# Review of Adaptive Shock Control Systems
## 2 Literature Review of Adaptive Concepts for Shock Control
### Preformed Spoiler Concepts  
#### 2.1.1 One-Actuator Concept  
In 2016, [PERSON] et al. [62] and [PERSON] et al. [63] published this concept of a preformed spoiler geometry and in 2019 the corresponding patent by [PERSON] et al. [64] was released. The spoiler forms the bump in its preformed state and can be transformed to an almost plane form--which represents the clean cruise shape--by increasing the pulling force of the spoiler actuator, which is shown in Figure 2.  
Since the flap serves as counter force, the contact point of the spoiler can slide on the flap when the actuator pulls the spoiler into its planar shape. Besides the preformed structure another structural element deserves attention. The authors invented a flexible solid body hinge which serves as an alternative to the conventional spoiler joint. Termed \"flexible hinge\", this part consists of a flexure hinge made of carbon fiber reinforced polymer (CFRP) which replaces the conventional jointed hinge [62; 63; 65]. Since this technology is gapless and stepless, it prevents the airflow from undesired disturbances, as they could occur through a conventional spoiler joint. Moreover, another part of the spoiler is structurally modified and reduced in its stiffness. This so-called bump hinge or cut-out part of the spoiler is located between the two stiffer sections. It is needed for an accurate positioning of the bump crest. On the one hand, this bump hinge introduces enough flexibility of the spoiler during the bump formation and, on the other hand, it provides sufficient stiffness for the airbrake load case.  
Figure 2: Adaptive spoiler with preformed shape and the spoiler actuator based on [62].  
The forces during the airbrake are not only a challenge for the bump hinge section but especially for the flexible hinge. Since this spoiler region must be designed with a rather small skin thickness to enable a large deformation, it would not be able to bear the loads on its own. For this purpose, [PERSON] et al. [65] describe guiding kinematics which serve as supporting mechanism to bear the aerodynamic forces, so that the flexible hinge is only loaded with pure bending.  
[PERSON] et al. [62] assume a bump height variation of 0.1 to 0.5% chord length and a variation of the shock location of 15 to 20% chord. While the height of the bump can be adjusted by a variation of actuator force, the bump crest position cannot be changed. [PERSON] et al. [62] instead utilize the variable camber (VC) functionality to adjust flap position by several degrees to ensure that the shock coincides with the fixed bump position which is described by [PERSON] [66] in more detail.  
An additional version of this concept is realized by the implementation of a secondary actuator which reinforces the bump hinge section of the spoiler. This is mentioned in the patent of [PERSON] et al. [64]. With this additional actuator the shape of the bump can be controlled more accurately and, moreover, the spoiler can form a plane shape in the high-lift configuration and the airbrake case due to the increased stiffness. Furthermore, a concept of using an accurate mechanism instead of a second actuator is also conceivable [64]. In the following section, the approach by using a secondary actuator is described.