Background

The Dymaxion car was a futuristic three-wheeled concept car designed and built in 1933 by U.S inventor and architect Richard Buchminster Fuller. It’s teardrop shape was designed to minimise aerodynamic drag giving it a fuel consumption rate of 36mpg and a claimed top speed of 128mph [1]. As part of a wider study into the aesthetics of low drag vehicles, TotalSim was given the opportunity to perform CFD simulations of the Dymaxion car in order to analyse it’s aerodynamic properties. The results were presented in a published paper at the SAE Conference in Turin 2011 (SAE Paper No. 2011-37-16, Turin, June 2011). The paper can be found here.

CFD Results

Below are key extracts from [1] based on the CFD simulations to assess the vehicle aerodynamic performance. One surprising aspect of results is that the Dymaxion actually generates downforce in straight-ahead flow*. However, we can also see from figure 1 that the distribution of lift at the front and rear axle would result in a large ‘nose-up’ pitching moment.

Figure 2 is a ‘drag accumulation’ plot which shows hows the drag builds up along the length of the vehicle. It’s is interesting to note that the total drag of the car up to the front wheels is almost zero for the straight ahead flow and negative for the 15 deg yaw case. In other words, a significant amount of thrust is being generated around the front of the car which offsets the stagnation pressure acting on the nose.

Figure 3 is a ‘CpX Plot’ which highlighting areas of the car that contribute to drag (red regions) and areas which contribute to thrust (blue regions).

Figure 1: Extract from [1] showing aerodynamic coefficients of simplified Dymaxion car.

Figure 2: Extract from [1] showing longitudinal drag accumulation.

Figure 3: Extract from [1] highlighting surfaces which contribute towards drag and to thrust.

* Results based on a simplified CAD model of the Dymaxion car which contains no internal, engine bay or cooling flow. Also absent are the suspension geometries and bodywork detail (hinges, louvres etc). Other simplifications include basic wheels and wheel arches.

Acknowledgement

TotalSim would like to acknowledge the contribution of Brian Clough who created the CAD model based on extensive patent drawings and photographs. Brian Clough is a senior lecturer in Automotive and Transport Design at Coventry University School of Art and Design – Industrial Design Department (http://www.coventry.ac.uk/life-on-campus/faculties-and-schools/coventry-school-of-art-and-design/departments/industrial-designs/staff-profiles/brian-clough/).

[1] Le Good, G., Johnson, C., Clough, B., and Lewis, R. (2011) ‘The Aesthetics of Low Drag Vehicles’. SAE International Journal of Engines 4, 2638-2658