930. Effects of Despun Masses and Aerodynamics on Dynamic Balance Error Terms

Paper

Abstract

This paper discusses the dynamic balance error terms of rotating aerospace vehicles for two effects. One effect is that of a ‘despun’ section attached to a spinning section on the balance machine. The other effect is that of aerodynamic forces that exist on the balance machine but do not exist in space operation.
Three error sources associated w i t h despun masses are discussed. One source is the misalignment of the despun bearing axis with the balance machine axis. The magnitude of this effect depends on the relative mass properties of the spinning and despun sections. In some cases, the error is less when the despun section is left attached. Other error sources are the bearing noise and the restraint system used to keep the despun section from spinning. This restraint system should not interfere with the normal operation of the balance machine.
Test results with an asymmetric pipe on a balance machine are used to illustrate the aerodynamic effects associated with centrifugal pumping. Comparative runs were made with and without airflow. Differential unbalance data is presented i n the non-dimensional form; SAR2/p and CAR3/p where p=density of air
The magnitude of the data is consistent with the parameters that were chosen to make it non-dimensional. Data is presented for the exit flow being directed out, up, down, forward, and back. I t is noted that some of the effects change sign when the direction of rotation is changed, while other effects are invariant with direction of rotation.
Various methods of reducing the aerodynamic effects are discussed. These methods include aerodynamic enclosures to inhibit the flow.