What was the problem?
Whether developed in response to military requirements or as a means to improve performance, fuel efficiency or passenger safety in commercial and private aircraft, new aircraft designs tend to include an increased number of control systems and surfaces.
Pilots carry out in-flight control and manoeuvring of aircraft by positioning the aircraft's control surfaces such as ailerons and rudders – also known as “effectors”. This modifies the airflow across these surfaces to obtain an aerodynamic response from the aircraft.
Such control systems and surfaces increase the number of tools available to pilots to help them achieve the most aerodynamic performance.
However, the previous generation of flight control systems used algorithms – mathematical formulae – that assumed that control effectors would react in a linear, or straightforward, way. These systems also failed to take account of possible non-linear interactions between the different control effectors.
More advanced systems were therefore needed to coordinate these larger control effector “suites” and to take account of this potential for dynamic and non-linear interaction between the various effectors.
What did we do?
LSE Lecturer in Mathematics Amol Sasane, together with Professor Naira Hovakimyan at the University of Illinois and Eugene Labretsky, a Senior Technical Fellow at the Boeing Company, carried out theoretical research to solve this challenge.
Their research led to what is now known as the dynamic inversion control law to deal with unexpected outcomes. It was published as a paper for the American Control Conference in 2005.
Their nonlinear dynamic inversion control approach is a systematic generalised approach for flight control. Using general aircraft nonlinear equations of motion and onboard aerodynamic, mass properties and engine models specific to the aircraft, a relationship between control effectors and desired aircraft motion is formulated.
“The present invention overcomes this control allocation problem by using as its foundation a dynamic inversion control law for nonaffine-in-control dynamic systems that was earlier developed by Naira Hovakimyan, Eugene Lavretsky, and Amol J. Sasane.”
- United States Patent, May 2012.
In May 2012 a patent was granted to The Boeing Company in the United States for an invention that used the solution that Sasane and colleagues had set out in their 2005 paper.
This United States patent covers a new method and apparatus for the allocation of control authority in real time between several control effectors of a controllable vehicle such as an aircraft in order to execute the manoeuvre that the pilot has commanded.
The control allocation method in the patent invention allows the apparatus to allocate control of pilot or auto-pilot flight commands among the aircraft’s control effectors in real time, despite possible unexpected interactions that the control effectors may have with the aircraft and with one other.
The apparatus first predicts how the aircraft will respond to both the manoeuvre and to the changes in the control effectors, and second modifies the command control to take account of any non-linear impacts on the aircraft’s performance.
This invention overcomes a challenge in newer aircraft, which are designed with sophisticated flight control systems to achieve greater agility (in the case of military aircraft) or improved fuel efficiency (in commercial and private aircraft). In both cases advanced control laws and systems were needed to maximise aircraft performance.
The Boeing Company is using the patent to design flight control systems for aerial platforms. The invention is also applicable to any space, sea, under-sea or ground vehicle whose dynamics are controlled via a selected set of control effectors, suggesting the potential for substantially greater future impact in other sectors and industries.