enclosed trailer aero kammback

[hotrodf1]

Hey all
been reading about the "pot of gold" that's lurking at the back of the trailer.
Been getting about 13mpg on average towing my racing trailer. I'm shooting for 16 for now.

Read on wiki that a reduction of area about 50 Percentgets close to the efficiency of a full boat tail. So i've started with 96 wide by about 85 high. Tail should then be about 68 x 60 I believe.

Using a 15 degree slope the length of the addition ends up around 44 on the angled part. Does that seem reasonable?

Building a frame from 3/4 conduit and bending and welding as needed. I plan to skin with some plastic sheet I can get at work. Heavier than coroplast but very available and very free. Probably just rivet it on.

I've attached a couple pics of back of trailer and start of frame. Thinking the pieces that connect the two will have several small bends to get closer to teardrop shape.

Anyone have any feedback on this. Would like to build once and be done.

The whole deal will be hinged on topside to get it out of the way to unload the racecar.

[ChazInMT]

It depends greatly on the execution, your pictures did not post. Just make another post then it will let you, or do as I have and create a Tinypic"dot"com account and just refer to your pictures in here, it is real easy to do. Let me know how I can help ya.

Don't feel bed creating another couple of one word posts to get your count up...your project is VERY interesting to all here and we would all love to help!

[hotrodf1]

I seem to have 2 issues.1 is the file size I think. I'll try again if I can resize or try the other account like you said.

[ChazInMT]

Picture size is funny here too, it needs to be less than 650 pixels wide to not be resized and < 800 wide to not look really bad when expanded. Keep that in mind. I really think having a Tinypic account is the best way to go due to the flexibility, the ecomodder blog is real finicky.

[hotrodf1]

It seems you are correct. I'll have to do the tinypic deal.

[aerohead]

Originally Posted by hotrodf1

Hey all
been reading about the "pot of gold" that's lurking at the back of the trailer.
Been getting about 13mpg on average towing my racing trailer. I'm shooting for 16 for now.

Read on wiki that a reduction of area about 50 Percentgets close to the efficiency of a full boat tail. So i've started with 96 wide by about 85 high. Tail should then be about 68 x 60 I believe.

Using a 15 degree slope the length of the addition ends up around 44 on the angled part. Does that seem reasonable?

Building a frame from 3/4 conduit and bending and welding as needed. I plan to skin with some plastic sheet I can get at work. Heavier than coroplast but very available and very free. Probably just rivet it on.

I've attached a couple pics of back of trailer and start of frame. Thinking the pieces that connect the two will have several small bends to get closer to teardrop shape.

Anyone have any feedback on this. Would like to build once and be done.

The whole deal will be hinged on topside to get it out of the way to unload the racecar.

with an 'ideal' boat tail nearly all the drag reduction has occurred by 80% of the length.Chopping it off at 50% would leave 26% of the drag on the table.
If you wanted to guarantee your job,you might want to search here at Ecomodder for 'Aerodynamic Streamlining Template Part-C'.this was intended for these kinds of projects.
Curves are your friend,angles will get you part way.
Edge curvature is also very important to a boat-tails performance.
I'll wait for your photos.

[hotrodf1]

Sorry for the delay on the pics. They aren't great but do show the trailer and the start of my framework.

Aerohead - I didn't know that 50% was a less than ideal number. Got it from widipedia. Perhaps not a great source, but when I searched for Kamm back that's what came up first, so . . . .

I kind of thought it seemed "too easy" to get there. Was planning on making it deeper, but then at 50% cross section and 15 deg. it was only 44" deep on the hypotenuse.

Anyway,
The piece was going to start out with straight corners since the corners on the trailer are straight anyway. Does this make sense or not? Could have easily used the bender to make them 6" radius curves.

The rear of the tail was going to just use the curves that the bender produces (seen in photo). I guess that's probably not enough curvature to make the most of it.

Thanks for the heads up on the template. that's what I needed yesterday but I didn't know what to look for. I'll look at that before I go any further.

Let's see if these pics will show up from photobucket.

First the trailer



Then the rear section of frame.

[drmiller100]

three different angles involved.

the top is REALLY safe at 20 degrees. 20 degrees is ABOUT 1 inch of drop in 3 inches of run.

The sides are "pretty safe" at 20 degrees, and REALLY safe at 15 degrees. Again, 1 inch of drop in 3 inches of run is pretty safe for the side.

the bottom is best left at 10 degrees. one in 5.

so. assume 96 wide. each side is 48 inches "wide". one in 3 would mean the back would be 144 inches long, which is pretty silly.

if you can make it 60 inches long you will get the vast majority of the benefit, as your top and bottom also taper.

[hotrodf1]

Originally Posted by drmiller100

three different angles involved.

the top is REALLY safe at 20 degrees. 20 degrees is ABOUT 1 inch of drop in 3 inches of run.

The sides are "pretty safe" at 20 degrees, and REALLY safe at 15 degrees. Again, 1 inch of drop in 3 inches of run is pretty safe for the side.

the bottom is best left at 10 degrees. one in 5.

so. assume 96 wide. each side is 48 inches "wide". one in 3 would mean the back would be 144 inches long, which is pretty silly.

if you can make it 60 inches long you will get the vast majority of the benefit, as your top and bottom also taper.

When you are saying "safe" are you assuming I'm making the sides a curved surface as best I can, or is that also ok even if the sides are just flat? I'm going to try to make the sides curved as best I can, but I don't have a way of rolling the tubing, I can only make multiple small bends in the tubing to approximate a large radius bend.

60" long seems like a fairly logical length from a feasibility standpoint. Any more than that is going to get unmanageable. Trailer is already 26' long without tongue.

I wonder why none of the new trailers out there have such features. Do ALL people pulling trailers seriously not care about fuel mileage? At $4/gallon for diesel I have to care. Would think they would have fuel saving options and show valid proof of such an addition. Seems like people would be interested if it was built in a way that looked "factory".

Is there a commercially available "drag reduction semi-cone" for the rear of trailers?

[hotrodf1]

Okay,

The Template as it is called. From what I can tell Aerohead you are a big part of this drawing I couldn't read all the pages on that thread tonight.



I say thanks for making such info available.

So how do I apply it to the back of my trailer? I guess I can transpose it to a CAD program and apply that way - and go back 60" and see where it comes out.

Also - I am planning to start the tail right below the top row of lights there on the trailer so that I don't have to make recesses in the tail itself for the lights. That puts me 2" below the top before the tail starts - this seemed insignificant to me at first, but now I"m wondering if that's really the case. Thoughts?