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Unformatted text preview: THE PENNSYLVANIA STATE UNIVERSITY Department of Civil and Environmental Engineering CE 321: Highway Engineering Chapter 2: Road Vehicle Performance Equations Section 2.2 – Tractive Effort and Resistance F f + F r = ma + R a + R rlf + R rlr + R g (2.1) where: F f = available tractive effort of front tires (lb) F r = available tractive effort of rear tires (lb) m = mass of vehicle (slugs) a = acceleration (ft/s 2 ) R a = aerodynamic resistance (lb) R rlf = rolling resistance of front tires (lb) R rlr = rolling resistance of front tires (lb) R g = grade resistance (lb) F = ma + R a + R rl + R g (2.2) where: F = F f + F r = available tractive effort delivered by front and rear tires R a = aerodynamic resistance (lb) R rl = rolling resistance of front and rear tires (lb) R g = grade resistance (lb) Section 2.3 – Aerodynamic Resistance 2 2 V A C R f D a ρ = (2.3) where: R a = aerodynamic resistance (lb) ρ = air density (slugs/ft 3 ) C D = coefficient of drag (unitless) A f = frontal area of vehicle (ft 2 ) V = vehicle speed (ft/s) 1100 3 V A C hp f D R A ρ = (2.4) where: hp Ra = horsepower required to overcome aerodynamic resistance (hp) ρ = air density (slugs/ft 3 ) C D = coefficient of drag (unitless) A f = frontal area of vehicle (ft 2 ) V = vehicle speed (ft/s) Section 2.4 – Rolling Resistance R rl = f rl W (2.6) where: R rl = rolling resistance (lb) f rl = coefficient of rolling resistance (unitless) W = vehicle weight (lb) ) 147 1 ( 01 . V f rl + = (2.5) where: f rl = coefficient of rolling resistance (unitless) V = vehicle speed (ft/s) 550 WV f hp rl R rl = (2.7) where: hp Rrl = horsepower required to overcome rolling resistance (hp) V = vehicle speed (ft/s) f rl = coefficient of rolling resistance (unitless) W = vehicle weight (lb)...
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This note was uploaded on 02/04/2009 for the course CE 321 taught by Professor Petrucha during the Fall '02 term at Penn State.
 Fall '02
 Petrucha
 Environmental Engineering

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