Hobbypower Airspeed Sensor MPXV7002DP Differential Pressure for APM Flight controller

Plane supports the use of an airspeed sensor, which can help in windy condition, slow flight and autonomous landings. It is not recommended for most new users, however, as it does require additional tuning and adds one more layer of control to set up.
The way it works is that the top tube is "active" (measures air pressure from the pitot tube that is open at the front and has air driven into it by airspeed) and the bottom one is "static" (measures ambient air pressure from tube with intakes on the side).
Connect the active sensor port using silicon tube to the straight tube exiting from the rear of the pitot tube. The angled tube is the static part connecting to the static port of the sensor (the port on the sensor closest to the PCB breakout board)
After you install an airspeed sensor don't forget to calibrate it!

More information please reference this link:
http://plane.ardupilot.com/wiki/common-optional-hardware/airspeed-3/

Package includes
1x Airspeed Sensor
1x Male to male cable
1x Pitot tube
1x Silicon tube