Flight Control of Commercial Aircraft Projects

Formation Flight at the ESL

Formation flying is defined as the flight of two or more aircraft under the command of a leading aircraft – it is typically used in military situations where pilots use formation flying as means of mutual defense and the concentration of fly power. In civil aviation, formation flying is performed at air shows and for recreation purposes. The benefits of formation flight have long ago been recognized by many researchers and aerodynamicists, showing interest due to its potential to reduce fuel consumption in long range flights. Since its recognition, various studies have been undertaken to investigate the effects and advantages of formation flight – existing literature studies have mainly focused on close formation flight, showing promising aerodynamic and control benefits.

Close formation flight minimises the induced drag of an aircraft and improves fuel efficiency in commercial aviation. Wind tunnel tests have shown that a substantial decrease in drag can be obtained in formation flight depending on the configuration. Along with the many benefits, dangerous handling characteristics exist due to trailing vortices and wake vortices which induce large aerodynamic forces and moments. This is commonly referred to as the Vortex Problem. Research done towards analysing wake vortices and the experimental systems and alleviation devices developed to cope with the vortex problem is well documented. Furthermore, close formation flight also leads to questions about the increased acceleration magnitudes and the associated passenger comfort levels in the trailing aircraft(s) of a formation flight.

The Formation Flight projects are divided into three master’s degree topics that would investigate different aspects of the flight control in formation flight problem. The research will be performed by three students over four years from 2013 to 2015. One student will be recruited for 2013-2014, and two students will be recruited for 2014-2015.

 

Current Projects

 

Flight Control for Formation Flight of Passenger Aircraft

Izaak van Zyl

It has been established that the option of flying passenger aircraft in formation is a feasible approach to increase fuel savings. A study by FG van Wyk showed that it is possible, for a formation size of two, to hold the follower aircraft in a position where fuel flow is reduced by approximately 25%, and that this position could be located using a procedure known as extremum seeking. This topic investigates formation flight for more than two aircraft in multiple formation topologies. Specific issues include which topologies are safest and offer most fuel savings, how formations would be formed and disengaged, and further refining extremum seeking to be optimal for these formations.

 

Completed Projects

 

Flight Control for Optimal Fuel Consumption in Formation Flight

Gerrie van Wyk

This topic investigates the design of optimum-seeking flight control algorithms for passenger aircraft that use feedback control to optimise the fuel consumption during formation flight. A study by Sanders showed that the actual fuel saving in formation flight is strongly influenced by the flight control activities. This research builds on the flight control system designed for stability and control performance by Denzil Buchner, and adds optimal fuel consumption as an additional design goal.

Flight Control for Optimal Passenger Comfort in Formation Flight

Evert Trollip

This topic investigates the design of flight control algorithms for passenger aircraft that use feedback control to provide optimal passenger ride comfort during formation flight. An aerodynamic model for passenger aircraft flying in formation was developed by Bizinos and Redelinghuys at the University of Cape Town. Simulations to assess the impact of formation flight on passenger comfort showed a significant increase in discomfort for lateral separations corresponding to the optimum drag benefit. However, a suitable flight control system can be designed to reject the disturbances caused by the wake of the leading aircraft and improve the ride comfort. This research builds on the flight control system designed for stability and control performance by Denzil Buchner, and adds optimal ride comfort as an additional design goal.

Upset Detection and Recovery at the ESL

Conventional flight control systems for aircraft are designed to operate within a specified flight envelope, which is defined as the allowable ranges of air incidence angles, airspeed and angular rates. An aircraft will typically stall and enter an uncontrolled spin when the aircraft is outside of its flight envelope. Pilots are not always aware that the aircraft entered the upset domain and may respond with incorrect actions.

The ESL is undergoing a number of projects under a collaboration agreement between Airbus and the National Aerospace Centre of South Africa which will allow an aircraft to detect “out-of-envelope” conditions using onboard sensor measurements and advise the pilot so that the correct recovery actions can be taken.

 

Current Projects

Upset Detection for commercial passenger aircraft

Pieter Malan

Loss of control is one of the largest contributors to fatal accidents worldwide. To reduce loss-of-control an upset detection system is required. This topic investigates an upset detection system for commercial passenger aircraft. The project consists of two sections, firstly state estimation algorithms using an inertial navigation system to add redundancy to anemometric sensors. The second part of the project consists of a classifier algorithm to integrate all the available data. The classifier will also identify whether the aircraft is in upset or not.

 

Flight Control for Upset Recovery of Unmanned Aircraft

Jannes Engelbrecht

Aircraft loss of control remains one of the main contributors to accidents in commercial aviation. This project aims to design an autonomous flight control system to recover an unmanned aircraft from upset conditions. It investigates alternative trajectory optimization techniques using numerical optimization algorithms to design a practical online system for upset recovery in real time. This project contributes to research on the larger upset recovery problem.

 

 

 

Stall and Spin Recovery of T-Tail Transport Aircraft / Fighter Aircraft

Gerhard de Wet

Basically we are looking for an aircraft that can go into a stall / spin state that is difficult to recover from, but not impossible. T – Tail may enter into a deep stall where the tail is in the “wake ” of the wings and the elevators are not effective . Aileron or rudder can maybe be used to get the tail out of the wake, so that the elevators can work again. Use model predictive control to solve the problem.