The combination of lightweight flexible membrane design and favorable control characteristics renders tethered inflatable airplanes an attractive option for high-altitude wind power systems. This paper presents an analysis of the flight dynamics and stability of such a Kiteplane operated on a single-line tether with a two-line bridle. The equations of motion of the rigid body model are derived by Lagrange's equation, which implicitly accounts for the kinematic constraints due to the bridle. The tether and bridle are approximated by straight line elements. The aerodynamic force distribution is represented by 4 discrete force vectors according to the major structural elements of the Kiteplane. A case study comprising analytical analysis and numerical simulation reveals, that for the specific kite design investigated, the amount and distribution of lateral aerodynamic surface area is decisive for flight dynamic stability. Depending on the combination of wing dihedral angle and vertical tail plane size, the pendulum motion shows either diverging oscillation, stable oscillation, converging oscillation, aperiodic convergence, or aperiodic divergence. It is concluded that dynamical stability requires a small vertical tail plane and a large dihedral angle to allow for sufficient sideslip and a strong sideslip response.
[Abstract] This paper presents the various structural considerations in designing a large inflatable kiteplane. Material issues are addressed and a departure from conventional inflatable kites is suggested by using a single material instead of a structural foil and an internal gas barrier. Furthermore, rigging the kite using bridle lines is given attention. It is shown that the required internal pressure for a beam to keep it stiff is greatly influenced by the location of the bridle line. An optimum placement of the bridle line is found through analysis of the bending behavior of the beam in combination with a stress-based wrinkling criterion.
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