**1. Introduction**

It was realized that aviation had a great potential in transporting goods as well as passengers in large distances in minimum possible time. The military also realized the advantages of having an offensive and defensive air power during the war and peace time. Today air power has become the essence of military supremacy of any country for maintaining country sovereignty during peace time and offensive attack capability to win war by destroying enemy vital installations, deterring troop transfer and military supplies.

The aircraft can be broadly categorized as lighter-than-air aircraft (balloons and airships) which generate lift due the buoyancy forces and heavier-than-air aircraft (aircraft, helicopters and UAV).
