## 1 Introduction
### State of the Art  
TM-UAVs can be categorized into fixed TM-UAVs and variable TM-UAVs. The fixed TM-UAVs have an inclined surface that is installed at the ends of the cantilever arms,thereby they can tilt the propellers. For example, the Hex-rotor's inclined surfaces are not parallel so that it resists wind gusts more efficiently [2], and the Tilt-Hex supports horizontal flight and maintains a level attitude [3]. Another design is to mount the propellers on inclined cantilever arms, such as the omnidirectional aerial vehicle [4], which has an eight-rotor configuration that maximizes the vehicle's agility in any direction, possessing full force and moment authority in all three dimensions. Variable TM-UAVs can be divided further into two types of mechanisms: those with specific mechanisms and those with additional servomotors to tilt the propellers. An example of the former is the Gemini II bi-copter [5], which controls attitude by using a cyclic flapping response in hinges that connect the blades. The \(T^{3}\)-multirotor combines the advantages of both specific mechanisms and additional servomotors by using two servomotors to create a universal joint connecting the propeller part and the body part, transforming the quadcopter from an underactuated system into a fully actuated system [6]. The TM-UAVs with additional servomotors are usually overactuated systems. Although they increase battery consumption, their contribution to fully actuated motion makes them meaningful. For example, the Gemini bi-copter utilizes two servomotors for yaw and roll control [7]. Using servomotors for yaw motion is more efficient, as the torsion originally produced by the moment difference between counter-rotating propellers is directly provided by the horizontal component of the propeller thrust. A classic example of a tiltrotor quadcopter is the Holocopter, designed for actuated flight in both the roll and pitch axes [8]. The Fast-Hex tiltrotor hexacopter is another example, converting an underactuated system into a fully actuated system [9]. The tiltrotor omnidirectional micro-aerial vehicle (OMAV) can exert a wrench in any orientation while maintaining efficient flight configurations [10]. Besides TM-UAVs, there are also foldable M-UAVs, aimed at reducing size for navigating through tight spaces, such as the foldable drone [11] and the midair reconfigurable quadcopter [12]. As an extension of M-UAV research, aerial physical interaction (APH) involves interactions in the vertical plane, curved surfaces, and horizontal plane. Research related to vertical plane interactions includes brushing for cleaning [13], installing a sensor on a tree [14], moving the manipulator on the surface of a glass wall [15], performing an 'aerial-writing' task [16], and performing a cleaning operation on a vertical surface [17]. These tasks share the commonality of being achieved through a fixed manipulator, as the vertical movement of M-UAVs is directly driven by the thrust of the propellers, making vertical plane interactions feasible. Research related to curved surface interactions includes cleaning an exhaust shaft [18], rolling along a curved surface [19], and force feedback control [20]. The design of TM-UAVs allows them to interact beyond flat surfaces. Research related to horizontal interactions includes pulling a drawer knob [21], pushing a rolling cart and hinged door [22], and extracting a wedged object [23]. However, the wrench in the horizontal direction is underactuated for M-UAVs. To address the potential issues of insufficient pulling and push force, the degrees of freedom (DOF) for these manipulators are three, two, and two, respectively. Another solution is to achieve horizontal interactions by tilting the propellers while still using a fixed manipulator, such as pushing a cart in an uncertain environment [24]. This approach's advantage is that it only considers the TM-UAV system itself.