Category Archives: Engineering

Coverts inspire adaptive wing design

Earlier this summer, when we were walking the South West Coastal Path [see ‘The Salt Path‘ on August 14th, 2019], we frequently saw kestrels hovering above the path ahead of us.  It is an enthralling sight watching them use the air currents around the cliffs to soar, hang and dive for prey.  Their mastery of the air looks effortless.  What you cannot see from the ground is the complex motion of their wing feathers changing the shape and texture of their wing to optimise lift and drag.  The base of their flight feathers are covered by small flexible feathers called ‘coverts’ or ‘tectrix’, which in flight reduce drag by providing a smooth surface for airflow.  However, at low speed, such as when hovering or landing, the coverts lift up and the change the shape and texture of the wing to prevent aerodynamic stalling.  In other words, the coverts help the airflow to follow the contour of the wing, or to remain attached to the wing, and thus to generate lift.  Aircraft use wing flaps on their trailing edges to achieve the same effect, i.e. to generate sufficient lift at slow speeds, but birds use a more elegant and lighter solution: coverts.  Coverts are deployed passively to mitigate stalls in lower speed flight, as in the picture.  When I was in the US last month [see ‘When upgrading is downgrading‘ on August 21st, 2019], one of the research reports was by Professor Aimy Wissa of the Department of Mechanical Science & Engineering at the University of Illinois Urbana-Champaign, who is working on ‘Spatially distributed passively deployable structures for stall mitigation‘ in her Bio-inspired Adaptive Morphology laboratory.  She is exploring how flaps could be placed over the surface of aircraft wings to deploy in a similar way to a bird’s covert feathers and provide enhanced lift at low speeds.  This would be useful for drones and other unmanned air vehicles (UAVs) that need to manoeuvre in confined spaces, for instance in cityscapes.

I must admit that I had occasionally noticed the waves of fluttering small feathers across the back of a bird’s wing but, until I listened to Aimy’s presentation, I had not realised their purpose; perhaps that lack of insight is why I specialised in structural mechanics rather than fluid mechanics with the result that I was worrying about the fatigue life of the wing flaps during her talk.

 

The picture is from a video available at Kestrel Hovering and Hunting in Cornwall by Paul Dinning.

 

When an upgrade is downgrading

I had slightly surreal time last week.  I visited the USA to attend a review of a research programme sponsored by the US Government and reported on two of our research projects.  When I arrived in the USA on Monday evening, I went to collect my rental car and was told that I had been upgraded to a pick-up truck because the rental company did not have left any of the compact cars that had been booked for me.  I gingerly manoeuvred the massive vehicle, a Toyota Tacoma, out of the parking garage and on to the freeway.  I should admit to having owned a large SUV when we lived in the USA and so driving along the freeway was not a totally new experience, except that the white bonnet in front of me seemed huge.

The following morning, I drove to the location of the review and strategically selected a parking space with empty spaces all around it so that I could drive through into the space and avoid needing to reverse the behemoth.  As I was walking across the parking lot, someone accosted me and said: ‘Nice truck, how do you like it?’  Embarrassed at driving such an environmental-unfriendly vehicle, I responded that it was a rental car that I just picked up.  To which he replied that the best protection against my Tacoma, was his Tacoma. And, that it was his dream car.  Then, I noticed that he had parked his black one alongside mine.

Our children learnt to drive in our ancient Ford Explorer and loved it.  We all knew that it was wrong to drive something that consumed fuel so voraciously even if it did get us effortlessly through the most horrendous winter storms.  However, we have left all that behind and now either use public transport or drive cars that achieve 60 mpg or more on good days. But here I was being admitted to a club that worshipped their pick-up trucks.

We walked together into the review which was held in a small lecture theatre equipped with comfortable armchairs, which was just as well because we sat there from 8.30 to 4.30 for two days listening to half-hour presentations with only short breaks.  We were presented with some stunning research based on brilliant innovative thinking, such as materials that can undergo 90% deformation and fully recover their shape and how the rippling motion of covert feathers on a bird’s wings could help us design more efficient aeroplanes.  More on that in later posts.  Of course, there were some less good presentations that had many us reaching for our mobile phones to catch up on the endless flow of email [see: ‘Compelling Presentations‘ on March 21st, 2018).  At the end of each day, we dispersed to different hotels scattered across town in our rental cars.  On Thursday, I drove back to the airport and topped up the fuel tank before returning my truck.  I worked out that it had achieved only 19 mpg (US) or 23 mpg (UK), despite my gentle driving – that’s almost three times the consumption of my own car!  On the plane home I started reading ‘Overstory‘ by Richard Powers, a novel about our relationship to trees and the damage we are doing to the environment on which trees, and us, are dependent.

Engineering correspondents needed

Society’s perception  of scientists and engineers is not well-balanced; scientists tend to get the headlines when they make new discoveries while engineers are only in the headlines when things go wrong.  Even worse, when I was a student, the successes of the NASA’s space shuttle were usually reported as scientific achievements while its problems were engineering failures; when the whole programme was an enormous feat of engineering!  Perhaps this is because news organisations tend to have science correspondents and editors but no engineering correspondents.  When you search for engineering journalism jobs most of the results relate to roles associated with the technology of journalism; whereas a search for science journalism jobs results in dozens of vacancies for science writers, correspondents and editors.  The lack of engineering correspondents has been evident in the UK during the past week in reporting about the potential bursting of the dam at Toddbrock Reservoir and flooding of the town of Whaley Bridge in Derbyshire UK.  A 188 year old dam has been damaged by the turbulent flow of water over its spillway following unprecedented levels of rainfall (e.g. https://www.bbc.co.uk/news/uk-england-derbyshire-49222956). There is little discussion of the significant achievement of the Victorian engineers who designed and built a dam in the 1831 that has lasted 188 years or that climate change is causing shifts in weather patterns which have altered the design specifications for engineering infrastructure including dams, bridges and sea defences.  We need more journalists to write about engineering and preferable more journalists who have been educated as engineers particularly as society starts to face the potential existential threat caused by climate change and over-population.

For more on the nature of engineering, and its relationship to science, see ‘Making things happen‘ on September 26th, 2018; ‘Engineering is all about ingenuity‘ on September 14th, 2016 and ‘Life takes engineering‘ on April 22nd 2015.

And on the communication skills of engineers: ‘Poetasting engineers‘ on March 4th, 2015 and ‘Einstein and public engagement‘ on August 8th, 2018.

Pareto principle in train travel

The moral of this story is don’t travel with me.  Last week, I wrote about my train being delayed by someone pulling the emergency handle before we got to the end of the platform in Liverpool [see ‘Stopped in Lime Street’ on June 26th, 2019].  Four days later, I was once again on a late afternoon train to London waiting for it to leave Lime Street station.  This time we didn’t even get started before the train manager announced that a road vehicle had hit a bridge between Crewe and Liverpool; and, so we were being held in Liverpool for an unknown period of time.  I sent a message to my family telling them about the delay and one, an engineer, replied that I was ‘hitting the low frequency failure modes on the service quality pareto’.  The Pareto principle is also known as the 80/20 principle.  I first encountered it when I was working at the University of Sheffield and the Vice-Chancellor,  Professor Gareth Roberts, used it to describe the distribution of research output in academic departments, i.e., 80% of research was produced by 20% of the professors.  In service maintenance, it is assumed that 80% of service interruptions are caused by 20% of the possible failure modes.  Hence, if you can address the correct 20% of failure modes then you will prevent 80% of the service interruptions, which is an efficient use of your resources.  The remaining, unaddressed failure modes are likely to occur infrequently and, hence, can be described as low frequency modes; including passengers pulling emergency handles or people driving vehicles into bridges.

How do you drive into a bridge and block the main railway lines between London and the north-west of England?  Perhaps the driver was using their smart phone which was not smart enough to warn them of the impending collision with the bridge.  So, there’s a new product for someone to develop: a smartphone app that connects to dashboard camera in your vehicle and warns you of impending collisions, or better still just drives the vehicle for you.  Yes, I know some vehicles come with all of this installed but not everyone is driving the latest model; so, a retro-fit system should sell well and protect train passengers from unexpected delays caused by road vehicles damaging rail infrastructure.

By the way, the 14:47 to London magically became the 15:47 to London and left on time!