A late production B-17 converted to turboprop testbed. Boeing converted three ships, one each for Allison, Curtiss-Wright, and P&W. Identified as model 299Z.
The pictured ship is P&W's with T34 in the nose. This ship was eventually converted back to B-17G configuration, named "Liberty Belle", & operated as a demo aircraft for a few years, but suffered a #2 fuel tank leak and inflight fire, 13 June 2011. Liberty Belle made a successful forced landing near Oswego, Illinois, but was destroyed by fire.