Abstract
In this chapter, preliminary sizing and performance calculations of unmanned air vehicles (UAV), with relation to its propulsion system, are explained. Starting with the mission profile of the air vehicle, which is one of the important design drivers, the UAV is sized for the requirements. The requirements in design consist of a set of target values (e.g., payload amount to be carried, range, endurance time, cost, etc.). Additionally, the parameters within mission profile such as cruising altitude and speed of aircraft affect engine type, power level required, fuel quantity, and therefore general dimensions and the gross weight of the aircraft. It is often an iterative process to size the air vehicle and engine together. UAV is designed in a loop of calculations in which sizing, flight performance, and engine performance are done for each phase of the mission or flight profile to satisfy the overall design mission and requirements.
TopBackground
In literature, there are numerous studies regarding the design of unmanned aerial vehicles. Austin (2010) presents a wide ranging knowledge of all aspects of UAVs. Gundlach (2014) covers a comprehensive range of all elements of unmanned aircraft systems, architectural options, and design drivers across diverse system classes. Fahlstrom and Gleason (2012) explains designers many aspects of the UAV systems including subsystem design choices, system-integration issues and lessons learned. In addition to many industry projects, some universities also perform projects on UAV design, manufacturing and fly to support undergraduate and graduate studies (senior design projects, master`s and Ph.D. dissertations etc.). Some university explained their studies and capabilities on UAVs as mentioned by Zbrutsky et al. (2013), Sanchez et al. (2018), Cinar et al. (2016). Some associations (e.g. AUVSI) organize student unmanned aerial systems competitions. The competitions typically require students to design, integrate, report on, and demonstrate a UAS capable of autonomous flight and navigation, remote sensing via onboard payload sensors, and execution of a specific set of tasks.
Similarly, some examples of parametric UAV conceptual design tools including engine performance models can be found in literature. Rapid Air System Concept Exploration (RASCE) is one example of design tools which was originally developed as an educational tool to support undergraduate student exploration (Chaput, 2010). It has generic propulsion models to calculate thrust and fuel flow as a function of power setting, speed and altitude for turboprop/turbofans (defined by bypass ratio, specific thrust, fuel-to-air ratio and thrust-to-weight) or internal combustion engine or electric motor with propeller installations.
Preliminary sizing and performance calculations of unmanned air vehicles are done based on many inputs and requirements. As a part of the technical requirements, we can start with the mission profile of UAV. The flight mission profile is one of the most important design inputs in aircraft design. The flight mission profile is a graphical representation of a scenario in which an aircraft needs to perform prescribed operations and includes parameters such as payload weight, range, speed, altitude etc. Mission requirements vary according to the type of aircraft. Flight mission profile varies according to the air vehicle category. When civil transport aircraft, military aircraft and unmanned air vehicles are classified into sub-categories, it is observed that each has a different flight mission profile. In other words, the flight mission profile is a schematic of the flight phases and the detailed descriptions of the activities performed on the flight. Therefore, it is very important in the conceptual design of the aircraft/UAV. While UAV/aircraft is sized per the technical specifications and requirements (payload, range, target cost, etc.), the parameters such as cruise altitude and speed within the flight mission profile affect the engine type/size, power level, the required fuel weight/storage volume and therefore the overall size and total weight of the aircraft.
Figure 1 shows a basic mission profile of a civil transport aircraft and Figure 2 depicts a typical reconnaissance UAV flight mission profile. Although both mission profiles look similar, at a quick glance, one can conclude that a reconnaissance UAV spends most flight time during loitering (reconnaissance/surveillance) whereas the transport aircraft in cruising.
Figure 1. Typical civil transport aircraft flight mission profile
Key Terms in this Chapter
UAV: An aircraft that can autonomously fly or can be remotely controlled to perform a specific mission without flying crew inside.
Mission Profile: A schematic of the flight phases (speed, altitude, etc.) and the detailed descriptions of the activities performed on the flight.
Interoperability: The ability of military equipment or groups (e.g., UAVs) to operate in conjunction with each other.
Turboprop Engine: A gas turbine engine used in aviation that produces shaft power and drives an aircraft propeller typically through a gearbox.
Loiter: A phase of flight in which a UAV typically spends most of its time for reconnaissance over a target area.
Nacelle: A housing that holds and covers an aircraft engine on the outside of an aircraft.
Swarming: A group of UAVs all moving together, communicating with each other while in flight, and can respond to changing conditions autonomously.
Endurance: The maximum length of time that an aircraft can spend in cruising flight.
Sizing: Calculation of dimensions and weight of an aircraft and its subcomponents.
Fuselage: The main body of an aircraft designed to accommodate the crew and the passengers or cargo.
Low Observability: A sub-discipline of military tactics and passive electronic countermeasures, which cover a range of techniques used with objects (e.g., UAVs) to make them less visible (ideally invisible) to radar, infrared, and other detection methods.