Acoustic Reflectometry for Pitot Tube Blockage Detection

Experimental and numerical acoustic results for Pitot tubes are presented to explore the theoretical basis for an acoustic blockage detection system. Three Pitot-statics from two different commercial aircraft were CT scanned to determine their internal geometry, and a finite element acoustic study was performed to determine the variation between blocked and unblocked reflected acoustic waves when subjected to a sinusoidal input. To validate this, supporting experiments were conducted on the same tubes when subjected to a range of blockage types, including tape, pre-deceased insects, foam, and metal. Experimental and numerical results confirm acoustic detection of all tested blockages is feasible in a quiet environment, for both the total and static pressure measurements, but only if the pressure line forms a clean waveguide along its length. The frequency range for detection is specific to each of the two Pitot designs, but a common feature is that the blocked/unblocked variation diminishes as frequency is raised due to an increase of impedance with frequency. A current limitation of the method is that is has not yet been shown to be operable in flight.