A400M Propellers

Dear Aircraft-clued-up-to-fückers,

I was having a bit of a butcher’s at an article on the new Airbus A400M military transport aircraft, and on one of the piccies, I noticed that the blade thingies (technical term) on each wing are not only a bit bent, but they also appear to be bent in different directions. So does this mean that one propeller twirls clockwise and the other anti-clockwise?

Here’s the piccie in question:
Here’s another computer-generated piccie from Wiki (see what I did there?): http://en.wikipedia.org/wiki/Image:A400M_propellers_DBE.jpg which shows the same configuration. So is this clockwise/anti-clockwise caper normal on four-engined aircraft? Or does it only apply to the Airbus A400M, and if so, what’s the advantage?



Book Reviewer
If you have all props spinning one way then you induce a torque force, this is more noticeable on a single engine aircraft but if you have contra-rotating or alternate rotating props then you remove this problem.

Mind you this may not be the reason airbus have done it.
Counter rotating propellers on a twin engine aircraft is a normal practice.
It reduces the yaw force of the aircraft if one engine fails, compared to both engines rotating in the same direction.
In the case of both engines rotating in the same direction, whichever one causes the greatest amount of yaw if it fails is called the critical engine.
Could be a similar principle on 4 engined aircraft, not sure.
Harmonics is the simple answer. :D

As mib and ff suggest, the loss of engines makes asymetric flying slightly easier. Not really too much of an issue with two engines on either side. On the harmonics side of life, having props spinning in opposite directions will aid to cancelling out all those nasty vibrations that these huge props will produce and you will find that it will to a certain degree give you a performance increase as the 'prop wash' behind each prop creates its own tunnel. If each prop wash went in the same direction, an amount of thrust would be lost as the dirty air from each prop hits each other. With them going in opposite directions, it doesn't have this problem and actually creates an almost linear boundary flow (also helps in slower speed configs as it gives a nice flow over the flaps). In older or smaller aircraft, the props all go the same way and this means each engine unit is common. If you had them going in different directions, it would mean you would need slightly different gearboxes on the opposing direction units.

The props are frickin huge too;

Ta a bunch for that, Ralf. That explains it very nicely indeed. :D :D :D

I did some research on it, but it was all getting a bit technical for me, I'm afraid. I know, I know, Flashy, t'ickie bog-trotter and all that. :oops: :oops: :oops:

So it seems that Flashy was essentially correct with his post anyway. I knew I should never have had any doubts about it. So my thanks go to Flashy too.


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