Closing the trailer gap - Ideas & Theory

[Tesla]

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".
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?

[BamZipPow]

How about this?

If you had a camper top/aero cap that extended past the pivot point on the hitch and the trailer was the same height or below the extended edge, you could reasonably use some shaped doors attached to the sides of the tow vehicle that should allow articulation of the trailer. Doors could be pulled tight with some bungee cords.

The trailer would need something that tucked up under the extended cap...probably something inflatable so you could easily take it down to unhitch the trailer.

[slowmover]

Defining the shape/size of the trailer contemplated would be a help to this thread even where a specific project is confined to another thread of its' own).

A 10' tall travel trailer that is also 8'6" wide is quite a different beast to mate to a much lower/narrower tow vehicle than a slick little teardrop trailer both shorter and narrower than the tow vehicle.

Trailers -- open, enclosed, etc -- can be most any size & shape.

.

[Tesla]

Originally Posted by BamZipPow

How about this?

If you had a camper top/aero cap that extended past the pivot point on the hitch and the trailer was the same height or below the extended edge, you could reasonably use some shaped doors attached to the sides of the tow vehicle that should allow articulation of the trailer. Doors could be pulled tight with some bungee cords.

The trailer would need something that tucked up under the extended cap...probably something inflatable so you could easily take it down to unhitch the trailer.

That's kind of what Aerohead did, but top and sides were articulated and had rollers on the trailer, the inflatable thing is good, but always seems to be unreliable unless many $$$ expended. I did also think of a series of inflatable hoops, like air matresses, but continuous over the shape, half inflated only so as one side compressed the air would expand the other side.

The biggest issue I came across when thinking about this is the fact that even though we call them bricks (cars) there isn't a staright panel or right angle anywhere on them they are all compound curves, so trying to hinge anything requires straight lines.

When I think back on all the threads I read Aeroheads was the only build that actually made any attempt at this, all others were mostly to build out the trailer with a radius or V shape or to put a spoiler on the back to deflect air over a bigger trailer.

[Tesla]

Originally Posted by slowmover

Defining the shape/size of the trailer contemplated would be a help to this thread even where a specific project is confined to another thread of its' own).

A 10' tall travel trailer that is also 8'6" wide is quite a different beast to mate to a much lower/narrower tow vehicle than a slick little teardrop trailer both shorter and narrower than the tow vehicle.

Trailers -- open, enclosed, etc -- can be most any size & shape.

.

I was looking for all ideas, in my case the trailer will be just slightly smaller than the vehicle in profile, but am also interested in ideas to tackle bigger trailers. There is likely to be a crossover of techniques and solutions that may be applied to either case with a bit of tweaking.

[aerohead]

They'll be dozens of solutions.Just like automatic coffee makers.
The thing I kept attempting to be as smart as,was all the possible deflections and their orientations such that I'd never find any of the structures binding or colliding.
I experienced almost daily failures when in early testing.
If you can get your trailer onto wheel dollies,where you can observe full range of motion side to side,while anticipating pothole and pressure ridge airborne antics.
It's like a monkey ______g a football.

[oil pan 4]

I lose 3 to 4 MPG when towing my little trailer empty.
About 1MPG is form the added weight and the rest is added drag.

[Tesla]

Originally Posted by oil pan 4

I lose 3 to 4 MPG when towing my little trailer empty.
About 1MPG is form the added weight and the rest is added drag.

Mine's not to bad only 1-2mpg down, though it is only a 6'x4', the only time it climbs is when it is over weight and/or the load is very high and obstructs the airflow above.

[Tesla]

Originally Posted by aerohead

They'll be dozens of solutions.Just like automatic coffee makers.
The thing I kept attempting to be as smart as,was all the possible deflections and their orientations such that I'd never find any of the structures binding or colliding.
I experienced almost daily failures when in early testing.
If you can get your trailer onto wheel dollies,where you can observe full range of motion side to side,while anticipating pothole and pressure ridge airborne antics.
It's like a monkey ______g a football.

What do you mean about "pressure ridge airborne antics"?
Is that to do with varying vortexes and pressures causing oscilations and unwanted flap?

Some sort of flexable/deformable gap filler would be ideal as long as it didn't flap around in the wind.

I have started thinking about ideas for the "ever elussive" inflatable gap filler/boattail idea, just read through some old discussions on the topic:
http://ecomodder.com/forum/showthrea...ack-22480.html

Seems the biggest hurdles are:
Inflation & deployment system.
Maintaining appropriate shape.
Minimising oscilations.
Fabric durability.
Simple attachment & removal for utility.

Would shade cloth be a suitable external skin "aero wise" as it is a fairly course weave?
From what I have read all indications are it should be fine as I have seen many comments suggesting that in reality we are actually moving turbulant air all the time so finer details of skin surface are irrelevant, the basic form is what is important.

*I'm thinking if one were to make the outer skin out of this type of material, it is cheap, strong & durable and is often used on the front of trailers as a stone deflector to minimise paint damage.
*Then use a lighter weight material internally to create a grid pattern lengthwise so individual inflation tubes could be inserted, visually looking into it like a case of wine, 12 individual bottles each in its own compartment.
*The inflation tubes could just be a suitable length and cross section of plastic tube sealed at one end and inflation tube attached to the other end.
*All tubes connected to one inflation manifold, where you can have one way valve, inflate/deflate etc.
*Use a duct from the front stagnation point, highest pressure on vehicle is there I imagine, supplementary blower if required. I could probably duct 2-3" flexitube without increasing frontal area on my car.
*Mount on vehicle side with a solid frame of appropriate design and angle to begin boattail shape.
*Trailer rotates around shape deforming as required, maybe a slip sheet of thick plastic attached flat on trailer face to protect trailer finish.
* Have one larger cell (or multiple) in the centre with a large rubber balloon attached to the manifold, this would remain deflated in normal operation, but when the trailer was turned hard the pressure from the compressed cells would inflate it temporarily until vehicle was in straight line again.
*It is a relativly low pressure set up < 3 psi most likely, aim to use commonly available materials to keep cost, but moreso inevitable maintenance down, one way valves can easily be made with ping pong ball, rubber O-ring and PVC pipe fittings, the pump/fan would be a negative, best avoided if possible.
*HD zippers, like on tents or larger luggage bags, could be incorporated for easy attachment and removal etc.

That's today's idea, see what else comes along.

[oil pan 4]

Originally Posted by Tesla

Mine's not to bad only 1-2mpg down, though it is only a 6'x4', the only time it climbs is when it is over weight and/or the load is very high and obstructs the airflow above.

Mine is a 4'x8' and it could very well go down to 1-2mpg if I took the wood sides off. But I built them because I use them.
It does a lot, I should put up a post. Little trailers like that could eliminate most of the need for a "pickup", they are very cheap buy, own and maintain.