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

There is a sensor (see Appendix 3) on Zephyr that measures the AoA, however ittends to have some error in its readings. The most likely reason for this is the lowtemperature causing the mechanism to fail as it is only rated by the manufacturer to -40°C. The sensor functions through a potentiometer which consists of a wind vaneconnected to a metal brush that wipes along a circular resistive track, outputting avoltage [10]. It is likely that in the cold temperatures (down to -80ºC), either thelubricant that allows the brush to move freezes, or the lubricant on the potentiometerfreezes thus breaking the contact between the track and the brush.As knowing the angle of attack is so important, new sensors had to be investigated inthe hope that they would be more accurate and reliable. These included the originalsensor but with a modified brush and lubricant which would allow the sensor to workat colder temperatures, and a non-contact sensor (in the way of magnetic or optical)which would remove the issue of parts needing to be in constant contact.After considerable research I found that the optical sensor (figure 11), whichconsisted of a glass disc that allowed light to shine through, was too delicate forZephyr’s environment.Figure 11. Diagram toshow the optical encodersetup [11]47