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Faro
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GE: New Advances In Open Rotor Technology

Fri Jul 06, 2012 8:51 am

http://www.flightglobal.com/news/art...-not-a-barrier-to-entry-ge-373817/

Fair use excerpts:

Quote:
"Initial performance and noise studies conducted in the wind tunnel show that an open rotor engine with counter-rotating propellers in pusher configuration will have margin for Stage 4 operations and will likely meet and exceed the more stringent Stage 5 levels to be set by ICAO next year and implemented by 2020, General Electric (GE) says."
--------

"Overall the results were outstanding," says Ron Klapproth, GE Aviation's director of commercial product strategy, of GE's wind tunnel tests. "In the 1980s, designers of the first unducted fan architectures had to compromise performance to achieve an acceptable acoustic signature. With what we tested in wind tunnels, we're confident we can design high performance blades [with acceptable] acoustic signatures."
--------

"He says "tall poles" in the technology development path include blade-out impacts to the fuselage and icing."



Funny that we should hear of OR advances from GE when RR seemed to be the main proponent of the technology...


Faro
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sweair
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RE: GE: New Advances In Open Rotor Technology

Fri Jul 06, 2012 10:54 am

What is the benefit of the open rotor compared to a ducted fan? I never understood why an unducted fan is more efficient.

GE tampered with these engines back in the 80s I think hardly anything new.
 
eaglepower83
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RE: GE: New Advances In Open Rotor Technology

Fri Jul 06, 2012 12:39 pm

Essentially, the more "bypass" air you have, the more efficient the engine. As in, the more air that bypasses around the engine as opposed to going through it's core.
Open rotors and turbo props have extremely high bypass ratios.
 
LH707330
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RE: GE: New Advances In Open Rotor Technology

Fri Jul 06, 2012 4:50 pm

Quoting sweair (Reply 1):
What is the benefit of the open rotor compared to a ducted fan? I never understood why an unducted fan is more efficient.

You get the high BPR because you have a much bigger fan that is not restricted by the nacelle.The nacelle is heavy, so that limits your fan diameter....
 
ferpe
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RE: GE: New Advances In Open Rotor Technology

Sat Jul 07, 2012 12:30 am

The nacelle also add a not insignificant additional wetted area. The nacelles on a A320 for instance generate more drag then the fin contributes.
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 08, 2012 1:52 am

Quoting EaglePower83 (Reply 2):
Quoting LH707330 (Reply 3):
Quoting ferpe (Reply 4):

It sounds like an interesting set of trade-offs   .

As far as I know, one of the biggest advantages of a duct is the reduction in tip losses around the end of the blades, the penalty being weight, drag and a restriction of bypass ratio. I wonder if such engines could ever be used mounted under the wings, given that the lack of a duct would make it harder to satisfy blade off requirements?

Regards, JetMech
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ferpe
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 08, 2012 4:34 am

Quoting jetmech (Reply 5):
I wonder if such engines could ever be used mounted under the wings, given that the lack of a duct would make it harder to satisfy blade off requirements?

It seems we are looking at pusher configs with the propfans so far back as to be behind the passenger cabin. Then it is a matter how you protect the frame from hydraulic and electrical failure in the tail region and damage to the other engine once an engine let go of it's blades.
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justloveplanes
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 08, 2012 5:06 am

Quoting EaglePower83 (Reply 2):

Essentially, the more "bypass" air you have, the more efficient the engine. As in, the more air that bypasses around the engine as opposed to going through it's core.
Open rotors and turbo props have extremely high bypass ratios.

This raises a question (for some of us anyway), what is the difference then, between a pusher turboprop and an open rotor pusher? Are propeller blade outs viewed differently as to rotor blade outs? How does icing compare between the two?

Thanks!
 
imiakhtar
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 08, 2012 12:03 pm

Quoting faro (Thread starter):
RR seemed to be the main proponent of the technology...

Faro

They still are.  

RR has been on record as saying they can have a OR engine ready for service by 2025.

However, as noted in the article, the development timeline will be decided by the next generation of narrow-bodies.

In the mean time, they're concentrating on the Trents where most of their money (62%) is made.
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 08, 2012 5:59 pm

Quoting ferpe (Reply 6):
It seems we are looking at pusher configs with the propfans so far back as to be behind the passenger cabin. Then it is a matter how you protect the frame from hydraulic and electrical failure in the tail region and damage to the other engine once an engine let go of it's blades.

Do turboprops not have the same problem?
 
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 08, 2012 6:44 pm

Quoting justloveplanes (Reply 7):
This raises a question (for some of us anyway), what is the difference then, between a pusher turboprop and an open rotor pusher?

Very little other than size. The turboprop certainly has a gearbox. The open rotor may or may not, depending on which exact architecture you're talking about. The open rotor is basically the logical evolution of the turboprop to jet engine sizes.

Quoting justloveplanes (Reply 7):
Are propeller blade outs viewed differently as to rotor blade outs?
Quoting Flighty (Reply 9):
Do turboprops not have the same problem?

It's a scale problem. The largest turboprop in existence is comparable to only the smallest turbofans.

Quoting justloveplanes (Reply 7):
How does icing compare between the two?

Same problems. Open rotors have more blades to ice and are typically spinning faster.

Tom.
 
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 08, 2012 9:43 pm

Quoting ferpe (Reply 6):
It seems we are looking at pusher configs with the propfans so far back as to be behind the passenger cabin.

The problem is that the blades will fly forward if they break off, because there is no more attachment that will block them, so their lift will send them forward in a somewhat erratic manner.

Quoting tdscanuck (Reply 10):
It's a scale problem.

There was a Viscount way back when with an overspeeding prop that threw a blade clean through the cabin, this would be made worse in an OR engine, but with a compostite fan blade you'd mostly have it delam and turn into little ribbons instead of having an intact blade flying around as you would with a turboprop. At this point it's just the (im)balance issue to handle. Would it be possible to certify a ribbon-failing blade (i.e. no intact blade flying around) and a strut that shears cleanly when the blades are unbalanced?
 
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RE: GE: New Advances In Open Rotor Technology

Mon Jul 09, 2012 3:05 am

Quoting LH707330 (Reply 11):
There was a Viscount way back when with an overspeeding prop that threw a blade clean through the cabin, this would be made worse in an OR engine, but with a compostite fan blade you'd mostly have it delam and turn into little ribbons instead of having an intact blade flying around as you would with a turboprop.

Modern turbopros also have composite blades.

At the first SK Dash-8 landing gear accident the pilot (for some mysterious reason) kept the engine over the failed MLG spinning. Even if pax had been removed from near the propeller disk, then the blades penetrated the cabin, parts flew around in the cabin and injured a few pax, one of them quite seriously.

Quoting justloveplanes (Reply 7):
what is the difference then, between a pusher turboprop and an open rotor pusher?

The difference is that open rotors are by many people seen as a substitute for turbofans.

Turboprops are quite wide diameter. Their blade tips rotate at just under Mach 1 speed. Therefore no sonic boom. That limits the speed of turboprop planes, as there is a limit how high pitch angle the blade can have and still operate efficiently.

Most turbofan planes cruise at Mach 0.8 give a take a little. Therefore the tips of the fan rotate much faster, typically Mach 1.6 or 1.7. The constant sonic boom is suppressed by the duct.

For decades they have been researching how to get around this problem with open rotors. Nobody has come up with anything substantial yet.

I have a feeling, that since this "new advances in open rotor technology" is popping up again for implementation on next generation narrow bodies, then it is because there are plans that those new narrow bodies are going to be Mach 0.65 planes rather than Mach 0.8 planes. By implementing newest blade tip technology for higest possible speed at acceptable noise level, that might be possible. And it might offer a very significant fuel saving potential for spending an hour more in the air on a US transcon flight.
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Faro
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RE: GE: New Advances In Open Rotor Technology

Tue Jul 10, 2012 8:16 am

Quoting prebennorholm (Reply 12):
I have a feeling, that since this "new advances in open rotor technology" is popping up again for implementation on next generation narrow bodies, then it is because there are plans that those new narrow bodies are going to be Mach 0.65 planes rather than Mach 0.8 planes.

Does that mean that GTF has substantially no future beyond the CSeries and Airbus NEO's?

Does it further mean that we will be going back to T-tails again with open rotors and the next generation narrowbodies?


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prebennorholm
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RE: GE: New Advances In Open Rotor Technology

Wed Jul 11, 2012 1:42 am

Quoting faro (Reply 13):
Does that mean that GTF has substantially no future beyond the CSeries and Airbus NEO's?

If open rotors one day delivers what optimists predict, then yes. Then the PW GTF will have no future beyond CSeries and Airbi NEO, just like CFM56 seems to have no future beyond Airbi ONO and 737NG.

However, depending on when open rotors are ready, that can easily mean a long and bright future for GTF. Already today more than 3000 engines have been sold.

Quoting faro (Reply 13):
Does it further mean that we will be going back to T-tails again with open rotors and the next generation narrow bodies?

Again, if optimists are right, then most likely yes.

I am rather sceptical about open rotors. It was first tried 57 years ago on the Republic XF-84H fighter test aircraft, and scrapped 56 years ago. Then some 30 years ago the idea was dusted off for transport application, and quite hastily scrapped again.

On the other hand the A400M military transport - with its funny shaped propellers with tip speed just under M=1 - demonstrates a speed potential, which is slow by modern standard, but anyway interesting if a substantial fuel efficiency gain can be achieved.

When reading new hype about open rotors, then the open question is: What is an open rotor? Depending on how you define it, also the Wright Brothers used open rotors back in 1903. GE doesn't tell us any details. But the only thing, which is sure, is that it is something very different compared to previous things, or it has no future on next generation narrow bodies.
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RE: GE: New Advances In Open Rotor Technology

Sat Jul 14, 2012 10:54 pm

Quoting sweair (Reply 1):
What is the benefit of the open rotor compared to a ducted fan? I never understood why an unducted fan is more efficient.
Quoting jetmech (Reply 5):
As far as I know, one of the biggest advantages of a duct is the reduction in tip losses around the end of the blades

   But I'll talk about the diffuser and nozzle later.

So it is a flight cruise speed tradeoff. An open rotor will fly slower than a ducted fan. For without the shroud, the fan tips would be very inefficient over Mach 0.7. The other advantage of the duct is a diffuser entering the fan. In other words, the incoming air is slowed before it hits the fan. Then the fan increases the pressure of the air and the fan nozzle translates that to a high exit velocity that produces thrust.

Without the diffuser, the fan hits fundamental limits in the mach number over the blades. That will limit the flight speed. Having a nozzle improves efficiency. The trade off between large fan diameter and the diffuser/nozzle has usually occurred below Mach 0.7 (usually closer to Mach 0.6). There have been technological advances to push the speed difference, but not to parity with a shrouded fan.

Quoting prebennorholm (Reply 14):
Then the PW GTF will have no future beyond CSeries and Airbi NEO, just like CFM56 seems to have no future beyond Airbi ONO and 737NG.

Which mission?

One is *not* going to fly at 400kts (or less) for more than 4 hours. While *many* narrowbody missions are less than 1000nm.

I think we'll see an open rotor platform. Consider it a 'super Q400.' A fast propeller plane that isn't as fast as a GTF. Time is money (block time=crew pay). There will be a distance beyond which a GTF has lower costs than an open rotor. Now, short missions should go to the open rotor. They have a climb efficiency advantage over the GTF as does any aircraft that has a fan optimized for a significantly lower cruise speed.

It comes down to which mission. Airlines do not buy for one mission but their fleet. Some airlines will but an open rotor (e.g., U2's shorter missions would be perfect) while some are unlikely (B6 has an unusually long average mission).

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RE: GE: New Advances In Open Rotor Technology

Sun Jul 15, 2012 4:30 am

Quoting lightsaber (Reply 15):
I think we'll see an open rotor platform. Consider it a 'super Q400.' A fast propeller plane that isn't as fast as a GTF. Time is money (block time=crew pay). There will be a distance beyond which a GTF has lower costs than an open rotor. Now, short missions should go to the open rotor. They have a climb efficiency advantage over the GTF as does any aircraft that has a fan optimized for a significantly lower cruise speed.

So if you're correct, then whatever replaces the 737X/A320-NEO will still have a ducted fan, but perhaps an open rotor is the best choice for regional aircraft? Perhaps it is the ideal middle-ground between small turbofans (like the CRJ) and turboprops. This is no market to be sneezed at! There are a lot more RJ's in the world than there are 747's!

It also seems that a platform that offers conventional turbofans would wind up being incompatible with an OR design. Conventional turbofans are best mounted under the wing while an OR can't be mounted there without unreasonably long landing gear.
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 15, 2012 5:02 pm

Quoting tdscanuck (Reply 10):
It's a scale problem. The largest turboprop in existence is comparable to only the smallest turbofans.

How do you mean that? In terms of Bhp or thrust? there are some very large and powerful turbprops out there, they just don't have the speed that a turbofan can produce.
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tdscanuck
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 15, 2012 6:50 pm

Quoting DC8FriendShip (Reply 17):
How do you mean that? In terms of Bhp or thrust?

Power density. The biggest turboprops in existence are equivalent to about a 15,000 lbs thrust turbofan; even something like a 737/A320 needs an engine about twice that size.

Tom.
 
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 15, 2012 6:50 pm

Is there any merit in an open rotor using the GTF type hub gearbox? A Geared Open Rotor? The P&W core / gearbox for the GTF might well be suitable for an open rotor configuration...

I'm not an aerodynamic engineer, so I've no idea of how OR rpm compares with either current fan rpm or GTF rpm, but I'm guessing that there must be an optimum that would benefit from the geared hub of the GTF.
 
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 15, 2012 7:13 pm

Quoting tdscanuck (Reply 18):
Quoting DC8FriendShip (Reply 17):
How do you mean that? In terms of Bhp or thrust?

Power density. The biggest turboprops in existence are equivalent to about a 15,000 lbs thrust turbofan; even something like a 737/A320 needs an engine about twice that size.

Four NK-12 @ 14,800 shp each drive the Tu-95MS. This can cruise at representative jet altitudes and airspeeds and has a MTOW of 414,000 lbs because of its *huge* fuel load which gives it a range of over 8,000nm.

With a 738 maxing out at around 174,000 lbs MTOW, I dare say 2 NK-12's could conceivably and adequately power 738.


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LH707330
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 15, 2012 7:29 pm

Quoting faro (Reply 20):
With a 738 maxing out at around 174,000 lbs MTOW, I dare say 2 NK-12's could conceivably and adequately power 738.

I'm not sure that would satisfy the engine-out requirements though. With one engine out, the TU-95 has 9.3 lb/hp, and the 738 would have 11.8 lb/hp with one out. Intuitively, I'm going to guess that won't fly with the regulators.

My guess is that the next generation will have an OR platform in the 120-150 seat range for 100nm. Maybe A and B will split from their duopoly and go after these different buckets.
 
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RE: GE: New Advances In Open Rotor Technology

Sun Jul 15, 2012 11:18 pm

Quoting lightsaber (Reply 15):
Time is money (block time=crew pay).

Ah... but on those new airliners we'll have SP ops (and perhaps even fewer FAs).  
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RE: GE: New Advances In Open Rotor Technology

Mon Jul 16, 2012 12:31 am

Quoting faro (Reply 20):
Four NK-12 @ 14,800 shp each drive the Tu-95MS. This can cruise at representative jet altitudes and airspeeds and has a MTOW of 414,000 lbs because of its *huge* fuel load which gives it a range of over 8,000nm.

Military bombers don't have to, and generally don't, meet the engine-out performance requirements for a modern airliner. The P-8 on one engine can out-climb the P-3 on all four.

Tom.
 
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RE: GE: New Advances In Open Rotor Technology

Mon Jul 16, 2012 12:55 am

Quoting tdscanuck (Reply 23):
Military bombers don't have to, and generally don't, meet the engine-out performance requirements for a modern airliner. The P-8 on one engine can out-climb the P-3 on all four.

Fair point. Even then, if a Q400 weighs around 64k and has 5k horsepower (one engine), multiplying all the numbers by 3 gets you close to your 174k 738 with a 15khp NK-12, so designing a plane around that engine is probably doable. That said, the Q400 is considered overpowered, so you may get a bit of margin for your bigger design....
 
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RE: GE: New Advances In Open Rotor Technology

Mon Jul 16, 2012 1:15 am

Quoting DocLightning (Reply 16):
So if you're correct, then whatever replaces the 737X/A320-NEO will still have a ducted fan, but perhaps an open rotor is the best choice for regional aircraft? Perhaps it is the ideal middle-ground between small turbofans (like the CRJ) and turboprops.

   But by being significantly faster than a turboprop (they have unswept wings for a reason... not enough speed to warrant swept wings). So they will be a transition. Just as a turboprop is more fuel efficient than a turbofan, the open rotor will be more efficient than a GTF. But the open rotor will be faster.

Personally, the *perfect plane* for an open rotor would have been the A400. Its not as if the program could have been delayed much more.     
Quoting planemaker (Reply 22):
Ah... but on those new airliners we'll have SP ops (and perhaps even fewer FAs).  

I think we will have single pilot ops. That just shifts the distance where the costs are equal.   Fewer FAs... Maybe. There are still door rules and such that just do not seem to go away.

Quoting faro (Reply 20):
I dare say 2 NK-12's could conceivably and adequately power 738.

Not unless 738 wing loading were to be reduced.

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Faro
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RE: GE: New Advances In Open Rotor Technology

Mon Jul 16, 2012 7:54 am

Quoting tdscanuck (Reply 23):
The P-8 on one engine can out-climb the P-3 on all four.

That is very very impressive indeed.


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RE: GE: New Advances In Open Rotor Technology

Mon Jul 16, 2012 9:11 pm

Quoting lightsaber (Reply 25):
But by being significantly faster than a turboprop (they have unswept wings for a reason... not enough speed to warrant swept wings). So they will be a transition. Just as a turboprop is more fuel efficient than a turbofan, the open rotor will be more efficient than a GTF. But the open rotor will be faster.

It just seems to me that this is a perfect application for missions shorter than 1.5 hours. At those shorter distances, the slower speed will only add a few minutes of flying time. For longer distances, the increase in flying time becomes more significant, and consequently more costly.
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planemaker
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RE: GE: New Advances In Open Rotor Technology

Mon Jul 16, 2012 11:47 pm

Quoting lightsaber (Reply 25):
Fewer FAs... Maybe. There are still door rules and such that just do not seem to go away.

It will take a while, for sure.

We are reaching the limits of max tube and wing efficiency and while Open Rotor could extend the platform a bit something more along this line (or MIT's design) could be required for a significant efficiency step change...



NASA (together with Boeing and Cranfield) is getting the X-48C ready for first flight of a projected 20 flight schedule later this year. Wonder what it would fly like with Open Rotors?

The C is different than the B in that it has 2 vs 3 engines and they are now mounted further forward. The C also has twin inboard V-Stabs instead of the winglets on the B.

Full-size prototype with a wingspan of ~240 ft with 11,000 nm range could fly in about 10 years.


Here is what the B looked like...

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RE: GE: New Advances In Open Rotor Technology

Mon Jul 16, 2012 11:55 pm

Quoting planemaker (Reply 28):
Wonder what it would fly like with Open Rotors?

Probably fine. You'd probably want to mount the rotors aft of the fuselage to minimize the possibility that a blade off would penetrate the trailing edge. They'll need long struts. Nothing that wouldn't be an issue with a tube/wing.
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RE: GE: New Advances In Open Rotor Technology

Fri Jul 20, 2012 12:45 pm

Quoting faro (Reply 13):
Does that mean that GTF has substantially no future beyond the CSeries and Airbus NEO's?

I think it has a lot of future, and the next application will be on widebody engines, where turbofans will still rule because of the long distances involved. But for short haul OR would be superior. The question is whether a manufacturer would be willing to split that segment into two families, as today A320's and 737's cover everything from 300 to 3000nm. Guesstimating, an OR could be good up to 1000nm, maybe somewhat more, and beyond that GTF should be better. So you may have to rethink how your aircraft families are laid out.

Quoting lightsaber (Reply 15):
Time is money (block time=crew pay). There will be a distance beyond which a GTF has lower costs than an open rotor. Now, short missions should go to the open rotor. They have a climb efficiency advantage over the GTF as does any aircraft that has a fan optimized for a significantly lower cruise speed.

  

Quoting prebennorholm (Reply 14):
On the other hand the A400M military transport - with its funny shaped propellers with tip speed just under M=1 - demonstrates a speed potential, which is slow by modern standard, but anyway interesting if a substantial fuel efficiency gain can be achieved.

Definitely interesting - the A400M can cruise up to M0.72, which is enough speed for typical intra-EU flying. Now if only those TP400's were a bit more reliable...

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