Airbus A-400M Counter rotation & handling
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Learned contributors,
How do the 'handed' counter rotating props on the A-400M affect the handling of the aircraft ( positive or negative) in particular in engine out conditions e.g. EFATO.
Thanks for your time and trouble.
How do the 'handed' counter rotating props on the A-400M affect the handling of the aircraft ( positive or negative) in particular in engine out conditions e.g. EFATO.
Thanks for your time and trouble.
The rationale for counter-rotating props on a twin is that there is no longer a critical engine.
The A400M is (I think) unique in that it has a pair of engines on each wing with the props rotating in opposite directions to each other.
Since that is (as with a C/R twin) a symmetrical arrangement, it's likely that the handling is the same whether, say, it's a port outer or starboard outer that has failed.
I would expect, however, that there are handling differences between an inner and outer engine failuure (as on any 4-engined aircraft, in fact).
The A400M is (I think) unique in that it has a pair of engines on each wing with the props rotating in opposite directions to each other.
Since that is (as with a C/R twin) a symmetrical arrangement, it's likely that the handling is the same whether, say, it's a port outer or starboard outer that has failed.
I would expect, however, that there are handling differences between an inner and outer engine failuure (as on any 4-engined aircraft, in fact).
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It gives a variety of benefits to the A400.
To quote the RAF.....
"This ‘Down Between the Engines’ counter-rotation produces a more symmetrical airflow over the wing, which improves lift, aircraft handling and stability. As well as allowing a reduction in the structural weight of the wing, the arrangement reduces the adverse yaw in case of an engine failure and gives a 4% increase in the lift at low speed and reduces the level of vibrations and therefore the noise inside the aircraft."
The quote below is strictly from another forum but sounds like an official statement...
"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%."
To quote the RAF.....
"This ‘Down Between the Engines’ counter-rotation produces a more symmetrical airflow over the wing, which improves lift, aircraft handling and stability. As well as allowing a reduction in the structural weight of the wing, the arrangement reduces the adverse yaw in case of an engine failure and gives a 4% increase in the lift at low speed and reduces the level of vibrations and therefore the noise inside the aircraft."
The quote below is strictly from another forum but sounds like an official statement...
"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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That would make sense that the arrangement reduces the maximum yaw in an EFATO. The maximum turning force is created by the outboard engine on which the prop blades are descending on the outboard side. IN the AM-400 neither engine has descending blades outboard.
Well done Airbus, I like that sort of thinking.
Of course another advantage of this DBE rotation is that you won't need such a large fin/rudder surface area, since the asymmetric forces in the event of a critical engine failure will be less. A smaller fin/rudder will increase range and save fuel throughout the airframe life.
This is one of those "why did nobody think of this before" innovations.
This is one of those "why did nobody think of this before" innovations.
I see issues with spares holding (props and gearboxes), particularly in a combat situation.
I have also heard that an engine change takes several days against a few hours for a C130.
However, I hope it is a success as a lot of investment has been made.
I have also heard that an engine change takes several days against a few hours for a C130.
However, I hope it is a success as a lot of investment has been made.
I wonder whether the 'counter rotating' props (DBE) is what causes some of the horrible noise the A400 makes.
Are the engines/gearboxes completely handed or do you just move a lever on the gearbox during installation to reverse the output shaft direction? I think I know the answer to that.
Are the engines/gearboxes completely handed or do you just move a lever on the gearbox during installation to reverse the output shaft direction? I think I know the answer to that.
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Many thanks for your contributions folks.
I would appreciate clarification on the technical points of the handed engines raised.
Are two sets of spares required or not ?
I would appreciate clarification on the technical points of the handed engines raised.
Are two sets of spares required or not ?
I am guessing, but I would have thought that intelligent design would mean that only the gearboxes and props would have to be different on the two contra-rotating engines, which is not a massive increase on spares requirement, considering the advantages. The engines would otherwise be identical.
Not sure why an engine change would take several days?
Not sure why an engine change would take several days?
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Not two full sets of spares. The engines are all the same. The difference is in the reduction gearboxs and the props. So as far as major spare assemblies, you'd have to have 2 props and 2 gearboxes. For parts smaller than those assemblies, it's hard to say without pretty specific knowledge. It could be possible to design the left and right turning props and gearboxes with the majority of parts interchangeable. It's also possible to design them with exactly zero interchangeable parts.
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I am guessing, but I would have thought that intelligent design would mean that only the gearboxes and props would have to be different on the two contra-rotating engines, which is not a massive increase on spares requirement, considering the advantages. The engines would otherwise be identical.
Well, I don't know if it accounts for "several days" but I can see that having to change gearboxes would take more time, perhaps a lot more time.
Just for example a Herc Quick Engine Change assembly has everything except the prop and associated controls (Valve housing) It even has almost all the cowling installed. You essentially hoist the engine into place. bolt it on, make the electrical and plumbing connections, then install the prop and Valve housing and rig the controls. I know that's simplifying it a bit, but having to install a gearbox on the engine will add to that, perhaps considerably. Installing the gearbox would seem to involve removing cowling and reinstalling , There's plumbing to connect, as the gearbox and engine share lubrication, and the installation itself seems pretty critical. you're making a connection which transmits a lot of power, and it has to be aligned correctly. Perhaps this has been engineered so that a gearbox installation is pretty much "plug and play", but even so, it's a process that isn't required on a Herc engine change.
