Easy trailer front-end improvement
 

I don't know if anyone has tried this, not sure what to search for.

I have seen photos of the Bonneville cars with the lip that extends forward, close to the ground, preventing air going under the car and directing it to the side instead. It is a horizontal surface, not the usual vertical front air dam (although that may be present as well, just above it). Can anyone give me the jargon term for that lip?

Anyway I was looking at the front of my trailer. I have a basic 6x12 enclosed trailer, the kind that has a smooth curve from front to side, but a sharp 90 degree corner from front to top. I always want to make a nice smooth radius up there but fabricating it would be a ***** because it would require curving the material in two dimensions. Finally it occurred to me to take that "Bonneville lip" and apply it up there. In other words it would be just a flat piece of rigid material screwed to the top of the trailer (which is also flat in my case) and projecting forward some distance, maybe something like a foot. Assuming the trailer is set up horizontally at the hitch, this lip would simply divide the air into two regions - above it the air would be undisturbed, while below it the air would strike the trailer front and then curve around to the sides (I'm writing as if it was the air moving, rather than the trailer).

If this makes sense, it would be very easy to implement compared to a big round radius up there.

An enhancement to this idea would be an additional curved surface reproducing the front trailer surface, under the lip, but with a more round front rather than flattened as with most trailers. Or maybe just a "V"; whatever is optimal. This would be material curved in one dimension so it would be easy. It would be easy to attach it to the underside of the lip as well.

Has anybody done anything like this?

I think you are describing a splitter. ;)
https://en.m.wikipedia.org/wiki/Diff...ive)#Splitters

Yes (thanks), except there is no intention to increase lift or down-pressure.

Do you mean recently?

Or a month ago?

At first I thought you were going to suggest adding a splitter below the tongue. That could work.

http://i1271.photobucket.com/albums/...titled19_6.jpg
posted by aerohead in one of those threads.

You don't have to enclose the sides, an open sided half pipe will work nearly as well. There's a company actually making and selling them like that.

I saw those two threads. Unless I missed something, I saw nothing in those threads about using a splitter on the top front edge. I like nice rounded fronts like in those threads, but you can't fabricate them with a piece of plywood. :)

The point of this thread is to get some aero improvement with little effort.

I should add one point. A completely rounded trailer front will direct some of the air that hits it to the sides and some to the top. My guess is that this is ideal. Using just a splitter on a trailer that I described will direct the air to the sides, but none to the top; I'm guessing this is somewhat less of an improvement. The photo you enclose directs the air that hits near the corners, to the sides and to the top. However it depends on having a tractor close in front, as any air that could hit the center of the front surface has nowhere to go. So for a car or pickup pulling a trailer, that solution might not work as well?

Just to give an example, this is what my trailer looks like up front:

http://www.looktrailers.com/gallery/...back_Cargo.jpg

Rounded on the vertical edges, sharp corner on top, and flat roof. An economy trailer. This is primarily what I am talking about.

In looking for this picture I noticed it was difficult to find an example. It seems most trailers for sale these days have a rounded top and the front top corner is a moulded plastic piece, curved in two dimensions. More like this:

http://www.looktrailers.com/gallery/...12_Trailer.jpg

Obviously for something like that, slapping a piece of plywood on top to make a splitter is not going to help anything. At least I don't think so.

The limit on material choice was not called out in the OP. So slap a sheet plywood on there, it'll make for easy A-B-A testing.

Here is a material called PolyMetal. It is 3mm thick and as stiff as 5/8" plywood. It cost about twice as much. (Now will it be easy and cheap?)

http://ecomodder.com/forum/member-fr...1-100-0866.jpg

Edit: How do you propose to fasten that mouldy dirt-magnet to your shiny metal trailer?

Screws through the top of course, into the two frame members that are up there. I was thinking of 1/4" plywood, or something similarly light, so if it flies off it won't kill anybody. :) But aluminum plate would be a more permanent material.

Yeah, if I used bolts instead of screws, I could do testing more easily.

When it doesn't help and you take it off, then you will have upward facing holes in your roof. You can replace the plywood with neoprene washers and put the screws back.

Else, build a tripod on the tongue and put the splitter on top of it. If you wrap the tripod there will be some additional improvement.

open-faced radius
 

upper splitter
 

If the top of the trailer is taller than the tow vehicle the splitter could create some positive lift,especially in a crosswind.
The air won't be able to bleed 'up',and as the dynamic pressure acts on the underside of the splitter it will be pushing upwards,affecting tongue weight,stability.
Something more stable,would be to split a 8" PVC pipe and attach the halves to the upper edges of the trailer face.This would be incapable of generating lift.

Also, Hucho suggests that a vehicle mounted deflector is worth more than re-profiling the top of the trailer. This could be roof mounted on a removable roof rack. He shows a fast back vehicle towing a caravan, with a large roof mounted deflector showing the lowest drag.

This puts me in mind of the Triceratops...
https://upload.wikimedia.org/wikiped...s_ontogeny.jpg
https://en.wikipedia.org/wiki/Triceratops#Growth_and_ontogeny

Juvenile Triceratops has an epoccipital fringe (that disappeared in the adults) similar to the serrations on modern turbojets used to suppress noise.

http://i.imgur.com/5L9wz.jpg

...on the back of a 1948 Cadillac Sedanette.

deflector
 

http://i1271.photobucket.com/albums/...head2/2234.jpg
http://i1271.photobucket.com/albums/...head2/2226.jpg

Hard to do since the front face has a curve in it.

That's a pretty small car towing that trailer, heh.

Those roof racks are interesting, but we aren't seeing what is happening at the trailer sides, with a cross wind, etc.

Isn't it true that almost any trailer shape generates lift? The way those streamers look in those pictures are similar to what happens with a wing. Added speed of air over the top causes reduced pressure, which means lift...

Almost any typical trailer but not almost any conceivable trailer.

http://ecomodder.com/forum/member-fr...wu5wo1-500.jpg

This is a Luigi Colani Bonneville car that obtained massive downforce without add-ons. Except the fenders are sort of add-ons. Flat on the top and convex on the bottom. Translated to trailer terms — sort of an upside down Airstream.

maybe aerohead will come along and say whether Airstreams have any lift to start.

I think any lift generated is just a tiny fraction of the weight. We aren't talking lightweight aircraft, and we aren't talking aircraft speeds. An airstream is actually a heavy trailer compared to some of the stuff made today.

I used the sheetmetal ductwork for my edges. If it were a curved surface you could cut some relief cuts in it to let it bend. They could just be simple cuts almost all the way across just leaving an inch in the center intact then they will slide inside themselves like an armadillo skin as it makes the bend.

The center 80% in lightly curved. If you have an half-pipe and spread the center or pinch the ends, it curves. On the ends if you don't want to use Hersbird's pie cuts, crimp the edges. There is a dedicated hand tool. But you can just grab the edge with a fork[-like object] and twist. That's how panel beaters start, then they hammer the crimps flat again.

lift
 

In road vehicle aerodynamics,lift is a function of flow separation,and the low pressure over the vehicle induced by low pressure present at the separation line.It has nothing to do with the displacement of the streamline filaments.
In the image below,the top vehicle would be extremely unstable at speed,whereas the bottom vehicle would be especially stable.
http://i1271.photobucket.com/albums/...ad2/scan35.jpg
Streamlined bodies are incapable of generating lift,as they have zero separation,or recover with reattached flow.
http://i1271.photobucket.com/albums/...titled10_4.jpg