I have spent a bit of time reading old threads as I have a trailer project coming up and the gap seems to be one of the major drag issues amongst all the threads I even read Aeroheads trailer thread which was like one of the old "Norse Saga's" or maybe "Gone with the Wind"
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Anyway, some of the things that stuck out for me were the numbers quoted for the gap, >48" and the two vehicles can be treated seperately and at <24" benefits wil begin to be realised 0 gap of course begins to approach perfection. The issue is how to deal with the articulation problem both vertical and horizontal, now it appears we do not need solid or perfectly smooth panels, this thread has a little discussion on how the appropriate membrane may actually be superior:
http://ecomodder.com/forum/showthrea...rms-23084.html
The bottom is probably the easiest as there is some verticle flex, but overall dimensionally the vertical change is minimal, so effectively it is primarily the horizontal plane which requires greater movement. An idea I had for the bottom was simply use two plywood panels joined by a piano hinge at the hitch point, this would alow the vertical plane flex, then the car side panel is fixed to the vehicle under the towbar. The other panel to be hung under the trailer with a mechanism that allows a little forward/back movement, but a lot of side to side movement when turning, this could be something like small double rollers and aluminium track, two sets of rollers back to back at 90 degrees the long side to side track fixed under trailer facing down and the front back track fixed to gapping panel. The panel would move with vehicle movement and just hang under drawbar(tongue).
As we move up to the sides and particularly the top, both dimensiones move the same amount potentially so we can go from 48"gap to nearly 0.
Aerohead had a solution that served his purpose, but IMO, possibly would have showed up deficiencies in extended use, so I suppose it would be good to quantify how much work is required to recover 80-90% of the gap drag loss and maintain real world utility.
The images I saw posted of drafting numbers between vehicles suggests simply filling the draw bar with a half dome that went from hitch point to either side and up to top of trailer would probably be half the job putting in a vertical splitter of deformable soft foam centred infront of this close to the vehicle would further reduce gap drag and crosswind effects, so maybe up to 60%, what else could be done to get to the 80-90%. Some of the things I read indicated just filling the void in any way possible improved the situation, I even thought of a canvas bag of appropriate dimensions filled with inflatable balls or ping pong balls, they would act as a fluid to some degree and shift around in the bag as it was distorted from vehicle movements but the mayhem that would ensue if the bag popped at full speed on a busy major highway ruled the idea out.
What about those elastic cargo nets pulled 60% tight to give enough flex in turns but still hold tight in a straight line, if the grid size was small enough, the angle of aproach to airflow it would almost appear to be a solid surface. Thinking about it, they only need to be tensioned lengthwise and this would help them maintain form, additional hoops of poly pipe or fibreglass rods could be used to support shape progressively from vehicle to trailer, these would be attached to the elastic and move with it in corners or over bumps. The elastic force may well add a few lb's to the tongue hitch weight, but probably minor. As a further developement it could be skinned in durable shade cloth (90% blockout) or light weight canvas which would help with the durability of the elastic as it rapidly deteriorates in UV light.
If one were really daring (or crazy) what about rather than the cloth use coroplast or a similar thing and attach scales to the cargo net, would take forever but if scaled (ha ha) to right size, say about two hands per scale long and they were cut to teardrop shape, that would be something to see slithering down the highway, why bother with a trailer skin, just scale the entire thing from the back of the car to the tail. Actually it wouldn't be that hard to do, stamp out the scales on mass, maybe plastics or garment manufacturer would have machinery, use large staple gun like for packaging with penetrating jaws to fold staples, stretch out on flat frame to right dimensions, anyway enough of those "pipe" dreams, must be having flasbacks from my youth.
Any ideas to add,
most of all how much of that gap do we need to kill to get 80-90% of the benefits?