CARABAS III Konstruktion av antenninstallation på helikopter
This report describes the construction work of a radar antenna for the radar systemCARABAS. CARABAS is a long wave airborne ground radar that has been developed bySAAB Microwave Systems and will now be mounted on a small helicopter, Schweizer 300.The antenna should be able to fold up and down. When the radar is in use the antenna islowered and under transport, start and landing the antenna is folded up. An emergency dropfunction should also be included in the design of CARABAS III.The extent of this report includes construction of the antenna, frame structure attached to thehelicopter, mechanism for folding the antenna up and down and mechanism for emergencydrop function. The mechanical design of the antenna and frame structure is based on modaland stress analysis, vibration measurement of Schweizer 300 and frequency analysis, andcalculations regarding aerodynamic drag and mechanics.The exciting frequencies of the helicopter and accelerations at those frequencies weredetermined by vibration measurement and frequency analysis. Including outer excitingfrequencies, frequencies of the main rotor, complete information of where the antennaseigenfrequencies should lie was established. The design of the antenna and frame structureand the laminate composition in the antenna was determined by the modal analysis of the totalsystem, both antenna and frame structure. Hence the systems eigenfrequencies does notcoincide with the exciting frequencies of the helicopter.The frame structure is pressed against the cargo frame of the helicopter at four support pointsby a mechanism consisting of a beam with a pin joint and a spring loaded bolt. The beam isattached to the cargo hook of the helicopter which can be opened from the cockpit. HenceCARABAS III can be released from the helicopter in case of emergency.The loads on antenna and frame structure constitute of drag and inertia forces and werecalculated analytically. The loads were used as input data in the stress analysis performed onantenna and frame structure and to design the folding mechanism and mechanism forpretention of the frame structure against the cargo frame. According to the performed stressanalysis the antenna and components in the frame structure will hold the loads that they aresubjected to.