History: Five US-Built Demonstrator Aircraft That Never Made It Into Serial Production

Many experimental aircraft are developed and may look like the promising future of military aviation to many, only to be canceled. Perhaps the most famously canceled rotary-wing aircraft is the Army's Boeing–Sikorsky RAH-66 Comanche, which was the stealth attack helicopter that never was. The Army, Navy, Air Force, and even NASA work on producing new aircraft for their needs. Sometimes the aircraft are canceled because they are obsolete or unneeded by the time they are ready, while others are built only as demonstrator aircraft, others still are canceled due to cost overruns.