Here's The Fighter Plane That Almost Replaced the F-35 Lightning II. Built to the same specifications, the X-32 and the F-35 had relatively similar performance parameters. Deciding to compete on cost, Boeing designed the X-32 around a single-piece delta wing that would fit all three variants. The X-32 lacked the shaft-driven turbofan lift of the F-35, instead using the same thrust vectoring system as the AV-8 Harrier. The X-32’s system was less advanced than the F-35’s, but also less complex.