# Review of Adaptive Shock Control Systems
## 2 Literature Review of Adaptive Concepts for Shock Control
### Shock Control Concepts Using Multiple Actuators or Adaptive Elements
#### 2.2.3 Pressurized Chambers  
In 2015, [PERSON] et al. [75] developed a SCB concept with several chambers on which pressure can be applied, to expand them. This concept has been refined by [PERSON] et al. [76] (2020). The expanding chambers push against a flexible spoiler skin, whereby the bump is formed, which is shown in Figure 9.  
Figure 8: Tube Spring actuator made out of carbon fiber reinforced polymer (CFRP) that can be activated via pressure (\(p\)) or a shape memory alloy (SMA) based on [49; 74].  
Figure 9: Adaptive spoiler with pressurized chambers and various pressures (\(p\)) for shock control bump generation based on [76].  
As with many others, this concept focusses on the spoiler but since the spoiler mechanisms and functions are not touched, a full redesign of the spoiler is not necessary, which is comparable to the Tube Spring and fish-mouth actuators. The morphing spoiler consists of three layers of which the bottom layer depicts the supporting structure while the top layer is represented by a flexible skin material. The layer in between comprises the pressure chambers. For these chambers flexible walls are implemented to enable a deformation. Since the chambers are independent of each other the pressure can be adjusted differently in each chamber.  
The chambers and the skin are fixed on the edges in chordwise direction. This leads to an expansion of the chambers towards the wing's suction side. Hence, the flexible skin is deformed. A means of sealing has to also be realized at the edges in spanwise direction. For the spoiler closings in spanwise direction, [PERSON] et al. [75] describe three different types: open ends, fixed ends and closed ends with a fiber glass plate (which has a thickness of 1 mm). With regard to the deformations, the fixed and closed ends show an almost equal behavior. Compared to the open ends, the fixed and closed ends lead to a much stiffer design, distinctly lower deformation than wanted and a different peak location. Furthermore, waviness close to the spoiler trailing edge occurs. Based on these phenomena as well as positive effects with open ends like an uniform bump shape and a lower actuation pressure, [PERSON] et al. [75] describe a spoiler with open ends that offers the best shape behavior, although the question of how to enclose the fluid remains.  
Since the number of chambers is directly linked to the weight increase and system complexity, [PERSON] et al. [75] analyzed the effect of two and three chambers in chordwise direction. The results show that the three-chamber design can lead to a reduction of the needed chamber pressure. However, with the third chamber an additional chamber wall has to be implemented which adds flexural rigidity to the system. This is why for every spoiler and wing configuration it should be analyzed how many chambers are optimal for the respective design.  
The 2D two-chamber design of the flexible skin is described by [PERSON] et al. [76] as a 5 mm thick glass fiber reinforced polymer (GFRP). The S-shaped stringer respectively wall between both chambers is also made out of GFRP. The supporting structure and the active layer consist of CFRP and unidirectional GFRP. With a chordwise spoiler length of 1 m, the maximum achievable bump height is 8.16 mm and the maximum principal strain amounts to 0.45%. Moreover, a focus was placed on the spoiler tips in spanwise direction. At both ends, the tips amount to 10% of the spanwise length of the spoiler. Nevertheless, the differences of the spoiler tip deformations only differ for about 1 to 5%, depending on the particular design.