Airframes 5

Compass A compass is essentially a magnetized needle that is mounted so that it is allowed to move freely The needle will then point towards the magnetic North Pole and display the aircraft's magnetic heading On most RPAS it is an electronic magnetometer Large pieces of metal or even magnetic substances in the soil can affect a compass So for RPAS it is very important to calibrate the compass often and avoid taking off and landing in areas with a lot of metal The Compass should also be calibrated whenever you move to a distant location because the magnetic variation will be different Altimeter An altimeter indicates altitude by measuring the outside barometric air pressure through a static port on the aircraft. The air pressure compresses the Aneroid in the instrument and that reading is shown on a dial or display; if the static port is blocked the altimeter won't be able to detect a change in pressure and so it will not show a change in altitude (it will be stuck.) There is an adjustment knob to calibrate to the correct air pressure. Airspeed Indicator An airspeed indicator indicates the aircraft's speed through the air measuring ram air pressure through a pitot tube and the static outside pressure. The difference between the ram air pressure and the static pressure compresses the diaphragm and is used to indicate airspeed on the front display on most RPAS the airspeed indicator is a tiny electrical unit using a flex resistor as the diaphragm. IMU An IMU is an Inertial Measurement Unit It contains a series of accelerometers and Gyroscope that can be used to measure changes in the attitude, pitch, jaw and roll of the aircraft It is a critical component for controlling most RPAS because it provides the flight controller with the key information about the RPAS attitude The IMU must be initialized with the RPAS at rest on a flat, level surface, or it can get errors GPS GPS or "Global Positioning System" is a very accurate method to determine position on the Earth it consists of two main components: Satellites - Grid of 24-30 Satellites orbiting the earth at altitude of approx 20,000km emitting a signal A Receiver - in our case, mounted on the UAV At least four satellites can be detected at any point on earth, precise position can be determined by "triangulation" using at least three satellite signals. Using these signals and the receiver can determine the distance to each satellite.