CORDIS - EU research results



Executive Summary:
Microtecnica (MT) has brought together leading industry and academic expertise to support the design and development of a full scale Active Gurney Flap (AGF) system.
The team has a combination of relevant experience in blade actuation across a range of technologies together with significant capabilities in fundamental engineering analysis to
support a comprehensive review of potential solutions.
The consortium was lead by MT who provided the technical and programme management and the detailed design and manufacture of the wind tunnel and whirl test hardware. MT has been
supported by University of Bristol (UNIVBRIS) and the “Politecnico di Torino” (POLITO) based in Turin. The team ensured a balance of technical depth together with a commitment and capability to exploit technology for commercial gain.
The objectives of the work plan have been directed to achieving a risk mitigated solution to AGF System in order to develop a product that could be adopted on a production rotorcraft.
The AGF development program have followed the key deliverables that can be summarized into 4 activities: requirements development, product design, hardware supply testing and evaluation.
The programme had a primary cycle of the 4 activities culminating in the delivery of the first prototype at T0 + 17 months. The cycle has been repeated picking up the lessons from the testing and evaluation with wind tunnel hardware deliveries in T0 +24 months. Output from the wind tunnel testing provides the input for the final hardware (T0 +30 months) for whirl tower testing.
The management of technical risk has been supported by a two tier approach. The primary risk mitigation has been achieved through a balanced approach to analytical and empirical techniques. The consortium used the most advanced predictive engineering tools using finite element techniques for magnetic, stress and thermal analysis. Equally, the electronics and system performance have been extensively analysed before hardware production. Previous experience in fact has shown that the most robust approach is to combine these analysis techniques with small
scale breadboard evaluations of elements of the design. These were particularly useful for phenomenon which typically are non-linear in nature such as wear mechanisms and threshold effects like friction.
The consortium has been chosen with a balance of skills and capabilities. The involvement of the University of Bristol was of particular value for both its broad analytical capabilities together with a proven record in rapid prototype and test methods. The involvement of the Politecnico di Torino was in thermal and performance analysis of the actuator, basing on their experience in the specific areas of flight control actuation systems, mechatronics.
Technical risk was underpinned by a choice of technology that can be reconfigured to achieve potential requirements growth. There is intrinsically an element of uncertainty in the final needs of the product. In order to fix this uncertainty one of the purposes of wind tunnel test was confirm the operating loads while the aim of the spin rig test was to verify the capability of the system to operate in high centrifugal acceleration environment.
In fact, it should be needed to be noted that during the execution of the program, the final Customer Agusta Westland (AW) has communicated their intention to promote the Active Gurney Flap to an experimental flight program. This caused the responsibility of the Gurney Flap structural parts to be taken by AW. Discussions have been conducted between MT and AW in order to anticipate the demonstration of the actuator performances in high-G environment before the whirl tower test. The spin rig test activities has been then performed to verify the capability of the actuator and its relevant control electronics to operate installed in a representative acceleration environment.

Project Context and Objectives:
It is clear that the success of the AGF program has to be measured by hardware entering active service. MT is investing in this program because it believes the technology will add value to the rotorcraft to a greater degree than its cost and will provide a return on the investment being made.
In order to achieve return MT is aware that the following elements need to be satisfied. Firstly, the technology must meet the system requirement of achieving increased blade performance. This is assured through meeting of the supplier specification and lower component specifications and drawings. Besides the equipment needs to be economically viable. The sum of the benefits must
outweigh the sum of the costs. That is, costs of development, cost of purchase and through
life costs.
In order to achieve these competitive advantages the main objectives of the program were focused to gain the key strategic benefits on the following relevant topics:

1. Weight Optimized - The actuator mass achieved was minor of 400g to operate >1m span of Gurney Flap. Besides the actuator has been designed utilizing proven technology packaged to achieve the minimum of envelope and power consumption.

2. Appropriate Technology Readiness – The technology has been demonstrated to be compatible with EM actuation that has completed high g high bandwidth testing.

3. Optimized Gurney Flap Transmission – The design of the flap transmission makes use of flexure motion to operate the flap . This allowed to reduce loads, frictions and hysteresis whilst permitting potentially ‘infinite’ life.

4. Optimized Gurney Flap Mechanism – The design of the flap mechanism has been performed achieving the optimization over the operating travel to reduce loads, power consumption and improve system dynamic performance.

5.Actuator for in-blade actuation – The actuator has been conceived to cover a wide range of in-blade actuation, in particular primary or secondary (high harmonic) control. This provided the AGF operating margin for power (from primary flight control) and bandwidth (from high harmonic control). This common approach to in-blade actuation enables maximum potential for commercial exploitation of the technology developed under the AGF program.

Project Results:
The primary components designed and prototyped in the AGF program are a dedicated high g EM actuator, a simple pushrod transmission, and Gurney Flap deployment system based on flexure mechanism and a dedicated Electronic Control Unit.
The actuator has been conceived to cover a wide range of in-blade actuation, in particular primary or secondary (high harmonic) control. This provides the AGF operating margin for power (from primary flight control) and bandwidth (from high harmonic control). The most significant change between these applications is a trade of operating stroke for bandwidth. The AGF requirements conveniently fall between the primary and high harmonic requirements for power and bandwidth respectively. This common approach to in-blade actuation enables maximum potential for commercial exploitation of the technology developed under the AGF programme.
Besides the actuator utilises proven technology packaged to achieve the minimum of envelope and power consumption and includes a number of innovative features which enable the product to meet the operational and environmental requirements for the minimum mass, risk and cost.
The actuator is constructed so that the primary centrifugal (cf) forces are balanced within the actuator. This removes the need to externally balance the output motion. The brushless motor has been designed to achieve high acceleration with minimum power consumption compatible with high bandwidth operation. The actuator incorporates a lubrication system that ensures the load bearing components are adequately lubricated without incurring the viscous drag penalty associated with fully submerged lubrication.
The output motion is geared down by a flexure mechanism which minimises small amplitude non linearity whilst increasing the output stiffness of the mechanism.
An innovative thinking has also been applied to the Gurney flap mechanism of which two possible topologies have been considered: rotation of a flap stowed against the underside of the blade, or deployment of the flap from within the blade. Both methods presents drawbacks and in considering this topic the consortium has sought to achieve the benefits of both approaches whilst managing the limitations.
The deployment of the flap is fully supported on a flexure mechanism, removing concerns of hysteresis and wear and providing a method of supporting the CF loads without the penalty of friction which the actuator is required to overcome. The analysis has also uncovered potential solutions to power drain associated with overcoming the aerodynamic loads. The mechanisms designed reduces the movement of the centre of pressure during deployment and hence reduce the energy require per deployment cycle. The programme explored further the ability to pressure balance the flap during the deployment cycle.
The Gurney flap mechanism has been recognised as critical to the overall operational success. considering the interdependence between the flap and actuator design. In particular two features have been considered critical, namely load and friction. Therefore the initial activities performed in AGF program work has been focused to the significant reduction of both parameters through an innovative approach to the flap mechanism design, resulting in a significant size and power consumption.
The chosen EM actuator has opened the option for position feedback embedded within the actuator as opposed to other solution where is more exposed locate on the external surface.
In fact one of the advantages of EM actuators is the ability to operate over large input strokes (as far as the flap mechanism permits) enhancing all elements of position feedback. An external sensor located on the flap has been designed to be used as comparator (failure monitoring) for surface position feedback.
EM actuation used also benefitted of further advantage in the power drive electronics being suitable to be operated at low voltage and simplifying the supply and control power management. A typical multichannel architecture has been implemented for the in-blade EM control system reflecting a conventional approach using a combination of analogue and digital techniques.

Potential Impact:
The interest in the AGF is both for the market potential for the control of a Gurney flap surface together with a broader interest in active blade technology. It is clear that works on this argument is being conducted in all major aerospace centers around the subject of controlling directly the aerodynamics of a rotor blade through some type of control surface. From published data it is evident that a helicopter producer has achieved whirl stand demonstration of primary flight control using in-blade EM actuation. Also from published data it appears that the proposed solution for AGF will provide the partners with both a performance and weight advantage over the competitor offering.
It was the stated aim of the AGF program to develop Electro-Mechanical (EM) based technology that has relevance for controlling aerodynamic surfaces other than a Gurney flap, in particular, high harmonic control surfaces and primary flight control surfaces. Whereas piezo technology is compatible with high harmonic control it is unsuited to the load and stroke requirements typical of primary flight control.
The most significant advantage of an EM approach is the flexibility of the technology to meet the specific application. EM motors can be configured either as moving magnet or moving coil, continuously rotating or limited angle, commutated or non-commutated. This flexibility ensures efficient use of materials to meet a given power output. Piezo-ceramic actuators, by contrast, are constrained by their ability to produce small output strains. This leads to high gearing to achieve the required displacement at the output. The greater the output power required the more acute this limitation becomes. A preliminary study in fact indicates an advantage of EM in both weight and power consumption of approximately a factor 2 compared to a Piezo based solution.
This common approach to a broad range of applications provides robustness in the achievement of a commercial application.
The consortium’s impact was to achieve a technology for the partners within Europe that is capable
of being leveraged for other in blade applications. The aim is overtake the US suppliers in this market segment.

List of Websites:
Marco Gianfranceschi
UTC Aerospace Systems