NASA and Boeing have effectively cancelled the X-66 Transonic Truss-Braced Wing (TTBW) concept demonstrator aircraft. Officially described as a “pause,” development of the thin-wing airplane is being halted in favor of ground-based testing.
NASA had high hopes for its X66 single-aisle research plane. Based on a modified McDonnell Douglas MD-90, it was designed to explore net-zero aviation emissions and faster, more economical passenger flight near the speed of sound using an ultra-thin wing supported by a truss.
The idea was, and is, to develop a new wing that is closer to what all aerospace engineers dream of: a perfect wing. Of course, such a wing isn’t a practical possibility because, according to the math, it would have to be infinite in span, which is a bit aggravating when it comes to finding a hangar it will fit in. Instead, engineers try to approximate a compromise of such a wing in order to make aircraft more efficient in particular circumstances.
In the case of the X-66, the goal was to develop a wing that would improve performance at transonic speeds. That is, in the gray zone between Mach 0.8 and 1.2 where the flow of air over parts of the airframe can sometimes move faster than the speed of sound, which causes all sorts of annoyances, if not moments of outright terror because it can screw up control surfaces.
NASA
Despite these challenges, commercial airline companies are keen to master transonic flight because it provides a number of advantages – not the least of which is shortened flight times and, therefore, bigger profits.
For the X-66, the modified fuselage was to be fitted with thin advanced-composite wings spanning 145 feet (44.2 m), which is significantly wider than conventional aircraft (the largest single-aisle airplane in service is the 737 MAX, with a wingspan of 117 ft 10 in (35.9 m)). In addition, the aircraft would have been fitted with next-generation ultra-high bypass ratio (UHBR) engines for greater fuel efficiency of up to 30% with lower emissions and a range of 3,000 nautical miles (3,452 miles, 5,556 km).
That is now all beside the point because the project is now abandoning the demonstrator aircraft and will concentrate on ground testing of the transonic truss-braced wing concept. This will include wind tunnel tests, computational fluid dynamics modeling, and structural design and analysis.
The reasons behind the shift have not been made public, but one major factor is likely cost. NASA has put in US$425 million but Boeing has ponied up US$725 million – money that the struggling aircraft giant can ill afford to waste at the moment. It’s very likely that Boeing wants to deemphasize the project in order to concentrate more on its passenger airliner business. In addition, NASA may be anticipating a shift away from green projects and toward its core mission priorities, with possible budget cuts under the current administration.
Source: NASA