|Innovative Control Effectors for Manoeuvring of Air Vehicles – Advanced Concepts|
|Applied Vehicle Technology|
Conceptual Design, Control Effectors, Flight Control, Flow control, Manoeuvre, multidisciplinary Design, Performance, Tailless
The culmination of these three activities was a Quality Function Deployment (QFD) evaluation where each flow control technology could be graded in an objective and consistent manner against a set of defined measures. Key outcomes from AVT-239 were:
• Aerodynamic control strategies using fluidic devices have sufficient control authority to enable future manned and unmanned military vehicle designs to achieve the transonic ‘ingress’ mission phase performance requirements (trim and disturbance rejection) without the requirement for deflecting external control surfaces.
• The novel flow control technology requirements for the ‘ingress’ mission phase are consistent with the limited ‘bleed air’ supply available from a typical military turbofan propulsion system. The flow control systems components (pipes, valves, nozzles etc.) are also capable of being integrated within the airframe taking into account the outer mould lines, structure and other aircraft systems.
• When used to augment conventional aerodynamic controls, these devices can reduce the size of the required control surfaces and their deflection. Consequently, this can reduce the number of ‘seams and ‘gaps’ or changes in the outer mould line of the aircraft in flight. These measures can significantly improve the survivability of future aerial vehicle configurations.
• For the ingress mission the use of fluidic controls to augment conventional controls imposes a potentially acceptable increase in system mass, occupied volume and complexity. To determine if fluidic controls can completely replace conventional controls further studies are required to explore the more challenging flight phases, where blowing massflow requirements will undoubtedly be greater than for the ingress mission. The trends of system volume, mass, complexity, etc. with blowing massflow requirements identified in the ingress mission study suggests that these parameters increase less than proportionally with increases in blowing massflow. While it remains to be confirmed (an objective of the work being proposed in this TAP), replacing existing conventional control systems with novel fluidic control systems has the potential to reduce aircraft weight and complexity, reduce the aircraft internal volume occupied by flight control systems and result in similar levels of system reliability. If realisable the benefits to aircraft weight and available volume open up possibilities for performance enhancement (lower weight, more fuel) or greater flexibility to incorporate additional systems within the same airframe volume.
• A framework for integrating flow control into the aerodynamic design of a next generation UAV and assessing its system impact on that aircraft was developed and validated. It is the hope of the group that this framework will become the enduring standard by which future novel control technologies are assessed.
• If attainable, full replacement of movable parts by non-moveable fluidic control systems will contribute to a smoother overall aircraft shape.
The RTG will build upon the outputs of AVT-239 and AVT-295 to extend those studies to more challenging regimes of the flight envelope (particularly to take-off, landing and manoeuvre) to:
Determine the viability and design/performance implications of a ‘fully flow control enabled aircraft’ capable of operating throughout the entire flight envelope without the need for conventional, moving control surfaces.
A secondary objective will be to explore the longer-term aspiration of gaining the understanding of how the consideration of fluidic control effectors at the conceptual design stage of an aircraft can impact the configuration layout and its overall performance. I.e. to answer the question:
“Are there fluidic dynamic mechanisms that can be further exploited that affect both the configuration layout and the manner in which the fluidic control devices are implemented to provide greater benefit than a retrospective application of technology to an existing conventional design can achieve?”
ET 193 has explored the approaches that could be adopted to achieve the above objectives and has proposed an organisational structure evolved from that successfully used in AVT-239 that can deliver the necessary work programme and expected goals of the proposed RTG.
The following activities and scientific topics have been nominated as being within the scope of the proposed work programme:
• Undertake the performance, integration, -ilities and maturity assessments of Active Flow Control (AFC) for the take-off, landing and manoeuvre mission phases: This will complement the ‘ingress’ mission assessments completed in AVT-239. To maximise the best application of the available resources applied to these studies a single air-vehicle platform (the Lockheed-Martin ICE configuration) will be the focus of this study. While AVT-239 also looked at the SACCON/MULDICON application running with two configurations was challenging in terms of resource and time. Adopting a single (and most challenging) configuration to focus on will ensure that a suitable number of design iterations can be achieved to deliver results of the highest possible fidelity and reliability. As part of this process it is expected to have to redefine mission performance and system/mission impact requirements for the QFD analysis to be appropriate to the new mission segments.
• Improved understanding of transonic performance of AFC: Undertake studies to better validate transonic performance data for flow control devices – This will be undertaken using a combination of CFD and, where possible, appropriate experiments.
• Transient response of AFC: Reviews of existing data will be undertaken and preliminary new aerodynamic studies (experimental and numerical) will be defined to assess/understand the transient behaviour of flow control effectors (such as Circulation Control, Apex Blowing and Fluidic Thrust Vectoring). The objective here is to gain appropriate knowledge and, if applicable, to build models capable of simulating the transient relationships that exist between the opening of a control valve and the forces/moments induced on the airframe as a result. These models need to account for both the transient responses of the flow control effector output to valve movement and also the response of the external aerodynamics to the flow control effector output. These models will be required to improve the existing aircraft control response models used to assess stability and control during dynamic manoeuvring and disturbance rejection during any subsequent RTG activity.
• Explore AFC applied at the conceptual design stage: The objective will be “Design of the aircraft with AFC in mind” compared to the retrofit of AFC to a design based on use of conventional controls. This approach could ultimately lead to more efficient, lighter, smaller, better performing aircraft. This activity will explore the application of CFD/experiment/design approaches to identify exploitable receptive flow features (wing sweep, leading edge radius, vortex structures) conducive to the application of flow control. The target of this study will be to develop understanding and ‘toolsets’ that can be used in future design studies rather than the undertaking of a specific vehicle design which would be the potential subject of a subsequent activity.
• System integration studies: The aim is to identify approaches to improve and validate the semi-empirical system models used to predict/represent the performance, mass and volume of flow control systems components (more refined models than previously used are required to assess the systems integration aspects associated with ducting, valves and fluidic end-effectors). This need to include better understanding of the redundancy/fail-safe aspects such that better system sizing and reliability models can be created.