Showing papers in "Journal of The American Helicopter Society in 1997"

Key Results from a Higher Harmonic Control Aeroacoustic Rotor Test (HART)

Abstract: In a major cooperative research program within existing US-German and US-French Memoranda of Understandings (MoU's) a comprehensive experimental study was conducted with a 40-percent geometrically and dynamically scaled BO-105 main rotor operated in the open-jet-anechoic test section of the German-Dutch Wind Tunnel (DNW). The objectives of the program were to improve the physical understanding and the mathematical modelling of the effects of the higher harmonic blade pitch control technique on blade-vortex interaction (BVI) impulsive noise and vibration reduction. A unique set of acoustic, dynamic, dynamic response, performance, and rotor wake data were acquired with a pressure and strain gauge instrumentedblade and by application of non-intrusive measurement techniques. This paper is focused on the experimental part of this research program, termed Higher-harmonic-control Aeroacoustic Rotor Test (HART) which was jointly performed by researchers from the.

Mathematical Definition of Helicopter Maneuvers

Abstract: Helicopter performance and handling qualities are now routinely assessed in relation to specific maneuvers. The use of inverse simulation is then attractive as it allows a helicopter mathematical model to be driven by a pre‐defined maneuver, and the control histories required to achieve this trajectory to be found. The manner in which maneuver is defined is then of great importance, and this paper aims to outline some appropriate techniques for modelling helicopter maneuvers. The basic principles and requirements for inverse simulation are introduced, and several methods of defining trajectories are described and examples given. Finally, for validation purposes, models of the Rapid Sidestep and Transient Turn Mission Task Elements (MTEs) are compared with flight data.

Detection of Helicopter Rotor System Simulated Faults Using Neural Networks

Abstract: Simulated fault data from a mathematical model of a damaged rotor system is used to develop a neural network-based approach for rotor system damage detection. The mathematical model of the damaged rotor is a comprehensive rotorcraft aeroelastic analysis based on a finite element approach in space and time. Selected helicopter rotor faults are simulated through changes in inertial, damping and stiffness properties of the damaged blade. A feed-forward neural network with back-propagation learning is trained using both 'ideal' and 'noisy' simulated data. Testing of the trained neural network shows that it can detect and identify damage in the rotor system from simulated blade response and vibratory hub loads data. (Author)

Test and Analysis of Composite Hat Stringer Pull-off Test Specimens

Abstract: Hat stringer pull-off tests were performed to evaluate the delamination failure mechanisms in the flange region for a rod-reinforced hat stringer section. A special test fixture was used to pull the hat off the stringer while reacting the pull-off load through roller supports at both stringer flanges. Microscopic examinations of the failed specimens revealed that failure occurred at the ply termination in the flange area where the flange of the stiffener is built up by adding 45/-45 tape plies on the top surface. Test results indicated that the as-manufactured microstructure in the flange region has a strong influence on the delamination initiation and the associated pull-off loads. Finite element models were created for each specimen with a detailed mesh based on micrographs of the critical location. A fracture mechanics approach and a mixed mode delamination criterion were used to predict the onset of delamination and the pull-off load. By modeling the critical local details of each specimen from micrographs, the model was able to accurately predict the hat stringer pull-off loads and replicate the variability in the test results.