Abstract: The passive partial strapdown platform which installs in rolling projectile works in the principle of compound pendulum movement under the action of gravity. Projectile flies under the action of air lift, consequently the acceleration in the vertical direction of projectile changes with the change in the lift. Accordingly the restoring torque of the platform cylinder’s equivalent compound pendulum changes, and the stability of the platform would be affected. To research the influence of air lift on the stability of passive partial strapdown platform, the mechanical analyses of the projectile and passive partial strapdown platform cylinder are fulfilled, and the differential equation of motion of the platform’s inner cylinder is established and solved. The stability of passive partial strapdown platform under the action of air lift is simulated. The results show that the larger the air lift is, the more stable the partial strapdown platform is. And when the air lift is less than 0.005 75m_pg (m_p is weight of projectile, and g is acceleration of gravity), the passive partial strapdown platform is unstable. The semi-physical simulation test is done in the three-axis high speed turntable. The dynamic model is proved by the test.

Key words: ordnance science and technology, inertial navigation, conventional shell, air lift, partial strapdown platform