Tilt Rotor Aerodynamics

Lead Research Organisation: University of Manchester
Department Name: Mechanical Aerospace and Civil Eng

Abstract

Purpose of this project is to investigate the aerodynamic performance of tilt-rotors in the conversion corridor, when the aircraft is converting from helicopter to aircraft mode. During this transition, the loads on the propellers, the wings and the whole aircraft are unsteady and the vehicle is in a critical flight condition. The student's role is to investigate these effects, develop a theoretical model to predict the rotor wakes and the rotor loads, in- and out of ground effect. Since the project is partly funded by the Aircraft Research Association (ARA, Bedford), the student will spend some time at the company's laboratory t understand the role of aerodynamic testing in the wind tunnels.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509565/1 01/10/2016 30/09/2021
1830568 Studentship EP/N509565/1 30/06/2016 30/06/2019 Wesley Jake Appleton
 
Description This work on tiltrotor aerodynamics focused on two main areas: the first was the development of an aerodynamic model for convertible rotor systems; secondly the development of a generic aerodynamic and flight mechanics (aeromechanics) model for tiltrotor aircraft. The aeromechanics model was used to investigate tiltrotor aircraft performance through the conversion corridor, where the aircraft transitions from rotor-borne to wing-borne flight through the tilting of the rotors from a vertical to a horizontal setting.

The aerodynamic model for the rotor was developed for arbitrary operating conditions throughout the conversion corridor covering helicopter, transition and aeroplane mode operation. The predicted performance has been compared with publically available experimental data and showed good levels of predictions overall. Due to the large operating domain of the rotor, the performance model was developed from reduced-order models to save computation time. Deficiencies in the different components of the performance model are implicitly linked and, therefore, to improve the predicted performance requires higher-order models incursive of greater computation time. The predicted performance showed that, due to the hybrid design for helicopter and aeroplane mode operation, the aerodynamic loading along the span was unconventional compared to typical blade designs.

This work on tiltrotor aerodynamics focused on two main areas: the first was the development of an aerodynamic model for convertible rotor systems; secondly the development of a generic aerodynamic and flight mechanics (aeromechanics) model for tiltrotor aircraft. The aeromechanics model was used to investigate tiltrotor aircraft performance through the conversion corridor, where the aircraft transitions from rotor-borne to wing-borne flight through the tilting of the rotors from a vertical to a horizontal setting.

The aerodynamic model for the rotor was developed for arbitrary operating conditions throughout the conversion corridor covering helicopter, transition and aeroplane mode operation. The predicted performance has been compared with publically available experimental data and showed good levels of predictions overall. Due to the large operating domain of the rotor, the performance model was developed from reduced-order models to save computation time. Deficiencies in the different components of the performance model are implicitly linked and, therefore, to improve the predicted performance requires higher-order models incursive of greater computation time. The predicted performance showed that, due to the hybrid design for helicopter and aeroplane mode operation, the aerodynamic loading along the span was unconventional compared to typical blade designs.

The aeromechanics model was configured to an available literature model for the Bell XV-15 tiltrotor and was used to investigate the effects of the different interactional aerodynamics on the conversion corridor boundaries and steady-state flight behaviour. The interactions considered consisted of the rotor-on-wing, rotor-on-empennage and wing-on-empennage. The results of the work showed that overall, the interactions had a small effect on the predicted boundaries but were found to mostly expand the corridor. The main effect of the rotor-on-wing interaction was an increase in thrust and power from hover to around 40 kn forward flight speed as a result of the download on the airframe. With the rotors in helicopter mode, the upwash caused by the rotor-on-empennage interaction was the most pronounced interaction and caused a more nose-down pitch attitude and aft stick position. Additionally, a shallow control stick speed-gradient was found at low speeds. As the rotors were tilted forwards, the increased pitch attitude to oppose the rotor tilts increased the wing downwash and the wing-on-empennage interaction became the most pronounced interaction. This had the opposite effect on the flight behaviour compared to the rotor upwash from the rotor-on-empennage interaction case - a reduced pitch attitude and more forward stick position. This has shown the effects of the interactions should be considered for accurate steady-state flight predictions and therefore there is a need for analytical and empirical models to predict these interactions for tiltrotor configurations and designs.
Exploitation Route The aeromechanics models have been developed in a generic manner to accommodate arbitrary geometries and configurations. Therefore, the conversion corridor performance and steady-state behaviour of different tiltrotor aircraft can be quickly and readily assessed using the developed framework, provided all the required input data is known. Furthermore, the model can be developed into a flight dynamics model and can be used to develop control strategies through the conversion corridor. Finally, the model can also be used to analyse methods to increase the conversion corridor boundaries to widen the operating space.
Sectors Aerospace, Defence and Marine