anybody know what the lift-drag ratio of Boeing 707 is?
Google is your friend:
"The aerodynamic efficiency of the 707-320B may be judged by the value of the maximum lift-drag ratio, which is estimated to be in the range from 19 to 19.5."
(
ch13-3)
That seems a little high compared to the values posted in this thread for more modern airliners... on the other hand, the same source goes on to say:
"Aerodynamic efficiency of the 767-200 can be judged by the maximum lift-drag ratio, estimated to be about 18. The larger ratio of wetted area to wing area of the 767-200, as compared with that of the 707-320B, results in a value of (L/D) max somewhat lower than that of the older aircraft. The much larger passenger capacity and more efficient engines, however, make the new aircraft more efficient in terms of cost-per-seat-mile."
(
ch13-6)
Which seems to square well with the number given by misd-agin.