2H4
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Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 3:00 pm

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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dragon6172
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 3:46 pm

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
 
cdekoe
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 4:16 pm

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%.
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flipdewaf
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 4:21 pm

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
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2H4
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 4:25 pm



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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mark5388916
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 5:05 pm



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
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Dougloid
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 5:32 pm

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.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
GST
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 7:22 pm



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.
 
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 7:24 pm



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
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2H4
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 7:35 pm



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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KELPkid
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 7:48 pm

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).
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CTR
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RE: Airbus A400M Counter-Rotating Prop Configuration

Thu Jun 26, 2008 11:34 pm

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
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Dougloid
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 1:06 am



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.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
tdscanuck
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 2:01 am



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.
 
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 3:17 am



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
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Dougloid
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 3:55 am

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]
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tdscanuck
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 4:35 am



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.
 
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Francoflier
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 5:52 am



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.
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keesje
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 8:48 am

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.
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dragon6172
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 11:39 am



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.
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bond007
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 12:57 pm



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


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dragon6172
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 1:10 pm



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.
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bond007
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 1:19 pm



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
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dragon6172
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 1:35 pm



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
 
buckfifty
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 2:09 pm

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.
 
Nicoeddf
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 2:16 pm



Quoting BuckFifty (Reply 24):
Therefore, the turboshafts themselves will be the same.

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.
 
2H4
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RE: Airbus A400M Counter-Rotating Prop Configuration

Fri Jun 27, 2008 2:25 pm



Quoting Tdscanuck (Reply 13):
I think the engines go the same directly and they just reverse at the gearbox.

I worded that poorly. I never intended to suggest that the engines themselves rotate in opposing directions. I should have used the word "propeller" instead of "engine".

Quoting Tdscanuck (Reply 16):
The suggestion was two identical engines that spin the same speed (with the same prop), just in opposite directions.

As I mentioned, that suggestion was mistaken and unintentional. I meant props, not engines.

Sorry about that.

2H4
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sprout5199
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RE: Airbus A400M Counter-Rotating Prop Configuration

Sat Jun 28, 2008 1:32 am



Quoting NicoEDDF (Reply 25):
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.

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 made much more sense.

Dan in Jupiter
 
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Francoflier
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RE: Airbus A400M Counter-Rotating Prop Configuration

Sat Jun 28, 2008 4:30 am



Quoting Sprout5199 (Reply 27):
But do the benfits of the DBEs outweight the added weight, and maintance of the gear box?

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 experience of battlefield ops of military transport aircraft, and the effect on it of having 2 different props and gearboxes on one aircraft type.

Time will tell.
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A342
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RE: Airbus A400M Counter-Rotating Prop Configuration

Sat Jun 28, 2008 8:52 am

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.
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GST
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RE: Airbus A400M Counter-Rotating Prop Configuration

Sat Jun 28, 2008 10:20 am



Quoting A342 (Reply 29):
the gearbox on two of the engines is 20 kg heavier than on the other two.

Personally I'm amazed its not heavier. Well done to Airbus for getting it so light.

Quoting Cdekoe (Reply 2):
Further aerodynamic advantages inherent in DBE have been found to give a 4% increase in lift from the wing at slow speed

I'm sure this, as well as whatever minor benefit to lift there may eb at higher speeeds will more than make up for the heavier gearbox, and perhaps leave some weight left over for the aircraft to carry some spare parts for it.
 
nomadd22
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RE: Airbus A400M Counter-Rotating Prop Configuration

Mon Jun 30, 2008 12:07 pm

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 remaining engines, and pointed crooked to compensate for slip from being banked made the flight fun. Maybe the counter rotating engines would make that situation a little less interesting on the 400.
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Pihero
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RE: Airbus A400M Counter-Rotating Prop Configuration

Mon Jun 30, 2008 9:13 pm



Quoting Nomadd22 (Reply 31):
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 remaining engines, and pointed crooked to compensate for slip from being banked made the flight fun.

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 side by the propwash will generate a bank toward the dead engines side ( again) . So the only way to fly a straight line is a bank on the live engines side. A pilotiong challenge as at lower speeds one could run into rudder effectiveness limits.

As an aside, the word *counter-rotating props* is normally limited to those attached to a single engine and using two concentric shafts like those :

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2H4
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RE: Airbus A400M Counter-Rotating Prop Configuration

Mon Jun 30, 2008 10:23 pm



Quoting Pihero (Reply 32):
As an aside, the word *counter-rotating props* is normally limited to those attached to a single engine and using two concentric shafts like those :

Actually, if the propellers are both mounted on a common shaft, the term would be "contra-rotating".

"Counter-rotating would describe separate engines rotating in opposing directions.

2H4
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timz
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RE: Counter-Rotating Prop Config

Mon Jun 30, 2008 11:53 pm

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.

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 twins? Light twins with C/R props use C/R engines, but ... not the P-38? How about the Hornet?

By the way-- the Me264 had C/R props on the same wing. (Or maybe just that six-engine ... Bv222, was it?)

[Edited 2008-06-30 17:05:56]

[Edited 2008-06-30 17:16:33]
 
nomadd22
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RE: Airbus A400M Counter-Rotating Prop Configuration

Tue Jul 01, 2008 12:36 am



Quoting Pihero (Reply 32):
He was pulling your leg.

I did get a little suspicious when the loadmaster suggested hiding the parachutes if the pilot came back.
Anon
 
timz
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RE: Airbus A400M Counter-Rotating Prop Configuration

Tue Jul 01, 2008 1:32 am



Quoting Timz (Reply 34):
the Me264 had C/R props on the same wing. (Or maybe just that six-engine ... Bv222, was it?)

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 alternating, with 1-3-5 rotating one way and 2-4-6 the other.
 
2H4
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RE: Airbus A400M Counter-Rotating Prop Configurati

Tue Jul 01, 2008 3:54 am



Quoting Timz (Reply 36):
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 alternating, with 1-3-5 rotating one way and 2-4-6 the other.

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 tired mechanics is anyone's guess...  Wink

2H4
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GST
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RE: Airbus A400M Counter-Rotating Prop Configuration

Tue Jul 01, 2008 8:42 am



Quoting 2H4 (Reply 37):
Now, whether that engine configuration is the product of design, or the product of very, very tired mechanics is anyone's guess...

That engine contiguration is a direct result of the aircraft failing to function as a glider, as it was origionally intended. It required multiple, multi engined, tug aircraft, which would have been a piloting nightmare for all concerned.
 
Pihero
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RE: Airbus A400M Counter-Rotating Prop Configuration

Tue Jul 01, 2008 9:09 am



Quoting 2H4 (Reply 33):
Actually, if the propellers are both mounted on a common shaft, the term would be "contra-rotating".

I bend to your superior vocabulary.
You're right, of course
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Pihero
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RE: Airbus A400M Counter-Rotating Prop Configuration

Tue Jul 01, 2008 9:27 am



Quoting Timz (Reply 34):
Light twins with C/R props use C/R engines, but ... not the P-38?

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 from the rear, that is), a failure of the left engine will cause a yaw to the left, therefore a bank to the left, aggravating the piloting problems...a failure of the right engine, on the other hand, with a yaw to the right will cause a bank to the left -again- which tends to counter the skid to the right.
With counter-rotating props, we eliminate the critical engine situation.
Historically, the P-38 was a handful with an engine failure and until the test pilot visited the squadrons and teaching them that, especially with a left engine out situation, the initial reaction would be to throttle back....a totally new non-intuitive maneuver.
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Dougloid
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RE: Airbus A400M Counter-Rotating Prop Configuration

Tue Jul 01, 2008 1:27 pm



Quoting Pihero (Reply 40):
Historically, the P-38 was a handful with an engine failure and until the test pilot visited the squadrons and teaching them that, especially with a left engine out situation, the initial reaction would be to throttle back....a totally new non-intuitive maneuver.

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 engine puked shortly after takeoff. He said it was a real nightmare bringing it to an airstrip to put it down.

The F7F was the absolutely smallest airframe and wing you could hang two R2800s off of.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
Pihero
Posts: 4196
Joined: Mon Jan 31, 2005 5:11 am

RE: Airbus A400M Counter-Rotating Prop Configuration

Tue Jul 01, 2008 2:03 pm



Quoting Dougloid (Reply 41):
The F7F was the absolutely smallest airframe and wing you could hang two R2800s off of.

But in my opinion the most beautiful twin of all times.
Cheers Dougloid !
Contrail designer
 
sonic67
Posts: 284
Joined: Mon Jan 24, 2005 2:43 pm

RE: Airbus A400M Counter-Rotating Prop Configurati

Fri Jul 04, 2008 4:14 am

The engines are the same two different gear box.

Advantages of Contra rotating propellers
-Recovery of energy lost in outlet swirl
- Can be smaller diameter for a given power
- Result in low torque reaction through mounts and aircraft structure-

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A400 prop rotation

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