There are some very interesting engine developments in the aerospace sector.
A quick trio…
Rolls Royce Open Rotor
In the 1980’s the open rotor concept was developed that used unducted contra-rotating blades in order to lower fuel consumption. Although flight trials on an MD81 went well, these UnDucted Fans (UDF’s) as they were called, ultimately did not achieve commercial success because of unresolved engineering issues, noise and the main reason, fuel prices stabilised.
Unducted fan engines are very similar to conventional high bypass turbofans, but instead of enclosed rotors they use a higher diameter open rotor without incurring weight penalties with a nacelle.
With rising energy prices and advances in engineering and materials technology the concept is currently being studied again. General Electric, NASA, Snecma and Pratt and Whitney refreshed the concept and started work on newer designs a few years ago under a number of ‘green’ initiatives.
There was a flurry of activity from around 2007 but since then not much has been publicly released. Rolls Royce are confident however, that they can make the design work and have stated it is the future.
Rolls Royce are participating in a number of research projects including the EU funded Clean Sky JTI and Dream Project.
As part of the Clean Sky project Rolls Royce is developing the Sustainable and Green Engine (SAGE)
From the project web page
Open rotor technologies offer the potential for significant reductions in fuel burn and CO2 emissions relative to turbofan engines of equivalent thrust. Higher propulsive efficiencies are achieved for turbofans by increasing the bypass ratio through increases in fan diameter but there is a diminishing return to this improvement as nacelle diameters and consequently weight and drag increase. Open rotor engines remove this limitation by operating the propeller blades without a surrounding nacelle, thus enabling ultrahigh bypass ratios to be achieved.
It is claimed that as much as a 30% decrease in fuel consumption can be achieved for a given journey although noise problems remain difficult to resolve. NASA concluded that noise remained a significant challenge although a full report into its two year feasibility study will not be published until later this year.
Rolls Royce are bullish about noise reduction though, this, and blade containment are the current focus. They point out that advances in design realisation tools means they are able to test concepts before going to prototypes. The engine in the picture is aimed at a 20,000 to 25,000 lb thrust range, the normal range for the 100-150 passenger narrow body market and that it should be much more efficient than expected new turbofan designs but noisier.
There are also a diverse range of other concepts and technologies being directed at reducing emissions and fuel consumption so who knows where it will end up.
Airbus have even patented a design for an aircraft equipped with one, click here to read, and even EasyJet are getting into the concept with their EcoJet, although it all seems to have gone quiet on that front..
Reaction Engines
The designers that formed the core team on the cancelled 1980’s BAE HOTOL project that used the Rolls Royce RB545 eventually went on to create Reaction Engines Ltd.
Reaction Engines are working on the Sabre Engine and the hypersonic unmanned Skylon Spaceplane.
Here is what Lord Drayson had to say
This is an example of a British company developing world beating technology with exciting consequences for the future of space. It is fantastic that Reaction Engines, the British National Space Centre and ESA have successfully secured this public-private partnership arrangement and I look forward to seeing how the project progresses
In April this year the BBC reported a successful first stage pre-cooler test
Steady progress
It will be interesting to see if funding continues and we can grasp this opportunity. It certainly holds the promise of low cost orbital transport, able to lift 12 tonnes into orbit.
Heavy Fuel UAV Engine
Perhaps not as glamorous as the first two the ability to use diesel engines in UAV’s is no less important. High octane petrol has been traditionally used for small UAV piston engines but its transport and storage presents many problems in a military context.
The Wolverine 3 engine was developed by Ricardo specifically for UAV’s and uses JP-8 fuel.
Since its first launch it has been developed further and is now available in a number of variants up to 55hp.
It doesn’t look like much but its impact on the operation of small UAV’s, especially in naval applications, will be immense.
Gd over view TD. Open rotor engine tech is quite interesting and has been concept for some time and it’s a proposed solution to the 737/a320 replacement project. The recent partnering of rr and p&w over geared turbo fan tech is I think a move to greater integration of the two companies. The more tech bit open rotors still have a nacelle however the inlet and fan containment case are removed. The inlet in traditional nacelles have very tiny perforation which help reduce noise and regulates flow to the compressor. The fans themselves cant get to big as the rotor tips start to go supersonic which degrades there prop effficiency. There main issue remains fan containment in the event of engine failure(mechanical or bird strike) the enery involved is massive and not something you want flying around the tail. A few other thing too but if rr get it right a Uav application may well be a precursor to manned jets. The main issue in uavs being you need a lot of power for the systems while keeping them small and lightweight.
Now you have said about UAV’s as a probable test bed for the technology the Mantis/Telemos engine configuration springs to mind.
Decreased fuel consumption I suppose means increased endurance
Is the blade containment issue any more or less serious an issue than normal turboprops?
That dinky diesel looks like a real winner!
I would imagine it’s the contra-rotation that adds to the problem if the props fail – double the impact speed between blades! I actually thought the Russians were already using these kinds on engines, just not with quite as many blades?
Simon, yes I think the AN70 uses a variant on a theme
TD
The open rotor blades turn faster. There location is an issue you can’t really put them under the wing as the blades are at the back of the engine and closer to the wing tank gives issues like the turbine break in the a380 and makes the flap design more problematic. Clean air flow in this area would also be an issue. The issue with putting engines at the tail is all you control and hydraulic lines come together at the tail. For redundancy you run one more line one down one side and one or more down the other the other side of the fuselage offering some protection. You could have a failed engine destroying the other engine if there together at the tail also.
Cheers Mark, interesting stuff isn’t it
eurocopter took a diesel engine design to an helicopter show about 2 years ago,they reckon it would take about 5 years for it to be in one of their light helos. The design used opposing pistons, similar i believe to a boxer style although this was only 2 cylinder as opposed to the boxer flat four. The main drive as well as reduced fuel comsumption is the diesel engine is not effected by altitude, unlike a turbine perfect for rotary wing.
Anyone else look at the demo aircraft and think, “oo extended range ie longer on station, high engines great for avoiding salt ingress,cough MPA, cough cough”!!
That Wolverine 3 engine… Just looked at the specs and the only thing I was interested in isn’t listed (weight). Perhaps it’s not quite as light as they’d like yet.
Hi Mark, re: engine positioning, if we’re using an advanced concept as propfans, then perhaps we should be looking at other alternatives such as fore-swept wings? With the engine nacelles at the back, it should reduce problems of interface with the flaps.
Alternatively, there’s always mounting one at the very rear, like the tristar/trident/727 with the other two engines mounted at the wingtips like the Skylon above. Personally, I accept the risk and treat it like a standard turboprop.
I’ve just had a read of the Skylon entry on Wikipedia, and although it looks an amazing project (I was a big fan of HOTOL back in the days of yore), however some of the problems seem to make the project appear unfeasible, at least to my technologically limited mind.
Things like the water cooled brakes, in case of an aborted take-off. With the water being jettisoned later ‘if’ the take-off is successful. Size and weight mean a specially built runway etc, I’m thinking why not go for a smaller and lighter craft which is then launched atop an Antonov An-225. This reduces the need for the extra fuel, making the vehicle smaller and no need for the water. When not being used to launch Skylon the An-225 can be shifting cargo around the world and still pay its way.
Just a thought….great project though.
Skylon = 12 tons to orbit? Oh Hell yeah! Can’t get too carried away; not there yet *crosses fingers*.
Talking of which:
http://news.yahoo.com/push-british-space-port-sparks-debate-230600567.html;_ylt=A2KJjahSSbdPQF8Al8PQtDMD
RE: UDF’s. I remember reading somewhere that one of the reasons the original Nimrod was so successful at sub-hunting was its enclosed engines, which were a lot quieter than the turboprops on other ASW aircraft.
One way to reduce the noise which is heard on the ground is to mount them above the body; a Blended body wing design as shown for example…
BTW if you let the wolverine video run, there are options to see similiar films. One option is the mini panther a small fixed wing tilt rotor UAV made by IAI. looks quite handy!
Propfan propellors would likely not be any more dangerous than other fan or prop technology, mainly due to the use of fibre-reinforced composites (continuous aligned).
The idea being a blade would degenerate to flailing mass of horse-tail style fibres in the event of animpact or other damage rather than allow chunks to spin off into the fuselage or elsewhere. I think a similar material is used on military helicopter blades (BERP on the upcoming Wildcat?) but I don’t have a source.
Couple of other systems to consider:
- D-DALUS http://www.popsci.com/science/article/2012-01/how-d-dalus-flies-nothing-else
- RR LiftFan from the LiftSystem http://www.rolls-royce.com/Images/Liftsystem_tcm92-6697.pdf
The ducted LiftFan could have potential VTOL applications using a gas turbine without direct use of a turbojet for propulsion.
TD
Blasts from the past and then some
1) These used to be called turboprops.
2) News filler for the past 25 years – it is one reason why UK aerospace is on the wane.
@FBOT
There is a difference in the fluid dynamic bypassing the nacelle between a turboprop and a propfan, though you are right, they are very similar. It’s enough of a design difference to be classed separately.
TOC @ 19.22
Turboprop with a pusher propellor vs UDF / Propfan
Any chance you could detail the differences?
Regarding a UDF / Propfan did this not die a death when geared turbofans became a goer?
P+W seem to the main men pushing this new tech.
RR have not covered themselves in glory with their attitudes to The IAE technology roadmap.
They – RR had a good patch in the 90s but recently they have struggled.
I wonder if the continuing high pound hurt them with a reduced R+D spend catching up with them eventually.
TD
On the subject of the UAV engine running diesel fuel.
What cycle is the engine running?
Are there two spark plugs in the picture?
So far this month we have MB running a diesel cycle using petrol.
Do we now have an otto cycle using diesel?
If yes then we really do have a funny old world.
@FBOT
The problem with a prop is that the faster you go, the more drag the tip of the prop experiences. At a tip speed of around Mach 1, the drag reaches such a point that your prop efficiency nose dives as it tries to propel the high pressure, high speed air and you deliver no additional power to accelerate you further. This point is normally reached when the aircraft itself is nowhere near Mach 1.
The first step to offsetting the tip speed compared to aircraft speed is swept blades.
The second way to do this is to add more blades and then start packing them more tightly (think turboject/fan). There’s a pressure limit with blade density that ducted fans help to mitigate.
The third approach is to start the air rotating before it reaches the propeller. You can do this by offsetting several sets of blades as you travel down the system (think how many sets of blades are in a turbojet).
This is difficult to do with a prop, however you can achieve similar results with a counter rotating set of blades.
The objective of all this being to delay when your blade tips reach Mach 1 before your aircraft speed.
The propfan takes this a step further. It loses the gearbox, reducing power loss through the transmission. The blades can handle higher revolutions because of the blade design, configuration and rotating air mentioned above.
A problem develops If the blades are at the front, the system would represent a turbojet with zero bypass ratio – back pressure builds up in the system and efficiency plummets as in a fighter jet, even if you can achieve higher power with more fuel consumption. Turboprops have this problem, but the airspeeds are low enough that the back pressure in the turbine isn’t too severe.
Moving the blades to the rear you return to high bypass system (because there’s no duct at all). Backpressure is reduced again and efficiency rises once more, only this time you’re pushing turbofan speeds instead of turboprop speeds.
I’m not sure why the propfan never took off. I always thought it was due to an unproven overall design vs turbofans/turboprops, that a lot of these tricks can be applied to turboprops as well, and the subsequent decrease in fuel prices compared to when the research kicked off.
Fbot as far as you critisim of roll Royce goes it very wide of the mark. There lead engine on 787 and launch on a350 also. There not idle in open rotor work but you won’t hear about it until airbus/Boeing see there beak point in replacing regional single aisle with a new a/c in about a decades time. Geared turbo fans are only the stepping stone .When the tech matures a new plane will launch in both materials used to make it and the engine were getting close..
From several years ago.
http://www.flightglobal.com/news/articles/r-r-undertakes-secret-studies-into-public-perception-of-open-317313/
Mark @ 21.06
RR played their joker and got maximum points when they worked their 3 spool big turbofan design model as hard as they could using parametric design and design re-use to the max. Consequently they were able to produce a whole family of engines very quickly and efficiently each tailored very closely to the needs of individual aircraft types.
However they have struggled to get the last 2-3% of efficiency out of their engines – both not delivering on launch and being a bit slow to match the efforts of others. This has been an ongoing issue, they have delivered market leadership on timing but struggled regarding fuel consumption. These are F1 standards of success and failure so they are competitive not front row competitive.
Next up are the reliability issues that have popped up from time to time in the last 10 years, again they are high standards but RR have had a few problems to deal with. Qantas was a big blow and they have no more Get out of Jail cards left.
Finally on the narrow body front RR needs to get their act together, in the IAE they were always second in the marriage stuck with the cold end and playing second fiddle in the market. Regarding the future RR is out on a limb relying on the Hail Mary pass that is their UDF tech play. The P+W GTF looks like a very good next step in the market and the fact that they now have control of the IAE combine means that they can put some heat on the market leader.
RR are now very much a follower in the marketplace with a ten year wait at best until they can start to move independently in a 3 pole marketplace relying on the airframe makers desire to get radical with their biggest sellers. To me that is a huge leap of faith, a huge leap to far given their own history and the current state of both the market and their competitors.
Looks to me they have taken the money and run.
I fear even if they get first mover status the market leaders will buy their way in.
@ the Other Chris – thanks for the info; was wondering what the detailed differences were.
Do you know how the fuel consumption compares between turboprops and UDF’s?
Props are more fuel efficient than turbofans/jets, the wave drag problems are what stops you hitting higher speeds as efficiency disappears very quickly. Compared to a turbofan at equivalent speeds, the efficiency figure is around the 1/3 more efficient mark.
Below isn’t the document I was looking for, but from page 218 are the fuel study results with different blade configurations:
- http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19820010328_1982010328.pdf
TD you must have had a field day when you found the Skylon video – anyone else see the ISO container being loaded for shipping into space? That plus the Thunderbirds music – very British what ho, rah rah.
Nice to see some original thinking by British designers – we really are cleverer than the Yanks in so many ways, just a shame we hardly ever put ideas into practice/production.
The Other Chris: “think a similar material is used on military helicopter blades (BERP on the upcoming Wildcat?) but I don’t have a source.”
I think the best example for flailing would be the MV-22 Osprey props. The last time I had the chance to have a good look at BERP blades on a Lynx (BERP IV?)they had a titanium leading edge with colbolt at the kink due to forming difficulties, I’m 100% sure they’re not designed to flail.
FBOT, credit where credit’s due, RR production of single crystal turbine blades really is something to behold. As for reliability, adopting the ‘pay per flying hour’ type of operation means that reliability is an issue they take seriously. I’m glad to see things have moved on since the wheezy Gem.
Osprey! Thank you very much, I was flicking through completely the wrong the materials in a fruitless search for details! You’ve saved me some searching Sir, and I am grateful.
I think RR have a proposal engine for advanced versions of the B777 that would have a bypass ratio of 12 to 1. So turbofans can still be improved.
Skylon needs £200 million to build a working Engine. £7 billion to build the whole space plane. Not sure about putting the engines on the wingtips. What happens if you lose one engine? Could become very unstable, very fast.
A 130 seat, 1300 mile range airliner using twin turboprops from the A400M, could be a real winner with low cost airlines. Would probably need swept wings, like Russian turboprops.
for alternative engines loot at
doylerotary http://www.doylerotary.com/ and
http://www.regtech.com
Interesting concept on the propfans. I can see it being used as a successor to small propellor planes, but I also see some problems using it in 747 type passenger aircraft.
For one, it’s much less effective energy-wise than a turbo-prop, key reasons being 1) No nacelle to pre-compress air to maximum efficiency before hitting the fan blades. 2) No combustion chamber.
There is also a problem with not compressing the air before the fans. Altitude. It means that the operating altitude of the aircraft would be lower than turboprops, being limited to higher density air (and ironically, increased fuel consumption + lower speed)
Another problem would be birdstrikes. A nacelle protects an engine’s blades from anything from the sides and to a limited extent, from the front as well. Having a huge prop area outside a nacelle increases the chances and occurance of something hitting the fan, and the further out from the center the hit, the more catastrophic it can get as the forces on the outer edge of the blades are much greater than near the center as was pointed out.
Maybe they should concentrate on making it a Cesna replacement rather than a 747.
Found the article on the proposed RB3025 engine for the Boeing 777X. Rated at 99,500 lbs, with a 15% better fuel burn than a Trent 800 that powers early 777s.
Would love to see a scaled down 44,000lbs version to re engine C-17s.
Observer
If your talking about the open rotor engine you don’t understand the concept as none of you comments are correct. If your talking about something else ignore this
An open rotor has a nacelle the weight saving is in removing the fan containment case. In very very basic terms an open rotor is a turbojet with a fan on the outside. Nacelle inlet is there to regulate the airflow and reduce its speed so as the compressor fans see air flowing at about 0.4 Mach number this is still present in an open rotor. The open rotor still has a combustion chamber even a turbo prop has a combustion chamber. Bird strike is an issue but it’s more to do with a lack of containment. Any impact in flight will be straight on not from the side. Open rotors will in theory offer turbofan performance with the fuel efficiency of a turbo prop.
Mark,
Do these open rotor engines suffer from rotor tip losses? I’d have thought they must as the vortex leaves the end? Isn’t that what a ducted fan or turbo fan avoids?
Simon
Yes they do. I understand the tip vortex and pylon flow interference on the blades is also the source of some of the noise issues with this type of engine. There has been some research to do with active vortex control on main fan blade tips which may develop further for this type of engine. I suspect geared turbofans and improvements to turbine efficiency will precede a move to geared open rotor technology in the 2020s. A lot of research in fuel efficient engines ongoing here and in the states.