Minimizing Aerodynamic Effect for Trailer Towing

[aerohead]

Thanks for doin' the experiment.It's valuable information and will become part of a growing database.

[ByDesign]

Trip #3. No mods, but slower speeds. OK, so it's a feeble attempt, but I' like to understand the relationship of speed and fuel consumption as it relates to pulling the trailer. Trip #3 was 189.6 miles on 14.1 gallons. 13.4 MPG. That's down 1.4 MPG from the baseline no trailer, and a 1.2 MPG better than the first trip with the trailer.

Interestingly, this is better fuel economy than with the gap filled.

The difference is speed. Don't have exact numbers, but the average speed on this trip was down something in the neighborhood of 10 mph from the first trip. Meaning, spending 20-25 minutes extra each way saved about the same in fuel as adding the gap filler inner tubes.

Of course, better aerodynamics makes more difference at higher speed, so the effect is diminishing, but with 3 people in the vehicle (that's an hour of man pay extra for the journey). Interesting balance to deal with on time v. savings v. cost.

I like the idea of time being irrelevant and just riding my bike. I'd have a hard time pulling said trailer, but aside from that, riding, even all day long, uses less gasoline than even the best of hybrids.

[PaulB2]

Please, someone invent a hitch that extends at low speeds and retracts (shortening the gap) at highway speeds...

I am amazed at the low mpg hit you are seeing. I have a 6x12 covered trailer like that, also one axle, and it kills the mpg on my Ram 1500. Not sure about freeway numbers though.

[freebeard]

But you want the shortest hitch-to-rear axle distance when backing up.

Maybe if it racked in and out based on the angle. You might could do it with a Watts linkage.

[ennored]

Originally Posted by freebeard

Maybe if it racked in and out based on the angle. You might could do it with a Watts linkage.

There's 5th wheel hitches that do this, most manually slide, but some do it automatically while turning. I've often wondered why I've never seen such an arrangement for semi-trucks. Small gap on the highway, larger for turning.

Here's an automatic one.



(Not a 5th wheel guy myself, maybe someone who tows a 5th wheel can add some details?)

[aerohead]

Originally Posted by ByDesign

Trip #3. No mods, but slower speeds. OK, so it's a feeble attempt, but I' like to understand the relationship of speed and fuel consumption as it relates to pulling the trailer. Trip #3 was 189.6 miles on 14.1 gallons. 13.4 MPG. That's down 1.4 MPG from the baseline no trailer, and a 1.2 MPG better than the first trip with the trailer.

Interestingly, this is better fuel economy than with the gap filled.

The difference is speed. Don't have exact numbers, but the average speed on this trip was down something in the neighborhood of 10 mph from the first trip. Meaning, spending 20-25 minutes extra each way saved about the same in fuel as adding the gap filler inner tubes.

Of course, better aerodynamics makes more difference at higher speed, so the effect is diminishing, but with 3 people in the vehicle (that's an hour of man pay extra for the journey). Interesting balance to deal with on time v. savings v. cost.

I like the idea of time being irrelevant and just riding my bike. I'd have a hard time pulling said trailer, but aside from that, riding, even all day long, uses less gasoline than even the best of hybrids.

*the power required to overcome wind resistance varies as the cube of the velocity.
* the power to overcome rolling resistance is more linear.
* mpg will track engine power basically,but won't necessarily have a linear relationship as its brake specific fuel consumption (which determines mpg) can vary as a function of engine load.
* every vehicle combination will have a sweet spot speed for highest mpg,but these best MPGs may occur at a velocity which is completely unacceptable.
*you can get 40-mpg in a new Corvette,but you'll have to drive 40-mph to get it.

[aerohead]

Originally Posted by ennored

There's 5th wheel hitches that do this, most manually slide, but some do it automatically while turning. I've often wondered why I've never seen such an arrangement for semi-trucks. Small gap on the highway, larger for turning.

Here's an automatic one.



(Not a 5th wheel guy myself, maybe someone who tows a 5th wheel can add some details?)

If Barbie and Ken squirt out in front of the big rig and it has to jackknife,it's bye-bye trailer face and tractor rear.Better just to do movable gap-fillers.

[ennored]

Originally Posted by aerohead

If Barbie and Ken squirt out in front of the big rig and it has to jackknife,it's bye-bye trailer face and tractor rear.Better just to do movable gap-fillers.

Not with the automatic type. It slides back when the trailer turns, No action from the driver required.

[aerohead]

Originally Posted by ennored

Not with the automatic type. It slides back when the trailer turns, No action from the driver required.

For semi-trailers?

[freebeard]

What force would it take to 'shorten' the hitch, when it is under tension from tons of stuff being dragged down the highway? Possibly equivalent to rolling resistance?