The US Air Force is scheduled to unveil B-21 Raider on Friday, considered to be the most advanced military aircraft ever built. The US has made the new stealth bomber for the first time in the last thirty years. Built by Northrop Grumman, the long-range strategic bomber jet will replace the ageing B-1 Lancer and B-2 Spirit aircraft. The B-21 has been developed with a budget of around $25.1 billion allocated to the US Air Force in 2010. Currently, six more bombers are being built in Palmdale at about $2 billion per aircraft and are expected to be flying next…