# Control Requirements for Future Gas Turbine-Powered Unmanned Drones: JetQuads
## 1 Introduction
This is still 1/10 of the energy density of diesel. As a result, the JetQuad will remain competitive for many years to come [13]. * The power-to-weight ratio determines how much power a given engine outputs for a given mass of that engine. Electrical drones have a large penalty in this regard. A brushless electrical motor, on its own, has a very large power-to-weight ratio. However, when added to the weight of propeller, electronic speed controllers, and batteries, this ratio is greatly decreased. Turbine-based engines, such as jet engines, do not suffer from this problem. More specifically, the JetQuad uses microturbines that have an ultrahigh rotation rate and lead to vast amounts of power produced from a small engine. In addition, electrical drones must limit current flow to prevent the overheating of electronics that support smooth motor operation. In contrast, fuel flow rate is the limiting factor for turbine-based engines. It gives jet-engine designers the flexibility to extract much more power from smaller motors [13]. However, the dynamic behavior and control requirements for the JQ are different from those of quadrotors. This topic has not been considered in the literature yet. Thus, the main contribution of this paper is to focus on control requirements and control mode identification of the JQ to enable researchers to focus on control system designs and optimization for this promising concept. The JQ is a quad jet engine-powered drone proposed by FusionFlight in 2016 [13]. It is based on patented air booster (AB) technology that allows for stable and high-performance flight through the atmosphere. It will push the frontiers of drone technology to a whole new level in the future. The main structure of a JQ is shown in Figure 1. It is composed of a main body and four microjet engines. Each microturbine uses an electric starter as well. The modeling and simulation of the JQ was presented and discussed in detail in References [14; 15; 16]. The bond graph as a graphical representation tool for physical dynamic systems was utilized to model and simulate the dynamic behavior of the JQ. A bond graph is a very suitable approach to modeling mechatronic systems, as it allows the conversion of the system into state-space representation [17; 18; 19; 20; 21]. The bond graph has been used in turbomachinery applications widely: Gas turbine modeling and analysis [22; 23; 24], noise prediction and control [25; 26], and surge prediction and control [27; 28; 29] are topics in which a bond graph has been successfully used. In previous studies by the authors, both propulsion and the main body of the JQ were modeled in a bond graph, and these models were then combined to predict the dynamic behavior of the system [14]. This model was used for this paper to generate more results in order to develop the control requirements for the JQ as well as to identify control modes that should be satisfied simultaneously for safe and optimal operation of the JQ. For this purpose, a brief summary of the modeling approach is first presented, and the developed model is explained in detail. Two different scenarios for thrust profile are then defined to analyze the dynamic behavior of the JQ from compatibility and robustness points of view. Based on the simulation results, the Jet Quad control requirements are identified and prioritized, and essential control modes are defined. A control structure with its associated control algorithm to satisfy all control modes simultaneously is finally proposed.