Don’t expect big increase in fuel efficiency

22nd July, 2008

A common defense by the aviation industry against its environmental critics is to point out the improvements that have been made in fuel efficiency over the last few decades and to claim that further massive improvements will be made. We quote from two recent works on the subject of future improvements.

The first work is ‘Sustainable Energy – Without the Hot Air’ – ‘A popular book by David J.C. MacKay, Physics professor, Cambridge University.’ This can be found from http://www.withouthotair.com/ (the book is a PDF file of 6.86 Mbytes).

Prof MacKay says “Planes unavoidably have to use energy for two reasons: they have to throw air down in order to stay up, and they need energy to overcome air resistance. No redesign of a plane is going to radically improve its efficiency. A 10% improvement? Yes, possible. A doubling of efficiency? I’d eat my complimentary socks.” [Main text, page 31]

“So whereas lowering speed-limits for cars would reduce the energy consumed per distance travelled, there is no point in considering speed limits for planes. Planes that are up in the air have optimal speeds, different for each plane, depending on its weight, and they already go at their optimal speeds. The only way to make a plane consume less fuel is to put it on the ground and stop it. Planes have been fantastically optimized, and there is no prospect of significant improvements in plane efficiency.” [technical chapter C, p.235]

Not very encouraging!

The second work is a study for German environment ministry. The report and press release are in German; we quote the ENDS (Environmental Data Services) report.

Aircraft improvements “insignificant until 2045”

Improvements in aircraft efficiency will not dramatically affect the all-round environmental performance of the German air fleet until after 2045, according to a new study for the German environment ministry.

“All industry efforts to reduce emissions are welcome, but they have to be strengthened,” German junior environment minister Michael Müller said.

The study analyses aircraft industry goals to halve aircraft fuel consumption and noise emissions and cut nitrogen dioxide (NO2) emissions by 80 per cent, all by 2020. It concludes that although more efficient engine features are now available, improvements beyond 10 per cent are not in sight.

Fuel efficiency goals cannot be achieved simultaneously with improvements in NO2 and aircraft noise emissions, due to weight and engine efficiency conflicts, it says. New, more efficient planes now going into service would not be a major part of fleets until 2017, researchers found.

Again, not at all encouraging!

It needs to be pointed out that both of these studies refer to technological improvements, that is how much better planes might be than the current designs. But, if there were no improvements at all, there would still be improvements in overall fleet efficiency as today’s design gradually replaced the older, less efficient, planes.  Nonetheless, these studies indicate that technological improvement cannot be claimed as a panacea.

It is also worth pointing that in its forecasts of carbon dioxide emissions, the British government (Department for Transport) assumes that improvements in fuel efficiency will only be around 1% pa up to 2030 or 2050. This takes account of both new designs and incorporation of current designs into the fleets.         

We give a couple of illuminating quotes:

“What we need to do is to look at how you make air travel more energy efficient, how you develop the new fuels that will allow us to burn less energy and emit less.” Tony Blair

“Hoping for the best is not a policy, it is a delusion“. Emily Armistead, Greenpeace

“There are no technological solutions to our environmental problems – only social, economic and political ones.” Source not known.