Sensitivity of Space Launch System Buffet Forcing Functions to Buffet Mitigation Options

Time-varying buffet forcing functions arise from unsteady aerodynamic pressures and are one of many load environments, which contribute to the overall loading condition of a launch vehicle during ascent through the atmosphere. The buffet environment is typically highest at transonic conditions and can excite the vehicle dynamic modes of vibration. The vehicle response to these buffet forcing functions may cause high structural bending moments and vibratory environments, which can exceed the capabilities of the structure, or of vehicle components such as payloads and avionics. Vehicle configurations, protuberances, payload fairings, and large changes in stage diameter can trigger undesirable buffet environments. The Space Launch System (SLS) multi-body configuration and its structural dynamic characteristics presented challenges to the load cycle design process with respect to buffet-induced loads and responses. An initial wind-tunnel test of a 3-percent scale SLS rigid buffet model was conducted in 2012 and revealed high buffet environments behind the booster forward attachment protuberance, which contributed to reduced vehicle structural margins. Six buffet mitigation options were explored to alleviate the high buffet environments including modified booster nose cones and fences/strakes on the booster and core. These studies led to a second buffet test program that was conducted in 2014 to assess the ability of the buffet mitigation options to reduce buffet environments on the vehicle. This paper will present comparisons of buffet forcing functions from each of the buffet mitigation options tested, with a focus on sectional forcing function rms levels within regions of the vehicle prone to high buffet environments

An Investigation of Soft-Inplane Tiltrotor Aeromechanics Using Two Multibody Analyses

This investigation focuses on the development of multibody analytical models to predict the dynamic response, aeroelastic stability, and blade loading of a soft-inplane tiltrotor wind-tunnel model. Comprehensive rotorcraft-based multibody analyses enable modeling of the rotor system to a high level of detail such that complex mechanics and nonlinear effects associated with control system geometry and joint deadband may be considered. The influence of these and other non-linear effects on the aeromechanical behavior of the tiltrotor model are examined. A parametric study of the design parameters which may have influence on the aeromechanics of the soft-inplane rotor system are also included in this investigation

Multibody dynamics simulation and experimental investigation of a model-scale tiltrotor

The objective of this investigation is to illustrate the steps involved in developing a multibody dynamics analytical model to simulate the dynamic response, aeroelastic stability, and blade loading of a soft-inplane tiltrotor wind-tunnel model and correlate that simulation with experimental data. The rotorcraft industry is currently developing requirements for a heavy lift transport rotorcraft that is expected to include, at a minimum, a 20-ton payload lift capability. Development of soft-inplane tiltrotor technology is beneficiai for providing viable lightweight hub design options for this future application. Experimental testing, either in flight testing or with a wind tunnel test article, is becoming prohibitively expensive. Advanced simulation and modeling of these complex tiltrotor hub configurations using multibody dynamics analyses may prove to be an alternative to such expensive experimental verifications in the future. The use of multibody dynamics analyses to predict and reduce the risk of encountering aeromechanical instabilities and adverse loading situations for a soft-inplane tiltrotor hub design is detailed in this investigation. Comprehensive rotorcraft-based multibody analyses enable simulation and modeling of the rotor system to a high level of detail such that complex mechanics and nonlinear effects associated with control system geometry and joint free-play may be considered. The influence of these and other nonlinear effects on the aeromechanical behavior of the tiltrotor model is examined in this study. Copyright © 2005 by the American Helicopter Society International, Inc. All rights reserved

Multibody Dynamics Simulation and Experimental Investigation of a Model-Scale Tiltrotor

The objective of this investigation is to illustrate the steps involved in developing a multibody dynamics analytical model to simulate the aeroelastic stability and blade loading of a soft-inplane tiltrotor wind tunnel model and to correlate those simulations with experimental data. Development of soft-inplane tiltrotor technology is beneficial for providing viable lightweight hub design options for future heavy lift transport rotorcraft application. Experimental verification of such advanced configurations using either subscale models in wind tunnels or full-scale flight testing is becoming prohibitively expensive. Advanced modeling and simulation of complex tiltrotor hub configurations using multibody dynamics analyses offers an alternative to such expensive experimental verifications. Comprehensive rotorcraft-oriented multibody analyses enable the modeling and simulation of rotor hub systems to a level of detail that allows the complex kinematics and nonlinear effects associated with rotor hub control systems and drive train free play to be considered. The influence of these and other nonlinear effects on the aeromechanical behavior of a tiltrotor model is examined in this study

Further Results of Soft-Inplane Tiltrotor Aeromechanics Investigation Using Two Multibody Analyses

This investigation focuses on the development of multibody analytical models to predict the dynamic response, aeroelastic stability, and blade loading of a soft-inplane tiltrotor wind-tunnel model. Comprehensive rotorcraft-based multibody analyses enable modeling of the rotor system to a high level of detail such that complex mechanics and nonlinear effects associated with control system geometry and joint deadband may be considered. The influence of these and other nonlinear effects on the aeromechanical behavior of the tiltrotor model are examined. A parametric study of the design parameters which may have influence on the aeromechanics of the soft-inplane rotor system are also included in this investigation