## 1 Introduction  
The actuators used in aircraft flight control systems are most often hydraulic elements [1, 2, 3], although in,,more electric\" [4, 5, 6] or,,all-electric\" aircraft [7, 8], electromechanical actuators are also successfully used [9, 10]. Hybrid servos can also be found in aviation onboard systems [11]. Hydraulic actuators ensure the transmission of very high power in relation to their weight [12], surpassing both electromechanical and pneumatic systems in this respect. The power of hydraulic systems is relatively easy to maintain and control, and properly designed and operated hydraulic systems are extremely reliable and safe [13]. Their structure is strictly defined by standards [14]. The hydraulic controls are automated [15], allowing direct operation, for example, the position of the actuator. The biggest disadvantages of hydraulic systems include the high costs related to the construction of their installation. They also require regular inspection and maintenance, and breakdowns related to the occurrence of leaks in the hydraulic system are particularly troublesome [12]. Designing actuators for control surfaces requires special consideration of the aspects related to their reliability, operational safety, and long-term operation in unfavorable environmental conditions (e.g., large-amplitude changes in ambient temperature, air pressure, and exposure to vibrations and shocks) [13, 14, 15]. Hydraulic systems made using classic technologies have long been able to meet these requirements. In view of current environmental degradation, the rise of fuel prices, and constrained sourcing and gathering of renewable energy, the aerospace industry needs to constantly conduct research on new materials and technologies. Reducing the total weight of an aircraft constitutes one of the most important tasks for contemporary aviation. Decreasing the weight of medium- and long-haul aircraft by 1 kg enables saving up to 150 liters of fuel per year [16]. Therefore, since fire-resistant oils based on phosphoric esters (e.g.,Skydrol or Hyjet [17]) are more lightweight than mineral oils by up to 7%, they have been applied in the field of hydraulic systems for several years. Despite research conducted on ways to increase the endurance of the most frequently applied aluminum, titanium, and stainless steel alloys used in the components of aircraft hydraulics, reducing the weight of mechanical components is considerably more difficult. It is estimated that the value of every reduced kilogram of the weight of an aircraft may be anything from USD 100 to USD 2000 [18]. In the context of reducing the weight of the aircraft, and thus reducing fuel consumption, CO\({}_{2}\) emissions, harmful substances, and noise emissions, taking actions related to the design, production, and implementation of lighter actuators realized in additive technology seems to be the right thing to do. This is also confirmed by the attempts being made by major producers in the aviation market [19]. The potential for the application of additive technologies in aircraft looks promising, and machine producers already have devices dedicated to metal printing that may be used to manufacture parts on an industrial scale [20; 21; 22]. The Domin company, in cooperation with Rzeszow University of Technology, conducted extensive research on the endurance of maraging steel 1.2709 as far as the process of laser melting is concerned (the actual research of SLM technology in relation to maraging steel 1.2709 is also described in the work of other teams [23; 24]). Furthermore, researchers have assessed whether the material in question may be used in aircraft for hydraulic components [25]. Hydraulic actuators have a highly complex internal structure, especially regarding operating conditions. Such a structure is particularly noticeable in a characteristic of the actuator presented in this paper and dedicated to the fly-by-wire (FBW) control system.