Tethered payload motion control using magnetorheological actuators for aerial vehicles

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Slung loads have been use for decades on conventional helicopter to lift heavy payloads, or large payloads that cannot fit inside the fuselage. The payloads are usually attached to a single hook underneath the helicopter fuselage, near the rotor thrust axis. External loads attached to rotary-wing aircraft can pose significant challenges to the pilot or the automated control system. First, instabilities can occur at high speed for light payloads or for bluff bodies, such as a canoe, or solar panels. Second, the dynamic motion of a payload well below the fuselage ("long lines") can be complex for a pilot to control manually without inducing long period oscillations. More recently, a gain in interest for slung loads has been seen from the unmanned aircraft (UAV) industry for the package delivery, where there is a need to drop a payload without the need to land. Since light payloads are more likely to be affected by wind gusts, those challenges should be more prevalent to UAV-scale aircraft than full-size helicopters. One approach to control the payload motion is to couple the dynamics of the two rigid bodies. Multiple tethers could be attached to the nose or tail of the helicopter. Such approach has been proposed, but helicopters and UAVs have very limited external forces (and moment) that can be applied safely, and any changes should be smooth. Due to the conventional control in position from mechanical winches (in series to the tethers) the risk associated with this approach exceed the potential benefits. This research aims at assessing the feasibility of using magneto-rheological (MR) actuators as the technology enabler to provide active payload motion control both for full-scale helicopters and UAV-size aircraft. MR actuators show great potential since they are controlled in tension (or torque), have a frequency response in the order of 50 Hz, and naturally can filter the rapid changes in forces. Both numerical and physical experiments are planned. This research projet will benefit Canada as it will provide new business opportunities for the Canadian company Exonetik, which aims at commercializing the products based on the research results in the coming years.************************************************