Towing distance? 1

[EdDanzer]

I would like someone to suggest the distance between vehicles to eliminate the affects of drafting so I can measure both rolling resistance and aerodynamic drag by towing a vehicle at different speeds (up to 70 mph) on flat ground.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[dicer]

I'd say the farther the better. 100 plus feet?

 

[patprimmer]

I'd say try it at 10' 20' 30', compare results then predict ballpark and try 3 evenly spread distances near the predicted point of insignificant effect

Regards

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[NormPeterson]

It'll depend at least partly on how big of a hole the towing vehicle punches through the air. The bigger the tow vehicle, the faster that it's traveling, and the more effectively it limits airflow "leakage" underneath it, the stronger the draft. Amazingly stronger, given appropriate circumstances.


Norm

 

[Bribyk]

Mythbusters tested fuel economy behind a semi-truck/trailer at 50 mph and noticed improvements at 150 feet (that was the furthest distance from the truck they tested).

 

[GMIracing]

Any reason you are deviating from the standardized SAE procedure of determining road load coefficients using the Coastdown method?

Maybe have a look at:
SAE J1263 Road Load Measurement and Dynamometer Simulation Using Coastdown Techniques
SAE J2263 Road Load Measurement Using Onboard Anemometry and Coastdown Techniques

 

[EdDanzer]

I need to know the actual power requirements to move the vehicle at different speeds to calculate the thermal efficiency required from the engine and drive train for our Progressive Automotive X PRIZE entry. Since we hope to enter a Class 2B truck with our hydraulic wheel motors we will need to remove the drive axles to eliminate loss from the third member, driveline and transmission.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[ivymike]

I believe that a coastdown test would allow you to determine that.

 

[ivymike]

...assuming you meant power at the wheels, rather than at the flywheel.

 

[TStaples]

Ed,

Based on one custom air pressure sensor project that I did for a NASCAR team, I know they were seeing effects at trailing distances up to 200 feet. This was behind a relatively slippery, with the exception of the rear spoiler, race car at speeds of 150 mph and up. It was quite amazing how far back behind the lead vehicle the effective air pressure was reduced.

-Tony Staples

http://www.tscombustion.com

 

[EdDanzer]

Thanks for the input.

The coast down test will have some additional power loss from the third member, drive shaft and transmission. So I think I will try the coast down method and towing with 200 feet between vehicles to see what the differences are. It might be May before I have time to do the tests but I’ll try to post the data.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com