Line-of-Sight Guidance Laws for Formation Flight

Abstract

Two-dimensional formation guidance laws for formation flight using only line-of-sight angle information are addressed. The main idea is to use the line-of-sight angles to two nearby vehicles to maintain the formation position of the current vehicle. Such a formation guidance law is useful because measurement of the line-of-sight angles does not require data communication between the vehicles. We propose two methods of using the line-of-sight angle information for formation guidance: the angle information is used to control the flight-path angle and the velocity of the formation vehicle. Approach guidance and formation guidance of the two leading vehicles are also proposed. Stability of the proposed formation guidance laws is analyzed by using the Jacobian at the equilibrium point. Multiple-vehicle formation flight is simulated to verify the guidance laws proposed. ORMATION flight of manned aerial vehicles is in general vi- sually coordinated by the pilots. The pilots maneuver their air- crafts to align other aircrafts on specific points inside their cockpit. However, continuing formation flight for an extended period of time is a tiresome job for the pilots. Autonomous formation flight relieves the pilots and is also applicable for a group of unmanned aerial vehicles (UAVs) performing complex missions. Recently, NASA used two F-18s to check the feasibility of autonomous formation flight and the aerodynamic energy benefits. 1 Also a study on tight- formation flight of Lockheed C-5 transport models has shown a reduction in power demand that is directly related to extension in range. 2 To achieve autonomous formation flight, communication is re- quired between the vehicles involved. Depending on the formation control method, some of the vehicle's data are broadcast to the en- tire group or they are passed on to the adjacent vehicles only. The simplest case involves transmitting only the leader's position to the followers. 2−4 All the vehicles in formation have an independent navigation system to acquire their own position and velocity infor- mation. In Ref. 5, a wireless communication network approach to formation control is introduced. It uses mobile nodes that require position and velocity data of each vehicle. Data received from other vehicles are first used to update the receiver's state of formation. Then the modified data are relayed to other vehicles. This reduces the total bandwidth of communications involved in the formation. For rapid formation maneuvers, the use of the leader's Euler data in addition to position and velocity is proposed for better performance. 6 In Ref. 7, a globally stable automatic formation flight control is de- rived on a formation that requires position, velocity, heading, and leader's input data by the aircrafts. Because most autonomous formation flight methods require an active communication link between the vehicles, damage to the re- ceiver or the transmitter is critical to mission success. Vehicles with defective sensors are commanded to leave the formation and a re- configuration of the formation is required. 8,9 Communication delay also affects the formation. 10 Thus, military missions generally pre- fer low-bandwidth communication and, if possible, radio silence for stealth purposes. Passive detection of another vehicle and main- taining the formation, if possible, would be much preferred to the methods that use two-way data links.