Do you remember Bernoulli equation? it simply says that if you know the difference between the total pressure (static + dynamic) and the the static pressure, then you can calculate the speed.

The airspeed sensor kit make use of this principle. The pitot tube have to two tubes. The first is in the direction of the airstream and therefore feels the total pressure. The second in perpendicular to airstream and thus feels the static pressure.

The two pressures are sensed by Freescale differential pressure sensor MPXV7002DP. Where DP stands for differential pressure as the sensor measure the pressure difference between the two pressures applied to the two ports.

The MPXV7002DP is designed to measure positive and negative pressure: -2 to 2 kPa (-0.3 to 0.3 psi) corresponding to 0.5 to 4.5 V Output .  It output a high level analog output signal that is proportional to the applied pressure.

Kit includes:

1.  Freescale differential pressure sensor (MPXV7002DP) on a board
2.  High quality pitot tube
3. Connecting cables 
4.  Air hoses

Features

• Pressure difference range -2 to 2 kPa
• Low pass filtered. 
• Temperature Compensated over 10° to 60°C.
• Durable Thermoplastic (PPS) Package. 

Diffrential pressure sensor Data Sheet

Air speed sensor Set up instructions