Engineering Data

Tyre Measuring Procedure

Before measuring, tyres are to be mounted on their proper rim, inflated to the unloaded pressure shown in the Dunlop Aircraft Tyres Rangelist, allowed to stand for a minimum of 12 hours at room temperatureand the inflation pressure adjusted to the rated value.

Radius of Gyration

The aproximate values for the radius of gyration for new tyre and tube assemblies are calculated using the following formula:


The aproximate values for the radius of gyration of wheel assemblies are calculated as follows:

Aspect Ratio

The aspect ratio is the ratio of the mean section height of the tyre to its mean section width. Aspect ratios must be considered when selecting a tyre for a particular speed requirement. The aspect ratio of a tyre is calculated as follows:

Where:

  • DM = Mean O.D
  • WM = Mean overall tyre width
  • D = Specified Rim Diameter

Use on Helicopters

When used on helicopters, standard aircraft tyres may be rated up to a factor of 1.5 times the maximum aircraft tyre load rating and 1.5 times the corresponding inflation pressure. The maximum permissible inflation for tyres used on helicopters is 1.8 times normal aircraft inflation.

The maximum dimensions for new tyres used on helicopters are 4% larger than maximum aircraft tyre dimensions. When calculating maxiumum outside and shoulder dimensions, te rim diameter should be deducted before applying 4%.

Inflated Tyre Dimensions

The dimensions of an aircraft tyre when inflated to its rated pressure are calculated as follows.



Where:

  • D = Rim ledge diameter
  • Df = Rim flange outside diameter
  • Do = Outside diameter
  • Ds = Shoulder diameter
  • W = Section width
  • Ws = Shoulder Width
  • H = Section Height
  • Hs = Max Shoulder Height
  • Ws (max) = 0.90W (max)
  • Ds (max) = 0.90H (max)

Aircraft Tyre Clearance Allowances

Clearance allowances between the tyre and adjacent parts of the aircraft must be made by the aircraft constructor. The allowances should be based on the maximum overall tyre dimensions plus growth allowances due to service, plus the increase in diameter due to centrifugal force and the tyre deformation above the horizontal centreline due to load.