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:
1. The development of a performance model for these unconventional rotor systems.
2. The development of a generic aeromechanics (aerodynamics + flight mechanics) model for tiltrotor aircraft.

The rotor performance model was developed for arbitrary operating conditions throughout the operating domain of tiltrotor aircraft: helicopter mode, conversion mode and aeroplane mode. Due to the large operating domain of the rotors, 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 was compared with publicly available experimental data and showed good levels of agreement overall. More experimental data is required for a thorough validation study, however. 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 helicopter blade designs.

The aeromechanics model was used to investigate aircraft performance through the unique conversion corridor. This region of flight transitions the aircraft from rotor-borne to wing-borne flight and is achieved by tilting the rotors from vertical to horizontal. The aeromechanics model was configured to an available literature model for the Bell XV-15 tiltrotor aircraft. The model was used to investigate the singular and combined effects of the interactions between the rotors, wing and empennage components on the aircraft performance, trim behaviour and conversion corridor boundaries. The results of the work showed that:
1. The fuselage pitch angle was reactive to the rotor tilt at lower airspeeds, i.e. as the rotors were tilted forwards the fuselage pitch increased.
2. The rotors-on-wing interaction was dominant in hover and low-speed helicopter mode flight, requiring a considerable increase in thrust and power.
3. The rotors-on-empennage and wing-on-empennage interactions were opposing and important to consider throughout the operating domain. In helicopter mode, the upwash at the empennage from the rotors was most pronounced and resulted in a more nose-down pitch angle of the fuselage in trim. As the rotors were tilted forwards, the downwash from the wing at the empennage was most pronounced and resulted in a more nose-up fuselage pitch angle. The wing-on-empennage interaction was also important to correlate the fore/aft pilot stick position against available data towards aeroplane mode.

These results showed the effects of the interactions were important considerations for the predicted performance and trim behaviour of tiltrotor aircraft. Such interactions are, therefore, important to account for when designing these types of aircraft. Furthermore, the strong interactions found at the empennage meant its configuration (size, type and location) is an important design consideration.
Exploitation Route The aeromechanics model was written using an object-orientated approach and templates for the required input files have been made. As a result, different aircraft models can be created quickly and efficiently for analysis by the code. As such, the aircraft performance, trim behaviour and conversion corridor boundaries for arbitrary tiltrotor aircraft can be investigated. The current model can also be developed into a flight dynamics model that can be used to investigate control strategies through different regimes of flight. Finally, the model can also be used to analyse methods to increase the conversion corridor boundaries to widen the operating domain of current and future aircraft designs.
Sectors Aerospace, Defence and Marine

URL https://www.research.manchester.ac.uk/portal/en/theses/aeromechanics-modelling-of-tiltrotor-aircraft(510418cd-64a1-48da-9377-227442998206).html
 
Description Post-graduate training; Introduction to Rotorcraft Aerodynamics 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Research output was presented to post-graduate students, researchers, colleagues from industry and government, overseas researchers.
Year(s) Of Engagement Activity 2020
 
Description Post-graduate workshop and training: Introduction to rotorcraft performance stability and control (Event #2) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Research output was presented to post-graduate students, researchers, colleagues from industry and government, overseas researchers. Second in a series of lectures and talks (held online due to COVID restrictions).
Year(s) Of Engagement Activity 2020