Zephyr: A High Altitude Long Endurance Unmanned Air Vehicle ...

Chapter 3My Projects3.1 RadiosondeCurrently a program has been created that allows the user to enter the altitude theywant the aircraft to fly at and it automatically calculates the power needed to achievethis height. The program takes into account the air temperature, pressure, air speedand density amongst other things in order to calculate the power. While the otherthree variables are being measured on the aircraft continuously, the density values thatare used are from the International Standard Atmosphere (ISA) model which showshow a number of variables, including density, change over a range of altitudes. Thishowever is a general model and in reality the density varies depending on yourlocation, the air pressure and temperature, and the weather systems present.While on trial, NASA transmits radiosonde data to the team which gives accurate dataabout the weather conditions in the area at that time. A radiosonde is a type ofweather balloon that is radio controlled, which measures and transmits currentweather data. By comparing the standard data to the actual data it was possible for meto calculate the difference between the two. Knowing this information allows an errorto be incorporated into the program in order to give a more accurate density andtherefore a more accurate power estimate. Eventually the density will also bemeasured on the aircraft along with the other variables and there will not be a need forthe radiosonde data.28