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Vehicles require thrust forces, generated at the tires, to initiate and maintain motion. These forces are usually referred to as tractive forces or the tractive force requirement. If the required tractive force (F) is broken into components the major components of the resisting forces to motion are comprised of acceleration forces (Faccel = ma & I forces), Gradeability requirements (Fgrade), Aerodynamic loads (Faero) and chassis losses (Froll resist ). | Mechanical Engineering ME 481 Vehicle Design Fall 2000 Lecture Notes By Richard B. Hathaway Ph.D. PE Professor Mechanical and Aeronautical Engineering Section 1 Energy Consumption and Power Requirements in Design 2 Aerodynamics and Rolling Resistance GENERAL FORMULAS - AERODYNAMIC Dynamic Pressure Pd 2 p v 2 Drag Force 1 Fd 2 P v2 Af RE Fd 1 p v2 CdA Fd 1 1.2 Cd A v v0 2 2 2 Aero Power P V3 A f RE 2 Cd coefficient of drag p air density 1.2 kg m3 A projected frontal area m2 f RE Reynolds number v vehicle velocity m sec Vo headwind velocity ENGLISH UNITS HPaero 6.93 X u Cd A V3 where A area ft2 V velocity MPH Cd drag coefficient
