UAV flight analysis with miniature inertial sensor

Multi-purpose airborne sensor carrier UAV

MASC is a small UAV developed for atmospheric boundary layer research. Moreover, the Environmental Physics group at Eberhard Karls Universität Tübingen, Germany, designed and operates it. The team chose the Ellipse-N to record UAV position, ground speed, and attitude angles. In addition, wind speed and direction can be accurately calculated by considering airflow.

However, in-flight wind computation is challenging because the airflow probe requires compensation for UAV behavior.
Thus, precise inertial measurement becomes essential for accurate flight analysis.
The typical payload for this UAV is a meteorological measurement system, designed to calculate turbulent fluxes.

Compared to terrestrial systems or aircrafts, the MASC UAV is a cost-effective and valuable tool for researches such as wind energy plant site evaluation in complex terrain.

“In-Flight” wind speed computation

In-flight wind computation presents challenges because the embedded airflow probe requires compensation for UAV behavior. Moreover, subtracting UAV ground speed and attitude from the airflow vector calculates wind speed and direction. Thus, a precise inertial measurement unit becomes essential for accurate UAV flight analysis.

Our Ellipse-N: the GPS-aided miniature INS

Turbulence plays an important role in the transport and exchange of energy in the lower atmosphere.

A high data rate is required to record these very fast fluctuations in the wind speed. “We were looking for a precise inertial measurement unit. Required specifications were an accuracy in attitude angles of <1°, and a high data output rate” declares Uwe Putze, Dr.-Ing. at the Eberhard Karls Universität Tübingen.

As the unit had to be mounted in a small unmanned aerial vehicle, small size and low weight were also important for the project. “The Ellipse-N was selected because it fulfills all the requirements and provides a unique balance of accuracy, size and weight”, adds the Project Engineer.

Small-size and lightweight, the Ellipse-N offers more than attitude and heading measurement. It fuses inertial data with GPS and pressure sensor information to provide a robust position and an enhanced altitude accuracy.

The report showing the sensor dynamic calibration over the full temperature range made the team even more confident that the system would meet the announced specifications.

Ellipse-N high quality data

The Ellipse-N integrated smoothly into the on-board measurement computer through a serial interface. Moreover, this seamless connection enabled efficient data transmission.

While the airflow probe measured airspeed and incident angles, the Ellipse-N recorded UAV position, ground speed, and attitude angles. In addition, the computer stored raw data for later use. Moreover, a telemetry link allowed real-time display on the ground station.

By using this sensor, the system measured wind speed with ±0.5 m/s accuracy across all three axes. Furthermore, it recorded speed variation at up to 20Hz, while the 200Hz output rate removed the need for interpolation.