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 that allow the small UAVs to fly. However, in all cases the basic aerodynamic principles and equations apply, and one needs to understand them before proceeding to the special conditions related to very small size or flapping wings. Part Two of this book introduces the basic aerodynamics and some discussion to the issues for small size and flapping wings.
Examples of very small UAVs include the Chinese DJI mini 2, which is a quadcopter that can hover (i.e., vertically takeoff and land); the Israeli IAI Malat Mosquito, which is an oval flying wing with a single tractor propeller; the US Aurora Flight Sciences Skate, which is a rectangular flying wing with twin tractor engine/propeller combinations that can be tilted to provide “thrust vectoring” for control; and the Australian Cyber Technology CyberQuad Mini, which has four ducted fans in a square arrangement.
The Mosquito wing/fuselage is 35 cm (14.8 in) long and 35 cm (14.8 in) in total span. It uses an electric motor with batteries and has an endurance of 40 minutes, and claims a radius of action of about 1.2 km (0.75 mile). It is hand or bungee launched and can deploy a parachute for recovery.
The DJI Phantom 4 Pro quadcopter has four electric engines, dimensions of 9.9 in × 15.7 in × 6.75 in, and a takeoff weight of about 3 lb. It is equipped with an electro‐optic camera and autopilot that allows fully autonomous waypoint navigation. It can be controlled via a smart phone as a ground control station using a Wi‐Fi connection, by which the live videos are received.
The Skate wing/fuselage has a wingspan of about 60 cm (24 in) and length of 33 cm (13 in). It folds in half along its centerline for transport and storage. It has twin electric motors on the leading edge that can be tilted up or down and allow vertical takeoff and landing (VTOL) and transition to efficient horizontal flight. There are no control surfaces, with all control being accomplished by tilting the motor/propeller assemblies and controlling the speed of the two propellers. It can carry a payload of 227 g (8 oz) with a total takeoff weight of about 1.1 kg (2 lb).
The CyberQuad Mini has four ducted fans, each with a diameter of somewhat less than 20 cm (7.8 in), mounted so that the total outside dimensions that include the fan shrouds are about 42 cm by 42 cm (16.5 in). The total height including the payload and batteries, which are located in a fuselage at the center of the square, is 20 cm (7.8 in).
The CyberQuad Mini includes a low‐light level electro‐optic camera or thermal camera and a control system that allows fully autonomous waypoint navigation. The toy has two onboard cameras, one facing forward and one facing down, and is controlled much like a video game from a portable digital device such as a tablet computer or a smart phone. Drawings of these UAVs are shown in Figure 2.2.
Figure 2.2 Very small UAVs
2.3.4 Small UAVs
What we will call “small UAVs” have at least one dimension of greater than 50 cm (19.7 in) and go up to dimensions of a meter or two. Many of these UAVs have the configuration of a fixed‐wing model airplane and are hand‐launched by their operator by throwing them into the air much as we launch a toy glider. In the past ten years, the quadcopters for this class – with VTOL capability – have been operational and gained a significant market.
Examples of small UAVs include the US AeroVironment Raven and the Turkish Byraktar Mini, both conventional fixed‐wing vehicles. There are also a number of rotary‐wing and multi‐copter UAVs in this size grouping, but they are basically scaled‐down versions of the medium rotary‐wing systems discussed in the following section and we do not offer an example in this group.
The RQ‐11A Raven is an example of a UAV that is in the “model airplane” size range. It has a 1.4‐m (4.6‐ft) wingspan and is about 1 m (3.3 ft) long. It weighs only a little less than 4.4 lb (mass of 2 kg) and is launched by being thrown into the air by its operator in much the same way that a toy glider is put into flight. It uses electrical propulsion and can fly for nearly an hour and a half. The Raven and its control “station” can be carried around by its operator on his/her back. It carries gimbaled visible, near‐infrared (NIR), and thermal imaging systems for reconnaissance as well as a “laser illuminator” to point out target to personnel on the ground. (Note that this is not a laser for guiding laser‐guided weapons, but more like a laser pointer, operating in the NIR to point things out to people using image‐intensifier night‐vision devices.)
The latest model, the RQ‐11B Raven, was added to the US Army’s Small UAV (SUAV) program in a competition that started in 2005. Built by AeroVironment, the Raven B includes a number of improvements from the earlier Raven A, including improved sensors, a lighter Ground Control System, and the addition of the onboard laser illuminator. Endurance was improved, as was interoperability with battlefield communication networks.
The Bayraktar small UAV was developed by Baykar Makina, a Turkish company. It is a conventionally configured, electrically powered AV somewhat larger than the Raven, with a length of 1.2 m (3.86 ft), wingspan of 2 m (5.22 ft), and weight of 5 kg (105 lb) at takeoff. It is advertised to have a spread‐spectrum, encrypted data link, which is a highly desirable, but unusual, feature in an off‐the‐shelf UAV. The data link has a range of 20 km (12.4 miles), which would limit the operations to that range, although it may depend on the local geography and where the ground antenna is located, as discussed in detail in Part Five of this book (Data Links).
Figure 2.3 Small UAVs
Figure 2.4 Boeing‐Insitu ScanEagle
(Source: U.S. Navy / Wikimedia Commons / Public Domain)
The Bayraktar has a gimbaled day or night camera. It offers waypoint navigation with GPS or other radio navigation systems. Despite its slightly greater size and weight, it is launched much like the Raven. It can be recovered by a skidding landing on its belly or with an internal parachute. It is fielded with small army units and has been heavily used by the Turkish Army since it was fielded in about 2006. Drawings of these examples are shown in Figure 2.3.
The Boeing‐Insitu ScanEagle (Figure 2.4) with a wing span of 3.11 m (10.2 ft) and a maximum takeoff weight of 58 lb (mass of 26.5 kg) is also classified as a small UAV. Insitu has produced about 3,000 EcanEagle air vehicles, which had a total of about 140,000 land and maritime sorties. The UAV carries a maximum of 5 kg of payload (EO/IR and ViDar sensors) for day/night and maritime surface search missions. The vehicle performance is: (1) maximum speed: 80 knots, (2) endurance: 18 hours, and
