Teardrop trailer aerodynamic advice

[ChazInMT]

Originally Posted by 4862forestgrove

I plan to skin the underside of the trailer with a sheet of continuous aluminum hiding the axle within the skin and place the axle on top the springs to lower the profile and reduce area under the trailer.

You really need to consider break over and under angles here or you'll constantly be dragging the back or front of your trailer with any kind of ramp angle you encounter. Aerodynamically, I don't think there is any significant advantage to "Low as you can go" on a trailer behind a vehicle. It could be argued that too low might hurt aero drag. I'd be very careful on the ground clearance of the trailer, or build in some extreme skid plates while engineering the trailer to not fold in half when suspended by both ends.

[freebeard]

ChazInMT demonstrates canonical use of the template.

I have also thought of fairing at least the top of the Jetta / Trailer unit to maintain flow as I have seen in other parts of the Forum.

Maybe save that for v2.0. That's a can of worms.

I plan on doing a little welding and reducing the weight by eliminating some of the frame cross members in order to reduce weight.

So you see the problem.

The axle would not be attached to the bottom of the trailer if I enclosed it. It would float in the open space. Are there other implications of that technique that you had in mind?

Where is this open space? Is it between the top of the deck and the bottom of the aluminum skin? I'd be looking at independent rubber torsion or elastomeric snubbers.

by blunt do you mean like a rounded wing leading edge as in a standard teardrop trailer or squared off in the front with a flat panel like a cargo trailer?

Half circular or V-shaped. I'd look at the wake from your Jetta, and fill it, e.g. wide and low. A bluff forebody will let it reattach the turbulent flow off the tow vehicle.

Kitchen cabinets on 4 bar links??

Hold that thought. I'm trying to spend a few days out of town before August is gone.

[4862forestgrove]

Created the following attachment today...

1. I decided to do out and measure actual values on my Jetta today rather than relying on computer pictures and estimated curves. I measured the peak of the roof line to be back 48 inches from the back of the Jetta. Maximum height at that point was 56.75 inches. Drop to the back was 1 inch. Height at back was 55.75 inches.

2. I used these values along with the xy coordinates of the AST II template to scale a spreadsheet graph and then fit an image of the Sportwagen under the curve.

3. I generated a scale factor to create the rest of the xy coordinates.

4. The top of the trailer frame is 17". The frame is 3.5" channel, so the underside is 13.5". The A frame tongue is 42" from the front of the frame to the hitch.

5. Using these constraints, I generated a trailer body at 8', 9' and 10' lengths of the frame, fitting close to the back of the vehicle

6. The top will be a simple lift of back first... block, then front... block. I'm thinking a simple pull out block (shelf) once the trailer body is lifted.

Thoughts so far?

BB

[aerohead]

Originally Posted by 4862forestgrove

Created the following attachment today...

1. I decided to do out and measure actual values on my Jetta today rather than relying on computer pictures and estimated curves. I measured the peak of the roof line to be back 48 inches from the back of the Jetta. Maximum height at that point was 56.75 inches. Drop to the back was 1 inch. Height at back was 55.75 inches.

2. I used these values along with the xy coordinates of the AST II template to scale a spreadsheet graph and then fit an image of the Sportwagen under the curve.

3. I generated a scale factor to create the rest of the xy coordinates.

4. The top of the trailer frame is 17". The frame is 3.5" channel, so the underside is 13.5". The A frame tongue is 42" from the front of the frame to the hitch.

5. Using these constraints, I generated a trailer body at 8', 9' and 10' lengths of the frame, fitting close to the back of the vehicle

6. The top will be a simple lift of back first... block, then front... block. I'm thinking a simple pull out block (shelf) once the trailer body is lifted.

Thoughts so far?

BB

*The 'full-boat-tail trailer for T-100' thread may have some pictorial drag tables which will help you think about your project.Also the half-body charts at 'AST-C additional drag tables' thread.
*The body drag of your combination will be factored from the new base area of the trailer's transom area,plus a penalty for the car-trailer inter-spacial gap interference(look at the Clark-Y wing with various gap combinations),and then the wheel/tire drag superimposed back onto the body (call that portion Cd 0.05 ).
*If the trailer nose is unshielded,make it as complex as you can stomach (Airstream's design is very good).This will help in crosswind.

[4862forestgrove]

Thanks for the input... could you take a quick look at the attached drawing of the treatment of the front radius and tell me which your intuition favors... I believe there are equally easy to build. Thanks in advance. BB

[aerohead]

Originally Posted by 4862forestgrove

Thanks for the input... could you take a quick look at the attached drawing of the treatment of the front radius and tell me which your intuition favors... I believe there are equally easy to build. Thanks in advance. BB

I would recommend the convex nose.If you never do gap-fillers you'll still be protected in crosswinds.
If you eventually do gap-fillers,you'll have a proper ball-and-socket articulation with the air shingling down the filler panel 'socket' and onto the trailer 'ball.'
Anything you can do to close off the gap will help cut fuel.But remember that the trailer will have range of motion in pitch,roll,and yaw,and sometimes all three simultaneously.It's easy to get things bound up.

[4862forestgrove]

Originally Posted by aerohead

I would recommend the convex nose.If you never do gap-fillers you'll still be protected in crosswinds.
If you eventually do gap-fillers,you'll have a proper ball-and-socket articulation with the air shingling down the filler panel 'socket' and onto the trailer 'ball.'
Anything you can do to close off the gap will help cut fuel.But remember that the trailer will have range of motion in pitch,roll,and yaw,and sometimes all three simultaneously.It's easy to get things bound up.

Great I'll think about that... any other MUST READ posts you can suggest would be great... Thanks again for your input. BB

[aerohead]

Originally Posted by 4862forestgrove

Great I'll think about that... any other MUST READ posts you can suggest would be great... Thanks again for your input. BB

You might do a Search EcoModder for 'Range Extending Trailers' and go to #10 permalink to see some projects and thought experiments.

[euromodder]

Originally Posted by 4862forestgrove

Thanks for the input... could you take a quick look at the attached drawing of the treatment of the front radius and tell me which your intuition favors... I believe there are equally easy to build. Thanks in advance. BB

Don't make the front of the trailer into a scoop that scoops air between the towing vehicle and the trailer.
Use a convex shape.


Don't use any circular shapes at the rear.
They'll destabilise the trailer.
Cut it off sharply at the rear, if possible with the sides / top / bottom plates extending a bit (2-4 inches) beyond the rear wall - i.e. forming a shallow box of thin plates around the tail end.


If you get around to covering the gap, the covers can rest on / slide over the convex front of the trailer.

[4862forestgrove]

Thanks Euromodder... looks like that's the advice I'm getting, but, however.... The convex shape was intended to make gap filling much easier to do, not make a scoop or allow a gap between the tow vehicle and the trailer. The intention would be to immediately make a fairing to join the car with the trailer like the "range extending trailers" I have seen on this site. Given that I was intending to create fairings before taking it out on the road, and only tow with the Jetta and not other tow vehicles, and the further intention would be long distance cross country trips, would aerohead and your advice still be the same?? BB