CARABAS III Konstruktion av antenninstallation på helikopter

Sammanfattning: This report describes the construction work of a radar antenna for the radar system CARABAS. CARABAS is a long wave airborne ground radar that has been developed by SAAB 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 is lowered and under transport, start and landing the antenna is folded up. An emergency drop function should also be included in the design of CARABAS III. The extent of this report includes construction of the antenna, frame structure attached to the helicopter, mechanism for folding the antenna up and down and mechanism for emergency drop function. The mechanical design of the antenna and frame structure is based on modal and stress analysis, vibration measurement of Schweizer 300 and frequency analysis, and calculations regarding aerodynamic drag and mechanics. The exciting frequencies of the helicopter and accelerations at those frequencies were determined by vibration measurement and frequency analysis. Including outer exciting frequencies, frequencies of the main rotor, complete information of where the antennas eigenfrequencies should lie was established. The design of the antenna and frame structure and the laminate composition in the antenna was determined by the modal analysis of the total system, both antenna and frame structure. Hence the systems eigenfrequencies does not coincide with the exciting frequencies of the helicopter. The frame structure is pressed against the cargo frame of the helicopter at four support points by a mechanism consisting of a beam with a pin joint and a spring loaded bolt. The beam is attached to the cargo hook of the helicopter which can be opened from the cockpit. Hence CARABAS 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 were calculated analytically. The loads were used as input data in the stress analysis performed on antenna and frame structure and to design the folding mechanism and mechanism for pretention of the frame structure against the cargo frame. According to the performed stress analysis the antenna and components in the frame structure will hold the loads that they are subjected to.