Experimental Validation of an Aerodynamic Sensing Scheme for Post-Stall Aerodynamic Moment Characterization

Abstract

A fixed-wing aircraft that is capable of low airspeed, high angle of attack flight can serve an expanded range of mission goals. A typical propeller-driven small unmanned aircraft can be equipped with an engine that provides greater thrust than airplane weight; in post-stall states, the aircraft then depends on propeller backwash over the tail for control moment generation. Due to this dependence on propeller wash and potentially negligible free-stream airspeed, conventional wind-vector measurements cannot adequately describe the aerodynamic forces and moments acting on the aircraft. This paper describes a distributed pressure sensing system for a small UAS, enabling in-flight estimates of pitch and yaw moments due to the tail surfaces. A wind tunnel test model was developed around an existing flight vehicle with a 1.8m wingspan. Embedded pressure measurements were taken across the tail surfaces at low-airspeed high-thrust conditions. Test data is used to develop a method of determining the in-flight aerodynamic pitch and yaw moments due to the tail surfaces on a fixed wing UAS. Through comparisons with torque transducer measurements, the pressure based measurements are shown to provide moment estimates within one standard deviation interval of transducer measurements at hover, thus are capable of providing accurate moment feedback for fixed wing UAS.

Aerodynamic Variables and Loads Estimation Using Bio-Inspired Distributed Sensing

“…Using the wing model and testing rig described in Section II, a series of characterisation experiments were carried out in the University of Bristol low turbulence wind tunnel [22]. Quasi-static as well as dynamic tests were performed at air speeds V = [8,10,12,14,16,18,20] m/s to characterise the aerodynamic loads, pressure and strain signals. These tests consisted of α sweeps at various pitch rates.…”

“…These systems have utilized a number of different types of sensors such as diaphram based pressure sensors [15], hot film sensors [16] and artificial hair sensors [17]. Studies of these systems in wind tunnel testing, as well as flight testing [18], have shown the potential of these systems for measuring a range of aerodynamic parameters.…”

Bio-inspired Distributed Strain and Airflow Sensing for Small Unmanned Air Vehicle Flight Control

“…This type of distributed information could be integrated as part of a physics based control approach, being based on the estimating the total forces and moments acting on the aircraft. [8][9][10] Or alternatively this information could be used to achieve a more robust estimate of the aircrafts dynamic state, where the state is estimated based on fusing the signals from a number of different sensors rather than a single sensor. This approach has many similarities to the "mode sensing" approach hypothesized to be used by insects, 5 but raises the question as to what are the appropriate states to measure when fusing information from distributed sensors or from different sensory modalities.…”

“…In some cases the pressure is integrated over the surface to provide measurements of the forces and/or moments acting on the aircraft. [8][9][10] While in other cases the sensors comprise part of a flush air data system used to give estimates of aerodynamic state variables such as air speed, angle of attack and sideslip. 11,12 There have also been investigations into the potential advantages offered by unconventional flow sensors such as artificial hair based flow velocity sensors.…”

Artificial Neural Network-Based Flight Control Using Distributed Sensors on Fixed-Wing Unmanned Aerial Vehicles

“…These systems have utilized a number of different types of sensors such as diaphragm based pressure sensors [18], hot film sensors [19] and artificial hair sensors [20]. Studies of these systems in wind tunnel testing [21], as well as flight testing [22], have shown the potential of these systems for measuring a range of aerodynamic parameters.…”