The dominant navigation system for low-cost, mass-market Unmanned Aerial Vehicles (UAVs) is based on an Inertial Navigation System (INS) coupled with a Global Navigation Satellite System (GNSS). However, problems tend to arise during periods of GNSS outage where the navigation solution degrades rapidly. Therefore, this paper details a model-based integration approach for fixed wing UAVs, using the Vehicle Dynamics Model (VDM) as the main process model aided by low-cost Micro-Electro-Mechanical Systems (MEMS) inertial sensors and GNSS measurements with moment of inertia calibration using an Unscented Kalman Filter (UKF). Results show that the position error does not exceed 14.5 m in all directions after 140 s of GNSS outage. Roll and pitch errors are bounded to 0.06 degrees and the error in yaw grows slowly to 0.65 degrees after 140 s of GNSS outage. The filter is able to estimate model parameters and even the moment of inertia terms even with significant coupling between them. Pitch and yaw moment coefficient terms present significant cross coupling while roll moment terms seem to be decorrelated from all of the other terms, whilst more dynamic manoeuvres could help to improve the overall observability of the parameters.

The work is funded by the INNOVATIVE doctoral programme. The INNOVATIVE programme is partially funded by the Marie Curie Initial Training Networks (ITN) action (project number 665468) and partially by the Institute for Aerospace Technology (IAT) at the University of Nottingham.

No 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 ...

The paper presents the error characteristics of a vehicle dynamic model (VDM)-based integration architecture for fixed-wing unmanned aerial vehicles. Global navigation satellite system (GNSS) and inertial measurement unit measurements are fused in an extended Kalman filter (EKF) which uses the VDM as the main process model. Control inputs from the autopilot system are used to drive the navigation solution. Using a predefined trajectory with segments of both high and low dynamics and a variable wind profile, Monte Carlo simulations reveal a degrading performance in varying periods of GNSS outage lasting 10 s, 20 s, 30 s, 60 s and 90 s, respectively. These are followed by periods of re-acquisition where the navigation solution recovers. With a GNSS outage lasting less than 60 s, the position error gradually grows to a maximum of 8⋅4 m while attitude errors in roll and pitch remain bounded, as opposed to an inertial navigation system (INS)/GNSS approach in which the navigation solution degrades rapidly. The model-based approach shows improved navigation performance even with parameter uncertainties over a conventional INS/GNSS integration approach.