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Airbus A400M Counter-Rotating Prop Configuration  
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Posted (6 years 1 month 1 week ago) and read 19171 times:
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Flightglobal ran an article today about the A400M rollout. The photos show engines 1 and 2 (and presumably, 3 and 4) in a counter-rotating configuration:



I understand the benefit to counter-rotating props, but I've never seen two engines that turn in opposing directions on the same wing. Then again, this configuration could be more common than I think, and the shape of the A400M's propellers simply makes their direction of rotation evident.

So what is the reasoning for this? What benefits does this configuration offer that a "traditional" counter-rotating configuration (ie: 1 and 2 opposing 3 and 4) does not?

2H4


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43 replies: All unread, showing first 25:
 
User currently offlineDragon6172 From United States of America, joined Jul 2007, 1202 posts, RR: 0
Reply 1, posted (6 years 1 month 1 week ago) and read 19174 times:

Interesting. Which engines have the extra gear to rotate the prop in the opposite direction? Whats the difference in weights?

I am guessing there is some aerodynamic benefit to this?



Phrogs Phorever
User currently offlineCdekoe From United States of America, joined Nov 2006, 57 posts, RR: 0
Reply 2, posted (6 years 1 month 6 days 23 hours ago) and read 19173 times:

Interesting indeed. And Google to the rescue...  Smile

http://www.a400m-countdown.com/index.php?v=2&spage=7

This counter-rotation characteristic is known as Down-Between-Engines (DBE) and the A400M will be the first aircraft ever to use such a configuration. The advantages of DBE have far-reaching effects both aerodynamically and structurally. Firstly, airflow over the wings is symmetrical, improving lift characteristics and the lateral stability of the aircraft. Secondly, DBE allows for an optimum wing design by eliminating most of the effects of torque and prop-wash on each wing, concentrating the airflow over the most efficient portion of the wing located between the engines. DBE also reduces the “critical engine” effect of severe yaw in the event of an outboard engine failure. The result allows a 17% reduction in the area of the vertical tail surface.

Further aerodynamic advantages inherent in DBE have been found to give a 4% increase in lift from the wing at slow speed, which enables, for the same total lift, a simpler, lighter flap system to be employed. As a consequence of the lessening of the aerodynamic forces applied to the flaps, the surface area of the horizontal tail-plane can also be reduced by 8%.



We can't solve problems by using the same kind of thinking we used when we created them.
User currently offlineFlipdewaf From United Kingdom, joined Jul 2006, 1562 posts, RR: 1
Reply 3, posted (6 years 1 month 6 days 23 hours ago) and read 19146 times:
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I believe, though im not 100% on this, that it helps with engine out performance and can reduce the control surfaces and helps the TE high lift devices because of where the air is "blown". I hope that describes it ok.

Fred


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 4, posted (6 years 1 month 6 days 23 hours ago) and read 19148 times:
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Quoting Cdekoe (Reply 2):
Interesting indeed. And Google to the rescue...

Bloody hell. It never even occurred to me to check the A400M website! Thanks!

Quoting Airbus:
This counter-rotation characteristic is known as Down-Between-Engines (DBE) and the A400M will be the first aircraft ever to use such a configuration.

Hmm..."ever" is such a strong word, I feel compelled to find an existing example of this configuration just to prove them wrong....  mischievous 

Overall, very interesting. I wonder if other airframe manufacturers will start adopting this configuration.

2H4



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User currently offlineMark5388916 From United States of America, joined Aug 2007, 377 posts, RR: 0
Reply 5, posted (6 years 1 month 6 days 22 hours ago) and read 19121 times:



Quoting 2H4 (Reply 4):
I feel compelled to find an existing example of this configuration just to prove them wrong....

If anyone can find, I'm sure your it!

Mark



I Love ONT and SNA, the good So Cal Airports! URL Removed as required by mod
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 6, posted (6 years 1 month 6 days 22 hours ago) and read 19112 times:

It does make certification of the engines a more interesting proposition, because you now have two different types. It could also make for spares provisioning problems.

User currently offlineGST From United Kingdom, joined Jun 2008, 930 posts, RR: 0
Reply 7, posted (6 years 1 month 6 days 20 hours ago) and read 19052 times:



Quoting Dougloid (Reply 6):
It does make certification of the engines a more interesting proposition, because you now have two different types. It could also make for spares provisioning problems.

I dont see why. Give me a single example of a military aircraft operator that uses only a single type of engine, and also has heavy lifting aircraft requirement. Most military forces use dozens of aircraft types from trainers to fast jets, to heavy lifters, many using different engine types. What is a single additional type between friends? Most of the maintenance procedures and spare parts will be the same also.


User currently offlineKELPkid From United States of America, joined Nov 2005, 6346 posts, RR: 3
Reply 8, posted (6 years 1 month 6 days 20 hours ago) and read 19051 times:



Quoting Dougloid (Reply 6):

It does make certification of the engines a more interesting proposition, because you now have two different types. It could also make for spares provisioning problems.

Obviously, with 8 bladed props, overall cost of ownership wasn't part of the design equation...  Wink



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 9, posted (6 years 1 month 6 days 20 hours ago) and read 19037 times:
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Quoting GST (Reply 7):
Most military forces use dozens of aircraft types from trainers to fast jets, to heavy lifters, many using different engine types.

That doesn't change the fact that an aircraft with four common engines will require the operator to inventory fewer spare parts than an aircraft with dissimilar engine components.

Will this make the aircraft uneconomical to operate? Not necessarily, nor does Dougloid seem to be arguing that. But while this sourcing/stocking challenge may not ruin the overall economics of the aircraft, it could absolutely be directly and solely responsible for canceled flights and failed missions.

2H4



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User currently offlineKELPkid From United States of America, joined Nov 2005, 6346 posts, RR: 3
Reply 10, posted (6 years 1 month 6 days 20 hours ago) and read 19015 times:

So, it would seem that this design configuration would give the aircraft two critical engines, one on each side  spin  (not that critical engine considerations seem to be that big a deal on a large transport...the Vy3e speed is probably a good speed above the stall margin in this bird).


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineCTR From United States of America, joined Jul 2005, 303 posts, RR: 0
Reply 11, posted (6 years 1 month 6 days 16 hours ago) and read 18856 times:

Could the four engines be common except for a reversing gear in two of the gearboxes?

This is how it is done in the V-22 with counter rotating prop rotors.

Have fun,

CTR



Aircraft design is just one big compromise,,,
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 12, posted (6 years 1 month 6 days 14 hours ago) and read 18808 times:



Quoting GST (Reply 7):
I dont see why.

That's because you aren't thinking clearly. You now have to certify two different types of engines. Engines that turn backwards to each other are different even if they share common parts.

Quoting GST (Reply 7):
Give me a single example of a military aircraft operator that uses only a single type of engine, and also has heavy lifting aircraft requirement.

what the hell is that supposed to mean?

Quoting GST (Reply 7):
What is a single additional type between friends?

If you're willing to pay for it that's ok-but it introduces an additional layer of complication and spare parts stocking and "not commonality" that is unnecessary.

Look at the stackup. Europrop now gets to develop 2 different types of engines, at no increase in profitability, because they aren't going to sell more-they'll sell half as many of each type. The people who make the props are faced with the same problems. And you haven't even started trying to figure out what the changed airflow will do to the engine operating parameters. it woul;d be just plain foolish to assume without knowing that they'll act the same.

Quoting GST (Reply 7):
Most of the maintenance procedures and spare parts will be the same also.

And you know this because..........?

Quoting CTR (Reply 11):
Could the four engines be common except for a reversing gear in two of the gearboxes?

That's not nearly as simple as it sounds. If you want to maintain the same prop speed, you're going to have to shoehorn those gears in there somewhere. This is not a freakin' bicycle, people.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (6 years 1 month 6 days 13 hours ago) and read 18782 times:



Quoting 2H4 (Thread starter):
I understand the benefit to counter-rotating props, but I've never seen two engines that turn in opposing directions on the same wing.

I think the engines go the same directly and they just reverse at the gearbox.

Quoting CTR (Reply 11):
Could the four engines be common except for a reversing gear in two of the gearboxes?

Yes.

Quoting Dougloid (Reply 12):
That's because you aren't thinking clearly. You now have to certify two different types of engines. Engines that turn backwards to each other are different even if they share common parts.

It wouldn't be that bad. If the only difference was the rotation direction and everything was just mirrored, qualification by similarity would be pretty straightforward.

Quoting Dougloid (Reply 12):
That's not nearly as simple as it sounds. If you want to maintain the same prop speed, you're going to have to shoehorn those gears in there somewhere. This is not a freakin' bicycle, people.

Yes, but a counterrotating gearbox is a lot less work and cost than two types of engine.

Tom.


User currently offlineCTR From United States of America, joined Jul 2005, 303 posts, RR: 0
Reply 14, posted (6 years 1 month 6 days 12 hours ago) and read 18748 times:



Quoting Dougloid (Reply 12):
That's not nearly as simple as it sounds. If you want to maintain the same prop speed, you're going to have to shoehorn those gears in there somewhere. This is not a freakin' bicycle, people.

Wow. The fact that the V-22 does it must be a miracle.

Have fun,

CTR



Aircraft design is just one big compromise,,,
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 15, posted (6 years 1 month 6 days 12 hours ago) and read 18736 times:

Quoting Tdscanuck (Reply 13):
It wouldn't be that bad. If the only difference was the rotation direction and everything was just mirrored, qualification by similarity would be pretty straightforward.

Quoting Dougloid (Reply 12):
That's not nearly as simple as it sounds. If you want to maintain the same prop speed, you're going to have to shoehorn those gears in there somewhere. This is not a freakin' bicycle, people.

Yes, but a counterrotating gearbox is a lot less work and cost than two types of engine.

Tom.

Tom, it's not a question of mirror imaging everything. You folks are all assuming that this is easily accomplished by merely "putting in a counterrotating gear in there.

Listen. I spent a lot of time working on TPE331s and we had two flavors. One was a straight, 2000 rpm clockwise rotation engine with a supr gear train. The other was a counterclockwise, 1591 rpm number that swung a bigger prop.

I can tell you that the reduction gearing was entirely different between two engines with tthe same model number. Here's how they did it and I think that here's how Europrop will do it.

The 2000 rpm model had a spur gear train and a fixed planetary gearset. The 1591 rpm reverse rotation one had to have a floating planetary hearset and an extra bull gear to get the reverse rotation while making sure that all the accessories worked properly.

Think about it. Draw yourself a little picture of a geartrain that will reduce shaft speed to prop speed.

Then think about what you have to do to get the prop to run backwards. Never mind what you've got to do with your accessories, prop governor, whatever, but don't forget it's got to occupy the same physical envelope.

You've got to get one gear that's gonna take all that torque and reverse it in there that's gonna handle 15,000 hp reliably.

Easy? Simple? In an armchair maybe.

[Edited 2008-06-26 20:56:22]

User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 16, posted (6 years 1 month 6 days 11 hours ago) and read 18709 times:



Quoting Dougloid (Reply 15):

Tom, it's not a question of mirror imaging everything. You folks are all assuming that this is easily accomplished by merely "putting in a counterrotating gear in there.

That particular portion of the thread was about having the engine run the other direction. It doesn't take any extra gears, you just mirror the whole thing and run it the other way.

Quoting Dougloid (Reply 15):
Listen. I spent a lot of time working on TPE331s and we had two flavors. One was a straight, 2000 rpm clockwise rotation engine with a supr gear train. The other was a counterclockwise, 1591 rpm number that swung a bigger prop.

Right, but that's not what was being discussed. The suggestion was two identical engines that spin the same speed (with the same prop), just in opposite directions. It's been done many many times before.

Tom.


User currently offlineFrancoflier From France, joined Oct 2001, 3740 posts, RR: 11
Reply 17, posted (6 years 1 month 6 days 10 hours ago) and read 18691 times:



Quoting Tdscanuck (Reply 16):
The suggestion was two identical engines that spin the same speed (with the same prop), just in opposite directions. It's been done many many times before.

Sorry to jump in, but 2 identical engines cannot turn in opposite directions. Their innards would all be backwards, hence different parts, hence different engines.

Unless you meant the different gearbox scenario, in which case it sounds like an easier solution, though not simple, as Dougloid mentioned. An extra set of gear could take care of the problem, even though it would make the gearbox slightly heavier and bigger, and might rob a bit more power from the turbine, all of which can be compensated for, I suppose.

It would make more sense if everything but the gearbox was interchangeable.



Looks like I picked the wrong week to quit posting...
User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 18, posted (6 years 1 month 6 days 7 hours ago) and read 18608 times:

I remember reading that the engine configuration also has advantages for people jumping from the side doors of the aircraft. It reduces downwash on one side.

User currently offlineDragon6172 From United States of America, joined Jul 2007, 1202 posts, RR: 0
Reply 19, posted (6 years 1 month 6 days 4 hours ago) and read 18534 times:



Quoting Dougloid (Reply 12):
That's not nearly as simple as it sounds. If you want to maintain the same prop speed, you're going to have to shoehorn those gears in there somewhere. This is not a freakin' bicycle, people

I find it hard to believe that anyone would want to maintain an inventory of TWO seperate engine types for ONE aircraft.

The TP400-D6 website clearly states that it's the PROP GEARBOX that provides for the two different rotations. It may be a complicated gearing, but clearly it was more cost effective than trying to convice buyers that maintaining two seperate engines would be a good idea.



Phrogs Phorever
User currently offlineBond007 From United States of America, joined Mar 2005, 5401 posts, RR: 8
Reply 20, posted (6 years 1 month 6 days 2 hours ago) and read 18499 times:



Quoting Dougloid (Reply 12):
Quoting CTR (Reply 11):
Could the four engines be common except for a reversing gear in two of the gearboxes?

That's not nearly as simple as it sounds. If you want to maintain the same prop speed, you're going to have to shoehorn those gears in there somewhere. This is not a freakin' bicycle, people.

But do we know how this is done, and how the engines are certified, or is this all speculation?

I'm certainly not an expert by any means, but all of the engines have a propellor gearbox, correct? Regardless of which way they turn. Is it not possible that this gearbox is just modified to run the opposite direction? Yes, I know this is not 'simple', but are we talking about a completely extra gearbox for the contra-rotating props, or just one gearbox that has 2 flavors?

Back to certification. Do we know they have to certify TWO types of engines?

It seems like a lot of guesswork is going on here  Wink


Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineDragon6172 From United States of America, joined Jul 2007, 1202 posts, RR: 0
Reply 21, posted (6 years 1 month 6 days 2 hours ago) and read 18490 times:



Quoting Bond007 (Reply 20):
Back to certification. Do we know they have to certify TWO types of engines?

Its just one engine

Quoting Bond007 (Reply 20):
I'm certainly not an expert by any means, but all of the engines have a propellor gearbox, correct? Regardless of which way they turn. Is it not possible that this gearbox is just modified to run the opposite direction? Yes, I know this is not 'simple', but are we talking about a completely extra gearbox for the contra-rotating props, or just one gearbox that has 2 flavors?

Like I said, it says on the engine website that it is the prop gearbox that allows for the different rotations.



Phrogs Phorever
User currently offlineBond007 From United States of America, joined Mar 2005, 5401 posts, RR: 8
Reply 22, posted (6 years 1 month 6 days 2 hours ago) and read 18486 times:



Quoting Dragon6172 (Reply 21):
Like I said, it says on the engine website that it is the prop gearbox that allows for the different rotations.

Duh, should have read a little more carefully, sorry!

Roger



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineDragon6172 From United States of America, joined Jul 2007, 1202 posts, RR: 0
Reply 23, posted (6 years 1 month 6 days 2 hours ago) and read 18477 times:



Quoting Bond007 (Reply 22):
Duh, should have read a little more carefully, sorry!

No worries, I should have added the link. Here it is:

http://www.europrop.aero/pages/tp400/default.html



Phrogs Phorever
User currently offlineBuckFifty From Canada, joined Oct 2001, 1316 posts, RR: 20
Reply 24, posted (6 years 1 month 6 days 1 hour ago) and read 18458 times:

I must admit I'm no engine specialist, and this is all conjecture on my part.

But if the Soviets were able to make a turboprop with counter rotating props on each engine over 40 years ago, not to mention the output of those turboshafts are more powerful than the TP400, I'm sure it's not such a big deal as everyone makes it here to be. I don't have any figures of gearbox reliability on the TU-95, but it's still flying, while it's more modern equivalents in the Russian Air Force have fallen by the wayside. That must say something about it's design.

As I understand it, the turboshaft and the prop in this application are not inline, and therefore, the gearbox itself should be a modular unit in application. Therefore, the turboshafts themselves will be the same.

http://commons.wikimedia.org/wiki/Image:MTU_TP400-D6.jpg

Doesn't look like anything needs to be shoehorned.


25 NicoEDDF : Exactly! The engine is the same; the gearbox then is providing the turn direction. The props don't care. A lot simpler than people want to make it.
26 2H4 : I worded that poorly. I never intended to suggest that the engines themselves rotate in opposing directions. I should have used the word "propeller"
27 Sprout5199 : But do the benfits of the DBEs outweight the added weight, and maintance of the gear box? Seems to me a tried and proven turboprop design would have
28 Francoflier : Good question. Airbus engineers are rather smart after all, so I'd trust they thought it over carefully. They might not, however, have an extensive e
29 A342 : I don't know where I read it, but IIRC the gearbox on two of the engines is 20 kg heavier than on the other two.
30 GST : Personally I'm amazed its not heavier. Well done to Airbus for getting it so light. I'm sure this, as well as whatever minor benefit to lift there ma
31 Nomadd22 : I was on a 130 with both engines on one wing out in the 80s. The degree it was banked because of what the pilot claimed was torque reaction from the r
32 Post contains links and images Pihero : He was pulling your leg. The thrust from both engines will generate a yaw toward the dead engines side and the lift generated over the lve engines si
33 2H4 : Actually, if the propellers are both mounted on a common shaft, the term would be "contra-rotating". "Counter-rotating would describe separate engine
34 Timz : How many turbine aircraft can we think of with C/R props? The J41 had them, didn't it? It reversed prop rotation at the gearbox? How about piston twi
35 Nomadd22 : I did get a little suspicious when the loadmaster suggested hiding the parachutes if the pilot came back.
36 Timz : It was the Me323 I was thinking of. The text in the book says the props on each wing rotated the same way, but one pic seems to show the props altern
37 Post contains images 2H4 : Found the pic. That does indeed appear to be the case: Now, whether that engine configuration is the product of design, or the product of very, very
38 GST : That engine contiguration is a direct result of the aircraft failing to function as a glider, as it was origionally intended. It required multiple, m
39 Pihero : I bend to your superior vocabulary. You're right, of course
40 Pihero : The reason why there is a critical engine lies mainly with gyroscopic moment of the remaining engine : for a clockwise rotation of both props, (seen
41 Dougloid : The FBO I worked at had a Grumman F7F Tiger Cat they bought for the museum (the AirZoo) and when John Ellis was down in Tennessee picking it up one e
42 Pihero : But in my opinion the most beautiful twin of all times. Cheers Dougloid !
43 Post contains images Sonic67 : The engines are the same two different gear box. Advantages of Contra rotating propellers -Recovery of energy lost in outlet swirl - Can be smaller di
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