Airframes 6

How is Distance Determined? • Each satellite has a VERY accurate atomic clock • The receiver has a (less) accurate clock • Distance is determined by comparing times and calculating how long it took the signals to reach the receiver Kev Point The more satellites you can detect the more accurately your position will be known (because of the inaccuracy of the clock in the receiver) Sources of GPS Errors Signal multi-path - this occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors Number of satellites visible - buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possible no position reading at all. GPS units typically will not work indoors, underwater or underground. Ionosphere and troposphere delays - the satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error. Receiver clock errors - a receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors. Orbital errors - also known as ephemeris errors, these are inaccuracies of the satellite's reported location. Satellite geometry/shading - this refers to the relative position of the satellites at any given time. Ideal satellite geometry exits when the satellites are located at wide angles relative to each other poor geometry results when the satellites are located in a line or in a tight grouping. Autopilot As the name implies, an autopilot is a piece of equipment that automatically operates some of the pilot controls on an aircraft typically it incorporates complex software (firmware) so it is critical to ensure that your RPAS firmware and ground station firmware is up to date and is using the correct software version from the manufacturer. There are different levels of autopilot control, ranging from simply stabilizing the RPAS up to completely automatically flying the RPAS A pilot must know exactly what mode the autopilot is in and understand clearly what it will do in each mode A pilot must also know how and be ready to disable the autopilot at any time if it isn't behaving properly