Friday, 3 July 2015

Towards a Silent Aircraft

The annual Athena Lecture at Imperial College London celebrates the achievements of women in Science, Technology, Engineering and Medicine (STEM). Women's scientific contributions and achievements have been neglected by history. Imperial College is active in encouraging more women to study science. Each year, a world-renowned woman scientist is invited to give a lecture and act as an inspirational role model to the next generation.

Professor Dame Ann Dowling CBE
On 17th June I returned to Imperial College to hear Professor Dame Ann Dowling CBE give the 2015 Athena Lecture. She is President of the Royal Academy of Engineering and Professor of Mechanical Engineering at the University of Cambridge. Her CV boasts an impressive list of achievements, recognitions and awards. Yet, perhaps somewhat typically for a high-achieving woman, there was barely a hint of boastfulness as she spoke.

The lecture was entitled Towards a Silent Aircraft. I have a direct interest in the subject. Planes landing at RAF Northolt fly low directly over my roof. Heathrow's expansion is also a hotly debated subject in the UK and very topical where I live in the London Borough of Hillingdon.

Professor Dowling described her career chronologically interweaving technical details with her personal journey. She described a research career that began with aircraft noise, expanded into other fields and then returned to the subject of her original fascination.

The journey began by studying Mathematics at the University of Cambridge. As a student, Ann Dowling's main interest was in Applied Mathematics - particularly in Fluid and Solid Mechanics. I was fascinated to hear that a summer holiday job with Concorde started her fascination with aircraft noise (just as my own early interest in French has a Concorde connection). At that time, Concorde's noise was a major issue. The supersonic jet faced the threat of a ban in the United States. The higher speed changed the character as well as the level of noise. Three years of funding lead to work on jet noise and its modelling.

Pic of the front of Concorde's nose against cloudy sky

Once Concorde had gained its approval to fly into the US, research into aircraft noise was no longer considered a commercial priority. With a PhD under her belt, Ann Dowling was approached by the UK's Ministry of Defence (MoD).  The ministry asked her to apply her techniques to solve their issue with noisy submarines. Submarines need to listen passively for other vessels in their vicinity. Just as turbulence is generated in a high speed jet, so unsteady flow creates noise in submarines. The ultimate solution applied flexible and compliant coatings for low noise and low drag.

Internal aircraft noise
Ann Dowling moved back to aircraft acoustics, but this time her research focused on noise inside aircraft. An aircraft's structure is ribbed, leading to a noise scattering effect throughout an airplane. A passenger's level of noise-related discomfort varies according to seating position. As with submarines, the solution was to apply a coating to the aircraft.

Road noise
Responding to commercial needs at Dunlop, Rover and Jaguar Land Rover (JLR), her next research project centred on road noise. She focused on the interaction between tyre tread blocks and road surfaces. At that time, tyre treads were a matter of aesthetics rather than effective mechanical design. Tyre designers knew how to deal wet road conditions, but not how to reduce noise.

Combustion and acoustics
Ann Dowling enjoyed 3 months in Rolls Royce's Combustion Department. She sampled results from their jet engine and analysed the interaction between combustion and acoustics. She likened combustion instabilities to the initial roar of a gas boiler starting up in the morning. The research tested adding fuel at an unsteady rate and out of phase with the engine. The aim was to stabilise the noise. Different operating conditions were also taken into account. She used models and adaptive control.

Silent aircraft initiative
She maintained her interest in aircraft, enjoying her hobby as a private pilot with a shared aircraft. A sabbatical at MIT saw further advancement in the engineering world. The Silent Aircraft Initiative brought her career full circle with a return to aircraft noise. Further improvements were getting difficult. In the past, noise was created by the jet and its speed. Reducing noise on a conventional aircraft requires analysis and incremental improvements throughout the aircraft. The project's aim is to be inaudible outside the airport perimeter. There were many partners in the project with the University of Cambridge and MIT.

The collaboration resulted in the conceptual design of a blended wing body. Ann Dowling discussed how the design achieved the best lift distribution. She smiled as she spoke about the somewhat ugly design if viewed from the side. The Americans were amazed by the results and reviewed the figures until they had confirmed the lift properties. Boeing has since asked NASA to develop the design's geometry.

The airframe is an important factor in reducing noise. Conventional engines are placed underneath the aircraft. This reflects the noise downwards. The new design places the engines on top of the aircraft, changing the direction of the noise. There was a brief mention that the new position was "riskier", but no elaboration as to how or to what extent.

The proposal is to approach the airport more slowly and use a displaced threshold for landing. The YouTube video below shows an example of such a landing.


The approach reduces noise on landing for surrounding residents. I would suppose that commercial airlines would also have to balance this with considerations for their passengers too.

Professor Dowling answered a few questions from the assembled audience at the end of her talk. In response to one question, she expressed her concern as a pilot about unregulated drones and their potential to cause accidents. She confirmed that she had no involvement in active noise cancellation or anti-sound research.

Women in STEM
Returning to the main theme of women in STEM, Professor Dowling was asked how she felt during her career as the only woman among so many men. The consideration seemed to be alien to her - something that preoccupied others rather than her. Her main motivations seemed to be a love of engineering and finding researched solutions to recognised problems with a team of collaborators.

Both before and after the talk, I discussed the subject of women in STEM with a member of Imperial's Physics Department. Imperial College receives 1,700 applications for Physics. They select just 200 A* students. Despite open days, there remains concern that the subject does not attract enough women students. Three main areas of concern were mentioned:
  1. Failure to create enough early enthusiasm for the subject, as primary school teachers there have very little knowledge and understanding of Physics
  2. Level of Mathematics on arrival at university
  3. Convincing the mothers of potential women students that Physics can offer a rewarding career for their daughters
Celebrating role models like Professor Dowling should help convince potential women students and their mothers(!) that STEM subjects can indeed offer a rewarding career.

Karen Andrews, content writer
Karen Andrews runs
Anglicity Ltd. She is
an entrepreneurial
French to English
translator, editor,
content writer and
marketing consultant. 

for further information 
on Anglicity's services.

Further viewing on aircraft noise and other considerations:
Interesting YouTube videos on Hong Kong airport's approach :
Aircraft noise mitigation
Building a green airport

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