1 Discard any hammer with mushroomed or chipped face or with cracks in the claw or eye sections. 2  Wear safety glasses or goggles, or a face shield (with safety glasses or goggles).  Strike a hammer blow squarely with the striking face parallel to the surface being struck.
The first jet airplane was the Heinkel He 178 made in Germany in 1939, right before the outbreak of World War II .
This supersonic research aircraft is famous for being the first manned airplane to break the sound barrier, in 1947. It was also the first X-plane, ushering in a series of rocket-powered aircraft. These experimental aircraft were used to test advanced systems and aerodynamics, and the lessons learned would propel the United States into space.