A400M Propellers
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Joined: Apr 2013
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From: Lexington
A400M Propellers
I noticed in this picture (http://i.imgur.com/yHlRKax.jpg) that the propellers on each wing rotate towards each other. I don't think I've seen that before on any airplane.
Does anyone know why they would design it in this manner?
Something is telling me that doing it the A400M-way would reduce the total propeller drag but I can't say for sure.
Cheers!
Does anyone know why they would design it in this manner?
Something is telling me that doing it the A400M-way would reduce the total propeller drag but I can't say for sure.
Cheers!
Last edited by Virtus; 29th April 2013 at 04:56.
Joined: Aug 2003
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From: Sale, Australia
The down between the engines counter-rotation of the propellers, which turn in opposite directions, allows a structural weight reduction. The arrangement preserves the symmetry of the aircraft when the four engines are operating, and reduces the adverse yaw in case of an engine failure, allowing in turn a reduction in the size of the tail fin by 17 per cent, hence reducing weight and drag. Another consequence has been the possibility to improve by four per cent the lift at low speed and thus to simplify the slats and, as a result, reduce by eight per cent the surface of the horizontal stabilizer. Furthermore, it also reduces the level of vibrations and therefore the noise inside the aircraft.
So says Airbus.
So says Airbus.
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Joined: Apr 2013
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From: Lexington
Thanks Brian!
Link for others - Airbus Military | A400M
The engine out scenario makes sense - the traditional design of all engines rotating inwards to the fuselage would increase Vmc (and decrease climb performance) compared to this design.
That's what I'm wondering about. Could this possibly have to do with the slipstreams joining together in more 'harmony' (compared to all props rotating toward the fuselage) resulting in a reduction of lift-induced drag which, according to the marketing department, is the same as an increase in lift? It makes sense that they specify low speed as this is where the direction of rotation really matters - in this regard.
Link for others - Airbus Military | A400M
The engine out scenario makes sense - the traditional design of all engines rotating inwards to the fuselage would increase Vmc (and decrease climb performance) compared to this design.
Another consequence has been the possibility to improve by four per cent the lift at low speed
Last edited by Virtus; 29th April 2013 at 05:01.
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From: UK
How about lack of commonality & associated cost of spares. Very significant to the civil marketplace - less so to the military. There have been other multi-engined a/c with "handed" props - one that springs to mind is DH Hornet twin engined fighter of late WW2. It was only a twin but had LH and RH Merlins - well the engines rotated the same way but a gearbox reversed the rotation of the props.
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From: Reading, UK
It was only a twin but had LH and RH Merlins - well the engines rotated the same way but a gearbox reversed the rotation of the props.
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From: TinselTown
The Continental TSIO-360 in Senecas is a direct drive engine, left and right. No gears. And the left one is designated LTSIO-360. How it is done I'd love to know - change the firing order? What about the valve timing? Engineers?
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From: FG central
Fairly straightforward to get a piston engine to run backwards. Typically just involves left and right hand rotation camshafts and distributors/magnetos.
Of course, that assumes the engine has been designed to run that way from the outset, which many industrial style engines are. Some things that need to be considered when designing such an engine are oil pump drive and cam shaft drive. Oil pump is easily fixed by direct crank driven pumps and the cam drive can easily be overcome by a chain with no tensioner or gear drive. But there are also many one off reverse rotation conversions out there that work well, it just takes more work to make it happen.
The older two stroke Detroit diesels can be easily changed to opposite rotation and was reasonably common to order LH and RH rotation engines in marine applications.
Of course, that assumes the engine has been designed to run that way from the outset, which many industrial style engines are. Some things that need to be considered when designing such an engine are oil pump drive and cam shaft drive. Oil pump is easily fixed by direct crank driven pumps and the cam drive can easily be overcome by a chain with no tensioner or gear drive. But there are also many one off reverse rotation conversions out there that work well, it just takes more work to make it happen.
The older two stroke Detroit diesels can be easily changed to opposite rotation and was reasonably common to order LH and RH rotation engines in marine applications.
