# Review of Adaptive Shock Control Systems
## 4 Conclusions  
The adaptive SCB concepts reviewed in this work use various actuator technologies and approaches to morph a flexible skin into bump shape. The highest degree of con trollability is given for concepts which use several smaller actuators (concepts 3 and 5, Table 1), although, for those concepts the complexity is often comparably high. Concepts which use a preformed spoiler shape in combination with the spoiler actuator (concept 2) use proven technologies and their complexity is comparably low. The preformed spoiler shape has been identified as a technology of great simplicity and utility. This is why the spoiler actuator concepts are found to be more advantageous if the shock is located on the spoiler and if simplicity is the main driver. Nevertheless, also the thin flexible plate which is deformed by only two actuators (concept 6 with two actuation points) seems to have accurate controllability and if it is designed with sufficient large skin thickness the robustness could be sufficiently high for an implementation in a real aircraft. Furthermore, it is simultaneously rather simple, which is why it is also found to be an appropriate concept. However, concept 6 (with two actuators) should be analyzed in due consideration with the bump's position variation, since it stays unanswered if this concept can fulfil both a large position variation as well as an accurate bump shape control of the SCB. This is also true for the pressure chamber approach (one variant of concept 5) if only two chambers are used and should be analyzed, before choosing this concept. The concepts that use several smaller actuators (fish-mouth and Tube Spring, concepts 3) or pressurized elements (concept 5) have the major advantage of ensuring the highest amount of SCB control (height, position and shape). The challenges are seen in the complex control of these actuators as well as in the manufacturing. Although SMAs are a promising actuator type for future aircraft wings, the energy demand has to be considered. A locking device or mechanism might be a solution to reduce the energy amount for the bump formation. The challenges for pressure actuated systems lie, on the one hand, in sealing the system and, on the other hand, in the weight increase by the pressure system. Nonetheless, the pressurized chambers offer reduced system complexity than the Tube Spring actuators, if they are driven by pressure. Moreover, SMA actuators provide large deformation energy also for small installation space. Especially for the outer wing regions their small size, and the fact that they depend only on electricity, makes them very interesting. Therefore, the SMA technology is found to be promising and it might work out well in combination with a thin flexible plate with, e.g., two actuators (concept 6). Although the compliant structures (concept 7) enable only a one-degree-of-freedom bump variation if designed as described in Section 2.4, the general idea of using compliant structures or mechanisms could provide an elegant solution for future SCB designs in terms of reduced part complexity in comparison with kinematic systems. Despite the advantages due to their simplicity, the thin flexible plate approaches (concept 6) without or with only one single actuator do not seem to be rather robust against mechanical influences and the control is limited. The SMA plate (concept 4) needs a lot of heat and energy supply and must be very well insulated or the energy amount needs to be reduced differently. Finally, the plasma heating elements (concept 8) in its current stage require a lot of energy and its technology readiness is low for shock control. In summary, several approaches already exist with a wide range of actuation concepts to form adaptive SCBs on aircraft wings. The focus lies often on an adaptive spoiler design, but also the installation in the outboard wing regions is possible with some approaches. Often an increased controllability goes hand in hand with increased complexity.