# An Adaptive Launch Control for Balloon-Borne UAVs with Large Wingspans
## 2 Background and Related Work
### Related Work  
_Unpowered Paradute Glider:_ Studies that are most related to ours include those on small unpowered parachute gliders [4; 5]. For instance, [4] analyses the \"parachute-dive-horizontal flight\" process of small unpowered parachute gliders and takes the parachute cut-off time as the start time of the automatic control. Our work uses near-space cruise flights as the only optimal design reference. The authors in [5] studies the attitude estimation and fusion algorithm of small unpowered parachute gliders from vertical launch to horizontal flight.  
Even though our study has similarities with the studies mentioned above, there are differences that can be summarized in terms of two aspects. First, the solar-powered UAV is a light and flexible large wingspan aircraft; however, small unpowered parachute gliders are small in size and have high rigidity. Second, the motion of solar-powered UAV is completely different from launching small-sized and high-rigidity aircraft. For example,  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test** & **Time** & **Country** & **Launch Height** & **Launch Aircraft** \\ \hline \multirow{3}{*}{
\begin{tabular}{c} **Purch** \\  
the former has high requirements on the overload limit of the release due to the limited strength of the structure, so it has high requirements on the pull-up time and pull-up speed. In addition, it also needs to consider the impact of elastic deformation on the structure and control. On the other hand, the latter does not need to consider the problem of structural strength limitations or the influence of stiffness on flight controls. We mainly focus on researching the launch of flexible aircraft with large wingspans.  
_Aircraft with large wingspans:_ The authors of [19] considered the effect of nonlinear geometries and proposed a nonlinear trim and flight load analysis method for large flexible aircraft based on the CR (Co Radical) theory. The authors pointed out that when elastic deformation occurs in a flexible wing aircraft with large wingspan, the attack angle of the local wing section increases, resulting in the problem of dynamic stall [20]. Studies established a structure/flight coupling dynamic model that can reflect the flexibility characteristics of solar-powered UAV by using the Lagrange equation, analyzed the longitudinal stability of UAVs using the Root Locus Method, and finally studied the impact of elastic deformations on longitudinal flight control [21]. However, these works only focus on the stability analysis and control of UAVs when elastic deformation occurs. On the contrary, our work focuses on the control a different process (launching and pull-up process) for aircraft with large wingspans.  
_Launch and pull-up control:_ The authors of [3] adopt different control methods based on the flight characteristics of different stages of a model-free flight test, which well solves the problems and provides a safe separation between the model aircraft and carrier aircraft and provides the control of horizontal flight at high attack angles. The authors of [22] established a dynamic model by considering elastic deformation, analyzed the static stability, and carried out controller designs and launch experiments for scaling UAVs. The authors of [23] analyzed the constraints that UAVs should meet during the launching process and optimized the command of the pitch angle by using the control variable parameterization method. Although these efforts focus on launching and pulling processes, they do not involve the launch of aircraft with large wingspans. The launch of aircraft with large wingspans is more challenging.