Investigation of Passive Flow Control Techniques to Enhance the Stall Characteristics of a Microlight Aircraft

Abstract

This report investigates the enhancement of aerodynamic stall characteristics of a Skyranger microlight aircraft by the use of passive flow control techniques, namely vortex generators and turbulators. Each flow control device is designed and scaled to application conditions. Force balance measurements and surface oil flow visualisation are carried out on a half-model of the microlight to further investigate the nature of the flow on the aircraft with and without the flow control devices. The results indicate a clear advantage to the use of turbulators compared with vortex generators. Turbulators increased the maximum lift coefficient by 2.8%, delayed the onset of stall by increasing the critical angle by 17.6% and reduced the drag penalty at both lower (pre-stall) and higher angles of attack by 8% compared to vortex generators. With vortex generators applied, the results indicated a delayed stall with an increase in the critical angle by 2% and a reduced drag penalty at higher angles of attack.Key Words: microlight; stall; flow control; vortex generator; turbulator; wind tunnel INTRODUCTIONThis project is an investigation of passive flow control techniques to enhance the stall characteristics of an in-house Skyranger microlight. Increased performance and safety gives assurance to the airworthiness of any aircraft and especially to 'self-build' aircraft like the Skyranger microlight due to the increased variability in these projects. The Skyranger (Figure 1) falls under the category of homebuilt aircraft, as described by the British Microlight Aircraft Association [1]. It has a MTOW of 450 kg, wing span (b) of 9.5 m, wing chord (MAC) of 1.5 m and uses a general aviation aerofoil with a thicknessto-chord ratio of 15%.Passive flow control techniques have been applied over the past 50 years in the aviation industry with progressive development through increased advanced research and technology. The techniques have been applied on commercial aircraft; examples include application of vortex generators on the B737 and B767 to eliminate shock-induced separation. These devices have also been applied in general aviation aircraft, including the Gulfstream V and Piper Malibu Meridian (Figure 2) to improve the performance and safety of these aircraft. On the Piper Malibu Meridian, the flap-mounted vortex generators enabled the aircraft to easily pass the FAA safety certification requirement of a slow stall speed (below 61 kts) [2]. Turbulators have also been applied in general aviation aircraft; for example, use of leading edge turbulators on BioniX15 to improve the stall and landing performance [3]. However, to-date there has been scarce work to compare the relative performance of such passive flow control devices.These devices improve the performance and stall characteristics of an aircraft by changing the nature of the airflow downstream of their location. They generate streamwise vortices which redistribute momentum across the boundary layer. In most wings, the stability of the boundary layer is affected by the ...

A Model-based Tightly Coupled Architecture for Low-Cost Unmanned Aerial Vehicles for Real-Time Applications

“…A second-order Gauss-Markov process is used to model the receiver clock ( = [ ] ) in both the filter and the simulator even though values used in each case are different. The receiver clock bias ( ) and drift ( ) dynamics are given by: ̇= + ̇= (25) In (25), and are independent white noise inputs to the clock model. In the filter, the rotation vector error is considered instead of the quaternion to simplify the assignment of uncertainties and the analysis altogether.…”

“…They, therefore, did not truly represent the aerodynamic characteristics of the current configuration. For the interested reader, a detailed discussion of Reynolds scaling effects and other considerations for both the wind tunnel setup and XFLR5 can be found in [25]. Determination of the static thrust coefficient is relatively straight forward, both simulated and experimental results [26] show good agreement to within 3% based on the evaluation of an Advanced Precision Composites (APC) 11x8 electric propeller as can be seen in Fig.…”