Improving Altitude Complementary Filter for Stable Helicopter Altitude Hold Modes during Search and Rescue Missions

Alternative filter designs are explored to address the deficiencies of the conventional filters used for radar altitude and barometric altitude filtering. In the first implementation, a simplified complementary filter is proposed to replace the conventional two cascaded 2nd order complementary filters. In a further implementation, the Kalman filter is adapted as another improvement compared to the conventional two cascaded complimentary filters. Tests show the new implementations ensure the proper phase relationship between filtered altitude and filtered vertical velocity with reduced startup transients.