Rolls-Royce brings propeller engines back in vogue

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.
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.

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party
http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff

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

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.

"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?"

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.

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.

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.

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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.

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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.