The Prize
This is something adapted from "The Optimization of Body Details-A Method for Reducing the Aerodynamic Drag of Road Vehicles",SAE Paper 760185,1976,by Hucho,Janssen,and Emmelmann.
* It shows some relationships between drag reduction,BSFC,gear-matching,top speed,and fuel economy. * In the original work,gross drag reductions were shown,from Cd 0.5,down to 0.4,and 0.3. * I've drawn in estimated positions for Cd 0.2 and Cd 0.10,to get it down to the theoretical (empirical ) minimum just to look at potentialities. -------------------------------------------------------------------------- *As the drag is reduced it unloads the engine and allows higher revs which is dangerous for the engine,and also moves it on the BSFC map to a lower efficiency. *If the final drive gearing is adjusted to maintain the original 100 rpm over rated power rpm,then the engine is protected,and it is moved back to it's original BSFC. *The top speed increases with drag reduction,in this case,from 97-mph,to 130 mph. *You can look at what the fuel economy does at any given velocity. *I've included an expanded-mesh Rolling Resistance Force Coefficient table from Hucho for Radial tires which reflects radial tire technology for the test vehicle. *With the aero data and R-R info,one could calculate the road load at any point and compare to the brake horsepower required to cover the road load. -------------------------------------------------------------------------- This is how engineers would build your car within a numerical environment,knowing the cars performance before it was ever constructed,a Rosetta Stone if you will,for the language of streamlining. http://i1271.photobucket.com/albums/...ad2/12-064.jpg http://i1271.photobucket.com/albums/...ad2/12-065.jpg http://i1271.photobucket.com/albums/...ad2/12-066.jpg http://i1271.photobucket.com/albums/...ad2/12-067.jpg -------------------------------------------------------------------------- *Taking the original top speed and factoring in the overall gear ratio you can reverse-engineer the dynamic tire circumference. *The tire circumference allows the axle rpm to be determined. *From an expanded-scale image,the original top speed engine rpm is found to be 5,818.This is your design engine rpm for all calculations. *Rated power of 55kW is at 5,718 rpm. *I went ahead and calculated the final drive ratios for the two added drag coefficients,along with new top speeds. *From the tire curve you can see the non-linear relationship between high velocity and R-R. *To use these relationships,one must first determine their cars performance at 100 rpm over rated power rpm. -------------------------------------------------------------------------- *Combining knowledge about Low Rolling Resistance tires,lower viscosity lubricants,weight reduction,and improved powerplants,modders will have useful tools with which to predict future performance from mods before spending a penny on materials. *You can see that even in 1976,streamlining would have produced a 32-mpg @ 100-mph car. *With today's 'Skyactive' engine technology,with BSFC 0.28 lbs/bhp-hr,compared to 0.51 for 1976,you might image what modern cars could do with really low drag.:D |
Thanks. The only thing I see that needs to be added is number of wheels on the ground. :)
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