# Control Requirements for Future Gas Turbine-Powered Unmanned Drones: JetQuads
## 1 Introduction  
Having recently reached the commercial mainstream, drones will be utilized in different aspects of human beings' lifestyles in the future. New advanced delivery systems designed and being used to safely get packages to customers in 30 min or less using unmanned aerial vehicles have a great potential to enhance the services provided to millions of customers in the future. This system also will increase the overall safety and efficiency of the transportation system [1]. There is also wide interest in flying robots in the toy industry. The different types of quadrotors and toy drones will help children to be creative, excited, and familiarize themselves with this cutting-edge technology [2]. The use of unmanned aerial vehicles (UAVs) for capturing visual information in areas that are hard to reach or dangerous for humans is another interesting application of drones [3]. This application would bring a huge advantage in terms of time saving, cost, and human risk when it is necessary to inspect areas that are either dangerous or difficult to reach for humans, such as power lines, power plant boilers, bridges, tunnels, hydraulic dam walls, and pipelines [4; 5]. The potential impacts of future aerial robots on other applications such as aerial photography and firefighting are also clear [6; 7]. In the last two decades, quadcopters (also called quadrotor helicopters or quadrotors) have been considered to be the most practical form of aerial robots [8]. The modeling and simulation [9], control and stabilization [10; 11], and dynamic behavior prediction [12] of these aerial robots have been widelystudied and investigated in the literature. Thus, different aspects of performance prediction and optimization of these robots are completely understood. The main conclusion of the literature has been that for aerial robots to become a standard tool in everyday use, it is vital that they can be operated efficiently by a non-expert pilot and that the navigation system be robust enough to remain operational in rough, industrial conditions. Consequently, the most important challenge for the development phase of this technology is the control system. In other words, having an accurate and precise control strategy is a \"must\" for safe and efficient operation of all types of aerial robots. In order to design a reliable control structure, a dynamic model (a control-oriented model (COM)) is needed to simulate the behavior of the drone in different working conditions. This model should be reliable, precise, and accurate to enable control experts to develop an effective control strategy for this mechatronic product. This model should also be fast enough to be used in iterative procedures of control system design. In 2016, a new type of aerial robots was introduced and patented: JetQuads (JQs). The JetQuad is a quadrotor in which the propellers are replaced with jet engines [13]. Thus, it is a jet engine-powered drone that could have a revolutionary impact in the next generation of aerial robots. The main advantage of using jet engines in drones is that the turbines can run on ordinary diesel fuel. As a result, the drone is mechanically simple and very powerful. The JetQuad outperforms conventional electrical drones in two aspects, energy density and power-to-weight ratio:  
* The energy density measures energy storage in a unit mass. The JetQuad uses diesel fuel with an energy density of 40 MJ/kg, whereas electrical drones use solid lithium-based batteries that at most have an energy density of 1 MJ/kg. Thus, for the same on-board mass of fuel (or battery) storage, the JetQuad stores 40 times more energy than the equivalent electrical drone. Although jet engines are heavier than electrical motors, they have much higher power-to-weight ratios, so this penalty is insignificant. The U.S. Department of Energy (DOE) has recently initiated a five-year research project to develop next-generation battery technology. The DOE targets an energy density achievement of 3 MJ/kg energy density.