Running the fans slower is likely to make less noise (unless the you get a gear-whine...), but how does it give you a greater by-pass ratio? Surely a slower fan pushes less air through the engine, so makes less thrust for the same turbine speed.

I suppose slower fans could run at a steeper blade pitch, but wouldn't that just increase the noise level again?

So which is more important? Saving the planet and/or conserving fossil fuel stocks, or cutting down on aircraft noise?

You can do both - not open fan but a much larger coweled (shudders at the word) one, or use one turbo to drive lots of fans? And stick it on top of the wing.

Or is it suddenly not a propeller if it has more than 4 or 5 blades?

Why do I get the feeling that "open rotor" is just a trendy marketing name for a modified turboprop engine.

This open rotor stuff - how do the engine manufacturers propose to contain a shedded blade within the engine casing (an airworthiness requirement)?

P&W's plan has the advantage that when the gears do fail, they're less likely to hit the passenger in seat 8A.

Let's see the gear wear on 10,000 hours testing

No idea. How does a turbo-prop pass it?

As i understood it it geared down to not to push too much air through

as it currently stand so much air is going through alot of the fuel is going through the system unburnt

Run the main fan slower you reduce the amount of air but more explosion ! :D

No One should be makling Highbypass turbo fans today!

if there are two techs with advantages, and one is available now for existing fit or retrofit then why are we not using them now?

@Peter

Slower fans use bigger blades and can push more air, reduced cavitation etc..

I think it might have something to do with the velocity of the air coming out the back.

Aero-engines are at peak efficiency when the air is coming out the back at the same speed it's going forwards through the air. Turbo-props peak around 300kts whereas turbofans are around 500kts. That's at sea level, turbofans get better with altitude, props less so as there's less air for them to bite into.

Overall, a future GTF-equipped airline industry would be a lot quieter and more pleasant for people living near airports." More pleasant? Don't you mean "less unpleasant"?

No, the author is correct "more pleasant". Although an assumption - I think that as no new large airports have been built on greenfield sites for years, that most people who live near airports these days have most likely chosen to move TO the location (i.e. by choice) in full knowledge of the noise issue, rather than suffering by having an airport built near to where they already live. Those that were truly annoyed by any noise would have excercised their choice to move away from the airport by now also. Unless they were complete idiots.

All said I think this is a great story : can't wait to see what the eco-mentallists find to moan about when all this new green technology comes to fruition. Oh, yeah... sorry I forgot... there's not much that can shut one up is there as the sounds of their own voices is music to their ears.

A turboprop has a few relatively heavy and securely attached blades, a turbofan has lots of lightweight slot-in blades.

http://www.rolls-royce.com/reports/environment_report_07/using-knowledge/noise-reduction.html

"...engine technologies are delivering significant progress towards achieving the ACARE goal of a 50 per cent noise reduction by 2020. SILENCE(R) technology has already been incorporated into the Trent 900 and Trent 1000 engines."

http://www.rolls-royce.com/civil/products/largeaircraft/trent_900/

"Despite its size and power it is extremely quiet, meaning that the Airbus A380 has only around one third of the noise level of previous 150 seat aircraft."

Seems like you can already have your cake and eat it. You would just have to buy British, which is a concept that I accept is complete anathema to Mr. page who seems to believe that if it isn't Made in the US of A then it must be shite.

Advance the GTF into serious testing. Roll it out after the serious testing is complete. Let the Open Rotor people demo their ideas and do the serious testing, then roll them out. If Open Rotor turns out to be the better option when it is ready, it supplants GTF. In the meantime, you get the immediate GTF benefits. If it isn't better, GTF is already in place and keeps on flying.

Problem solved.

Oh, as long as the efficiency goes up, I'm happy. And given the cost of the noise abatement projects the governments have been undertaking lately (at least here in The States), GTF is more likely to have a positive impact on the most people's money concerns.

Oh. It's -you-.

In case you missed it before, ODFO.

I have no idea if either GTF or the open blade approach will live up to their manufacturer's claims, only time will tell. Imagine for a minute though that they do deliver 15% fuel improvements, how long will it be before any of the airlines can afford them?

Bear with me here-

From a quick scan of the net (and some very rough calculations) I see that a brand new RR Trent 1000 (which seems to be a decent, modern turbofan) costs something like 30 million US dollars. I got this number by taking 2.6 billion US dollars and dividing it by 86, the number of engines Virgin Atlantic are getting in a deal that was signed just a few months ago. Now those are for brand new planes, I believe they are for Boeing 787s, but how often do the airlines upgrade their fleets?

If you did want to fit 4 brand new engines to an existing aircraft then how long will it take you to pay back that 120 million US dollars (and that's presuming they cost the same as the current tech, which I seriously doubt will be the case) from the 15% fuel savings? Those planes are not going to be refitted in 5 minutes either. I guess that comes down to how much the fuel costs. Also, where do you get the money to buy those engines in the first place if business isn't that good? As someone pointed out earlier, airlines like BA are pretty strapped for cash right now.

Will be interesting to see how long it is before we see any aircraft with either of these engine technologies.

I know this isn't Tomorrow's World or The Currant Bun, but any chance we could have some pictures (or links to some) of the tech involved so we can get more background on what's being discussed...?

You're missing the Joker in the pack, the BAe 146 / AVRO RJ.

This already has something very similar. The engines on these aircraft were originally designed as turboshafts for helicopters and rev too highly to be converted directly into a bypass fanjet. The solution is the same, there's a gearbox to allow the fan to revolve at a lower speed than the turbojet bit.

The 146 is not so affectionately known amongst crews as the "flying gas chamber". There have been numerous incidents of both passengers and crew being overcome by toxic fumes in the cabin. In common with most modern aircraft, the compressed air for cabin ventilation / pressurisation is taken as a bleed from the bypass fan ducting of the engines (cheaper than having a seperate compressor). The problem here is that the gearbox lubricants are highly toxic and if a seal leaks........

It's unlikely in practice these engines will be retrofitted to existing airplanes for the reasons you mentioned. They will most likely be available on new Airbus A320s from about 2015.