Numerical Study on Parameters of the Airborne VLF Antenna by Quasi-Stationary Model

When a Very-Low-Frequency (VLF) antenna is towed in a circular flightpath at a constant altitude, the spatial configuration of the antenna can become relatively stationary with the orbiting aircraft. Accordingly, a quasi-stationary model of the towed antenna is established based on the force balance, which can efficiently solve a large number of parameter optimization problems. This work studies the influence law of all relevant parameters, including the physical properties of the drogue and the towline, the flight conditions, the wind profile, and the phase of the flight. The results show that the towline verticality and towing force are highly sensitive to the flight conditions, wind profile, and the phase of the flight; followed by sensitivity to the towline itself, and slight sensitivity to the drogue. The flight conditions of the aircraft can change the verticality of the towline from 15% to 80% or more. In addition, as the maximum monthly average wind speed exceeds 7 m/s, the antenna system in hover will oscillate seriously, resulting in a range of up to 50% variation in towline verticality between different positions.