Table 2.4 Army tiers
| No. | Tier | Mission/Group | Example |
|---|---|---|---|
| 1 | Tier I | Small UAV | RQ‐11A/B Raven |
| 2 | Tier II | Short‐Range Tactical UAV | Role filled by the RQ‐7A/B Shadow 200 |
| 3 | Tier III | Medium‐Range Tactical UAV |
The most recent classification of systems in use in the United States is related to missions although the old Tier system is still in existence. Eighteen missions relate to four general classes of UAVs – small, tactical, theater, and combat. It is quite specific to US military requirements and is not presented in this book.
2.3 Examples of UAVs by Size Group
We attempt here to provide a broad survey of the many types of UAVs that have been or are being designed, tested, and fielded throughout the world. The intent of this survey is to introduce those who are new to the UAV world to the wide variety of systems that have appeared over the few decades since the revival of interest in UAVs began in the 1980s.
There are a variety of guides to UAVs available and a great deal of information is posted on the Internet. We use The Concise Global Industry Guide [6] as a source for quantitative characteristics of current UAVs and a variety of open‐source postings and our own personal files for information on systems no longer in production.
As a general organizing principle, we will start with the smallest UAVs and proceed to some that are the size of a corporate jet. The initial efforts on UAVs in the 1980s concentrated on AVs that had typical dimensions of 2 or 3 m (6.6–9.8 ft), partly driven by the need to carry sensors and electronics that at that time had not reached the advanced state of miniaturization that has since become possible. In more recent years, there has been a growing interest in extending the size range of UAVs down to insect‐sized devices at one extreme and up to medium air transport sizes at the other end.
Some of the motivation for smaller UAVs is to make them man portable so that a soldier or a border guard can carry, launch, and control a model‐airplane‐sized UAV that allows him or her to take a look over the next hill or behind the buildings that are in front of him or her. Further miniaturization, to the size of a small bird or even an insect, is intended to allow a UAV to fly inside a building or perch unnoticed on a window sill or roof gutter and provide a look inside the building or into a narrow street.
The realm of small UAVs is one in which there is no competition from manned vehicles. It is unique to vehicles that take advantage of the micro‐miniaturization of sensors and electronics to allow humans to view the world from a flying vehicle that could land and take off from the palm of their hand and can go places that are not accessible to anything on a human scale.
The motivation for larger UAVs is to provide long endurance at high altitudes with the ability to fly long distances from a base and then loiter over an area for many hours using a larger array of sensors to search for something or keep watch over some area. Increasingly, in the military arena, the larger UAVs also provide a capability to carry a large weapons payload a long distance and then deliver it to the destination area.
There now is increasing talk about performing missions such as heavy air transportation, bombers, and even passenger transportation with unmanned systems. Whatever may be the outcome of those discussions, it is likely that there eventually will be unmanned systems of all sizes.
In the following sections, we use intuitive‐size classes that are not in any sense standardized but are convenient for this discussion. In the next six sections, general features of micro, mini, very small, small, medium, and large UAVs are presented.
2.3.1 Micro‐UAVs
A new class of UAVs called micro‐UAVs is of growing interest, which have the attributes of large insects and very small birds. This is a term for a class of UAVs that are, as of this writing, still largely in the conceptual or early stages of development. They are envisioned to range in size from a large insect to a model airplane with a one‐inch wingspan. The advent of the micro‐UAV produces a whole new series of challenges associated with scale factors, particularly micro‐autopilot and control in atmospheric phenomena such as wind and gust.
Although there are still no active micro‐UAVs in existence, DARPA have attempted a program to develop micro‐UAVs including a flapping wing. The world’s smallest and lightest micro‐helicopter UAV was experimented and demonstrated by Japanese Epson Corporation – with a prop diameter of 130 mm and a mass of 8.9 g. Insight into the art of bird‐size UAVs may be obtained from Hank Tennekes’ book, The Simple Science of Flight from Insects to Jumbo Jets [7].
Assuming that payload and power‐plant problems can be solved, the low wing loading of these types of air vehicles may prohibit operation in all except the most benign environmental conditions (e.g., no wind). Some of these problems, and solutions, will be discussed in Part Two of this book.
2.3.2 Mini‐UAVs
This category stems from the old expendable definition and includes hand‐launched as well as small UAVs that have some type of launcher (could be hand‐launched). It is not officially defined by the JPO as a class of UAVs, but numerous demonstrations and experiments have been conducted over the past ten years.
These UAVs are exemplified by the electric‐powered Raven and Bayraktar mini‐UAVs in the selection of UAV examples earlier in this chapter. The Wasp UAV described among the previous examples is another example of a UAV at the upper limit of what might be called a “mini”‐UAV. The ANAFI Parrot can be considered as a mini‐UAV where it has a mass of about 0.5 kg, equipped with two 4K 21‐megapixel cameras, and can fly for about 32 minutes.
Another example for this class is the HR quadcopter, which has four electric engines, dimensions of 7.1 in × 6.7 in × 1.5 in, and a takeoff mass/weight of about 120 g (4.23 oz). It is equipped with a 1080P HD Camera and can take aerial photos/videos, with the built‐in WiFi module to broadcast a live video on a mobile device.
2.3.3 Very Small UAVs
For the purposes of this discussion, “very small UAVs” range from “micro” sized, which are about the size of a large insect, up to an AV with dimensions of the order of a 30–50 cm (12–20 in). There are two major types of small UAVs. One type uses flapping wings to fly like an insect or a bird and the other one uses a more or less conventional aircraft configuration, usually rotary wing for the micro size range. The choice of flapping wings or rotary wings often is influenced by the desire to be able to hover and land/perch on small surfaces to allow surveillance to continue without having to expend the energy to hover. Another advantage of flapping wings is covertness, as the UAV may look a lot like a bird or insect and be able to fly around very close to the subjects of its surveillance or perch in plan‐view without giving away the fact that it is actually a sensor platform.
At the small end of this range and for flapping wings, there are many special issues related to the aerodynamics