What are these on the engines?
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On the subject of the A380, an alternative to reducing the number of reversers being studied by Airbus was dropping them all together, that decision came about as part of a massive weight loss and cost cutting program circa 1998 with the aircraft on offer at that time being not being anywhere near close to the ~20% cost reductions that Airbus wanted (and needed to sell any) over the 747-400.
To quote from 'Airbus A380' by Norris/Wagner,
To quote from 'Airbus A380' by Norris/Wagner,
Another cost and weight saving change discussed at great length with the airlines involved reducing or eliminating the use of engine thrust reversers. As the name suggests, these devices redirect the engine power - or some of it - forward to help slow the aircraft after touchdown. Whereas some early low bypass engines redirected all thrust by blocking the entire flow out of the exhaust, the later generation and much larger high bypass ratio engines deflected only the bypass stream. This limited but valuable reverse thrust was generally seen as a supplement to the stopping forces and helped reduce break wear on landing.
In itself, cutting wear and tear on brakes was a major cost saver, and the decision to eliminate some of even all the reversers was not to be taken lightly.
Airbus canvassed airlines on the proposals about November 1998, emphasizing potential weight saving and performance improvement from the the move. In the end, a compromise was reached and the reversers were dropped on the outside engine pair only, particularly since most airlines agreed that the increased braking thrust, from the improved efficiency engines to be used on the A3XX would help achieve a predicted stopping distance similar to, or better than the A340.
In itself, cutting wear and tear on brakes was a major cost saver, and the decision to eliminate some of even all the reversers was not to be taken lightly.
Airbus canvassed airlines on the proposals about November 1998, emphasizing potential weight saving and performance improvement from the the move. In the end, a compromise was reached and the reversers were dropped on the outside engine pair only, particularly since most airlines agreed that the increased braking thrust, from the improved efficiency engines to be used on the A3XX would help achieve a predicted stopping distance similar to, or better than the A340.
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20legend:
to answer your query more accurately, looking at the image(A343 on TDown),
this particular crew still had the nose extremely high for thrust reverser activation!
was it not for the spoilers all being extended, one could mistake the image for a take off, with the nose so high.(thrust reversers deploying, excluded)
as for the different stages of deployment,(#3 full open & #4 just cracking) this is also dependant on how synchronously the pilot selects all 4 levers, plus some doors on some engines may deploy/stow at diffferent rates, due friction/winds etc.
NOTE: no reverser can/should be operable until the landing gear has contacted the ground, plus time delay, couple of seconds, however this can be activated before all 4 wheels on each main gear, touch the tar.
no eng power can be applied in reverse until all 4 doors on each respective engine is fully open, & furthermore, #1 and 4 engines cannot be powered up until both engines have all 4 of their doors fully open, this to prevent an asymetric yaw situation, should 1 of the outboard engs not open fully, and the opposite goes to max reverse power! bad situation.
outboard engines have a far greater yaw effect on an aircraft due to the distance from the centre turning point, & the lever-arm length.
As already mentioned, modern reversers only deflect the fan or low pressure air, which on this particular engine is approx. 65-70%. small fan.
trust this clarifies, an unusually captured shot!
to answer your query more accurately, looking at the image(A343 on TDown),
this particular crew still had the nose extremely high for thrust reverser activation!
was it not for the spoilers all being extended, one could mistake the image for a take off, with the nose so high.(thrust reversers deploying, excluded)
as for the different stages of deployment,(#3 full open & #4 just cracking) this is also dependant on how synchronously the pilot selects all 4 levers, plus some doors on some engines may deploy/stow at diffferent rates, due friction/winds etc.
NOTE: no reverser can/should be operable until the landing gear has contacted the ground, plus time delay, couple of seconds, however this can be activated before all 4 wheels on each main gear, touch the tar.
no eng power can be applied in reverse until all 4 doors on each respective engine is fully open, & furthermore, #1 and 4 engines cannot be powered up until both engines have all 4 of their doors fully open, this to prevent an asymetric yaw situation, should 1 of the outboard engs not open fully, and the opposite goes to max reverse power! bad situation.
outboard engines have a far greater yaw effect on an aircraft due to the distance from the centre turning point, & the lever-arm length.
As already mentioned, modern reversers only deflect the fan or low pressure air, which on this particular engine is approx. 65-70%. small fan.
trust this clarifies, an unusually captured shot!
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Well thanks for all the great replies, certainly learn't a lot there!
http://www.airliners.net/open.file/1254670/M/
http://www.airliners.net/open.file/1254670/M/
