Tire Friction with Ground: Rolling and Braking Friction Coefficient

Ground movement would experience friction between the tire and the ground. Dur­ing the takeoff run, this friction is considered drag that consumes engine power. Figure 7.15 is a representation of the ground-rolling friction coefficient, л, versus aircraft speed for various types of runways. Conceptual studies use the value for the friction coefficient, л.

• A Type 3 runway (concrete pavement) = 0.02 to 0.025 (0.025 is recommended for coursework)

• A Type 2 runway = 0.025 to 0.04 (0.03 is recommended for coursework)

• A Type 1 runway = 0.04 to 0.3, depending on the surface type, as follows:

hard turf = 0.04

grass field = 0.04 to 0.1 (0.05 is recommended for a maintained airfield) soft ground = 0.1 to 0.3 (not addressed in this book)

The braking friction coefficient, ль would be much higher depending on the run­way surface condition (e. g., dry, wet, slush, or snow – or ice-covered) (Table 7.7). A typical value is лЬ « 0.5. Locked wheels skid that wear out a tire to the point of a possible blowout. Most high-performance aircraft that touch down above 80 knots

have an antiskid device when the p, b value could be as high as 0.7. Slipping wheels are not considered during the conceptual study phase. Tire-tread selection should be compatible with the runway surface condition (e. g., to avoid hydroplaning). The braking friction coefficient, p, b = 0.45 to 0.5, is the average value used in this book. The tire load is based on a brake coefficient of 0.8.