|Innovative Control Effectors for Manoeuvring of Air Vehicles – Advanced Concepts|
|Applied Vehicle Technology|
Control Effectors, Flight Control, Flow control, Manoeuvre, Performance
• The novel flow control technology requirements for the ‘ingress’ mission phase are consistent with the limited ‘bleed air’ supply available from a typical 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 reduce the radar signature of future aerial vehicle configurations.
• It has been shown that, for the ingress mission phase, replacing existing conventional control systems with novel fluidic control systems could reduce aircraft weight and complexity, reduce the aircraft internal volume occupied by flight control systems and result in similar levels of system reliability. 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 comprehensive 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.
As a result of work in AVT-239 it has become clear that there were limitations with the studies undertaken:
• The use of the SACCON geometry for a practical operational configuration had many limitations including: impracticable aerodynamic behaviour at moderate to high angles of attack; limited authority for its trailing edge controls; no practicality with respect to structural and systems layout. Partly overcome by adopting the MULDICON layout for a system integration study.
• Issues related to the transient response of the novel control effectors was not addressed due to constraints on the available time/effort available and a lack of existing data. These transients could significantly impact overall vehicle stability and controllability in response to disturbance rejection and requires further study.
• While it has been demonstrated that novel control effectors offer significant promise for the ingress mission phase time has not been available to explore the other mission phases such as take-off/landing and evasive manoeuvring. Based on the evidence to date it is thought possible that the novel flow control effectors could offer opportunities in these more demanding regions of the flight envelope. The vision is now that instead of ‘augmenting’ conventional controls with ‘flow control effectors’ it may be possible to totally replace them and achieve the goal of a ‘fully flow controlled aircraft’ - thereby realising the full potential of these technologies with regard to signature reduction and their potential for enhanced manoeuvrability at angles of attack where conventional control devices lose their authority.
This proposal for an Exploratory Team activity stems from the desire to respond to the successes and recognised deficiencies of the AVT-239 research activity. It proposes a one year study to put together a detailed work programme that would be envisaged being undertaken in the form of subsequent RTG activity.
The ET will build upon the outputs of AVT-239 and AVT-295 to identify the applicable configuration geometries, mission performance requirements and detailed work programme for a subsequent RTG activity that will evaluate the application of novel control effector technologies to a ‘fully flow control enabled aircraft’ capable of operating throughout the entire flight envelope without the need for ‘conventional, moving control surfaces.
• Review of the available air vehicle configurations for future studies – AVT-139 was particularly constrained by the use of the SACCON configuration (done for good reason related to the availability of comprehensive aerodynamic data). SACCON had issues when trying to translate performance to a practical configuration with realistic mission requirements. A more practically relevant configuration is required – this may be fulfilled by adoption of the MULDICON configuration (from AVT-XXX) but other available concepts need to be assessed for their suitability. The requirement Is that the chosen configuration must have sufficient maturity in respect of its aerodynamic performance and its structural/systems definition in order for system integration evaluation to be both possible and realistic.
• Identification and specification of mission performance requirements that can be used to undertake system evaluation. Here the focus will be on the performance requirements in more challenging corners of the flight envelope – to include take-off/landing and evasive manoeuvers during combat scenarios. These will be based on the initial work undertaken in AVT-239 expanded to take into account the adoption of new configurations.
• 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 able 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.
• Studies 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. It is necessary to identify the data resources and skill sets that could undertake the development of these improved models within a subsequent RTG activity.