The effects of rim and web thickness on gear contact and natural frequency in aerospace accessory gears

Aerospace accessory gearboxes are critical systems that provide mechanical power transmission between the engine and sub-systems. The gears used in these systems are precision components that operate at high rotational speeds and are integrally designed with the shaft. Lightweight design and reliability are among the primary design objectives in such systems. In accessory gearbox design projects, especially the optimization of gear weight and reliability presents a challenging process. In this study, the effects of rim and web thicknesses on the gear contact condition and natural frequencies were investigated using a spur gear pair modeled in accordance with AGMA 2001-D04 standard. For this purpose, both static and modal analyses were performed. The evaluations focused on the distribution of contact forces, housing deformations, and the influence on natural frequencies. The analyses conducted within the scope of this thesis showed that, depending on geometric variations, gear contact sliding variations of up to 8% due to body deformation were observed in the Z53 gear, and corresponding changes in the first six mode frequencies were identified. Similarly, in the Z76 gear, contact sliding variations reached up to 20%, with notable changes in the first six mode frequencies. The contact force distributions showed that, in the thinnest configurations of both gears, the peak contact force increased by approximately 21%. The outcomes of this study enable faster design iterations at the conceptual and preliminary design stages of accessory gearboxes. For the gear-shaft components, which are designed as one piece, rim and web thicknesses can be varied within reasonable limits to improve gear geometry with minimal modification, depending on the magnitude of the observed effects. As a result, the overall design process becomes more cost-effective and manageable.