Boeing yesterday showed off the heavily modified version of the Boeing X-48 blended wing body (BWB) remotely-piloted research aircraft which is set to begin a planned six-month flight test program next month at NASA Dryden Flight Research Center, Edwards AFB.
The X-48C is a rebuilt twin-engined derivative of the three-engined X-48B which clocked up 92 flights while being tested between 2007 and 2011. In this new configuration the engines are mounted further forward from the trailing edge and shielded between vertical tails which are moved inboard and replace wingtip-mounted tails. The low-noise design is “a configuration of the BWB that represents a vehicle we are actually studying,” says Boeing X-48B/C project manager Mike Kisska.
The BWB concept, which is also being studied as part of NASA’s ERA program, holds considerable promise for efficient operations. Studies to-date indicate the blended shape could be up to 50% lower in fuel burn and 40dB less noisy than a similarly sized tube-and-wing aircraft.
Initial testing of the first generation X-48B showed it was not prone to stalls at high angles of attack and high sideslip angles, both a potential concern with this unusual configuration. The upcoming testing with the new engine and tail arrangement “gives us the opportunity for back-to-back testing” says Kisska who adds the test effort will run through to December and include around 25 flights.
Boeing originally hoped to develop purpose-made miniature turbofans to power the X-48C. However this evidently proved more difficult and expensive than expected and it was forced to adopt turbojets developed by Advanced Microturbo (AMT) of Geldrop, Netherlands. The AMTs replace the X-48Bs original trio of JetCat P200s, and are enclosed in the larger nacelle ducts representative of the higher bypass engines which were due to have powered the X-48C.
The company has therefore shelved plans to validate the noise characteristics of the low-noise configuration and Kisska confirms that the use of the low bypass AMTs rules out any acoustic evaluation. Longer term, Boeing hopes to use the X-48C as a stepping stone to tests of a scaled BWB demonstrator vehicle “large enough for a pilot to fly.”