The propeller engine led aviation to some of its greatest early achievements, but the noisy engine was quickly replaced by the quieter, fuel-guzzling turbojet engines primarily used today. But now that fuel costs are much higher and airlines are feeling the pressure to green-up, Rolls-Royce has redesigned the historic technology to be quieter and more energy efficient.
The company claims that their new open-rotor engine design could cut airline fuel bills by $3 million and CO2 emissions by 10,000 tons per year per aircraft if implemented on 100-200 seater aircrafts. To address the noise issue, more blades were added to the rotors and their shape was changed to be squatter and thinner. The company claims that this allows the rotors to spin at a slower speed, reducing the noise, while maintaining high efficiency.
Their design increases efficiency by using two sets of propellers near the rear of the engine that rotate in opposite directions. This set up reduces wasted energy because the second set of propellers untwists the air from the first set, recovering the energy in that air and producing more force.
Rolls-Royce isn’t alone in their innovative nostalgia -- General Electric, Pratt & Whitney and Snecma all are working on propeller engine prototypes.
Air travel produces about 2-3% of the world’s total CO2 emissions and passenger distances are growing at annual rate of 6-7%. This means that in the long run, introducing greener aviation technology now will make a large impact. And, in my opinion, it’s always great when an existing technology can be made better. The cost to implement it is usually lower, which gives it a greater chance of being used, and really, that’s what it’s all about.
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written by Ken Roberts, October 22, 2008
Hank, this is not nostalgia. Such engines are very common, and are called turboprops. They're on a great number of airplanes, like the C-130 for instance. They're better than turbojets at moderate speed. I'm glad Rolls-Royce is working on more efficient and powerful ones.
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written by Linda, October 22, 2008
I agree - it is always great when existing technology is improved. The skyrocketing fuel and energy prices are a blessing in a way - basically forcing companies to develop green alternatives to save money.
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written by Clinch, October 22, 2008
Even if some modern planes use propellers, this can still be seen as nostalgic (though it's more of an opinional matter, than a factual one).
There are some other questions I have about this, firstly, wasn't the main reason for abandoning propellers, and using jet engines, because propellers have problems above certain speeds?
And is the sound really that big of a problem, seeing as you're going to be inside of the plane, away from the engine.
The increace in efficiency is good, but how is it comparable in performance?
There are some other questions I have about this, firstly, wasn't the main reason for abandoning propellers, and using jet engines, because propellers have problems above certain speeds?
And is the sound really that big of a problem, seeing as you're going to be inside of the plane, away from the engine.
The increace in efficiency is good, but how is it comparable in performance?
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written by nicster, October 22, 2008
Elsewhere they list this open rotor technology as part of their "Vision 20" (which at least implies that it's 20 years out). They also say that it gives a 15-20% reduction in fuel consumption. Even if it only takes 10 years to implement this, aircraft fleets are very long-lived so it will take many, many years before this technology makes appreciable inroads lowering fuel consumption (assuming, of course, that they can't be retro-fit on existing aircraft).
Just a quick example of how old aircraft fleets can be: MD-80s were made for 20 years. On the 20th birthday virtually all of them were still flying. Nearly 10 years later, Alaska Airlines finally got rid of a whole bunch of them. Presumably, the ones that were sold off are still flying for some cheaper airline.
Just a quick example of how old aircraft fleets can be: MD-80s were made for 20 years. On the 20th birthday virtually all of them were still flying. Nearly 10 years later, Alaska Airlines finally got rid of a whole bunch of them. Presumably, the ones that were sold off are still flying for some cheaper airline.
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written by campbell, October 22, 2008
Moderate increases in fuel efficiency is all well and good....but aviation industry can do better; a form of transportation that can reasonably use solar power instead of fossil fuels, or even biofuels. IF moved to airships instead of airplanes. Just as sailing ships moved to steamships, and horse drawn carriages moved to automobiles.
Solar Powered airships (NOT BLIMPS) are the future of aviation
turtleairships dot blogspot dot com
Solar Powered airships (NOT BLIMPS) are the future of aviation
turtleairships dot blogspot dot com
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written by Dave, October 22, 2008
In the past focus groups were afraid to fly on planes with this type of engine for the fear of the large blades in the back breaking off and slicing through the cabin. Of course, now with the green label maybe the fear isn't there anymore.
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written by bobbobberson, October 22, 2008
I heard that airships were being looked at by the DoD for moving heavy things. It seems that under certain circumstances it would be more efficient to use airships (like for things that don't get impatient), although is using airships less efficient than using sea-ships?
http://www.popularmechanics.com/science/air_space/4242974.html
Of course if popular mechanics says it will happen then you know it will not.
But anyways, if it saves money do it. Future planes will continue to be produced and will fly.
http://www.popularmechanics.com/science/air_space/4242974.html
Of course if popular mechanics says it will happen then you know it will not.
But anyways, if it saves money do it. Future planes will continue to be produced and will fly.
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written by Anthony, October 23, 2008
This is called unducted fan (UDF). There was actually GE developed UDF engines put on an old 727 -
http://www.airliners.net/open.file/0001821/L/
http://www.airliners.net/open.file/0001821/L/
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written by Justin, October 23, 2008
Re-imagining what an existing design is or should be, is a great way to end up with a better model. I find it interesting when the re-design for efficiency moves to something closer to the "older" version. I think there can be a lot to learn from these instances.
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written by Ken Roberts, October 23, 2008
This is a modified turboprop design type commonly referred to as a 'propfan', due to the props being in the rear. You can check out the Wikipedia entry. http://en.wikipedia.org/wiki/Propfan
The important thing to note is that turbine-prop combination are more efficient at moderate speeds. Wikipedia lists the optimal speed at sub 450 MPH. Past that, the speed of the prop begins to cause enormous drag. I have an excellent graph on this in one of my pilot books, but alas can't find anything like it online.
So that's the trade off. Speed versus efficiency.
The important thing to note is that turbine-prop combination are more efficient at moderate speeds. Wikipedia lists the optimal speed at sub 450 MPH. Past that, the speed of the prop begins to cause enormous drag. I have an excellent graph on this in one of my pilot books, but alas can't find anything like it online.
So that's the trade off. Speed versus efficiency.
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written by Robbert, October 23, 2008
@Clinch
In most countries the airports are situated in the middle of populated areas. Here in the Netherlands, Noise pollution form airplanes is a huge problem.
Up to the point that whole towns are considered unlivable due to an airplane coming over every 2 minutes, day and night.
So yes: it matters.
And is the sound really that big of a problem, seeing as you're going to be inside of the plane, away from the engine.
In most countries the airports are situated in the middle of populated areas. Here in the Netherlands, Noise pollution form airplanes is a huge problem.
Up to the point that whole towns are considered unlivable due to an airplane coming over every 2 minutes, day and night.
So yes: it matters.
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written by Peter, October 23, 2008
Modern jets use very high bypass turbofans (not turbojets) where 80 percent of the air does not go into the combustion chamber, but bypasses to the fan that increases the speed. This design removes the outer case, increasing efficiency but increasing noise. I prefer the Pratt and Whitney approach of a geared turbofan that improves efficiency, but without the noise penalty. They run the compressor at a different speed than the turbine using a geared shaft.
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written by P C Childs, October 23, 2008
This isn't a really new idea. The only thing that is new is the counter-rotating props being at the back of the engine. Otherwise all of this is existing design that is in use today. There are a lot of turboprop airplanes in use around the world and sales are growing. As for the counter-rotating prop design, that's been in use on the TU-95 since 1952, making it the only turboprop strategic bomber in the world. It's also the fastest turboprop in the world.
So this design shouldn't take long to get to market, since it's an off the shelf build project using components already available.
So this design shouldn't take long to get to market, since it's an off the shelf build project using components already available.
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written by Joe, October 23, 2008
The biggest drawbacks to the older turboprop design were noise and speed. If RR has beat those problems, booyah to them! A poster above dumped on the "moderate" energy savings but 30% is nothing to sneeze at. The question I have is could the engines be retrofitted on older planes or can these engines only be used on new planes purchased by the airlines. Without retrofitting, the impact of such a new engine will only felt incrementally over time.
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written by Nick Aster, October 23, 2008
I believe the Q400 has something like this already implemented, or at least something close. I'd rather fly on one of those any day before a Regional Jet, but people still have a psychological fear of props...
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written by Mike, October 23, 2008
These designs have been around for a while, and were shelved, iirc, for cost reasons when fuel prices dropped.
The most significant design issue with these is that, in order to minimize shock losses at high speeds, the blades have to be thin. They need withstand the forces involved, however, and this usually requires that they be thick. The enabling design discovery was when engineers worked out that they could be made broad and thin.
At the time, another factor that contributed to their demise was noise. Blade tips traveling in excess of the speed of sound at takeoff tend to produce quite a racket. With advances in CFD and in our understanding of aircraft noise generation there's every reason to be optimistic about this technology again. I was just reading the other day that Rolls-Royce (iirc) was working on one of these and their spokesperson claimed that they had a significant market advantage with their proprietary understanding of the noise issue.
Also, the wikipedia article linked to by Ken Roberts is just awful and misses the point entirely. (I place the blame on the article, not on Ken.)
The most significant design issue with these is that, in order to minimize shock losses at high speeds, the blades have to be thin. They need withstand the forces involved, however, and this usually requires that they be thick. The enabling design discovery was when engineers worked out that they could be made broad and thin.
At the time, another factor that contributed to their demise was noise. Blade tips traveling in excess of the speed of sound at takeoff tend to produce quite a racket. With advances in CFD and in our understanding of aircraft noise generation there's every reason to be optimistic about this technology again. I was just reading the other day that Rolls-Royce (iirc) was working on one of these and their spokesperson claimed that they had a significant market advantage with their proprietary understanding of the noise issue.
Also, the wikipedia article linked to by Ken Roberts is just awful and misses the point entirely. (I place the blame on the article, not on Ken.)
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written by colinnwn, October 23, 2008
I would love to see airships become another air travel option as the idea of a cruise in the sky sounds great. Unfortunately they will never be a practical replacement for mass air travel.
Airships require lots of resources per passenger. Worse still since the Hindenburg, they have used Helium for lift. Peak He happened years ago, we are now in the long tail of production. He is almost gone forever (at least on a human timescale.)
Once He is recovered during nat gas production, it is used, escapes into the atmosphere, percolates up into space never to be recovered. We have no ways to make more, and it takes millions of years of radioactive decay for the Earth to tease up more from its belly.
Airships require lots of resources per passenger. Worse still since the Hindenburg, they have used Helium for lift. Peak He happened years ago, we are now in the long tail of production. He is almost gone forever (at least on a human timescale.)
Once He is recovered during nat gas production, it is used, escapes into the atmosphere, percolates up into space never to be recovered. We have no ways to make more, and it takes millions of years of radioactive decay for the Earth to tease up more from its belly.
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written by Jeff, October 23, 2008
Turbo Jets were replaced years ago by high bypass Turbo Fan engines. Turbo Fans are far more fuel efficient than the older Turbo Jets. The Fan in the engine is in essence an enclosed ducted propeller.
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written by will, October 23, 2008
turbojets haven't been in vogue on commercial or military cargo planes for quite some time.
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written by AirMover, October 23, 2008
I'll try to answer a previous poster's question on the rise of the turbofan. It basically comes down to money (doesn't it always!).
While a turboprop is more efficient than a turbofan, in terms of specific fuel consumption (SFC), it also needs to operate at a slower aircraft velocity. This means that the plane doesn't get from point A to point B as quickly, and the passenger fare is spread over more time, essentially lowering the "hourly rate" each passenger pays. There is also an associated lifespan of the aircraft, often in lease terms, that can play into a sort of hourly rate.
Turbofans were developed with fan bypass ratios that hit the sweet spot where the economics of the passenger payments & mechanical deterioration costs best balance the fuel costs. Going faster burns too much fuel, going slower doesn't generate enough cash flow via paying customers. (Note that the military has much different operating costs and therefore often uses prop planes for large aircraft)
Now that fuel is more expensive, it starts to make sense to go a little slower for a fuel efficiency benefit. Hence the resurgence of the turboprop for commercial aviation.
As to the improvements you see in this RR design, it basically comes down to decreased noise, increased efficiency, and increased speed. Modern engineering, materials, and manufacturing make this possible. It was not possible even 10 years ago to make this happen.
While a turboprop is more efficient than a turbofan, in terms of specific fuel consumption (SFC), it also needs to operate at a slower aircraft velocity. This means that the plane doesn't get from point A to point B as quickly, and the passenger fare is spread over more time, essentially lowering the "hourly rate" each passenger pays. There is also an associated lifespan of the aircraft, often in lease terms, that can play into a sort of hourly rate.
Turbofans were developed with fan bypass ratios that hit the sweet spot where the economics of the passenger payments & mechanical deterioration costs best balance the fuel costs. Going faster burns too much fuel, going slower doesn't generate enough cash flow via paying customers. (Note that the military has much different operating costs and therefore often uses prop planes for large aircraft)
Now that fuel is more expensive, it starts to make sense to go a little slower for a fuel efficiency benefit. Hence the resurgence of the turboprop for commercial aviation.
As to the improvements you see in this RR design, it basically comes down to decreased noise, increased efficiency, and increased speed. Modern engineering, materials, and manufacturing make this possible. It was not possible even 10 years ago to make this happen.
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written by David Mills, October 26, 2008
There's a lot more to these things than just new design ideas. A prop needs air to push against. As one goes higher and air is less dense, they become less effective.
A jet doesn't need air to push against. Traditional jets, though (turbojet or turbofan), need air (oxygen) for combustion. Since they don't want to carry it as extra load, they depend upon that which is in the atmosphere.
Speed, per se, is not the governing factor. If it were, the Concorde and descendants would be flying today. If one is flying from Boston to Sydney, then speed is definitely important. One would like to get there in this lifetime.
If one is flying a mere few hundred miles then the benefits of raw speed tend to disappear in the grass. One spends more time getting to and from the airplane, being screened, checking luggage, etc., than one spends in the air getting from A to B.
For maximal effectiveness (not the same as absolute efficiency - time, not just fuel, is worth money), one needs a range of options.
These options could range from bicycle (or ankle express) for trips down to the corner convenience store to hypersonic suborbital craft for that critical trip halfway around the world.
For each mode within that range one should strive for maximal efficiency, given ROI (ROI including the concomitant penalties of destroying our world).
A jet doesn't need air to push against. Traditional jets, though (turbojet or turbofan), need air (oxygen) for combustion. Since they don't want to carry it as extra load, they depend upon that which is in the atmosphere.
Speed, per se, is not the governing factor. If it were, the Concorde and descendants would be flying today. If one is flying from Boston to Sydney, then speed is definitely important. One would like to get there in this lifetime.
If one is flying a mere few hundred miles then the benefits of raw speed tend to disappear in the grass. One spends more time getting to and from the airplane, being screened, checking luggage, etc., than one spends in the air getting from A to B.
For maximal effectiveness (not the same as absolute efficiency - time, not just fuel, is worth money), one needs a range of options.
These options could range from bicycle (or ankle express) for trips down to the corner convenience store to hypersonic suborbital craft for that critical trip halfway around the world.
For each mode within that range one should strive for maximal efficiency, given ROI (ROI including the concomitant penalties of destroying our world).
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written by Haldane Dodd, October 27, 2008
David makes a good point about a range of options being necessary... perhaps the aviation industry needs to start thinking in terms of a 'total transport system' rather than each of the transport sectors fighting for who is the best.
Each type of transport (trains, aircraft, ships, coach, car and yes even human powered transport), fulfill different purposes and are each the most efficient at doing certain tasks. We would no more expect modern business travellers to cross the Atlantic in a ship than we would transport logs by air.
What each of us in the different sectors now must do is work out how to make what we do more efficient and reduce our environmental impact. Aviation is certainly doing that - the Rolls-Royce news that Megan profiles in the original blog post is a good example of how we are using technology to reduce emissions. The aviation sector is also exploring operational and infrastructure innovations to bring our 2% of world CO2 emissions down even further.
We have established a website - [url=www.enviro.aero[/url - as a resource centre to outline the projects underway and progress being made in reaching our goal. I also blogged www.enviro.aero/blog]www.envir....aero/blog about the Rolls-Royce news last week.
Haldane Dodd
Air Transport Action Group, Geneva
Each type of transport (trains, aircraft, ships, coach, car and yes even human powered transport), fulfill different purposes and are each the most efficient at doing certain tasks. We would no more expect modern business travellers to cross the Atlantic in a ship than we would transport logs by air.
What each of us in the different sectors now must do is work out how to make what we do more efficient and reduce our environmental impact. Aviation is certainly doing that - the Rolls-Royce news that Megan profiles in the original blog post is a good example of how we are using technology to reduce emissions. The aviation sector is also exploring operational and infrastructure innovations to bring our 2% of world CO2 emissions down even further.
We have established a website - [url=www.enviro.aero[/url - as a resource centre to outline the projects underway and progress being made in reaching our goal. I also blogged www.enviro.aero/blog]www.envir....aero/blog about the Rolls-Royce news last week.
Haldane Dodd
Air Transport Action Group, Geneva
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written by Nick Hein, October 29, 2008
Good evening,
I'm an aerospace engineer and I've had the fortune of working on the 1980's propfan, airships and wind turbines in my rather erratic career. When I worked at McDonnell-Douglas in the 1980's we had a design for an MD80-derivative propfan that would have entered production in 1991 with 60% lower fuel burn rates than contemporary jets. It was cancelled in 1989 due to falling fuel prices, anticipated $1B cost of final development and concerns about ice shedding from the blades. In 1991 the Gulf War drove fuel prices up 60%. If the propfan hadn't been cancelled it would have allowed ticket prices to remain the same. By now we would be several generations into the technology, with a solution for ice-shedding and other concerns of the time.
Instead, conventional turbofans got bigger fans which resulted in substantially higher thrust and economy - but no where near that of a full prop.
Concerns about noise were quickly being resolved at the time of cancellation.
Airships are another under-appreciated and under-utilized technology. They have been much more robust and forgiving than expected in actual operation.
Lower speed of either of these modes is really irrelevant when you consider how much time you spend in getting to the airport and getting through security and baggage. Both aircraft would bring airports closer to destinations, so there would be less ground travel at the ends.
I'm currently out of work, so if anyone is pursuing either of these technologies I'm available :-)
I'm an aerospace engineer and I've had the fortune of working on the 1980's propfan, airships and wind turbines in my rather erratic career. When I worked at McDonnell-Douglas in the 1980's we had a design for an MD80-derivative propfan that would have entered production in 1991 with 60% lower fuel burn rates than contemporary jets. It was cancelled in 1989 due to falling fuel prices, anticipated $1B cost of final development and concerns about ice shedding from the blades. In 1991 the Gulf War drove fuel prices up 60%. If the propfan hadn't been cancelled it would have allowed ticket prices to remain the same. By now we would be several generations into the technology, with a solution for ice-shedding and other concerns of the time.
Instead, conventional turbofans got bigger fans which resulted in substantially higher thrust and economy - but no where near that of a full prop.
Concerns about noise were quickly being resolved at the time of cancellation.
Airships are another under-appreciated and under-utilized technology. They have been much more robust and forgiving than expected in actual operation.
Lower speed of either of these modes is really irrelevant when you consider how much time you spend in getting to the airport and getting through security and baggage. Both aircraft would bring airports closer to destinations, so there would be less ground travel at the ends.
I'm currently out of work, so if anyone is pursuing either of these technologies I'm available :-)
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