CONCLUSIONS
1. The values of rolling-friction coefficient obtained from
the concrete runway varied from 0.009 to 0.035;
the fim turf surface, from 0.023 to 0.054; and on
the soft turf, where onlY the high-pressure ti& Were
tested, from 0.064 to 0.077.
2. The most important factor affecting the rolling friction
coefficient was the character of the ground surface.
3. For comparable conditions, either on a concrete
runway or on firm turf, the standard-type wheels and
tires had the lowest values of rolling-friction coefficient;
the values for the low-pressure tires were only slightly
higher. The highest coefficients were obtained with
the extra low-pressure wheels and tires.
4. In general, the variation in rolling-rfiction coefficient
with either wheel load or tire inflation pressure
Was fairly small.
5. The rolling-friction coefficient was appreciably
greater for wheels equipped with plain bearings than
for the same wheels having roller bearings.
6. The effect on take-off of all the variablea, with the
exception of the ground-surface condition, was generally
quite small; so that, for ordinary calculations of takeoff
performance, the assumption of an average vahe of
rolling-friction coefficient corresponding to a given
ground-surface condition would probably be satisilctory.
Where greater accuracy is desired, however,
the other factors, although of less consequence, should
nevertheless be considered.
