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#12
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Rolls-Royce brings propeller engines back in vogue
On 21 Okt, 19:44, Dirk Bruere at NeoPax wrote:
wrote: On 21 Okt, 14:04, James Robinson wrote: "True Blue" wrote: A staggering article. The Guardian makes a fool of itself yet again. Turboprops with or without counter-rotating propellers have been used extensively, in many parts of the world, for many years. Yet The Guardian report this as a new-found technology which will "save the planet". They should stick to the arts. Except they aren't talking about traditional turboprops. *They are describing a propfan, or unducted fan engine, "Unducted fan" is a bit of a misnomer. Traditionally the fan refers to the big cold whirry thing at the front rather than than small hot whirly thing at the back. http://www.fas.org/nuke/guide/russia/bomber/tu-95.htm The Bear's wings are mid-mounted, swept-back, and tapered with blunt tips. Its engines consist of four turboprops with contrarotating propellers located on the wings. I think I mentioned the Bear somewhere else in this thread. THe engines on the Bear or conventional turboprops (i.e. there is a jet engine or "gas generator" with essentially a PTO and gearbox which drives a whopping great propellor, or pair of props. The engine the Guardian are making a mess of reporting is slightly different - axial in design (i.e. the propblades are spining around the same axis as the compressor and they apparently replace or at least augment the turbine stage rather than being a seperate as in a turboprop) compa http://www.flug-revue.rotor.com/FRHe...7/FR0707e1.jpg with:http://media-2.web.britannica.com/eb.../78/24078-004- ED5F210D.gif During tests, while carrying a load of 5000 kg, it reached a range of about 15,000 km, a speed of 993 km/h and a ceiling of 11,300 m. Series production of the aircraft -- now designated as TU-95 -- started in January 1956 at Plant Nr. 18 in Kuibyshev, while production tests were still underway. Hell of a plane. The prop-blades were transonic, possibly supersonic at revs. When the RAF QRA planes used to go up to shoo them off they could hear them, over the noise of 500 kt skipstream and their own engines, from a considerable distance.. -- Dirk http://www.transcendence.me.uk/- Transcendence UKhttp://www.theconsensus.org/- A UK political partyhttp://www.onetribe.me.uk/wordpress/?cat=5- Our podcasts on weird stuff |
#13
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Rolls-Royce brings propeller engines back in vogue
Pratt & Whitney improved on its turbo prop engines to produce the one
used by the Dash-8 400. New blades, improved turbine, and higher cruise speed, lower fuel burn. This is why the -400 outsells the -300 nowadays since it cost less to operate despite bigger size. With the good old turboprops making a come back, I guess Rolls wants a piece of the pie. You'll note that the market for jet powered planes smaller than 70 seats is all but gone. And if its research results in really big improvements, it might even be good enough to replace jet engines in the 100-150 seat category. Airlines have begun to fly their jets a bit slower to save on fuel. So the speed difference for short haul flights might be even less noticeable with turboprops. The big question is whether this would result in a huge change when Boeing and Airbus decide to build 737/320 replacements, or whether engine manufacturers will produce new jet engines that will continue to be the core of all planes above 100 seats. Note that P&W is now working on the geared turbofan to be used on the Bombardier C series and a Mitsubishi jet of same size (100-130pax). If this pans out, the technology would be usable for larger engines and provide a reason for Boeing/Airbus to revamp their 737/320 aircraft. |
#14
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Rolls-Royce brings propeller engines back in vogue...yes michaelnewpoort, what is your point ?????
"Sue Veneer" a écrit dans le message de ... http://www.guardian.co.uk/environmen...ort-rollsroyce Rolls-Royce brings propeller engines back in vogue Aviation company claims the design could cut an airline's fuel bills and greenhouse gas emissions by 30% * Alok Jha, green technology correspondent * guardian.co.uk, * Monday October 20 2008 10.36 BST * Article history Charles Lindbergh poses with his plane The Spirit of St Louis in 1927. Photograph: AP It evokes images of the vintage days of aviation, when flying around the world was a luxury few could afford. But propeller-driven aircraft, inspired by the iconic Spirit of St Louis, could make a return thanks to innovative fuel-saving designs. The Guardian has learned that Rolls-Royce recently cleared a major hurdle in testing its new design for a propeller-driven engine, involving a double rotor and new blade shape. Engineers have called Rolls-Royce's design a "tremendously significant" step forward. The company claims the design could cut an airline's fuel bills and greenhouse gas emissions by 30%. "We're talking about saving $3m or 10,000 tonnes of CO2 per year per aircraft if you introduce an open- rotor on to a 100-200-seater aircraft," said Mark Taylor, an engineer at Rolls-Royce who is leading a project to design the next generation of aircraft engines. Modern propeller-driven engines, also known as advanced open rotors or turboprops, are acknowledged to be more fuel efficient than the turbofan and turbojet engines used by most aircraft today. But, despite much research and testing by all the major engine manufaturers in the early 1980s, they never caught on, partly because they are far noisier. But with the growth in aviation causing major environmental concerns, aeronautical engineers believe that the open-rotor engine could have a new lease of life. "We believe that, based on our test, we can produce a quiet and efficient open-rotor engine," said Taylor. The company believes its design would be quieter than any aircraft in operation today. Rod Self, an acoustic engineer who works on aircraft engines at Southampton University said Rolls-Royce's latest work was "tremendously significant — they are a significant player in this market. On the noise front, they've got the best models going and … a lead on others in the field." Efficiency improvements are sorely needed, said Alice Bows, a climate scientist at the University of Manchester's Tyndall Centre who specialises in aviation's environmental impact, said: "The amount of CO2 from aviation looks to be 2-3%, a relatively small proportion of the world's total. But you've got annual growth of 6-7% in terms of passenger kilometres with efficiency improvement only at around 1%." Turbofan engines work by sucking in air with a enclosed fan at the front of the engine. Most of this air is pushed out of the back to produce the thrust needed, with the rest used to burn fuel to drive the fan. The more air that is pushed out rather than burned, known as the bypass ratio, the more efficient the engine is. Put simply, open- rotor engines have a higher bypass ratio than turbofans or turbojets for an equivalent-sized device. Another reason for the higher efficiency of open-rotor engines is that, unlike traditional engines, they do not have a casing around the propeller. The casing increases weight and drag. "Because you've removed the [casing], you're able to go to much bigger fan diameters and not incur the weight and drag penalties," said Taylor. The airline industry has been here before. The oil crisis in the late 1970s encouraged engineers to design engines inspired by the old propeller-aircraft of the first half of the 20th century but incorporating the jet technology used in the more modern aircraft engines. American engine manufacturers Pratt & Whitney and General Electric, both funded by Nasa, flew open-rotor designs for several hundred hours on McDonnell Douglas and Boeing aircraft. But two factors prevented open rotors from being used commercially — noise and propeller designs. In addition, the drop in the price of oil meant there was no great incentive to save fuel. But the rise in the price of oil over the past year coupled with environmental concerns mean that efficient engine designs once again look attractive. Rolls-Royce's design uses two sets of propellers near the rear of the engine, which rotate in opposite directions. This reduces the energy wasted when propellers twist some of the air, rather than pushing it all straight backwards. "If you have a second set spinning in the opposite direction, you untwist it and recover the energy from that air. That goes into useful force to drive the aircraft forward," said Self. "But it's even more noisy." The sources of noise in an open-rotor engine come from different aspects of the propeller, such as their thickness and whether the tips spin faster than the speed of sound. Rolls Royce's engineers specifically tackled these problems by increasing the number of blades on the rotors, changing their shape from the traditional elongated to a more squat design and making the blades thinner. The result was, claims Rolls-Royce, a set of rotors that can turn at a slower speed — and hence make less noise — while maintaining a high efficiency. The British-based company is not the only one investigating the open- rotor concept. General Electric, Pratt & Whitney and French company Snecma all have open-rotor prototypes under construction, though commercial secrecy means their progress is unclear. Taylor said there was a choice for airlines. "You could go for a low- noise advanced turbofan or you could trade that for some noise and go for a much more efficient engine and that is the question we're asking the aviation industry. What would you rather have — a bit better noise profile or better fuel burn and lower CO2?" |
#15
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Rolls-Royce brings propeller engines back in vogue
wrote in message ... On 21 Okt, 14:04, James Robinson wrote: "True Blue" wrote: A staggering article. The Guardian makes a fool of itself yet again. Turboprops with or without counter-rotating propellers have been used extensively, in many parts of the world, for many years. Yet The Guardian report this as a new-found technology which will "save the planet". They should stick to the arts. Except they aren't talking about traditional turboprops. They are describing a propfan, or unducted fan engine, "Unducted fan" is a bit of a misnomer. Traditionally the fan refers to the big cold whirry thing at the front rather than than small hot whirly thing at the back. not necessarily. Remember the Convair 990 Coronado, which had what they called "Aft-Fan" engines. |
#16
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Rolls-Royce brings propeller engines back in vogue
On Oct 22, 5:08*am, John Doe wrote:
Pratt & Whitney improved on its turbo prop engines to produce the one used by the Dash-8 400. New blades, improved turbine, and higher cruise speed, lower fuel burn. This is why the -400 outsells the -300 nowadays since it cost less to operate despite bigger size. With the good old turboprops making a come back, I guess Rolls wants a piece of the pie. You'll note that the market for jet powered planes smaller than 70 seats is all but gone. And if its research results in really big improvements, it might even be good enough to replace jet engines in the 100-150 seat category. Airlines have begun to fly their jets a bit slower to save on fuel. So the speed difference for short haul flights might be even less noticeable with turboprops. The big question is whether this would result in a huge change when Boeing and Airbus decide to build 737/320 replacements, or whether engine manufacturers will produce new jet engines that will continue to be the core of all planes above 100 seats. Note that P&W is now working on the geared turbofan to be used on the Bombardier C series and a Mitsubishi jet of same size (100-130pax). If this pans out, the technology would be usable for larger engines and provide a reason for Boeing/Airbus to revamp their 737/320 aircraft. The Mitsubishi Regional Jet (MRJ) is a bit smaller than the CSeries. The 4-abreast MRJ takes about 70 to 90 passengers. |
#17
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Rolls-Royce brings propeller engines back in vogue
On 21 Okt, 15:59, James Robinson wrote:
wrote: James Robinson wrote: wrote: Modern propeller-driven engines, also known as advanced open rotors or turboprops, are acknowledged to be more fuel efficient than the turbofan and turbojet engines used by most aircraft today. But, despite much research and testing by all the major engine manufaturers in the early 1980s, they never caught on, partly because they are far noisier. What ABSOLUTE bull****. Plenty fo short range commuter flights use turboprops. They'r enot so efficient for long haul because they can't reach the high altitudes a jet can (the thrust from a turboprop gets significantly less the higher it goes, a turbofan has the opposite effect. They are talking about propfans. No, they are not *- "Modern propeller-driven engines, also known as advanced open rotors or turboprops...never caught on, partly because they are far noisier." Yes, they are. No, they arenät. THey make THINK they are, but they arenät *The clues are the comments about advanced open rotors, What about their comments about turboprops? and the fact that they are noisier. T-props are also generally noisier than turbofans. Not much of a clue there.. *While they are related to turboprops, design estimates show a significant savings for stage lengths of 1500 miles, in comparison to standard turboprop or turbofan engines. * The Guardian article makes it clear they (the Guardian) are talking about contra-rotating turboprops. I suspect what RR have actually built is an engine where the turbine stage, rather than the compressor stage has been replaced with uncased, large diameter blades. ISTR seeing a MD80 fitted with these in Flight International back in the early 80's Those are called propfans. Quite. Not turboprops. Another reason for the higher efficiency of open-rotor engines is that, unlike traditional engines, they do not have a casing around the propeller. The casing increases weight and drag. "Because you've removed the [casing], you're able to go to much bigger fan diameters and not incur the weight and drag penalties," said Taylor. ..but you can't go as fast, or as high. They have about a 10 percent speed penalty, compared to current turbofans at top cruising speed. *This is not significant for shorter haul flights, where they are only at cruise for a small part of the overall trip. The use of propfans might add 5 minutes to a 500 mile flight, for example. Well, no, because the Guardian were quite clearly talking about turboprops. I'm fully prepared to believe that's not what RR were telling them, though. They are talking about propfans, which can be considered a specific type of turboprop. The Guardian doesn't know WHAT it's talking about. - Dölj citerad text - - Visa citerad text -- Dölj citerad text - - Visa citerad text - |
#18
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Rolls-Royce brings propeller engines back in vogue
wrote in message ... On 21 Okt, 15:59, James Robinson wrote: wrote: James Robinson wrote: wrote: Modern propeller-driven engines, also known as advanced open rotors or turboprops, are acknowledged to be more fuel efficient than the turbofan and turbojet engines used by most aircraft today. But, despite much research and testing by all the major engine manufaturers in the early 1980s, they never caught on, partly because they are far noisier. What ABSOLUTE bull****. Plenty fo short range commuter flights use turboprops. They'r enot so efficient for long haul because they can't reach the high altitudes a jet can (the thrust from a turboprop gets significantly less the higher it goes, a turbofan has the opposite effect. They are talking about propfans. No, they are not - "Modern propeller-driven engines, also known as advanced open rotors or turboprops...never caught on, partly because they are far noisier." Yes, they are. No, they arenät. THey make THINK they are, but they arenät The clues are the comments about advanced open rotors, What about their comments about turboprops? and the fact that they are noisier. T-props are also generally noisier than turbofans. Not much of a clue there.. IIRC, it's turboprops with contra-rotating blades that cause the most noise. The Bears you mentioned earlier were apparently audible to the RAF interceptor pilots above the noise of their own engines from a distance of 400 yards. **** knows what it must have been like inside the damned things. They were very powerful and as you say, very fast. I have been told that by reducing the pitch of the blades and spinning the engine at full tilt, and then opening-up the blades, they could initially out-accelerate a Jaguar. While they are related to turboprops, design estimates show a significant savings for stage lengths of 1500 miles, in comparison to standard turboprop or turbofan engines. The Guardian article makes it clear they (the Guardian) are talking about contra-rotating turboprops. I suspect what RR have actually built is an engine where the turbine stage, rather than the compressor stage has been replaced with uncased, large diameter blades. ISTR seeing a MD80 fitted with these in Flight International back in the early 80's Those are called propfans. Quite. Not turboprops. Another reason for the higher efficiency of open-rotor engines is that, unlike traditional engines, they do not have a casing around the propeller. The casing increases weight and drag. "Because you've removed the [casing], you're able to go to much bigger fan diameters and not incur the weight and drag penalties," said Taylor. ..but you can't go as fast, or as high. They have about a 10 percent speed penalty, compared to current turbofans at top cruising speed. This is not significant for shorter haul flights, where they are only at cruise for a small part of the overall trip. The use of propfans might add 5 minutes to a 500 mile flight, for example. Well, no, because the Guardian were quite clearly talking about turboprops. I'm fully prepared to believe that's not what RR were telling them, though. They are talking about propfans, which can be considered a specific type of turboprop. The Guardian doesn't know WHAT it's talking about. Precisely: "Rolls-Royce brings propeller engines back in vogue". The journo will have conjured up an image of a Lancaster with perspex-covered holes in its side with smiling tree-huggers gazing out of them. - Dölj citerad text - - Visa citerad text -- Dölj citerad text - - Visa citerad text - |
#19
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Rolls-Royce brings propeller engines back in vogue
Sue Veneer wrote:
http://www.guardian.co.uk/environmen...ort-rollsroyce Rolls-Royce brings propeller engines back in vogue Aviation company claims the design could cut an airline's fuel bills and greenhouse gas emissions by 30% * Alok Jha, green technology correspondent * guardian.co.uk, * Monday October 20 2008 10.36 BST * Article history http://www.q400.com/q400/en/home.jsp T. |
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