NASA’s Langley Research Center has developed a new method for calibrating pitot-static air data systems used in aircraft. Pitot-static systems are pressure-based instruments that measure the aircraft’s airspeed. These systems must be calibrated in flight to minimize potential error. Current methods — including trailing cone, tower fly-by, and pacer airplane — are time- and cost-intensive, requiring extensive flight time per calibration. NASA’s method can reduce this calibration time by up to an order of magnitude, cutting a significant fraction of the cost. In addition, NASA’s calibration method enables near-real-time monitoring of error in airspeed measurements, which can be used to alert pilots when airspeed instruments are inaccurate or failing. Because of this feature, the technology also has applications in the health usage and monitoring (HUMS) industry. Flight test engineers can be trained to use this method proficiently in 12 days without costly specialized hardware.
The method for pitot-static calibration is a novel application of modern system identification methods for in-flight airspeed calibration. True airspeed is calculated using measurements from a global positioning system (GPS) by vector summing ground speed and estimated wind speed. This value is used to estimate actual impact pressure, which is compared with the impact pressure measured by the flight instrumentation for a range of airspeeds. The difference between these values is the error in impact pressure measurements. The optimization process calculates a mathematical model of the pressure error as a function of calibrated airspeed and an estimate of the wind speed and direction. A statistically based maximum likelihood method known as output-error is used to estimate the parameters describing the pressure error model and the wind vector values. This method can work with any airplane with a digital flight data system.
The technology can be used in aerospace applications replacing current legacy pitot-static calibration methods, and in aerospace health usage and monitoring systems measuring error in airspeed instruments in near-real-time to improve air safety.