MODELING AND CONTROL OF TRAILING EDGE FLAPS FOR GUST ALLEVIATION AND HANDLING QUALITIES

Open Access
Author:
ONeill, Eric Paul
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Joseph Francis Horn, Thesis Advisor
Keywords:
  • SH-2G
  • UH-60
  • Trailing Edge Flaps
  • Handling Qualities
Abstract:
Operating a helicopter in a turbulent wind environment is a difficult challenge for a pilot. Tasks that would be simple in a calm environment become a unique challenge when wind gusts begin changing the behavior of the rotorcraft. The requirements of constantly correcting the attitude of the aircraft can increase the pilot workload to unacceptable levels. Recently research has been focused on using automated control designs to compensate for wind disturbances, relieving some of the workload from the pilot. Control designs using swashplate actuation have run into trade-off issues between stability margin constraints and disturbance rejection considerations. The topic of this thesis is the modeling and design of an alternative control mechanism, on-blade control devices called trailing edge flaps, to improve handling qualities and disturbance rejection capabilities over those of the swashplate. A primary objective of this thesis is to establish an accurate model of the aerodynamic effects and dynamics of trailing edge flaps. A study of the dynamics of the rotor shows that a flap on the UH-60 would behave as a moment flap, working to twist the blade to change the distributed lift as opposed to creating only a local lift increment. The Genhel-PSU model is modified with a torsion degree of freedom to accurately model the effects of a flap on a UH-60 helicopter. To verify the accuracy of this implementation, the Genhel-PSU model is configured for the SH-2G Helicopter, since significant flight data and identified model is available for this aircraft. The identified model from previous research is compared with a linear model produced by the converted Genhel-PSU model. Significant differences are noticed in roll-flap and pitch-flap modes causing changes in the frequency responses. Model structure analysis reveals that the rotor time constant is significantly different from the value in the identified model. The identified value was substituted into the linear model, which corrected the discrepancies. Flap damping was added to the non-linear model, and the resulting linear model had a much closer frequency response match, as well the rotor time constant value matched the identified model much more closely. The rotor Lock number was varied in an attempt increase the predicted flap damping. A significant decrease in flapping inertia (~40%) created a model with a rotor time constant that matched the identified model, however the response for the modified model did not match the identified model. The cause of this discrepancy could not be identified. Actuation methods are an important consideration when using on-blade trailing edge flaps. Piezo-electric tube actuators are experimental designs that are both extremely fast, compact, and can be made to achieve the desired deflection. These actuators are still experimental and are just being used as a theoretical design. A model of a Piezo-electric actuator implementation for trailing edge flaps is developed. This model is then simplified and converted to work with the Genhel-PSU linear model. Different control architectures that make use of on-blade trailing edge flaps are explored to see if any advantage can be gained by utilizing them. Control designs are built in the control design software CONDUIT®, combining the proven performance benchmark ADOCS control architecture with a trailing edge flap compensator. Initial optimization attempts are unsuccessful, and upon analysis, the trailing edge flaps are found to be too similar to swashplate inputs to provide any advantages for direct gust rejection. Alternative control designs are attempted and it is shown that the flaps are effective when combined with rotor state feedback, achieving a 14% increase in the maximum disturbance rejection bandwidth, and may provide an advantage for implementation. A control design to reduce the cross-coupling effects achieves an incremental improvement in cross-coupling specifications, however the small improvements suggest the same advantages could be achieved using the swashplate.