Wind Drag & Turbulance

[asianflava]

What if you put speed sensitive linear actuators on the tongue. Once you hit say, 60mph it will pull the trailer to within a foot of the TV. Once you drop down to 50 it will extend out to the normal length. You could hook a relay up to the spoiler of your Corrado or Porsche since they have speed actuvated spoilers.

I'm only joking of course, but it come to mw when I was following a Porsche one time.

[Trackstriper]

Andrew,
Thanks for the input. I think I'll just keep it simple and tucked behind the vehicle. It sounds like I'd have to borrow a wind tunnel over at Lockeed to get it right.

Rocky,

Thanks. As though my van had speed sensitive anything. It's got 330K on the clock and is getting a little tired, thus the reason for a low drag travel trailer. I did toy in my head for a few minutes with the linear actuator idea. Sounds like a place where Mr. Murphy would like to hang out and play. First time it didn't extend.....

J.B.

[Arne]

Asianflava.. not a bad idea... once you get on the highway, stop at a rest area, and slide the tongue back to shorten it.... when you get off, stop and move the bolts to lengthen if for city travel...

Since the worst mileage is on the highway, I think it has good possibilities..

On my new on, the front of the tear body will only be 2.5 feet from the rear of the van.. just enough to get the hatch open...

But I'd bet I could get it closer than that for open road, mostly straight line travel.

[brian_bp]

The extensible tongue idea is not all that radical. I've heard of boat trailers which extend to allow launching without dunking the tug so far, and retract for towing. The "slider" fifth-wheel hitches do the same thing from the other side, moving the hitch trailer back in the truck box for better clearance when parking, and forward for towing (to get the weight over the axle); some of them move with the change of angle between tug and trailer (not speed).

I wouldn't want any manual movable scheme which would have me towing in configuration which would restrict my turning angle, either for unexpected sharp turns, or in a way which would make it likely that in a severe avoidance maneuver the trailer would jam against the tug.

[Seanie]

Here in Australia, the speed limit is around 60MPH- with main highways about 68MPH. (that's 100KMH/110KMH)

I'm amazed at the speeds you guys tow at! I generally like to keep to 55MPH, & 60 out on the highway. If that's not fast enough for people, they can pass. There's always secondary roads anyway. I wouldn't tow anything over 60, & I've driven all kinds of vehicles & towed all sorts.

I agree with Sam- the best way to improve fuel economy is to just slow down.

Anyway, if you want to go fast- buy a motorcycle!

[asianflava]

Most highways have speed limits set to 65MPH (105KMH) which means everybody travels at 70MPH (112KMH) because the law officers usually give you a 5mph leeway. Some of the desolate highways in West Texas have a speed limit of 80MPH (128KMH) I kept to 70MPH to reduce my fuel consumption.

There are some states like California that limit any vehicle towing a trailer to 55MPH no matter what the highway speed limit is.

[gyroguy]

There are other drag producers to consider that haven't been mentioned.

VENTS: Many tiny trailers have a 14" square or 9" square air vent on top of the trailer. This spoils the airflow over the trailer and causes vortices and turbulent air that spread out behind and at an angle toward the sides.

RACKS: A rack on top of the trailer produces drag much larger in proportion than the size of the roof rack tubing would suggest. Things get much worse if you actually tie anything on the rack.

ANTENNAS: A radio antenna also causes drag.

TIGHT CURVES: So does a small radius curve, like the one at the junction of hatch and roof on my trailer. Andrew is right, there would be airflow separation there. But as I said, the drawing was theoretical.

TIRES: On the sides, probably the biggest cause of drag is tires.

FENDERS: Rounded fenders can decrease tire aerodynamic drag somewhat. The old-fashioned rounded fenders that extend backward to a point would be best. But to be most effective, the fenders would need to be three times the tire diameter in length... not possible on a teardrop.

SMALL THINGS: Little things like doorknobs, clearance lights, and windows also add drag and produce vortices that create turbulent air and drag.

SMALLER THINGS: Littler things like rivet heads, edges of bent aluminum angle at the top and sides of the trailer, and piano hinges are great drag producers.

When you look at drag reduction, you have to look at ALL of the trailer.

Despite my efforts, the Crocodile Tear is aerodynamically a draggy little trailer. The one saving grace is frontal area -- 16 square feet -- which makes it possible for my small pickup truck to tow without overheating.

I'd be interested in seeing a discussion on reduction of rolling resistance of tires. My thought was to over-inflate the tires, but the benefits of reducing rolling resistance probably wouldn't compensate for the cost of uneven tire wear. Or would it, with higher fuel prices?

FYI, just completed a 3,500 mile trip with Crocodile Tear. I'll start a new topic, "3,500 miles in a TTT."