Abstract:
The project sponsors design and manufacture skewed roller brake devices for use in
aircraft flight control actuation systems. Design tools have previously been developed to
predict the torque characteristics ofthese devices. A fundamental deficiency ofthese
tools is the use ofempirical friction coefficient data gathered from a limited test sample.
A need was identified to develop a friction coefficient model based on the operational
parameters ofthe design, namely load, speed and lubricant viscosity. The development
and validation ofthis model formed the basis ofthe technical research objective.
A cost benefit analysis indicated that the sponsors could reasonably expect to gain a
significant technical competitive advantage over their competitors ifthe technical
research objective could be achieved. This advantage should provide opportunities for
premium pricing ofthe product and enhanced opportunities to enter new markets.
Additionally, the sponsors could expect lead time reductions and cost savings of
£69000 from the removal ofthe need to conduct prototype tests to assess the effective
friction coefficient.
A friction coefficient model and skewed roller torque equation design tool have been
successfully developed, satisfying the technical research objective. The friction
coefficient model is defined in terms of lubrication number. The lubrication number
parameter incorporates lubricant viscosity, roller speed, roller load and contact surface
roughness terms, fully describing the operational parameters ofa design.
Experimental evidence has validated the model using two lubricants, a hydraulic fluid,
Brayco 795 and a mineral oil, Catenex 79. The tests cover a lubrication number range
from 2 x 10-5 to 6 X 10-2 with a mean Hertzian stress from 0.27 to 0.61 Gpa.
The success ofthis project has ensured that the sponsors will reap the cost and design
lead time savings predicted in the cost benefit analysis and have the tools necessary to
develop new markets and premium pricing business opportunities.