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carbon bike wheels with 5 tri spoke system, what it is and how it works?
2016-04-06
Description of the improvement:Developed originally by Dr. James D. Hammond while working on several advanced aviation projects for the Taiwan government, the double cusp rotating airfoil is possibly the first attempt to optimize a low drag wing section that is subjected to constant chordal changes due to being in constant rotation.
The problem:
As the body, in this case a spoke (that has zero camber for test purposes) rotates; the chord thickness, or aspect ratio of the body changes in parallel with its changing orientation to oncoming airflow.
These chordal changes theoretically, and in practice give rise to very large changes in the drag of the body. As the body becomes longer and aspect ratio decreases as it becomes more parallel to the oncoming airflow, the drag reduces proportionally and the conversely, as the body presents itself at minimum chord, the drag increases with the shortening
aspect ratio.
The solution:
Firstly we should point out that there is no “solution” per se to this problem, but we can however, by clever use of the airflow, make some useful improvements in the overall performance of the carbonwheel.
What we have done here is to try to make an airfoil section that will react to these changes in Chord with minimum increase in drag; and to do this we have utilized a double cusped airfoil section in order to create pockets of dead or slow moving air that provide temporary “cushions” for the faster moving main air stream to move over. This in turn minimizes the drastic drag penalties of constantly changing chordal aspect ratio as the carbon wheel rotates.
The results:
Test have shown that the double cusped rotating airfoil section shows good improvements in overall drag levels, plus some useful improvements in side wind tolerance.
James D. Hammond PhD – inventor of this device.
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