AERO–EXPERIMENT

PURPOSE

A preliminary experiment to determine the effects of streamlining add-on panels on the aerodynamics of a truck trailer combination.

METHOD

The equipment used:

  • a vehicle with an elevated horizontal platform built at the front
  • 2 identical model truck/trailers
  • 2 weigh scales

The model trucks were placed on the platform and secured by way of a sliding rail. The rail allowed the trucks to freely move backward and forward while preventing them from lifting off the platform.

A cable attached to the front of the trucks was fed through tubing and attached to a lever which applied a force or weight onto the scales. As the trucks were pushed backwards by the air resistance the force would be transmitted to the scales.

The 2 trucks (truck A served as base, truck B was modified) were placed facing forward on the platform 0.5m apart. The platform was driven with the 2 model trucks at 3 speeds (80, 100 and 120 KPH) per run.

Several weights readings for each speed were recorded from the scales.



Four runs were performed:

Run
Truck A Truck B
 
1.
Base Truck trailer gap closed and a Kamm Tail on trailer (in red)
 
2.
Base Kamm Tail on trailer (in red)
 
3.
Base Truck trailer gap closed on trailer (in red)
 
4.
Base Base

Run # 4 was driven at 100 kph to confirm that Truck A and Truck B had similar aerodynamic properties when unmodified.

The Add-on panels were made of thin aluminum sheets, cut to form assumed aerodynamic shapes that fitted the modified Truck B. The shapes were not predetermined to be the most efficient. For this test the pieces were made to assume an aerodynamic shape. The pieces were held onto the Truck B using clear tape.

The testing was done on a divided 4 lane highway with driver maintaining recording speeds of 80, 100 and 120kph for 2 to 3 minutes and a passenger for recording data.

OBSERVATIONS

The data was recorded by observing Scale A attached to Truck A and Scale B attached to Truck B.

The force was recorded as weight in grams on the scale and is shown in table 1. The chart 1 indicates the average for the readings from the 4 runs.

When truck A and truck B were both base in run #4, the weight readings were very similar.

Table 1

  80 km/hr 100 km/hr 120 km/hr
Grams
  Run 1,2,3,4 Average - Truck A 145 255 384
  Run 1 All on- Truck B 117 171 286
  Run 2 Tail Only - Truck B 136 189 325
  Run 3 Gap Only - Truck B 141 196 313
  Run 4 Base - Truck B   281  

 

Chart 1

CONCLUSION

This test was performed under less than ideal conditions using scaled model trucks and weigh scales while travelling on a public highway with vehicle turbulence and wind. It does however demonstrate that forces acting on objects going through air at highway speeds can be reduced by modifying the shape of the object.

In a model truck/trailer combination travelling between 80 to 120 KPH

  1. The combined Kamm Tail and the gap closing can reduce air forces by 19 to 25%.
  2. The addition of a Kamm Tail may reduce air resistance by 6 to 15%.
  3. The covering or closing of the gap between truck and trailer indicates that the air resistance may be reduced by 3 to 19%.

Further designing and testing of ideal shapes for the add-on panels could further improve the streamlining and lower the air resistance on the truck at highway speeds.

The model trucks used had most aerodynamic improvements including truck side extenders, fairings and trailer skirts. The experiment indicates that closing the gap between the truck and trailer resulted in greater reduction of air resistance than the Kamm Tail. I assume the improvement to the frontal area is important to streamlining the air for the rear surfaces. Some of the creases on the tape holding the panels could have influenced the results.