# The OFW as the NLA

Studies by McDonnell Douglas Aerospace West provide guidance on how many passengers a large OFW might carry, how much it might weigh, and at what speeds and altitudes it might fly for the Mach number range 1.3-1.6 (418]. (419]. We choose a frecstrcam Mach number of !2 for simplicity, and a sweep angle of 60 degrees for ease of control and acroelastic stability Higher speeds are possible with more sweep, but the wing’s control becomes increasingly difficult, with 60 degrees being judged acceptable in previous studies.

These parametric studies guide us to conclude that a high aspect ratio. 800 passenger aircraft will have a wing with a maximum chord of about 55 feet and a span of about 550 feet. This 10-1 maximum chord to span ratio provides an aspect ratio of 12.7. a wing area of 23.758 square feet and a wing volume of 127.815 cubic feet. This OFW should have a trans-Pacific nautical mile range

A conservative guess as to its weight and volume provides an OFW transport that will enter cruise at about 1.9 million pounds and leave cruise ai a weight of 1.3 million pounds For nominal conditions we take the weight to be 1.6 million pounds and the cruise altitude to be 43.500 feet.

Using these results and the nominal conditions, we calculate the turbulent skin friction drag on a flat plate, and more directly, the other terms to conclude that the drag in pounds is:

D = 4.37 x 104 (skin friction) ♦ 2.31 x 104 (induced)

+ 5.19 x 103 (wave-lift) ♦ 3.74 x 104 (wave-volume).

Here we use the wcll-vcnftcd method of Sommer and Short, assuming adiabatic flow, to calculate the skin friction (420J, (421 ]. This drag gives an inviscid L/D of 24.4 and a viscous L/D of 14.6. The minimum drag OFW of the same thickness (but less volume) has inviscid and viscous L/D values of 26.0 and 15.2. If we correct this lifting line result using Eq. (92). the respective viscous L/IH arc reduced to 14.5 and 151.

A practical design, with the engines in the wing and only one vertical fin. should nearly achieve these L/Ds. In Chapter 19. Van der Velden describes in some detail a 250 passen­ger oblique wing with four external engines that cruises with its wing swept to 68 degrees at Mach 1.6 and 50.000 feet. This OFW has a 5000 nautical mile range. Its I95t thick wing has a maximum chord of about 50 feet and a span of about 370 feet. Its maximum cruise L/D is about eleven. Because the component of the Mach number normal to the wing is only 0 6. a 1991 thick wing should be possible.