Teardrop trailer aerodynamic advice

[4862forestgrove]

Hi all. I am new to this forum but have spent several nights reading old posts. I am building a teardrop trailer and am in the design / materials purchase mode. I will note several of the choices I have made so far and materials I have acquired, and then pose some design questions.

* I have read here that the traditional teardrop design is not really that aerodynamic, so I am trying to design in aerodynamic features that are not associated with a traditional teardrop as seen in the TNTTT forum.

* I will pull this trailer with a 2004 Jetta TDI Sportwagen.

* I have acquired sheets of 5052 aluminum sheet with a clear anodized gloss finish that is 12 feet long that I will use for the skin. I hope to attach this to the frame using 3M double side ultra tape to minimize rivets.

* I have acquired a Harbor Freight trailer with 1720# capacity that I will stretch to be 4x10 foot frame. 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.

* I plan a Kamm back design using your AST template for the top surface, running out to the 50% to 60% bulkhead.

* The front of the trailer will lift up, hinged at the rear to increase headroom and interior space, while minimizing height while traveling. (Picture a car hood or hatchback.)

Now for the questions...

1. ? For the front of the trailer profile, I am thinking of several options.

a. try to recreate the shape of the rear of the Jetta, making the front of the trailer concave to try to match the convex profile of the rear door of the Jetta and matching the shape of the Jetta as seen from the rear. (although I wouldn't be able to run the trailer THAT close to the rear of the Jetta.

b. make the front traditional with a rounded front like the leading edge of a wing and the sides of the trailer flat (very easy to construct with flat panels.)

c. use the superellipse or square half body plans documented by freebeard... (the square would be much easier to construct.)

d. try to reproduce schlorwagen shape and raise the top half of the trailer with pop up trailer jacks.

2. It there that great of a benefit to round / slope the trailer sides from bottom to top or are straight sides acceptable?

3. How great a benefit are rounded edges at the corners.

I thank you in advance for some discussion and apologize for my newbie questions :-)

Once I am further in the design process and make some decisions I will post some drawings and pictures...

[fidalgoman]

Of course a fully rounded nose and aerodynamic shape would cut Cd. And making it five feed wide with wooden extensions to HF trailer makes it more comfy for two but also sticks out wider and increases Cd. I'd still make it five wide.

I guess the low profile and tucking into the cars slipstream is the real drag reducing design of the teardrop. The aero side profile is perhaps more style than substance apart from that. some people even put luggage racks on top of them adding lots of braking effect;-0 There are several builder forums you might want to Google for advice and ideas.

It sounds like you're onto a good start.

[4862forestgrove]

Yes, I am going to re-post this to the TNTTT (Teardrop Trailer) Forum. Thank you for the advice... BB

[freebeard]

I don't know if you saw this thread: http://ecomodder.com/forum/showthrea...tml#post383403

I mention it reluctantly, because I haven't updated it in 2 weeks; but a lot of what I had to say is there. There's a lot I haven't touched on, though:

• curving corrugated materials
• kitchen cabinets on 4-bar links
• telescoping canopies and pop tops
• fiberglass-rod-and-fabric teardrop fenders

As to you questions; I'd go with a blunt nose making it generic instead of tying it irrevocably to one tow vehicle. The superellipse, in case it isn't apparent, is achievable with the 'Roswell' design.

Your Harbor Freight trailer frame is twice as heavy as a purpose-built frame and you may not have thought through the implications of burying a live axle within the floor.

Once I am further in the design process and make some decisions I will post some drawings and pictures...

You need to get 5 posts in before you can post pictures.

[Frank Lee]

My Harbor Fright supposedly weighs 272. Off and on I think about putting a removeable streamlined bolt-on shell on it, for camping or hauling stuff or flatbed use.

[4862forestgrove]

I did see the thread, but just scanned it. I am trying to digest some of the 12 billion posts here :-)

I have done several "thinking drawings" one of which superimposed the template over the top of my Jetta. The ground to the top of the frame with 1" of flooring material with the lowered trailer measures 18". The ground to the top of the template just in back of the Jetta measures 54". This gives me 36" of trailer height (not much) so I did plan on some sort of pop up. With the taper of the template I get 18" in the back of the trailer. If I telescoped the whole thing I get 72" in the front and 36" in the back.

I have thought of attaching 3/4 plywood to the bottom of the trailer frame members and have a "sunken space" which gets me back 4.5".

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.

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

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?

The body would be wide enough to enclose the outside of the tires / fenders at that point.

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?

Kitchen cabinets on 4 bar links??

BB

[4862forestgrove]

Attached picture of the Jetta with the template laid over the top. Height at first dotted line from ground is about 54-58". Distance between "bulkheads" is about 5 feet.

BB

[4862forestgrove]

Just ran onto this trailer thread for a TDI wagon and am loving it!!

http://ecomodder.com/forum/showthrea...tdi-26132.html

BB

[MetroMPG]

Subscribed. Looking forward to visuals to watch where this is headed.

[ChazInMT]

To start with, here is a picture of your wagon with an aerotemplate in a debatable placement due to the fact that it is a wagon.....no real hard & fast rule for where it should go. I'm putting it here because it seems if I move it forward, the back of the roof pokes into it and I have no idea how you're supposed to recover after that.

Anyway, this is close to optimal if you were going to build a boat tail on the wagon, which you're not, so in essence, this is a fairly meaningless image. I just wanted to show what the ideal thing to do in the back would be.



Since there is no practical way to build a trailer that would be livable in the space within the template and also because it would not be close coupled thereby having a fair gap, you really need to think about the front shape of what you're towing a lot to minimize its parachute effect on your aerodynamics. And of course, the rear of the trailer will have a good impact as well.

If I were to do something like this, I would look into making a hard pop-up version of something that was very aero and low while towing, but could be expanded easily and quickly when it was time to set-up camp.

So here's what I got for you, this was fun.



Much Bigger Version Here

I envision a solid box (gold dash) under a aero shell (Dk Blue) when moving. To set up camp, lift the front, pull out gold solid part and reattach, (Red) Then lift the back to attach to gold dash, (Green).

Lift, slide, lift, camp. I figure you got about 5 feet of head room and 10 feet of length all under solid sides. A door could be engineered between the front of the wheel and back of gold solid giving you about 6 feet in back for the bed/dinette and 4 feet forward.

Have not given this any thought in plan (top) view, I just worked out the basic shell and hinge point dimensions (Dk Blue Arc Line) here.

It's a start of something I suppose.