Professor Ian Poll came to Kingston on February 8th to talk to members about aviation in the 21st century.
Ian remembered with pleasure the start of his career at HSA Kingston in John Allen’s Future Projects department. He now is Professor of Aerospace Engineering at Cranfield University and the Technical and Business Development Director of Cranfield Aerospace (a wholly owned subsidiary of Cranfield University) which he founded in 1997 as the commercial arm of the College of Aeronautics.
He has worked in the field of aircraft drag reduction for 30 years
and on developing a better understanding of the thermodynamic
efficiency of the whole aircraft system.
Citing Sir George Cayley (1772 - 1857) as the father of the aeroplane, inventing the concept in 1799 in response to his perception of a commercial transport need, Ian observed that historically a good idea takes 100 years to mature and that only in the last 50 years has Cayley’s vision been realised.
Civil aviation is now a major business essential to world commerce.
Civil aircraft are now commodities with customer satisfaction as top
priority. The drivers of civil aviation used to be “further, faster,
bigger” but now they are “cheaper, safer, cleaner” - not so
Cost reduction techniques, outside the realms of the aircraft and
its engines, include health and usage monitoring, innovative air
traffic control solutions, de-skilling pilots, better use of
information technology to reduce the cost of sales, and more efficient
Safety can be improved by reducing pilot interventions (80% of accidents involve human error), by utilising virtual reality technology to give all round and poor weather vision, and by having air traffic management systems which separate aircraft rather than bunching them, and more efficient training.
Security improvements can come from screening for weapons and
explosives, creating an international database for the rapid
identification of undesirable individuals, and by denying access to
designated sensitive areas through the flight control system.
Environmental impact will be reduced by using fuel cells for ground
power supplies, treating airport run-off water, and employing
multi-mode transport linking to reduce congestion.
However, civil aviation is the victim of 50 years’ success. In 1995 some 3,500 billion seat-miles were flown which growth forecasts (5% pa) take to 12,000 billion s-ms by 2020. Freight, growing at 7% pa, will increase from 100 bn tonne-km to 500 bn tonne km. There is a four-fold increase in fuel burn in a 30 year cycle and a real danger that aviation is damaging the planet. Ian could not believe that politically this will be allowed to happen so the projected growth in air transport will be capped unless fuel burn can be reduced.
Is global warming really happening? This is not contentious. Lots of temperature measurements are made world-wide to give a global mean and this is rising. Warming may indicate climate change but this is too difficult to predict. Gas turbine emissions: soot, water vapour, carbon dioxide and nitric and nitrous oxides, contribute to atmospheric warming. If the global average temperature rises the atmosphere holds more water which leads to “more weather”. Notably, aircraft are the only source of pollution in the stratosphere and effects here, where altitudes are important, are different from effects in the troposphere. A 50% reduction in fuel burn per passenger km by 2020 is the industry target but this is not feasible as it would take 20 - 30 years to get the necessary changes into the complete civil fleet. Con-trails are triggered by engine water vapour emissions but are made up from atmospheric ice particles and can lead to persistent cirrus clouds which have a direct and large impact on global warming by reducing the earth’s heat rejection and increasing heat retention at night. Contrail formation can be avoided by changing the aircraft altitude but there are no rules at present.
What can be done in the fields of the gas turbine engine, the mode of propulsion and the airframe configuration? In gas turbines the maximum turbine entry temperature is 1900 deg K, close to the maximum obtainable from kerosene so can’t be increased; the pressure ratio is about 40:1, again close to maximum; compressor and turbine efficiencies are already higher than 90%; the ideal thermal efficiency is 65% and now is 56% and the law of diminishing returns is in force. So overall only about 15% improvement seems feasible. However, propulsive efficiency is about 70% now and a substantial improvement here is thinkable.
There is more opportunity for improvements in the airframe. Today’s A380 layout is just like the B-47 of 1945. The way ahead is to get rid of the non-lifting volume - put everything in the wing. There is a new interest in such blended wing-body (BWB) configurations which may yield a 30% improvement in lift to drag ratio (L/D) when carrying the same number of passengers as a ‘conventional’ airliner, which is the same L/D as a conventional airliner with laminar flow control (LFC). Fuel burn per passenger would be 25% lower. A BWB airliner with LFC would have an L/D four times that of a conventional airliner. Such an aircraft would be expensive to develop but the gains make the concept difficult to ignore. Cranfield Aerospace have designed and built two sub-scale unmanned X-48B BWB aircraft, for Boeing, which have been flying at NASA Dryden for four years.
Ian then moved on to the military field but there is no room here to cover this part of his talk in detail. However, in closing he listed possible ‘spin-offs’ into civil aircraft including reduced costs, lower accident rates, improved security, greater automation, easier training of cockpit crew and crewless cargo aircraft.
The vote of thanks for this brilliantly delivered, interesting and provocative talk was given by Ralph Hooper