The second prototype of the X-45A Unmanned Combat Air Vehicle has been completed; it will fly the end of this year. The first prototype has completed two flights and will make six more by year's end, and will drop its first practice bomb next spring. The X-45A is intended to develop and prove the concept. It is too small to be an effective combat aircraft and (while it is a stealth shape) lacks any radar absorbent coating. The X-45A is 26.5 feet long with a wingspan of 33.8 feet; it weighs 8,000 pounds empty and can hold 2,690 pounds of fuel and 1,500 pounds of bombs. The next step, the X-45B, will be larger at 36 feet long with a wingspan of 47 feet. It will weigh 14,000 pounds empty and carry 2,000 pounds of bombs and 5,400 pounds of fuel, and will use a single engine derived from the F404 used on the F-18. Even this is only the advanced test version; an operational combat aircraft would be about the same size but hold 3,600 pounds of bombs and enough fuel for a mission radius of 900 miles. The stealth shape (no tail, wings swept at 43 degrees) has performance costs. Landing speed is very high (the prototype has landed at 170 knots) because tailless aircraft cannot be properly balanced in low-lift conditions as the wing shape is already pretty awful at generating lift. When attacking enemy air defenses, the UCAV will use on-board sensors to detect an enemy site, then scan it with synthetic aperture radar and show that picture to a human on the ground who will approve or disapprove attacking it.--Stephen V Cole