Reach for the sky

A mix of disciplines and software is being used by engineers developing a program to simulate wind tunnel tests on aircraft controls. Siobhan Wagner reports

It sounds a bit like the Biblical story of the Tower of Babel — an ambitious project to build high in the sky is cursed by a lack of uniform language. However, Arthur Rizzi’s EU-funded project does not aim to build a tower, but aircraft simulation software.

The Stockholm-based aeronautical engineer and researchers from across Europe will spend the next two years creating a software program that mimics wind tunnel conditions to test the performance of aircraft control systems. The aim is to speed up the entire design process, saving aerospace companies time and money.

The software will draw on knowledge from the fields of aeronautics, structural engineering and control theory. Rizzi said the challenge will not only be integrating simulation software that was not designed to ‘talk to each other,’ but also incorporating ideas from engineers who specialise in different disciplines.

‘The structures people speak a broken language of aeronautics,’ said Rizzi. ‘The control people — they have another one.’

Simulating Aircraft Stability and Control Characteristics for Use in Conceptual Design (SimSAC) has 17 university and industry partners, including Saab and J2 Aircraft Dynamics, from nine European countries. Bristol and Liverpoool Universities are the two UK participants from academe.

Rizzi, a professor at the Royal Institute of Technology in Stockholm, said he and his colleagues decided to focus on the aircraft’s control system because it is key to the safety and efficient operation of an aircraft.

Today’s control systems are usually constructed only after the main features of the plane have been determined. ‘The reason it’s not done earlier is because in order to design the flight control system you need wind tunnel data,’ said Rizzi. ‘You need to know the aerodynamic forces that are going to take place on the ailerons, the flaps, the vertical rudder and the horizontal elevators.

‘With the standard design process, engineers aren’t ready to make the wind tunnel model until the end of conceptual design or the start of preliminary design.’

At this point, fixing mistakes is expensive. Faulty assumptions about stability and control lead to costly and failed test flights, which can involve the loss of prototypes and, in the worst case, human life.

Rizzi and his researchers hope their software will allow engineers to include the control system earlier in the developmental process, and therefore increase the chances of getting the design right the first time.

All of this is only now technically possible, said Rizzi, because of advancements in IT and the simulation techniques within the disciplines of aeronautics, structure and control. ‘Now the next step is putting it all together,’ he said.

Advances in simulation will not only save airlines time and money but will also lead to more innovative aircraft.

‘Our method would not make a much better 707 than they did in 1977,’ said Rizzi. ‘Those planes are built with empirical knowledge gained over the past 40 to 50 years. If we don’t use empirical data and compute things from first principles and believe them, maybe we can come up with the unconventional aircraft.’

The new software will not make wind tunnel tests redundant. Rizzi said: ‘We will need them even more, not for generating the database but generating the certainty and refining our models. We want to do the models because the models are general.’

He added: ‘If we get the physics right, it doesn’t matter what kind of aircraft it is. If you generate empirical data it’s tied to a specific kind of aircraft.’

When the project concludes in October 2009, Rizzi expects to have a tailor-made environment of aircraft design, with support for how better design should be carried out and for producing the best possible data for decision-making.

‘The ideal that we’re aiming for is what comes off the drawing board will be right the first time,’ he said. ‘We’ll never really reach that ideal, but it’s a good one to have as a goal.’