Lightweight futility?

[dwgriff1]

Shape of the trailer is a serious consideration, but there is nothing that limits that shape to "standard" tear design or to box design. There are a lot more options.

I am going to continue thinking and planning and making drawings and even models, whether or not I ever build such a rig is another question.

At my age I choose big projects carefully!

Thanks for the input everyone.

dave

[Corwin C]

I've been watching this thread for a while now. It reminds me of a discussion that I was involved in during college concerning aerodynamics, friction, and efficiency. I feel that it's time to submit my 4 1/2 cents...

The textbook answer is that weight is not a factor when considering simple horizontal linear motion in an absolutely frictionless environment. If you are changing the elevation of the item then weight (mass) is a factor because you are adding or removing potential energy. One of the laws of physics is that energy cannot be created or destroyed. That being said, if you return to the same location, the vertical motion of the item has had ZERO impact on the energy used because it is in the same potential energy state as it was before you left. What makes things inefficient is friction.

Friction is a funny thing...it comes from places that you would least expect. For example: describe the rolling of the rubber on the road, distortion of that rubber to conform to the road surface, flexing of the sidewalls, motion of the air within the tire, airflow around the tire, texture of the tread pattern, does it make a noise (noise is a "loss" of energy), ANYTHING out of balance, is the valve stem long or short, does the valve stem have a cap... Pretty complex already and we haven't even started to address the metal parts. Many of these things can be controlled or adjusted to an extent. Air pressure can be raised, hence less flex, smaller contact surface. The formulation of the rubber in the tire, harder surface, "slick" to airflow, etc.

However, in the real world, friction cannot be completely eliminated. Assuming that you could create a perfect frictionless exterior to your teardrop (now you can forget that beautiful paint job, it just won't stay there) ... when you pull it through the air, the air will have to move out of the way, let the trailer pass, then return back to where it was previously. This creates friction. Any motion that the air has after the trailer has passed has robbed even more energy from the system. Here is where aerodynamics comes in. The whole idea is simply this ... allow an object to pass through the air and return that air back to a motionless state instantly after the object has passed. (If you can figure this out, I can make us both rich ) Aircraft fly by intentionally creating a downward motion to the air as they go by. This is what creates the lift that keeps them in the air. These things can also be manipulated to an extent ... smoooooth surfaces, gradual transitions, "sharp" trailing edges, equal distances for the airflow around the object, etc.

To make a long story short ... in the real world, weight is a factor, but it is a small one, and it it a function of the "friction" that is created by that weight, i.e. the flex in the tires, etc. Aerodynamics helps, replacing the grease filled hub with a "wet" one using lightweight oil would help, rounded corners, no exposed handles, minimize frontal area, get rid of those sliding magnets in the braking system, reduce the speed of travel, etc. There are literally limitless ways to improve efficiency, but each comes at a cost and each improvement, unfortunately, will be less and less cost effective. Eventually there will come a point where further improvement is not worth the effort ... I leave it up to you to decide when you reach that point.

Corwin

[dwgriff1]

Thank you Corwin.

My gut thought was along those lines, but you confirmed it. Thanks very much.

I will spend the time I was going to use building a new trailer doing something else!

dave

[Corwin C]

I just received an e-mail from the instructor of the thermodynamics class where this discussion took place (I can't believe that he remembers me and this discussion, it was 18 years ago) ... apparently a correction is in order.

Corwin wrote:

What makes things inefficient is friction.

This is true ... however, TECHNICALLY it is the unintentional transfer (or lack of transfer) of energy (generally due to friction) that makes things inefficient. Energy is often lost as heat like when braking friction or repeated accelerations (turning friction, stopping friction, starting friction, etc.), heat dissipated by the radiator of the TV largely caused by ... friction, improper fuel/air mixture in the engine I'll give you this one, just inefficient, etc.

Now, Dr. B_____ can I have my "A" back? And NO, I'm not going to try to explain how to determine the energy loss created by the motion of an aluminum trailer skin through the Earth's magnetic field.

For everyone reading this thread ... thanks for your indulgence, and apologies for the hi-jack ... I just HAD to get my grade back.

[Roly Nelson]

Hi "dave", if you are willing to build your lightweight teardrop out of 1/8 inch plywood, use a hollowcore door for the floor and make it 40 inches by 72 inches, you can probably duplilcate my "Stacker" It only weighs 245 lbs. (95 lb for the wooden part and 150 lb for the HF trailer). You can see a few pics of it in my Gallery. Personally, I feel all of this refined aerodynamic talk, only applies if you plan to place it on the top of a rocket and shoot it into space. Compared to pulling my 4 x 8 woody, the Stacker definately pulls easier. Just my 2 cents.
Good luck, Roly

[dwgriff1]

Roly,

Ahh, but my current tear is made of 1/8 plywood and the floor is a "hollow core door." The door is one I made, and I made it like a regular door, but the size i wanted.

Mine is 5 by 8 insulated and lined with a galley, so at 580 it is pretty light. But I dream of an even lighter trailer, hence the question.

I appreciate your unending nudges to all of us to keep it light.

Keep it up!

dave

[Roly Nelson]

You're welcome, but the next one will have to be styrofoam, floor, walls and roof. Good luck, perhaps you can break the 200 lb ceiling, for the lightest TD ever. Keep us informed, we're all ears...........
Roly

[robertaw]

I have nothing scientific to offer but can throw in my two cents worth of personal experience.

I drive a 1993 Jeep Grand Cherokee. The gas gauge has been broken for many years so I must closely monitor my mileage. (19/20 mpg in town - 21/22 hwy)

I have towed an Apache hard sided pop-up for years. I believe it weighed around 1,700 lb and was shorter than my TV. It made exactly ZERO difference in my mileage.

I towed a 1,900 lb U-Haul trailer 350 miles empty. It was taller than my TV and once again made ZERO difference in my milege.

The same U-Haul fully loaded and towed over 900 miles made only made 1 mpg difference in mileage.

So, in my case at least, height makes no difference and weight didn't matter much either.

[dwgriff1]

Roberta, your observation lines up with others and seems to agree with the engineers on this board.

Roly: with what I learned on this thread I'll not likely build another tear. There is no real point to a really super light tear (though it could be done I think), at least not by me.

BTW, if any of us are going to get really light we will need to stop looking at trucks and other trailers for inspiration, and start looking at Piper Cubs and Bellancas and stitch and glue and frame and skin and so on.

The big rub still is that axle/wheel/tire combination.

dave

[artwebb]

I have nothing scientific to offer but can throw in my two cents worth of personal experience.

I drive a 1993 Jeep Grand Cherokee. The gas gauge has been broken for many years so I must closely monitor my mileage. (19/20 mpg in town - 21/22 hwy)

I have towed an Apache hard sided pop-up for years. I believe it weighed around 1,700 lb and was shorter than my TV. It made exactly ZERO difference in my mileage.

I towed a 1,900 lb U-Haul trailer 350 miles empty. It was taller than my TV and once again made ZERO difference in my milege.

The same U-Haul fully loaded and towed over 900 miles made only made 1 mpg difference in mileage.

So, in my case at least, height makes no difference and weight didn't matter much either.

Suspension of local laws of physics, horribly inneficiect TV, or sloppy book keeping (gas in miles out)?

[Ageless]

Roberta has a very valid point. Aero has very little effects at speeds less than 85 mph. A vehicle travelling at 70 mph for one hour only generates enough friction to raise the skin temp 1 degree.

Weight; an object in motion tends to remain in motionGetting that weight in motion takes energy. Once you have the weight to speed; mileage will level out. I ran out from CO with a 96 Explorer and got 27 mpg . . . .running downhill.

[robertaw]

I have nothing scientific to offer but can throw in my two cents worth of personal experience.

I drive a 1993 Jeep Grand Cherokee. The gas gauge has been broken for many years so I must closely monitor my mileage. (19/20 mpg in town - 21/22 hwy)

I have towed an Apache hard sided pop-up for years. I believe it weighed around 1,700 lb and was shorter than my TV. It made exactly ZERO difference in my mileage.

I towed a 1,900 lb U-Haul trailer 350 miles empty. It was taller than my TV and once again made ZERO difference in my milege.

The same U-Haul fully loaded and towed over 900 miles made only made 1 mpg difference in mileage.

So, in my case at least, height makes no difference and weight didn't matter much either.

Suspension of local laws of physics, horribly inneficiect TV, or sloppy book keeping (gas in miles out)?

"Inefficient" is spelled like this. If my book keeping were sloppy I would run out of gas since the gauge is broke. Soooo

[artwebb]

[vwbeamer]

Look at the little PUCK trailers that only wiegh 750 lbs or so. They have a space frame, and not a heavy cargo frame and axle.

You are right, the plywood on a metal frame is cheap, easy and strong, but it is not the lightest way.

Roberta, your observation lines up with others and seems to agree with the engineers on this board.

Roly: with what I learned on this thread I'll not likely build another tear. There is no real point to a really super light tear (though it could be done I think), at least not by me.

BTW, if any of us are going to get really light we will need to stop looking at trucks and other trailers for inspiration, and start looking at Piper Cubs and Bellancas and stitch and glue and frame and skin and so on.

The big rub still is that axle/wheel/tire combination.

dave

[KBS]

Would the tow vehicle get better mileage pulling a 300 pound trailer than a 6 or 800 pound one?

I am sure it would get better mileage, but would the margin be enough to justify the search for the lighter weight solution?

dave

600 pounds of trailer weight is the same as 600 pounds of passenger weight, as far as pulling uphill and mass acceleration go. The difference is in the friction of the tires and the added wind resistance. The engine doesn't care if the weight is in the back seat or attached to the trailer hitch. It still has to pull it and your brakes have to stop it. So, if you have a low wind profile, the trailer isn't going to reduce your fuel economy much more than two sumo wrestlers in the back seat. However, you will get worse mileage overall, regardless of where the weight is distributed.

As far as whether the mileage difference is great enough to warrant the effort to lighten the load, that depends on your vehicle and your wallet.