Fuel efficiency in a turbine is somewhat counterintuitive as around two thirds of the energy is used to drive the compressor. However, the high by pass turbofan and twin jet ETOPS did result in material gains in efficiency, mainly in the 1990’s, as this study shows.
http://www.theicct.org/sites/default/files/publications/ICCT_Aircraft-FE-Trends_20150902.pdf
George Monbiot a couple of days ago published an interesting article (ironically with crude at $28 a barrel), on share of CO2 emissions by commercial air transport.
http://www.monbiot.com/2016/01/20/mumbo-jumbo-jets/
NASA and the ICAO do worry about this, possibly more than Monbiot suggests, and in the 1970’s a renaissance in turboprop technology was a possible solution. Inspired by the long haul capabilities of Soviet turboprop bombers!
http://history.nasa.gov/SP-4219/Chapter14.html
Why turboprops are not used for short and medium haul is absurd. Runways would be shorter, with new propeller technology noise footprint would be reduced, and they would be a real impetus to passenger seat mile efficiency. Remember the venerable PT6 is like our Lycosaurus, field maintainable bush technology, not exactly a paragon of fuel efficiency. Despite this 1950’s technology the turboprop is more efficient, because it accelerates a larger volume of air more slowly than the turbofan.
Long haul cargo might also be usefully undertaken with turboprops.
Debates on expanding Heathrow would be redundant as LAHS (land and hold short as used in the US) would free up hundreds of slots.
Or leap frog into something really efficient involving electric propulsion? For the applications you mentioned, that would need to be hybrid systems of course. Over the next 10 years we are going to see serious increases in solar cell and battery performance (price, weight, power output) and aviation can nicely ride this wave. This trend is not going to be stopped by this recent oil price decline that is temporary by definition.
Well, first of all, Mr. Monbiot would like us all to eat self-grown veggies and live in caves…..
That said, weren’t there trials with ‘unducted fan’ technology not that long ago? The Russians and Ukrainians (Antonov) have indeed developed that whole concept much further than the West. I remember seeing the aircraft they hoped to sell to the EU as replacement for the aging mil transport planes at the Antonov factory some 15 years ago and it had counterrotating props. Airbus then sort of stole the concept and tried – and are still trying and obviously failing – to make the A400.
My guess is that to a large degree this comes down to pax perceptions. As has been discussed here several times, pax just react differently to a jet than a turboprop. Perhaps because they don’t see the rotating blades….
RobertL18C wrote:
Debates on expanding Heathrow would be redundant as LAHS (land and hold short as used in the US) would free up hundreds of slots.
Nope. LAHSO only works on intersecting runways, not the case at LHR or any other London airport.
Well, first of all, Mr. Monbiot would like us all to eat self-grown veggies and live in caves…..
Disagree. It is guys like him that made the industry move in the right direction. Or short: No environment, no flying ;-)
In terms of fuel efficiency, turboprops have to be the winner.
The most brutal examples I have seen were the direct comparison between the CRJ200 and the Saab 2000. Both carry 50 pax, both carry about 1200 kg of baggage and both have around equal range. The CRJ is slightly faster, but will not gain substantial flight time over the SB20 on an up to 2 hour flight.
On the standard trips I saw them operate parallel, the Saab used exactly HALF of what the CRJ used. When the CRJ wrote 1500 kgs trip fuel on the loadsheet, the SB20 had 700 – 800 kg.
That one comparison did open my eyes quite dramatically. Even when the Embraer 135 replaced the SB20 and again was a 48 seater with similar loads but much newer, it again used up to 1.8-2 times the fuel.
So I’d stand with those who say yes, the turboprop would probably do the best. One massive problem they have however is public perceptance and acceptance (noise). Jets are massively less noisy both in and out. And props always carry the stigma of WW2 technology for the uneducated, even though the truth is very different!
Hi 172driver, agree some of Mr Monbiot’s off the grid suggestions are straight out of Walden.
LHR does have some old intersecting runways which are used as taxiways today. Turboprops can spread a lower noise footprint as they wouldn’t all be on a flight path of 09/27. Building intersecting runways with 5 degree approach paths might also be politically more acceptable.
The NASA investigation of multiple electric engines creating induced flow on the leading edge of large wings is interesting, but not sure passenger application is likely in the next ten years. Agree lo cost self loaders are snooty about propellers, but there is a political debate about airport capacity and emissions, and this seems a practical way forward. Didn’t Boeing look at ducted pusher turbofans for the 717 (old MD-80)? This approach gives a jet experience, but you lose the STOL benefits?
172driver wrote:
Airbus then sort of stole the concept and tried – and are still trying and obviously failing – to make the A400.
I was under the impression that the A400 had entered service…
Mooney Driver thank you for the real life example. Is the overall noise footprint worse for turboprops? I thought that with Q tips and low RPM, five plus blades, they were quieter than jets, perhaps not inside, but outside?
Mooney_Driver wrote:
Jets are massively less noisy both in and out.
I find the high pitch whine of a jet engine much more annoying than the low pitch rumble of say a Junkers 52 engine, even if lower volume on a dB(A) scale.
172driver wrote:
My guess is that to a large degree this comes down to pax perceptions.
I would be very surprised if that perception didn’t very quickly change if the difference in ticket price between a jet and a turbo prop was say 20%…
I don’t think there is much of a driver for lower prices.
Already, loco pricing is at the level of car parking at/near the airport, and at many places (not just Switzerland 
) you can spend the ticket price on a meal.
The required average ticket price (of the order of 150 quid for a 737 for a 700nm trip) is achieved by selling a lot of short-notice tickets for 300 quid, and people seem to pay that when they are over a barrel.
Turboprops own the “Greek Island” kind of run
and AFAICT nobody has a problem with that, but nobody seems to be making big turboprops anyway.
