Unmanned Aerial Vehicle (UAV) is an aircraft with no on board pilot. Instead, it is remotely controlled or can fly autonomously based on pre-programmed flight plans or more complex dynamic self thinking’ systems. While to some extent such unmanned aircraft resemble cruise missile, they differ that they return to base for further use once they have fulfilled their mission. Wilderness search and rescue (wisar) is a complicated problem requiring thousands of hours of search over large and complex terrains. Using mini uavs to support WiSAR has the potential to dramatically improve search efficiency UAVs are often categorized based on performance (linked often to size). There are several categorizations from producers, users and researchers.
UAVs can be classified according to the way their flight is controlled, of which there are three methods. They are
- Remote control
- Self thinking (which can be combined)
Each means of control provides both challenges and opportunities Remote control is the most common control system for UAVs. By radio, the operator receives flight data from the UAV and sends flight commands back. The weak points of this system lie in the vulnerability of the continuous radio links, which reveal the positions of both the controller and the UAV, and the fact that radio links limit the UAV’s range. More advanced, less vulnerable radio links and indirect radio links (e.g. via satellites or relay UAVs) are a partial solution. Self thinking UAV's are still a futuristic option. The technical challenges to develop a fully autonomous UAV are still insurmountable. nevertheless, as element of self thinking has been achieved in a much as UAV's are able to react to threats, for example, when attacked by air defense missile UAV's and UCAV's are themselves just aircraft with on board systems, however they are usually linked to additional equipment outside, such as remote controlled and launching equipment.
A throttle controls the thrust produced by an engine and is used to make the plane go faster or slower. Planes with more than one engine like passenger jets will have one throttle for each engine. The way that the throttle works depends on the type of the engine, but it will generally increase the amount of fuel being consumed by the engine, which will in turn generate more heat or spin a propeller faster. Depending on the position of the engines, increasing the throttle may also cause the plane to climb, roll or turn. In fact computer programs have been written that allows planes with two or more engine to be flown and landed using only the throttles. These programs are to help the aircraft to land safely when the other controls have failed.
An aircraft is flying because force called lift is grater than the gravitational force. Four forces acting on the aircraft are
Gravity is easy to determine. It is difficult to access other three forces. These forces are determined by the aerodynamics that describes the forces generated by an object moving though the atmosphere. Together these forces determine where the plane goes. For example, if thrust is greater than drag, plane will accelerate.
Radio Frequency Remote Control
R/C pilot controls the model by a radio link using electromagnetic radiation. Transmitter is operated by the pilot and the airborne units consisting in a receiver together with one or more Servo's depending on the number of channels used and a battery pack. A typical RC transmitter have 4 to 6 channels which are proportional which means that the device will move proportionally to the movement of the control sticks. The RC transmitter sends the data to the RC receiver by generating a modulated radio frequency carrier, while the receiver is turned to detect the transmitters carrier frequency. Crystals are used for accuracy. receiver detects the data from the modulated carrier , decodes and delivers it to the respective Servo.
Pulse width modulation is used to control the servo. With PWM technique, direction of applying pulses of variable width, by changing or modulating the pulse width of the power. With the pulse width small, the average voltage applied onto the motor is low, and the motors speed is low. if the width is wide, the average voltage is higher, and therefore motor speed is higher.