Vibration in a Helmet Mounted Sight (HMS) Using Mechanical Linkage.
Abstract
The purpose of this experiment was to determine the extent to which aircraft vibration was coupled to a crewman's flight helmet by the mechanical linkage of a helmet mounted sight (Fire Control Subsystem, Helmet Directed XM128). Two variations of the SPH-4 flight helmet were tested: (1) SPH-4 with standard web suspension, (2) SPH-4 with a form-fit foam liner suspension. The system was tested in the front seat of an AH-1S 'Cobra' helicopter. Five (5) flight conditions were used in the experiment: (1) hover, (2) 40kn, (3) 80kn, (4) 120kn, (5) standard left turn. Two conditions of the helmet mounted control linkage were tested: (1) connected, (2) disconnected. A triaxial accelerometer was mounted on top of the flight helmet to measure vibration. The data were analyzed using a fast Fourier transform analyzer and a desk-top computer. The following observations were made: (1) Both helmets vibrate more with the sight attached. (2) The response to the sight coupled vibration of the standard SPH-4 differed from that of the form-fit SPH-4. (3) The form-fit SPH-4 helmet vibrated more in a narrow band centered at about 30Hz. (4) The standard SPH-4 helmet vibrated more over a wide band of frequencies above 30Hz. Based on a review of published literature with respect to known or probable physiological problems related to the effects of vibration, we concluded that the significant increase in vibration of the helmet caused by the mechanical sight linkage may be expected to degrade pilot/gunner visual performance and hearing acuity, and increase fatigue rate to some extent.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1981
- Accession Number
- ADA098533
Entities
People
- David B. Priser
- John C. Johnson
- Robert W. Verona
Organizations
- United States Army Aeromedical Research Lab