Unmanned Aircraft Design. Mohammad Sadraey H.
CHAPTER 1
Design Fundamentals
1.1 INTRODUCTION
The Unmanned Aerial Vehicle (UAV) is a remotely piloted or self-piloted aircraft that can carry payloads such as cameras, sensors, and communications equipment. All flight operations (including take-off and landing) are performed without on-board human pilot. In some reports of DOD, Unmanned UAV System (UAS) is preferred. In media reports, the term “drone” is utilized. The UAV mission is to perform critical flight operations without risk to personnel and more cost effectively than comparable manned system. A civilian UAV is designed to perform a particular mission at a lower cost or impact than a manned aircraft equivalent.
UAV design is essentially a branch of engineering design. Design is primarily an analytical process which is usually accompanied by drawing/drafting. Design contains its own body of knowledge that is independent of the science-based analysis tools that is usually coupled with it. Design is a more advanced version of a problem solving technique that many people use routinely.
Research in unmanned aerial vehicles (UAVs) has grown in interest over the past couple decades. There has been tremendous emphasis in unmanned aerial vehicles, both of fixed and rotary wing types over the past decades. Historically, UAVs were designed to maximize endurance and range, but demands for UAV designs have changed in recent years. Applications span both civilian and military domains, the latter being the more important at this stage. Early statements about performance, operation cost, and manufacturability are highly desirable already early during the design process. Individual technical requirements have been satisfied in various prototype, demonstrator and initial production programs like Predator, Global Hawk, and other international programs. The possible break-through of UAV technology requires support from the aforementioned awareness of general UAV design requirements and their consequences on cost, operation and performance of UAV systems.
In June of 2016, the Department of Transportation’s Federal Aviation Administration has finalized the first operational rules for routine commercial use of small unmanned aircraft systems [27], opening pathways toward fully integrating UAS into the nation’s airspace. These new regulations aim to harness new innovations safely, to spur job growth, advance critical scientific research and save lives. Moreover, in June of 2017, European Commission has released a blueprint for UAV standards which will “unify laws across the EU” by creating a common low-level airspace called the U-space that covers altitudes of up to 150 m.
The design principles for UAVs are similar to the principles developed over the years and used successfully for the design of manned UAV. The size of UAV varies according to the purpose of their utility. In many cases the design and constructions of UAVs faces new challenges and, as a result of these new requirements, several recent works are concerned with the design of innovative UAVs. Autonomous vehicle technologies for small and large fixed-wing UAVs are being developed by various startups and established corporations such as Lockheed Martin. A number of conceptual design techniques, preliminary design methodologies, and optimization has been applied to the design of various UAVs including Medium Altitude Long Endurance (MALE) UAV using multi-objective genetic algorithm.
The first UAV designs that appeared in the early nineties were based on the general design principles for full UAV and findings of experimental investigations. The main limitation of civil UAV’s is often low cost. An important area of UAV technology is the design of autonomous systems. The tremendous increase of computing power in the last two decades and developments of general purpose reliable software packages made possible the use of full configuration design software packages for the design, evaluation, and optimization of modern UAV.
UAVs are air vehicles, they fly like airplanes and operate in an airplane environment. They are designed like air vehicles. They have to meet flight critical air vehicle requirements. You need to know how to integrate complex, multi-disciplinary systems. You need to understand the environment, the requirements and the design challenges.
A UAV system is much more than a reusable air vehicle or vehicles. The UAV system includes five basic elements: (1) the Environment in which the UAV(s) or the Systems Element operates (e.g., the airspace, the data links, relay UAV, etc.); (2) the air vehicle(s) or the Air Vehicle Element; (3) the control station(s) or the Mission Control Element; (4) the payload(s) or the Payload Element; and (5) the maintenance and support system or the Support Element.
The design of manned UAV and the design of UAVs have some similarities; and some differences such as: design process; constraints (e.g., g-load, pressurization); and UAV main components (autopilot, ground station, communication system, sensors, payload). A UAV designer must be aware of the: (1) latest UAV developments; (2) current technologies; and (3) known lessons learned from past failures. Designers should appreciate breadth of UAV design options.
UAV are not new, they have a long history in aviation. Their history stretches back to the First World War (1920s), Cold War, Korean War, Vietnam War (RPV), Yugoslavia, Afghanistan, First and Second Persian Gulf war, and other wars (e.g., Pakistan, Yemen, Syria, and Africa). At least 20 countries are using or developing over 76 different types of UAVs. The contributions of unmanned UAV in sorties, hours, and expanded roles continue to increase. As of September 2004, some 20 types of coalition UAVs, large and small, have flown over 100,000 total flight hours in support of Operation Enduring Freedom and Operation Iraqi Freedom. Their once reconnaissance-only role is now shared with strike, force protection, and signals collection.
In this chapter, definitions, design process, UAV classifications, current UAVs, and challenges will be covered. In addition, conceptual design, preliminary design, and detail design of a UAV based on systems engineering approach are introduced. In each stage, application of this approach is described by presenting the design flow chart and practical steps of design.
1.2 UAV CLASSIFICATIONS
It is a must for a UAV designer to be aware of classifications of UAVs which is based on various parameters such as cost, size, weight, mission, and the user. For instance, UAV ranges in weight from Micro Air Vehicles (MAV) weighing less than 1 pound to UAV weighing over 40,000 lb. Moreover, these diverse systems range in cost from a few hundred dollars (Amazon sells varieties) to tens of millions of dollars (e.g., Global Hawk). In addition, UAV missions ranges from reconnaissance, combat, target acquisition, electronic warfare, surveillance, special purpose UAV, target and decoy, relay, logistics, research and development, and civil and commercial UAVs, to environmental application (e.g., University of Kansas North Pole UAV for measuring ice thickness).
The early classification includes target drones and remotely piloted vehicles (RPVs). The current classification ranges from Micro UAVs (less than 15 cm long, or 1 lb); to High-altitude Long Endurance (HALE); to tactical and combat UAVs. In this section, characteristics of various classifications are briefly presented.
The Micro Unmanned Aerial Vehicles (MAV) was originally a DARPA program to explore the military relevance of Micro Air Vehicles for future military operations, and to develop and demonstrate flight enabling technologies for very small UAV (less than 15 cm/6 in. in any dimension). The Tactical UAV (e.g., Outrider) is designed to support tactical commanders with near-realtime imagery intelligence at ranges up to 200 km. The Joint Tactical UAV (Hunter) was developed to provide ground and maritime forces with near-real-time imagery intelligence at ranges up to 200 km. The Medium Altitude Endurance UAV (Predator) provides imagery intelligence to satisfy Joint Task Force and Theater Commanders at ranges out to 500 nautical miles. The High Altitude Endurance UAV (Global Hawk) is intended for missions requiring long-range deployment and wide-area surveillance or long sensor dwell over the target area. Table 1.1 shows the UAV classifications from a few aspects including size, mass, and mission. The MLB Bat 4, a mini-UAV (Figure 2.7) with a length of 2.4 m, a wingspan of 3.9 m, and a maximum takeoff mass of 45 kg has a maximum cruising speed [54] of 120 knot.
In the U.S. military, the classification is mainly based on a tier system. For instance, in the U.S. Air Force the Tier I is for low altitude, long endurance missions, while Tier II