Drag Measurement on HPVs
Future Developments
The measurement technique is still far from being perfect. You have to find a good test path, wait for good weather (no wind) and you have to do several tests for good statistics. Because the statistical error decreases only with the square root of the number of tests, an in crease of accuracy by increasing the number of tests seems impractical. Although it is possible to achieve an accuracy of 5% with only 6 tests under good conditions, it is not easy to arrange for good conditions. Consequently, further developments should aim on decreasing the sensibility to wind and slope variations. The following extensions seem feasible:
- Add a real time wind measurement (proposal by Angus Cameron: hot wire anemometer).
- Add slope measurement, maybe by measuring the vertical accelerations with an accelerometer.
- The accuracy is better if the initial speed is higher. Does someone have a good idea how to accelerate the HPV other than pedalling?
- Investigate an other evaluation method proposed by Anugs Cameron: do a direct curve fit to the raw data with the solution of the differential equation modelling the system. Compare the two evaluation methods regarding their systematic errors.
Author: Christian Starkjohann <cs@hal.kph.tuwien.ac.at>