Air Data Calibration and Measurement

IAR is currently developing a technique for the real time aerodynamic modeling of aircraft. The technique, known as RAMI (Real-time Aerodynamic Model Identification) will meet the stringent real time requirements of aerodynamic mathematical modelling used for developmental purposes.

RAMI and other aircraft modeling flight test programs require the measure of aircraft airflow angle (angles of attack, sideslip and other parameters). Common techniques for the measurement of these parameters rely on an externally mounted nose boom or nose cone equipped with pressure sensors. These installations are time consuming and require both physical hook-ups and electrical wiring.

IAR's experience with time-sensitive flight test programs has led to the development of an innovative angle of attack and sideslip sensor that quickly attaches externally as a 'mask' over the existing aircraft nose cone. The ongoing development of this nose mask encompasses state-of-the-art technologies in the following four areas:

1. the use of advanced miniature integrated digital and radio-frequency (RF) electronics
2. the construction of the mask from composite materials
3. the use of ultra small and highly accurate piezoresistive differential pressure transducers
4. the use of thin, rechargeable Nickel Metal Hydride (Ni-MH) cell batteries.

The nose mask employs a '4 hole' differential pressure sensor technique. The resultant data is transmitted by a short-range RF link at 418 MHz to a receiver possessing neighbouring noise rejection capabilities, within the aircraft cabin. An integrated battery within the nose mask provides the power to complete a self-contained remote sensor capable of operation within a temperature range of -40°C to +50°C.

The temperature compensated pressure transducers produce a static accuracy equivalent to 0.2° angles of attack and sideslip. The ongoing development of an additional temperature sensor at the mask will improve the overall accuracy. The Ni-MH battery cells with a 450 mAH power rating provides sufficient power for 15 hours of continuous operation at -20°C.

The installation time and effort is considerably reduced over that of existing methods and only very minor repair of the nose cone is required. The remote nose mask enables simultaneous calibration of the aircraft's air data system using the DGPS. The resulting air data coefficients for (i) position error corrections, (ii) upwash and (iii) sidewash effects were compared to the results obtained from the conventional ground speed course methods, the steady level, climb and descend flight and beta-sweep derived coefficients.

The unique combination of nose mask and the air data systems calibration technique flown in an optimal flight maneuver, which provides the position error correction, angles of attack and sideslip information, allows IAR to develop a more time and cost efficient method to validate air data systems.

The lab is also experimenting with another technique using Kalman filtering in real-time for air data calibration and measurements as well as model parameter estimation.

Related Information

Institutes:

• NRC Institute for Aerospace Research