-line state estimation and identification of the stability derivatives of a F-111 type of vehicle. The conceptual basis for the MGEKF is the existence of a class of nonlinear functions that allow a universal linearization with respect to the measurement function. This class includes the problem of identification of linear systems. The previous single-output formulation is extended to a multioutput formulation where the only available measurements are acceleration and pitch rate, but not elevator deflection. The filter formulation includes a simplified Dryden wind gust model. The inclusion of the wind gust model results mainly in a slowed response in the estimation of the stability derivatives associated with the acceleration state; estimates of the stability derivatives associated with the pitch rate still respond very quickly. The accuracy of the acceleration stability derivatives depends upon the amplitude and frequency components of the persistently exciting dither signal.

Uses of parameter estimation in flight test

An overview of the experience gained at the NASA Dryden Flight Research Facility in aircraft parameter estimation is presented and the ways in which this experience is used in flight test are explained. Some of the reasons for the current importance of parameter estimation in most modern aircraft test programs are discussed, and three examples from projects underway at Dryden are used to illustrate how parameter estimation of stability derivatives can be integrated into a flight-test program.

Lateral dynamics of flight on a great circle.

The lateral stability of a hypersonic vehicle representative of a space shuttle or hypersonic transport is calculated at two lift coefficients at speeds up to parabolic. Linearized equations of motion are used and Newtonian Impact Theory is utilized for stability derivative estimation. The damping in the natural modes is very small or negative, the dominant motion being an extension of the conventional Dutch Roll mode. The mode is unstable for high subcircular speeds. Coupling of the roll-convergence and spiral modes occurs at about 40% of circular speed and after decoupling, some instability exists at supercircular speeds. A new undamped mode describing lateral position variation's found exactly. The results are not very sensitive to CL and approximations to the modes are discussed and compared with the numerical solutions.

Estimation of Stability Derivatives and Indices of Various Ship Forms, and Comparison With Experimental Results2

The analytical method of reference [1]3 for estimating stability derivatives, and hence stability on course, which combines Albring's empirical modifications of simplified flow theory with low aspect-ratio wing theory, is extended to take into consideration the effects on course stability of higher aspect-ratio fins as well. The method, which has been applied in the earlier report to a family of eight hulls of 0.5 block coefficient, is tested further by application to eight Series 60 forms differing in block coefficient as well as in beam, draft, and displacement—with and without rudders; to an extreme vee modification of a Series 60 model; and to three other forms—a Mariner Class model, a destroyer, and a hopper dredge. Comparison with experimental results shows that the values of stability derivatives and indices determined by the analytical method are of the right orders of magnitude and indicate correct trends. Application to a variety of ship forms has demonstrated that the method can predict relative effects of changes in the geometry of a ship form, as well as the effects of changes in skeg and rudder area.