Tethered aerostats operating under wide13; range of altitudes and atmospheric pressure conditions13; employ ballonets within the hull filled with13; air. These ballonets exhaust the air into the13; atmosphere whenever necessary to maintain the13; difference between the atmospheric pressure and13; the internal pressure within a desired range.13; Assuming that the air exhaust is made periodic,13; studies are made on the effect of the periodic13; jet force and the resulting pitching moment on13; the responce of the aerostat system. In the first13; phase, the stability of the system is studied by13; analyzing the eigenvalues and eigenvectors. The13; result shows that the aerostat system is unstable13; in the wind speed range of 0-15 fps and stable13; in the windepesd range of 15-100 fpamp; When13; the system is subbcted to a suitable periodic13; forcing from the exhaust jet, it is observed that13; It is not only possible to extend the stability13; boundary of 15 fps down to typically 5 fps, but13; much more interestingly, there exist forcing periods13; of the extraust jet which render the system completely13; stationary.13;
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