# An Adaptive Launch Control for Balloon-Borne UAVs with Large Wingspans
###### Abstract  
Near space has attracted major countries' attention due to the fact that it is a new cognitive space of Earth and acts as an important national security space. Near-space solar-powered unmanned aerial vehicles (UAVs) are becoming a focus of research in the aviation field. However, it is difficult for solar-powered UAVs to climb such high heights and achieving optimal cruising levels is challenging. A balloon-borne-based aircraft that rises with the help of a balloon avoids difficult climbing processes and initiates a new research direction in the near-space aviation domain. Simultaneously, the special mode of taking off poses a great challenge for the pull-up control of balloon-borne aircraft, especially for large wingspan aircraft. In this paper, we propose an adaptive launch control for the pull-up process of large-scale balloon-borne-based aircraft. First, the flight control of the pull-up process for a large-scale balloon-borne-based aircraft is analyzed. Then, a flight dynamic model considering elastic deformation is established. Finally, an adaptive aircraft pull-up control algorithm is proposed. We evaluate it by performing simulation experiments and comparing it with the latest control algorithm utilized in physical experiments. The experiment's results demonstrate the effectiveness of the proposed algorithm with respect to overcoming challenges in controlling pull-up processes and its superiority compared to the latest control algorithm. near space; balloon-borne launching; solar-powered UAV; large wingspan; pull-up control +
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On the other hand, the climb state needs to be considered in the design of the aircraft. It is hard to make the most optimal cruise point as the only design point. In order to solve the above problems faced by UAVs with large wingspans, based on relevant research studies [2; 3], we proposed and implemented the scheme of launching large wingspan UAVs with balloons in near space for the first time in China. The process can be simply described as follows. First, a high-altitude balloon rises to a certain altitude. Second, it is launched and cruises in the air. Finally, it lands via a runway. The balloon-based large-wingspan UAV can quickly rise to the height of adjacent spaces and reduce the impact of strong winds and jet-stream areas. This avoids the risk of overheating with respect to the UAV's motor caused by high-power continuous outputs in the climbing stage and also solves the problem of the limited payload weight caused by the increase in the weight proportion of the entire machine's structure due to the large wingspan. In addition, the balloon-based large wingspan UAV can use near-space cruise flights as the only optimal design reference, which improves the aerodynamic efficiency of the aircraft and the propeller. Even though the increase in height with the balloon does notinvolve the complex states of the UAV in the climbing-up process and can beneficially arrive at a certain altitude, the characteristic of having a large wingspan poses a new challenge for launch processes. When UAVs with large wingspan are released, their flight process after being launched is accompanied by drastic changes in airspeed, attitudes, and attack angles. Drastic changes lead to a large elastic deformation in aircraft with large wingspan and introduce an important impact on flight control and flight safety. Hence, the control model is more complex due to the large elastic deformation compared to having a common wingspan. An inaccurate control model may lead to failures during launching. In addition, at the initial time of launching, the speed of the aircraft is zero or it moves upward with the high-altitude balloon with a small increase in speed. Thus, obtaining suitable airspeeds and attack angles that can maintain a UAV's cruise flight is another challenge. Currently, launch tests of aircraft are mainly carried out for small-sized rigid aircraft, and there is little study on launching aircraft with large wingspans and elasticity.