From: firstname.lastname@example.org Date: 04 Feb 93 02:36:33 PST References: 1 2 3 4 5 6
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In an article on the S-duct Karl Swartz writes: > The biggest advantage of the DC-10's design for McDonnell Douglas was > that it was simpler and cheaper. Another factor, though as far as I > now one not germane to the DC-10, is that it relaxes constraints on > the engine's overall length -- Lockheed indicated that using the > General Electric CF6 instead of the more compact Rolls-Royce RB.211 > would require the sacrifice of two rows of seats at the rear of the > cabin. I would just like to add one point in favor of the S-Duct particularly on the L-1011. The use of an S-Duct as opposed to the straight intake philosophy of the DC-10 is that allows a much greater rudder area and consequently more rudder effectiveness. This becomes of significance particularly in the event of the failure of either engine #1 or engine #3 on the DC-10 wherein a greater rudder deflection is necessary to counter the yawing moment produced by dissimilar thrust. It may be noticed that the two wing-mounted engines on the DC-10 are more inboard when compared to the wing-mounted engines on the L-1011. I remember reading that it was to reduce the rudder deflection in the event of an engine outage that McDD decided to mount these engines futher inboard. As a consequence, bending moments produced on the wing of the DC-10 will be more thereby the necessity of using a stronger wing structure. So, although the design of the DC-10 duct itself was simpler, higher costs had to be paid elsewhere.