With the widespread application of Staggered Counter-rotating Rotor (SCR) systems in eVTOL and UAV configurations, a comprehensive understanding of SCR performance under Out-of-Ground Effect (OGE) and In-Ground Effect (IGE) conditions is crucial for aircraft design and landing safety. This study experimentally measured the changes in thrust and torque of the upper and lower rotors in an SCR system under varying axial and radial distances. It focuses on the interaction mechanisms between the upper and lower rotors and conducts specific IGE state experiments for certain SCR configurations. The findings reveal that changes in the lower rotor predominantly influence the overall performance of the SCR system, regardless of OGE or IGE conditions. Under OGE conditions, radial distance has a more significant impact than axial distance. Conversely, under IGE conditions, the axial distance plays a critical role in improving SCR system performance. These results provide a broad parameter range to assess SCR system performance variations, offering guidance for the design of new concept rotorcraft configurations and the development of aerodynamic prediction models under IGE conditions.

The issue of nonlinear dynamic stability in aircraft landing system has consistently posed a significant challenge in the design of both aircraft and landing gear systems, involving complex geometric nonlinearity, physical nonlinearity, and their interactions. Although the traditional time domain analysis method can effectively determine the stability, it exhibits limitation of high computational load in analyzing parameter influences and in achieving rapid and accurate parametric design. In recent years, the numerical continuation method has been widely applied in the field of nonlinear dynamic stability analysis of the landing system. This method enables rapid and precise analysis of the stability variation of the dynamic model with parameters, thereby significantly enhancing the design efficiency of aircraft and landing gear. Firstly, this paper describes the methods of dynamic stability, bifurcation analysis, and continuation calculation. Then, according to the functional classification of the landing system, the research status of the shimmy stability, taxiing direction stability, and retraction mechanism stability of the landing gear are summarized. The application research of bifurcation analysis methods and nonlinear dynamic stability based on the numerical continuation method in landing gear systems is mainly discussed. Finally, the research on the shimmy stability, taxiing direction stability, and retraction mechanism stability of aircraft landing gear is summarized and prospected.

Sidestay lock mechanism is an important part of landing gear system, and the locking performance can be analyzed based on changes in its stability. However, during numerical continuation analysis of fully-rigid dual-sidestay landing gear without clearance, it has been found that the appearance of bifurcation points does not necessarily imply that both sidestay links can be locked synchronously. This problem reveals the limitations of fully-rigid model with ideally-articulated in solving dual-sidestay mechanisms with extremely high motion sensitivity. Therefore, this study proposes a bifurcation analysis method for synchronous locking of dual-sidestay landing gears, which takes into consideration the joint clearance. For in-depth analysis of this problem, we initially build kinematic and mechanical models of a landing gear mechanism that consider joint clearance. Then, the models are solved based on continuation. The fundamental causes of synchronous locking are discussed in detail, and the number of bifurcation points is found to be closely related to whether the landing gear is completely locked. Finally, the effects of structural parameters on the synchronous locking are analyzed, and the feasible region of parameters satisfying synchronous locking condition is given, which agrees well with the test results.