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Old 1st Jan 2011, 01:02
  #44 (permalink)  
Old Fella
 
Join Date: Feb 2008
Location: Wingham NSW Australia
Age: 79
Posts: 1,349
B727 reverse thrust. Use airborne.

Four Engine Jock. In the B707 and B747 it is possible to introduce reverse thrust whether on the ground or airborne. The Thrust levers (Forward & Reverse) are protected by an inter-locking system which prevents simultaneous application of both forward and reverse thrust on any individual engine. To move the Reverse Thrust lever toward reverse the Forward Thrust lever must be at, or within a couple of degrees of Idle. When Reverse Idle is selected the reverser system moves to the full reverse position and allows further application of Reverse Thrust. As the Reverse Thrust lever is moved toward Maximum Reverse Thrust the Forward Thrust lever is mechanically locked against any forward movement toward Forward Thrust. There is no other "protection" of which I am aware to prevent selection of reverse thrust. I have never operated the B727, however given the system on both the B707 and B747 Classics, I would think that the B727 would be the same in respect to Engine control systems.

As for the discussion of what relative effect on speed retardation is provided by either "Inlet Drag" or "Thrust Reversal" I wonder why it is that aircraft/engine manufacturers go to the trouble and cost to design a "Thrust Reverser" system which enables acceleration of the engine to relatively high gas/fan discharge settings if it need not be done, i.e. simply removing thrust and allowing "Inlet Drag" to provide the retardation force. The adjustments to Landing Distance required with Reverse Thrust inoperative leads me to believe that "Thrust Reversal" is a significant contributor to the overall speed retardation achieved. HAPPY NEW YEAR TO ALL.
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