[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.