This paper presents a simulation of wind effects on a flying unmanned aerial vehicle (UAV) and a simulation of wind measurements taken from an airborne UAV. The wind acts as a disturbance on the flying UAV by altering its attitude and velocity. Therefore, the airborne measurement should be taken dynamically to reflect the instantaneous motion of a vehicle that is affected by wind. In order to understand and validate the algorithm that measures wind and the interaction between wind and the UAV, an investigation using simulation is extremely valuable. Considering real applications, this study implements modeling of the interaction between wind and a UAV from the perspective of the UAV's onboard sensors, and a wind measurement formula is clarified based on the established model. The results of the simulation confirm that, if an accurate measurements for angle-of-attack and sideslip are available, the wind can be accurately measured regardless of the control scheme used in flight.
We designed a rotary valve for a multi-cylinder pulse detonation rocket engine (PDRE), and constructed a greatly simplified rotary-valved four-cylinder PDRE (inner diameter and length of detonation tube: 37 mm and 1,600 mm, respectively). The partial-fill effect of a propellant in a multi-cylinder PDRE under high-frequency operation was investigated. The suctioned-air fill fraction was estimated using the model of Sato et al., which is a semiempirical formula for the partial-fill effect of a propellant based on two-dimensional numerical analysis [Sato et al., Journal of Propulsion and Power, Vol. 22, No. 1, 2006, pp. 64–69]. A maximum propellant-based specific impulse of 251 s and a time-averaged thrust of 242 N were achieved using C2H4-O2 as the propellant and an operation frequency of 129.6 Hz/tube (fill pressure: 1 atm). The maximum operation frequency was 160.3 Hz/tube (641.2 Hz/all tubes).
The aerodynamic characteristics of a ski jumper model in various postures are analyzed using a commercial computational fluid dynamics tool. The purpose of this study is to understand the aerodynamic characteristics of ski jumping. The range of flying postures for ski jumpers is determined as widely as possible to simulate the optimal flight position of ski jumpers. The computational results are in good agreement with experimental results. The aerodynamic characteristics are influenced by the hip and body angles of the ski jumper model during the flight. The lift-to-drag ratio of ski jumpers is increased as hip angle increases. However, as the hip angle increases, the region of the angle of attack becomes restricted for stable flight. The augmentation of the body angle can enhance the most favorable angle of attack, because the body angle is likely to result in a cambered airfoil. In conclusion, the ski jumper should maintain a high hip angle with an angle of attack that stabilizes the flight condition, to improve flight distance.
The angular and energy dependence of the sputtering yield of a carbon-carbon composite due to xenon ion bombardment was investigated. Instead of assuming surfaces to be flat, a simple carbon fiber distribution model was introduced to account for the carbon-carbon composite surface structure observed using a scanning electron microscope. Yamamura's semi-empirical sputtering formula, which accounted for 14% xenon adsorption, was used to calculate the sputtering yield of the carbon fiber surface. The proposed model provided fairly good estimates of the angular and energy dependence of the sputtering yield for the carbon-carbon composite. A comparative analysis of sputtering yield models demonstrated that the proposed model most accurately predicted both the accelerator and decelerator grid mass changes in the μ10 PM ion engine endurance test. In this paper, we present sputtering yield data over a range of xenon incidence energies from 0 to 2 keV and angles of incidence from 0 (normal incidence) to 90°.
A new method of strengthening adhesive bonding structures, introducing a slit near the bonding layer, is proposed in order to solve a problem affecting composite pressure vessels; that is, delamination of the bonding layer between the composite and metal, especially around a mouthpiece. The effect of the slit is studied on the basis of an analytical solution, and evaluated using actual double cantilever beam experiments and finite element method calculations. An example of composite pressure vessel design is presented to illustrate the effect of the slit.
To reduce the cost of space transportation, air-breathing engines are considered to be candidates for propulsion. However, to cover a wide range of flight speeds, the propulsion system has to operate in various modes to be efficient under incoming atmospheric-air conditions. The Japan Aerospace Exploration Agency is proposing a rocket-based combined cycle engine for operation under various condition, an ejector-jet mode being adopted for the low-speed regime. The suction performance ejector-jets has long been studied experimentally and numerically at JAXA, and little success has been achieved in explaining the deterioration of suction performance with high-temperature gas or light gas such as helium. In the present study, based on former models, a simple one-dimensional model was introduced incorporating the mixing effects of the primary flow (rocket flow) and secondary flow (induced air flow). The results were compared using several experimental and numerical data to check the plausibility of the model. It was found that if greater mixing occurs, suction performance is degraded, explaining the actual phenomena of the experiments.
A half model of a scaled aircraft is designed and tested in a wind tunnel. Based on the step-sinusoidal swept frequency test, the aeroservoelastic frequency response function is measured and compared with the predictions of a theoretical model. According to the discrepancies, the key uncertainty factors such as actuator model uncertainty, aileron aerodynamic uncertainty and structural damping uncertainty are investigated. Therefore, the original theoretical model is modified and updated with these model uncertainties considered, respectively. Motivated by the still existing discrepancies of experimental data and comprehensive updated theoretical outcomes, we take the above aeroservoelastic model uncertainty as an aleatory probabilistic one. Hence, the probability of each model uncertainty is quantified by Bayesian Posteriori Estimation theory. In addition, the uncertainty probabilities of aeroservoelastic response and aeroservoelastic stability boundary are predicted. The aeroservoelastic uncertainty quantification methodology with model uncertainty is validated by comparing the probabilistic predictions of the theoretical model set with experimental data. Taking model uncertainty into consideration, the present method is able to predict the probabilistic aeroservoelastic stability bounds and response as well. Results indicate that the updated comprehensive model is the best theoretical model with the highest posterior probability. In addition, the unsteady aerodynamics due to aileron deflection has the most significant effect on aeroservoelastic response.
A satellite’s inertia properties can be changed after launch due to consumption of propellant, deployment of solar panels, collision with space debris, sloshing, etc. For reliable and efficient satellite control, it is necessary to predict accurate information regarding the satellite’s inertia properties. In this note, we suggest a new real time method to estimate the inertia properties. First of all, we filter the noise of the gyro data with the extended Kalman filter. Then we estimate the inertia properties using the recursive least squares algorithm. For an improved estimation result, we combine the angular acceleration method and the angular velocity method. We have verified the performance of the suggested method through the case of STSAT-3, a Korea Science Technology Satellite, which has already been developed.