Waters, et al. studied the design of OFWs. They considered their aerodynamics, structures, and layout (429). This first comprehensive study highlights several critical issues for OFWs. Principal among them were the design of the structure to carry the pressurization load, and the design of the landing gear to meet FAA taxi bump requirements
Galloway ct al. assessed the economics of 200. 400 and 500 passenger subsonic transports (M = 0.85). 300 passenger OWAs operating at Mach numbers 1.6 and 2.0. a 400 passenger OWA operating at Mach 2. and 291.440. and 544 passenger OFWs operating at Mach 1.6 (430). They assumed a five year development penod, with 500 aircraft produced in the 15-year delivery schedule.
Aircraft prices varied from $114M to S158M for the subsonic transports, from S172M to S239M for the OWAs. and from S212M to S260M for the OFWs. For a manufacturer and the operating airlines to achieve a 12# return on their investments required II to 10.1 cents per Revenue Passenger Mile (RPM) for the subsonic transports, decreasing with increasing size. 12.4 to 12 cents per RPM for the OWA and 14.2 to 111 cents per RPM for the OFWs. again decreasing with increasing size. Tins trend toward economic equality between OFWs and advanced subsonic transports is depicted in Figure 144. The fares on a large OFW should compete well w ith the fares of its subsonic counterparts.
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Figure 144 NASA Amts economic assessment of the revenue required per RPM to provide a 125fc returnon investment (RODfor advanced subsonic transports, and for a M = 1.6 OFW (OAW) aircraft as a function of size (from Ref. ).
Computational Fluid Dynamics tools were used extensively to optimize a realistic Mach 1.6 OFW design with the wing swept to 68 degrees |431) Related numerical studies were also conducted by Cheung (4321. This optimized design, and that by McDonnell Douglas reported in the following section, were tested in the NASA Ames 9- by 7-fool Supersonic Wind Tunnel at Mach number 1.6 |433|. The NASA design was tested at Mach numbers between 1.56 – 1.80 w ith unit Reynolds numbers of 1.0 to 4.5 million per foot. The angle of attack was varied from 0 to 6 degrees at a single sweep angle of 68 degrees. The 1.8Я – scale model included four nacelles and two vertical fins, one on the top and the other on the bottom of the trailing tip. The results of these studies are not yet published Preliminary results indicate that the experiments validate the numerical studies which resulted in a design that, while not optimum, was realistic in layout The experimental wing alone L/D. corrected to flight conditions at 52.000 feet, gives an estimated L/D оf 10 5 (private communication. R. Kcnnclly).