# Control Requirements for Future Gas Turbine-Powered Unmanned Drones: JetQuads
## 3 JetQuad Simulation Results
### Discussion of Scenario (ii) Results  
Figure 11 shows the variation of displacements of the JQ in the \(x\), \(y\), and \(z\) directions. As can be seen in this figure, the variation in the \(x\) and \(y\) displacements was negligible even with severe changes of thrust in a short time duration. It seems that the system performed robustly. However, the \(z\) direction displacement was very huge, and it might result in overspeed or integrity issues, as well as exceed regulations for drones. In order to investigate this matter more precisely, Figures 12-14 show the variation in linear velocity and acceleration, as well as the angular velocity for the JQ. These results clearly confirmed the above conclusion. Figure 12 shows that the velocity of the JQ in the \(z\) direction increased up to 280 m/s, with a very high acceleration value (43 m/s\({}^{2}\) from Figure 13). Thus, this confirmed the necessity of having a physical limitation control mode for the JQ to protect the system from overspeed, overacceleration, and other malfunctions. However, the velocity and acceleration values in other directions were very low and negligible. Therefore, the robustness control mode could be considered to be a lower priority than the physical limitation control mode. predefined displacement (trajectory) for the JQ, and the output would be the thrust profile for each jet engine as a function of time. * The criteria for testing the compatibility control mode would be the value of displacement, velocity, and acceleration of the JQ in different directions. For instance, if the target is a vertical movement, the value of the displacements and velocities on the \(x\) and \(y\) axes should be zero (or negligible). * A stability control mode should also be considered for the JQ. However, with respect to the values of angular velocity and acceleration in the compatibility test, it could be considered to be a lower priority than the compatibility control mode. * The necessity of the stability control mode depends on the application of the JQ. Thus, a control loop could be designed in this regard with a predefined angular velocity and acceleration profile as the input and the modification of the thrust profile as the output of the controller. * The robustness test showed that the structure of the JQ was robust and performed well even with severe changes in thrust profile. Thus, the robustness control mode is not a \"must\" in the first version of the JQ controller. * The robustness test also showed that there is a vital need for a physical limitation control mode to protect the JQ from overspeed and other malfunctions. The inputs of this control loop would be the maximum and minimum allowable values for the velocity and acceleration of the JQ, and the outputs of this loop should be compared to the compatibility control loop as constraints. Taking the above-mentioned conclusions into account, the proposed control structure for the JQ is shown in Figure 15.  
The proposed control algorithm would work as follows:  
* First, the compatibility control loop calculates the appropriate thrust profile for each jet engine to minimize the error between the desired and actual trajectory of the JQ. Figure 15: Proposed control structure for the JetQuad. * The stability control loop then calculates the required modifications on the thrust profiles to minimize the instability parameters. * The compatibility and stability control loops work together and have mutual effects on each other. * The physical limitation control loops (e.g., maximum speed, maximum acceleration, and minimum speed) calculate the limitations for the thrust profile to protect the engine from malfunctions. * The outputs of the physical limitation control loops are compared to the outputs of the compatibility control loop (modified by the stability control loop) in a selection mechanism, and an appropriate and safe thrust profile for each jet engine is generated as the final output of the controller.