MIL-DTL-43511D Detailed Specifications: Visors, Flight Helmet, Polycarbonate

The MIL-DTL-43511D Detailed specifications: visors, flight helmet, polycarbonate standard, developed by the United States Department of Defense , describes the general and performance requirements for curved polycarbonate pilot helmet visors used by flight crew personnel.

According to this standard, visors must be of the following classes:

• Class 1: Transparent
• Class 2: Neutral gray
• Class 3: Neutral gray gradient (air force)

The requirements in this standard are described as follows:

• First item: When specified, a sample shall be subjected to first item examination in accordance with this standard.
• Design and dimensions: The design and dimensions of the visor must be as specified in the applicable final product specification, drawing or contract.
• Materials and components: Unless otherwise specified in the applicable final product specification, drawing, or contract, the visor shall be constructed of bisphenol-type polycarbonate plastic molding material conforming to ASTM D3935. All other materials and components used in the visor construction shall be as specified in the applicable final product specification, drawing, or contract.

Recycled, recovered or environmentally preferable materials should be used to the maximum extent possible, provided the material meets or exceeds operational and maintenance requirements and promotes economically advantageous life cycle costs.

• Fields of view: Unless otherwise specified, the viewfinder shall have three fields of view: outside field of view (no optical requirements), non-critical field of view, and critical field of view. The center point for right and left optics is defined as point "C." The location of point "C" and the location and size of the three fields of viewfinder defined above shall be as specified in the applicable final product specification, drawing, or contract. The critical field of view is the field of view with a radius of approximately 50 degrees from the intersection of the primary line of sight on the viewfinder for the intended right and left eye positions. Areas within 1 mm of the edges of the viewfinder are non-critical areas. Areas abutting the helmet shell are outside the field of view. Unless otherwise specified in the applicable final product specification, drawing, or contract, numbered circles within the critical areas are designated as preferred points for prismatic and distortion tests. Points bearing the same number, for example, 5R and 5L, shall be compared with each other when measuring refractive power or prismatic aberration, excluding points 2R and 2L (the outermost points on the left and right sides of the viewfinder).
• Performance:
  • Prismatic deflection: Prismatic deflection specified here includes the inherent prismatic force resulting from the non-parallel surfaces of the material and the different curvature between critical areas. Vertical and horizontal prismatic deflections shall be tested as specified in this standard.
  • Vertical prismatic deviation: The vertical prismatic deviation through point "C" for the left and right eyes should not exceed 0,18 prism diopters. The vertical prismatic deviation along any individual line of sight through the critical area should not exceed 0,25 prism diopters.
  • Horizontal prismatic deviation. The horizontal prismatic deviation through point "C" for the left and right eyes should not exceed 0,18 prism diopters "Base in" and 0,25 prism diopters "Base out." The horizontal prism deviation along any individual line of sight passing through the critical field should not exceed 0,25 prism diopters.
  • Refractive power: Refractive power, when tested according to this standard, shall not exceed plus or minus 0,125 diopters at point “C” and all other selected points for the left and right optics.
• Light transmittance:
  • Class 1 visor: The light transmittance of a Class 1 visor shall not be less than 852 percent throughout the critical area when tested in accordance with this standard.
  • Class 2 viewfinder: The light transmittance of a Class 2 viewfinder must be between 12 percent and 18 percent when measured at point "C," left and right optics. The total apparent transmittance of the viewfinder must not change by more than 3,0 percent.
• Optical density: Class 3 viewfinder: The optical density of a Class 3 viewfinder should be between 0,83 and 0,60 when measured at point "C" on the left and right optics. The optical density at any point on the horizontal meridian of a given viewfinder should not vary by more than 0,1 from other points on the same meridian.
• Optical settings at critical resolution: Optical distortion in critical fields of view, when tested as specified in this standard, shall meet the acceptable standards shown in the figure.
• Haze: The haze value of the viewfinder shall not exceed 2,0 percent when tested as specified in this standard.
• Ultraviolet transmittance: Erythema ultraviolet transmittance shall not be more than 1,00 percent when calculated as the average spectral transmittance at wavelengths 290, 300, 310, and 320 nm when tested as specified in this standard.
• Neutrality of Class 2 and 3 viewfinders: The spectral transmittance of a Class 2 viewfinder may vary over wavelengths between 430 and 730 nm; the average percentage deviation within the nine spectral bands shall be less than 12 when tested as specified in this standard. The spectral distribution curve shall show a reasonably uniform distribution across the visible spectrum to ensure that color distortion will not be excessive. The neutrality of a Class 3 viewfinder shall conform to the requirements specified for a Class 2 viewfinder, but the average percentage deviation shall be less than 20 when tested as specified in this standard.
• Chromaticity of Class 2 and 3 viewfinders: The chromaticity coordinates x and y of Class 2 and 3 viewfinders, when calculated as described in this standard, shall be within the limits specified in the figure.
• Ballistic resistance: The ballistic resistance of the lenses must be such that they pass the test when tested as specified in this standard.
• Abrasion resistant coating: After being subjected to the abrasion tests specified in this standard, the increase in haze shall not exceed 2 percent and the decrease in permeability shall not exceed 2 percent.
• Bayer abrasion resistance: After subjecting to the Bayer abrasion test, the Bayer ratio must exceed 4,0 or higher as specified in this standard.
• Coating adhesion: Before and after moisture exposure, the visor shall show no loss of coating when tested in accordance with this standard.
• Weather resistance: Coated visors shall not show yellowing or other changes, or loss of coating, when tested as specified in this standard.
• Chemical resistance: When tested in accordance with this standard, the visor shall not increase by more than 2 percent for transmittance and haze.
• Workmanship: Visors must be free from any defects that could affect proper operation in service. Visors must conform to the product quality and grade specified in this specification.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the "MIL-DTL-43511D Detailed specifications: visors, flight helmets, polycarbonate" standard.