# Review of Adaptive Shock Control Systems
## 2 Literature Review of Adaptive Concepts for Shock Control
### Preformed Spoiler Concepts
#### 2.1.2 Two-Actuator Concept  
Based on the work of [PERSON] et al. [62] and [PERSON] et al. [63], [PERSON] and [PERSON] [67] presented in 2017 a concept of an adaptive spoiler that uses a secondary actuator in addition to the main spoiler actuator. Aside from the two actuators, this system consists of two structural reinforced skin parts and guiding rails for the main spoiler actuator, which is shown in Figure 3. Furthermore, the spoiler TE section is preformed and also the flexible hinge is used instead of a conventional spoiler hinge, which mandates the use of guiding rails. Moreover, the structure between the two reinforcements is modified and enabled to be more flexible. This leads to a maximum forward bump position located at the thin spoiler skin between the two reinforcements while the maximum backward bump position is created just behind the reinforcement near the TE.  
Contrary to the concept of the former section, the spoiler of [PERSON] and Monner can vary its bump position within a limited range of 7.5% chord. However, the position variation is only limited to the location of the reinforcements, which means that if enough installation space is given larger position variations could also be possible. Furthermore, maximum bump heights of 0.76% chord for the maximum forward bump crest position and 0.62% chord for the maximum backward position have been reached.  
[PERSON] and [PERSON] [67] investigate four primary load cases: (i) The cruise flight with a pressure load of 4000 Pa and \(\pm\)10% load variation, (ii) the airbrake case with  
Figure 3: Two-actuator concept of an adaptive preformed spoiler bump system based on [67].  
5000 Pa as well as (iii) the maximum forward and (iv) maximum backward SCB positions. Moreover, the primary installation actuator angle is varied in a range of 10\({}^{\circ}\), 20\({}^{\circ}\) and 30\({}^{\circ}\), as shown in Figure 4, to lower the actuator forces.  
The increase of the primary actuator angle from 10\({}^{\circ}\) to 30\({}^{\circ}\) decreases the primary actuator force by approximately 50%. Also, the necessary forces in the other load cases decrease. The forces of the secondary actuator were not influenced distinctly by this angle variation of the primary actuator. The design driving load case for the primary actuator is the airbrake since a maximum force of 40 kN is reached. The secondary actuator needs 20 kN at airbrake conditions. With an opposite direction of force, the other three load cases lead to forces of maximum 25-27 kN in both actuators. Thus, all loads stay within the given limit of about 40 kN which represents the spoiler actuator force of a typical short-medium range aircraft. Moreover, the deviations of the spoiler shape to the reference shape should stay below the limit of \(\pm\)0.5 mm, which is the case for the cruise pressure load variations of \(\pm\)10% simulated in this design process [67].  
From a structural point of view, again the airbrake load case is design driving. The flexible hinge region has been reduced to 1.5 mm skin thickness which results in a maximum principal strain of 0.8%. Two general possibilities to reduce the strain in this hinge region are to decrease the skin thickness or extend the length of the flexible hinge. However, in this design the thickness of 1.5 mm is already approaching practical minimum limits [67].