Posted 19 December 2009 - 03:29 PM
Regarding the A-400 military bird... the props are scimitar shape to reduce shock wave formation at the tips, and to reduce noise. The silver leading edge strip you see is called an erosion strip and it is only found on the outer section because the inner section contains AC powered deicing heaters. Because the outer section has an increased rotational velocity, thus more cetrifugal force deicing is automatic because the rotational forces will shed any ice accumulation.
The reason that the left and right side props both turn in towards one another is to maintain a uniform thrust vector when one or more engine is lost or shut down. The down going blade will create a thrust moment and the closer this moment is to the aircraft centerline, the easier the handling is during single or mulitple engine operations as well when turning into a dead engine. It is always safer (if you can) to turn the aircraft into the remaining engine because the remaining engine has more induced lift on the wing and if the speed is allowed to drop to a critical level then the aircraft can suffer a dynamoc roll over that without sufficient altitude to recover from, can be deadly. I lost a good friend to this trap back in Canada while flying a Grumman Goose.