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Old 17th Jul 2011, 09:20
  #19 (permalink)  
rudderrudderrat
 
Join Date: Oct 2009
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Hi truefaith,

Old Aero Guy (and others) is correct.

In the old days, the B707 had servo tab flight controls (no hydraulic power). The pilots' imput simply displaced the control tab on the trailing edge of the control surface. The tab's movement changed the pressure over the control surface which then moved to give the correct response. Hence the control tab always moved in the opposite direction to the main control surface. The side effect was that some effectiveness was lost due to the tab's movement.

In order to improve VMCA, a hydraulic control system was installed (rudder boost) which not only moved the rudder in the correct sense, but it moved the control tab even further in the same direction as the control surface - thus improving the rudder's effectiveness (responsiveness). The tab was then called an anti balance tab.

Which answer would you now choose?
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