Predictive Analyses with Random Variables in a Bolted Helicopter Tailcone Substructure

Abstract

This paper presents results from an ongoing investigation to understand and quantify the limitations of traditional industry methods for vibration prediction in rotorcraft airframes. Examples are included of probabilistic analyses to predict both static and modal behavior of a scaled helicopter tailcone. One set of analyses evaluated the effect of two random, static vertical loads in numerical models of the tailcone. Vertical displacement at the tip of the structure and stress at the root were observed as output responses to the random loads. A second set of analyses was conducted on the boundary condition of the tailcone. The bolted connection at the boundary was shown to have an unexpected impact on the fundamental frequencies of the tailcone. Experimental data is included for comparison with the modal analysis. Generalized Polynomial Chaos Expansion (GPCE) was the technique utilized for uncertainty propagation. The analysis incorporates uncertainty propagation with Gaussian and non-Gaussian probability distributions. Contributions to the literature include use of the polynomial chaos technique on a complex structure with experimental data for validation. Additionally, demonstration of a mixed probability distribution GPCE extends the utility of this method beyond homogeneous probability distributions. These outcomes are promising for a wide range of efforts to update complex models in general and helicopter structures in particular.