43 www.drivesncontrols.com July/August 2023 mini-tabs for wind tunnel testing. The tunnel can recreate unsteady conditions that simulate a tilt-rotor wing undergoing whirl flutter. The aim of the study is to gain fundamental knowledge on the effectiveness of counteracting whirl flutter. If successful, the principle could be turned into a reality on real-life tilt-rotor aircraft. Experimentation For the experiments, the mini-tab device was installed towards the rear of the wing, ahead of the hinge line where an aileron would be located on a real aircraft. The wing was suspended from the wind tunnel ceiling, with a set of hydraulic actuators driving oscillations in three degrees of freedom – parallel to the airflow (known as surge), perpendicular to the airflow (known as plunge), and rotation (known as pitch). The mini-tab performance was monitored using pressure sensors. Powering the mini-tab is a motor mounted in the wing. To achieve accurate test results, the team needed to deploy the device at high frequencies, with high precision and low latency. They chose a 200W maxon EC 60 brushless motor with integrated Hall sensors for position feedback. The motion system is driven with both feedforward and feedback control. The combination of the two reduces lag time and helps to oppose the acceleration effects of the wing vibrations, which would otherwise cause the mini-tab to drift from the intended deployment position. “What we were most concerned about was accurate position feedback,” says Bull. “We needed really clean feedback signals so we could achieve high positional accuracy at a given deployment frequency. The maxon motion system gives us this performance. “Our experimental pressure data shows that when you start deploying a mini-tab, it changes the pressure field around the entire wing,” he adds. “Already we know that you can use these devices to augment the pressure and the loads around the wing to counteract whirl flutter vibration.” Nobody has tested this concept before on a moving wing before, so the IPM team are the first in the world to achieve this. What could the discovery mean for the future of tilt-rotor aircraft design? “The aerodynamic response from the minitab is non-linear, so it’s difficult to predict,” says Bull. “This adds to the challenge of designing a controller that can effectively deploy the minitabs to counteract whirl flutter. We’re at the stage where we’re understanding and characterising the aerodynamics, but if we could develop a model of this in the future, we could potentially design a controller to tame whirl flutter vibrations. That would be the next stage.” n The motion system inside the wing section built by the IPM team to test mini-tabs in a wind tunnel INDUSTRIAL SENSORS NEXT GENERATION Reduced Power Consumption Increased Precision & Accuracy Large Variety of Communication & Mechanical Con昀gurations www.posital.com Absolute & Incremental Industrial Encoders Multiturn Kit Encoders No Battery - No Gears Thanks to Wiegand Technology Enhanced Protection Against Dust & Moisture Easy Installation - Reduced Housing Dimensions Visit us at EDS 2023 Booth E41
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