ausias

WE are trying to substitute large 7 meter van (with 15.6 m3 volume capacity, 6 europallet or 4 isopallet, 1200 kg payload) by a medium van + trailer (we are assessing the combination between 4 different little/medium vans with 3 aerodynamic trailers). BEfore crisis we were getting aprox 22 mpg at 65 mph, now we are in 26 mpg at 59 mph, but we want go somewhere near the 33 mpg.
I show you a cfd test design beginning in 0.36 cd (only the van) resulting in a 0.233 cd if trailer attached and gap filled.


Fill the gap between car and designed trailer hidden in front view with a kamback it will permit -35% reduction between car only S·cd and the new one. I'm designing and testing CFD with solidworks for a Van and even having a 110% front surface with a spoiler, the hidden boat tail trailer give me a total cd reduction from 0.36 to 0.233. WE are trying to achieve also a low lift force or little negative. The rolling over lateral wind speed limit when unloaded we want also some were 60 mph wind (some test of track width and gravity center heigh combinations will permit rollover above 120 mph lateral wind when loaded).
I needed to fill the wake of the van and some 50 cm to 100 cm kamback to fill the wake of the trailer.

Some details of the images: 30m/s front wind, 108 kmh, 67mph,
Sfront vehicle = 2.5 m height, 1.9 m width, 4.8 m length
trailer 2.3 m x 1.7 m x 4.3 m
resulting length 9.6 meters :-O
drag force reduction -35%, expected fuel consumption saving -25% to -15 % L/100km (+33% mpg to 17% mpg) unloaded(2200 kg) to 3500 kg total mass.
Resulting capacity of the showed combination:
5.7 + 12 m3 volume
1100 kg payload
2+4 isopallet
3+6 europallet

I did some trailer desgin with coefficient of drag from 0.72 to 0.26 without towing van first of all, and when understood the aerodynamics I did this design where 0.36 + 0.52 = 0.23, ahahaha I'm physicist and I will show any mathematician that this addition is possible.
I was very surprised when i tried 0.36 towing van + 0.27 (polygonal aproach to streamlined box with kammback) trailer and total cd was around 0.39, because of larger surface and not efficient wake filling.

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aerohead

When you consider a 12.5% thickness fuselage with the aft-body completely cut away,at Cd 0.374,then the same fuselage with the tail restored,at Cd 0.066,you realize the significance of the trailing surface of any vehicle.
So there's no element of surprise with your results.I hope you have a blast passing gas stations with the new combination.

ausias

The surprise is the short version of the trailer wich yesterday achieved cd=0.201, if i could build a trailer extension of my "future" van with that shape I could do the same work but above de 42 mpg when full loaded with the standar gearings. Oh my god! I need to win one jackpot and start building a prototype. Why we changed the fleet some months ago? Why? Double mpg instead some percentatge increase (+13 to +25% mpg) we achieved could be done if we thinked a ¿little? before. I was focused on little driving tips, speeds, aeromods (and axle ratio) changes instead of thinking we could go far away from the make.
If you are a big enterprise like UPS its easier to R+D: UPS Testing High-MPG Composite Vans (video) they design their own vans using aluminium, diesel, custom body, and now composites.

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aerohead

The technology has been languishing for 90 years or so,and 'cheap' fuel has been a popular argument for not embracing low drag.
The U.S. Pentagon is paying over $400.00/gallon in Afghanistan and all branches of the military are investigating 'efficiency' like a vengeance.So far,no one's genitals have fallen off despite fears of many a manly American male that these technologies are reason enough for homophobia.
When 'men' lose their fear of spontaneousautopenileatrophy,we may see some new interest in Class-6,7,and 8 low drag.REALLY low drag!
Until then,you'll be one of trucking's nouveau-riche,laughing all the way to the bank with your tax-free wealth.

wyatt

With regards to building the trailer to have little/no/slightly negative lift, keep in mind that a diffuser of approximately 3 degrees will offset a generous slope on top.

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