Research spotlight

ASTEROID: Aircraft Surface Tolerances for Enhanced Repair, Operations and Design

Dr Andrew Shires, Associate Professor of Aeronautical and Aerospace Engineering, has 20 years’ experience in the aerospace industry with a specific interest in the field of aerodynamic design, research and development. Previous positions at QinetiQ and Cranfield University, have led to him becoming a leading authority on wing design, flow control technologies, aerodynamic performance simulation and analysis, numerical design optimisation and wind tunnel test techniques. With experience of working with civil and military aircraft, racing cars and wind turbines, he’s perfectly positioned to bring together the key industrial and academic partners in this exciting ASTEROID project.

What’s it all about?

Launched in 2016, ASTEROID is a two-year research project combining talents from industry and academia to examine the effects of small local changes in external aircraft shape (excrescences and flow leakage) on aircraft performance. The aim is to produce software that can predict these effects to aid aircraft design and manufacture, as well as maintenance strategies, resulting in reduced aerodynamic drag and lower fuel burn. ASTEROID is the first research of its kind in the world since initial empirical models and data sheet type methods were devised to account for ‘excrescence drag’ in the 1970s by one of the current research partners (IHS ESDU).

As Andrew Shires explains: ‘When aircraft are designed there’s an assumption that their external surfaces are perfectly smooth but that’s not the case – aircraft surfaces are actually made up from many panels that are riveted together. This can introduce small gaps and steps between panels as well as protrusions and holes due to rivet heads, etc. These excrescences all have an impact on aerodynamic drag and fuel burn. It is not practical for the designer to explicitly model these excrescences due to their small size and number. Instead, a design is developed assuming a perfectly smooth external shape and an allowance is made for the additional excrescence drag on a typical aircraft.

Rivet

Photo of an aircraft wing showing the joints between neighbouring wing panels.

There’s currently a trade-off between the ideal aerodynamic shape and the manufactured shape –tightening up on manufacturing tolerances, for example, can help reduce excrescences resulting in a cleaner aircraft shape and lower drag. This benefits the airlines due to lower fuel costs. However, it’s currently not possible to build an aircraft with a perfectly smooth shape and there is a cost associated with tightening up manufacturing tolerances, which leads to an increase in the acquisition cost of the aircraft to airlines. Consequently, we hope to offer improved methods of quantifying the impact on aircraft performance that comes from deviations from the ideal design shape.

Current methods for calculating excrescence drag were based on work carried out in the 1970s and these haven’t been revisited until now. Through a series of low speed and supersonic wind tunnel experiments, ASTEROID will develop a better understanding of excrescence drag and improved prediction methods.

A further concern is that as aircraft age then their surface finish can deteriorate and seals, around windows and doors for example, can develop leaks. As long as the aircraft remain safe and airworthy, maintenance strategies don’t tend to look at the impact of these effects on drag. If maintenance engineers know what the problem is and how it will affect fuel burn then they can make clearer and more informed decisions as to how to proceed. The project will also deliver a tool for airlines to use to work out the reduced fuel burn that may be achieved by taking maintenance action to improve the aerodynamic cleanliness of their aircraft.’

Who’s funding ASTEROID?

The total value of ASTEROID is just under £1 million. It’s 50% Government funded through Innovate UK and the Aerospace Technology Institute. 

Who’s involved?

In addition to the team from the University of Leeds, the project has six other key participants from industry and academia:

  • University of Cambridge: the research team will use the University’s supersonic wind tunnel facilities and benefit from the University’s expertise about test instrumentation and the analysis of the recorded data.
  • Cranfield University: the research team will use the University’s wind tunnel for low speed aircraft. Experts from Cranfield will offer input about test instrumentation and analysis of recorded data.
  • IHS ESDU: known for its development of aerospace design data, Data Items and accompanying software, which have been rigorously validated by committees of technical experts and are used globally by aerospace design organisations, the Transonic Aerodynamics Committee will technically scrutinise this research project.
  • BHR Group: an independent engineering research and consultancy company with core expertise in fluids engineering.
  • British Airways: the airline will offer expert advice on the repair and maintenance of turbofan-powered aircraft that operate at high altitudes and high subsonic Mach numbers.
  • Eastern Airways: the airline, which operates turbo-propeller-powered aircrafts, will provide expert advice on maintenance and repair of aircraft that operate in the lower speed/altitude regime over relatively short distances.

It is expected that Undergraduate and Postgraduate Aeronautical and Aerospace Engineering students will contribute to the ASTEROID project through a series of student projects that will analyse some of the experimental data and make comparisons with numerical predictions.

Interested in finding out more? More details can be found on the project website.