Sources of Error

Although the results' reliability has been confirmed through comparison to predictive calculations and the results of related other similar experiments, there were no doubt several sources of error in the experiments conducted.

The lack of a rolling road surface was partially addressed by placing the tractor-trailer model on an elevated, flat block but this likely did not fully deal with the issue. One would expect a more significant undercarriage air flow with a vehicle moving over a road rather than being placed in a wind tunnel.
The Reynolds number of the conditions in the wind tunnel may not have been high enough to completely reproduce normal conditions. In order to reach equivalent conditions as are found with full-size vehicles in normal conditions, the wind velocities used in model testing need to be incredible. The conditions in the wind tunnel were proven to be acceptable for making comparisons and taking general measurements but were probably not sufficient for the results to be scalable and exactly applicable to vehicles in normal conditions.
The percentage of the wind tunnel’s cross sectional area that was occupied by the model was too high, particularly when the trailer height was extended. As a result, the flow across the entire model was not as uniform as would have been ideal. This error is discussed in the results for the trailer height experiment.
The method of measuring force relied on human interpretation and use. Consequently, any misjudgments directly affect the measured results.
The model, although scaled in size, featured accessories that were oversized. This likely created excess drag that a full-size tractor trailer would not experience.
The model was not a full-size tractor-trailer and so experimental results can, at best, be considered to be directly related to the forces a full-size tractor-trailer would experience but not precisely scalable. The use of a scale model also adds a degree of inaccuracy overall as some aspects of the flow likely change slightly at the smaller scale.
The presence of the force measurer lever arm in the wind tunnel disrupted the flow and likely affected the resultant measurements of drag flow. The movement of the lever arm was probably affected and the flow of air over the model was probably also altered.

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Project Info References Acknowledgments Conclusion Sources of Error Further Research Overview Hypothesis Procedure Results Overview Background Objectives Hypothesis Construction/Details Testing Overview Background Plan	Sources of Error Although the results' reliability has been confirmed through comparison to predictive calculations and the results of related other similar experiments, there were no doubt several sources of error in the experiments conducted. The lack of a rolling road surface was partially addressed by placing the tractor-trailer model on an elevated, flat block but this likely did not fully deal with the issue. One would expect a more significant undercarriage air flow with a vehicle moving over a road rather than being placed in a wind tunnel. The Reynolds number of the conditions in the wind tunnel may not have been high enough to completely reproduce normal conditions. In order to reach equivalent conditions as are found with full-size vehicles in normal conditions, the wind velocities used in model testing need to be incredible. The conditions in the wind tunnel were proven to be acceptable for making comparisons and taking general measurements but were probably not sufficient for the results to be scalable and exactly applicable to vehicles in normal conditions. The percentage of the wind tunnel’s cross sectional area that was occupied by the model was too high, particularly when the trailer height was extended. As a result, the flow across the entire model was not as uniform as would have been ideal. This error is discussed in the results for the trailer height experiment. The method of measuring force relied on human interpretation and use. Consequently, any misjudgments directly affect the measured results. The model, although scaled in size, featured accessories that were oversized. This likely created excess drag that a full-size tractor trailer would not experience. The model was not a full-size tractor-trailer and so experimental results can, at best, be considered to be directly related to the forces a full-size tractor-trailer would experience but not precisely scalable. The use of a scale model also adds a degree of inaccuracy overall as some aspects of the flow likely change slightly at the smaller scale. The presence of the force measurer lever arm in the wind tunnel disrupted the flow and likely affected the resultant measurements of drag flow. The movement of the lever arm was probably affected and the flow of air over the model was probably also altered. Click here to move on to the Further Research page.