747-8i Landing Spoiler Schedule
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747-8i Landing Spoiler Schedule
Was asked in class today why the 747-8i has a different spoiler extension schedule on landing to the 400.
400...all panels extend to max deflection in one movement.
8i...inboards extend half way till either nosewheel has planted then deflect fully. Outermost spoilers are fairly similar. Only the inner speedbrake panels seem to go to full deflection apon touchdown.
Only explanation I could give is maybe the new wing has a stronger pitch up tendency with speed brake deployment while the nose wheel is off the runway.
or, I could be totally wrong, so I said I'd put the question to the experts.
https://www.youtube.com/watch?v=h-pEeHro1Ks
400...all panels extend to max deflection in one movement.
8i...inboards extend half way till either nosewheel has planted then deflect fully. Outermost spoilers are fairly similar. Only the inner speedbrake panels seem to go to full deflection apon touchdown.
Only explanation I could give is maybe the new wing has a stronger pitch up tendency with speed brake deployment while the nose wheel is off the runway.
or, I could be totally wrong, so I said I'd put the question to the experts.
https://www.youtube.com/watch?v=h-pEeHro1Ks
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They did the same thing on the MD-11, the aircraft is longer and the stab smaller. The DC10 had a tenancy to pitch up upon spoiler extension but not as violently as the -11 and of course the longer airframe means an easier tail strike. The fix was restricting full spoiler deflection until the nose was on the ground. Still I had a 35 year Captain come off an MD-11 completely disheveled a few weeks ago as he had one run away from him and almost struck the tail. Who knows? A ground sense glitch, environmental factors. All checked good for us and the aircraft has flown W/O incident since. A quick check with Mr. Boeing says that the -8 is 20 feet longer than the -400.
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I believe most if that is to make the -8 behave like a -400 which was the goal of Boeing. Obviously having FBW spoilers goes a long way towards simulating the way a -400 handles.
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AFAIK, the spoilers are not FBW. The outboard ailerons are, but that is primarily to resolve a flutter problem discovered in flight test.
747-8 Design Highlights | Boeing Commercial Airplanes
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The outboard ailerons are, but that is primarily to resolve a flutter problem discovered in flight test.
The 777 spoilers also have a unique extension programme on the ground due to issues discovered during flight test.
To elaborate a bit on what SMOC wrote:
The wing on the 747-8 is aerodynamically pretty much all new relative to the -400 ('structurally similar but aerodynamically new'). As a result of the new aerodynamics, the pressure distributions across the wing changed rather dramatically, which in turn lead to large increases in many of the control surface loads.
The decision was made early on in the development that, as long as the spoiler and outboard aileron systems needed to be redesigned, we might as well go with FBW systems - which also made it easier to mimic the characteristics of the -400.
The wing on the 747-8 is aerodynamically pretty much all new relative to the -400 ('structurally similar but aerodynamically new'). As a result of the new aerodynamics, the pressure distributions across the wing changed rather dramatically, which in turn lead to large increases in many of the control surface loads.
The decision was made early on in the development that, as long as the spoiler and outboard aileron systems needed to be redesigned, we might as well go with FBW systems - which also made it easier to mimic the characteristics of the -400.
