Drag Coefficient
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Transcript of Drag Coefficient
NormalCalculation of Vehicle Drag Coefficient and Coefficient of Rolling ResistanceTrials in Direction 1Trials in Direction 2timeV1V2V3V4V5V6V avgseckphkphkphkphkphkphkph070707070707070.01kph=0.2777777778m/s1061606060616060.31mph=0.4444444444m/s2052525151525151.53044444343434443.540373738373737.537.350323232.53232.1602727.52727.2702222.522.3rho1.22kg/m^3density of air (adjust for your altitude)g9.81m/s^2gravitational constantA2.3m^2frontal areaM1000kgmass of vehicle plus occupantstimeV actualV modelFaError^2secm/sm/sNewtonsm/s^2019.4419.44299.80207292720.29980207290.00000517.9454340798270.73216273090.27073216271016.7616.5917732662246.48381925740.24648381930.028051515.3593541699226.06034573280.22606034572014.3114.2290524412208.71428069950.20871428070.005852513.1854810377193.87584804910.1938758483012.0812.2161017975181.10441901510.1811044190.017633511.3105797024170.05486561510.17005486564010.3510.4603053743160.45378420190.16045378420.01279459.6580364533152.0824023630.1520824024508.928.8976244415144.76409920540.14476409920.00068558.1738039455138.35516611660.1383551661607.557.4820281149132.73788008420.13273788010.00413656.8183387145127.81525160440.1278152516706.186.1792624564123.50700166640.12350700170.00000Sum of Error^2 (minimise by changing Cd and Crr)0.06913Drag coefficientCd =0.3696811693Coefficient of rolling resistanceCrr =0.0105711271
What should be the velocity now based on the acceleration 5 seconds ago?
Normal
ActualModelTime [sec]Velocity [m/s]Vehicle Velocity vs Time
How to use this spreadsheet:1. In Cell B6, specify whether your data will be in "kph" or "mph".
2. In Cells B7 through G14, enter the vehicle speed you recorded at 10 second intervals as the vehicle decelerated in neutral. Always start the clock (t=0) at the same speed (ex 70 kph). Do 3 trials in each direction on a flat stretch of road (Columns V1 through V6). Don't worry if you can't fill in the lower speeds on some trials due to traffic. An average will be calculated based on the available data.
3. In Cell B18, enter you best estimate of your vehicle's frontal area in m^2.
4. In Cell B19, enter your vehicle's mass including occupants in kg.
5. Using Solver (Tools/Solver...) set Cell F39 to a minimum by changing cells F41 and F42.
6. Confirm that the "Model" line matches the "Actual" datapoints in the graph.
7. Cells F41 and F42 now give the drag coefficient and coefficient of rolling resistance for your vehicle.
8. Make modifications to your vehicle and repeat the test to see if you improved things.