FAAM CORE 5-hole turbulence probe, measuring incident airflow and 3-d wind components.
 
The turbulence probe on the FAAM aircraft consists of a five-port pressure measurement system in the aircraft radome, combined with two scientific static ports - S10 - symetrically placed on either side of the aircraft. The system also utilises measurements from the RVSM-compliant air data computer and science measurements of the ambient air temperature, corrected for kinetic effects.

Outputs from the Turbulence system are the angles of attack and sideslip and a measurement of true airspeed. These data are used in conjunction with other core measurements of aircraft attitude and aircraft velocity components to derive northwards, eastwards and downwards components of wind velocity.  

Images

Probe Schematic 5-hole Arrangement in Radome Internal Ports

Documentation

The original Acceptance report for the turbulence probe system is available for registered users. This document includes the calibration and iteration scheme to derive airflow angles and TAS from trubulence probe differential pressure measurements:
 
 
This Met Office report documents the initial calibration process of the Turbulence probe, again it is only available to registered users:
 
 

Data

Data from the Turbulence Probe is reported at 32Hz.
 
The original system specification called for BAES to provide a turbulence probe capable of measuring to the following accuracies: airspeed to ±0.4 m/s, air incidence to ±0.1° and static pressure to ±2 hPa. Assessment of the actual turbulence probe uncertainties is ongoing, but indications are that the overall 1-sigma uncertainty for air incidence angle meets the specification at around ±0.1° (Alan Woolley, 7/8/07)
 
Under some flight conditions, generally when the aircraft penetrates cloud containing supercooled water droplets, ice can form on the aircraft skin. The radome is especially susceptible to this problem and is not in one of the critical aerodynamic areas that benefit from the aircraft's anti-icing systems. When ice forms on the radome this has in the past led to invalidation of the turbulence probe measurements. Occasionally in-flight manoeuvres can be used to remove the icing but on the whole, where the turbulence probe freezes to some extent, data are likely to be lost.
 
Following icing occurrences, small amounts of water tend to be retained inside the pressure ports after landing. To avoid potential condensation problems within the probe ports it is important that the internal 'dashpots' are emptied regularly. This is normally performed on a weekly basis.
 
In June 2007 a modification was made to the Turbulence centre-port (P0) in which a small heater was installed. This is intended to reduce the susceptibility of P0 to icing, and to assist in recovery from severe icing events.
 
Icing events followed by extreme changes in height can affect the calibrations of the turbulence probe pressure transducers. Data quality may be adversely affected following these instances.
 

Further Details

Contact Alan Woolley at FAAM