While we are talking ducts, has anyone considered the loss of efficiency in the 727 and L1011 S-Duct? First of all, the air (at high volume and velocity) is bouncing off walls, creating drag. Second, would the shape of the duct not generate lift and thus an up-load on the tail, which would require an even greater down load (and more drag)? I have often wondered if the DC-10/MD-11 layout with a straight duct was more fuel efficient. The DC always seemed to cruise more level than the L10, at least from the perspective in the cabin. I don't have the fuel specifics on the two widebodies, but note that the DC10 survived economically much longer than did the Lockheed. That is not to say that the L10 did not enjoy technical advantages not shared by the MD products.
TR <img src="confused.gif" border="0">