Skip to main content

Regional turboprop loads control through active and passive technologies

Periodic Reporting for period 2 - RELOAD (Regional turboprop loads control through active and passive technologies)

Reporting period: 2017-06-01 to 2019-03-31

Loads Control and Alleviation (LCA), applying both active and passive concepts, has been identified as one of the key technologies for future regional turboprop aircraft. Adaptation of LCA in future aircraft designs will allow excessive gust and manoeuvre loads to be avoided. The ReLOAD project is targeted at investigating both active and passive load control technologies, focussed on the Flying Test Bed 2 (FTB2) configuration, which will undergo flight trials following the end of the project.

The use of LCA in future aircraft designs will diminish the peak loads at the edge of the aircraft envelope, enabling the use of enhanced structural wing designs, eventually leading to considerable weight savings. This reduction in weight translates to reduced fuel burn and hence reduced engine emissions, implying significant environmental benefits.

In terms of active LCA concepts, the objectives of ReLOAD are to characterise the aileron and spoiler behaviour on the FTB2 configuration using a combination of CFD and wind-tunnel testing. This data will be used to derive Handling Qualities and optimal control surface schedules for the FTB2 flight tests. These objectives were met with aerodynamic characterisation data for both aileron and spoiler at full-scale Reynolds number being delivered at cruise, take-off and landing conditions. This data focussed on power-off conditions (no propeller); a future project will focus on the powered effects for the same configuration.

In terms of passive LCA concepts, the objectives of ReLOAD are to select and evaluate candidate control device concepts, such as morphing or floating spoilers, and to derive a structural concept for an aeroelastic winglet capable of reducing manoeuvre and gust loads. The original idea of using a magnetic spoiler as the passive load alleviation device was shown to be unfeasible and focus switched to using active devices – aileron and spoiler – as gust load alleviation (GLA) mechanisms. The aileron was shown to be the more effective device. An aeroelastically tailored winglet was designed with the thickness distribution and stacking sequence suitable for GLA; this had lower weight than the current winglet on the FTB2.
For active load alleviation, extensive CFD computations were performed to characterise, separately, the aileron and the spoiler of the FTB2 configuration. A variable fidelity approach was used to enrich the CFD database. CFD results were obtained at both wind-tunnel and full-scale Reynolds numbers. These results were then used with wind-tunnel data from the one atmosphere RUAG facility in a data fusion approach, to obtain corrected data at full-scale Reynolds number. In this variable fidelity approach, the CFD data was classed as the lower-fidelity data, which described the Reynolds number dependence of the aerodynamics. The higher-fidelity wind-tunnel data then provided a correction to the CFD data. The results for aileron aerodynamics showed a clear Reynolds number dependence for roll increment, with control power increasing as Reynolds number increases, whereas for all spoiler deflections only a weak dependence on Reynolds number is indicated.

The output from the active load alleviation work has been exploited in two main ways. Firstly, the processes developed and the knowledge accrued in ReLOAD have allowed ARA to successfully bid for other Clean Sky 2 projects. Secondly, ARA has been able to enhance its commercial offering to its customer base. The Company is actively promoting a more integrated approach between its CFD and wind-tunnel businesses and the Reynolds number extrapolation work done in ReLOAD is entirely consistent with this.

The capability to use the spoiler as a passive loads alleviation device was investigated in the first part of the ReLOAD project. The fully passive spoiler results showed that it was possible to alleviate the loads, however, the spoiler did not close automatically after gust encounter. Therefore, the spoiler needed to be closed actively rendering the spoiler semi-active rather than fully passive and this was investigated. A new aerodynamic methodology was developed for the spoiler, as well as for the aileron, which made use of high-fidelity Navier Stokes CFD loads. The newly developed aerodynamic methodology was validated and successfully applied to aeroelastic simulations of a free-flying flexible aircraft model. It was demonstrated that the aileron is more efficient as compared to the spoiler when it comes to active loads alleviation.

The loads alleviation potential of a flexible winglet was also investigated using a parametric study. Parameters investigated were the shear centre location, the winglet weight, and the winglet flexibility. The parametric winglet was exposed to a series of vertical gusts, and it was shown that the loads at the root of the wing were alleviated to a limited extent only. Designing the winglet for minimum weight resulted in an increase in wing root bending moment. A novel measure was derived through minimising the frequency of a mode coupling wing and winglet bending. A 30% lighter winglet could be designed using this approach.

The ReLOAD research was exploited in other Clean Sky 2 projects. There, the ReLOAD methodology is refined and used for the design of the next generation movables to be applied to commercial and business jet aircraft. Furthermore, the ReLOAD project resulted partially in the initialization of a TUD internal project called SmartX which also involves the European aeronautical industry.

The ReLOAD results were disseminated in four international conferences related to smart structures and aeroelasticity. The work was also disseminated in academia at workshops for TU Delft specifically and for all technical universities in the Netherlands. Finally, the work was disseminated in industry during an Airbus PhD day.
Progress beyond the state of the art for active load alleviation is threefold. Firstly, the use of overlapping meshing was used for the CFD computations for both aileron and spoiler deflections, thus giving additional computational efficiency and a reduction in mesh-induced errors in the results. Secondly, variable fidelity modelling was used for the spoiler aerodynamic characterisation, allowing a much-enriched high-fidelity dataset at reduced cost. Thirdly, a novel data fusion approach was used to merge CFD and wind-tunnel data to provide high-fidelity aerodynamic data at full-scale Reynolds number. Such an approach negates the need for costly wind-tunnel testing in pressurised/low temperature facilities.

Progress beyond the state of the art for passive load alleviation is threefold. Firstly, new models including high-fidelity CFD in industry-standard loads processes were developed for the aeroelastic analysis of wings including the effects of spoilers. This method was verified and proven to be valuable in terms of computational efficiency. Secondly, a new semi-active spoiler was developed which contributed to alleviating the loads on the wing in a mainly passive manner. Finally, a new loads-sizing method for wings with winglets was initiated, which can be used to assess and design more flexible and lighter wing designs.

The impact of all the above advances are to reduce loads on wings, and hence their weight. This will reduce the use of materials and fuel consumption, which will contribute to the partial fulfilment of the ACARE FlightPath 2050 goals.