Aerolid mod for Trailer Towing

[slowmover]

Originally Posted by deejaaa

I also like the look. I will be more than surprised and demand a recount if there's not a noticeable difference.

It's the crosswind problem. Assuming Interstate and opposite traffic far from ones own lane, it's mainly the natural winds. Sail area and nearby opposite traffic creates deleterious crosswind pressures which produce rig wander.

[Hersbird]

In order to get the king of crosswinds represented in those pictures wouldn't they have to be 40 mph or higher directly to the side? Seems at 60-65mph with a normal 15 mph wind hitting somewhere short of directly to the side would be much less drastic. Also I was looking at an article on train crosswind analysis that shows how a big crosswind is reduced closer to the ground depending on terrain https://www.google.com/url?sa=t&sour...Uk0dCgEYsDwY_w
We will be headed across eastern Montana in a few days to try out our new modded camper but hopefully will just face mild wind conditions.

[aerostealth]

Dash pic after we left Lordsburg, NM. While we were still climbing grade to the continental divide 20 miles east of Lordsburg at 4,580 ft we had a tail wind. We often seen 13+ MPG on level ground and easily seen 15+ MPG going down slight grades we usually seen 10 to 11 mpg climbing slight grades. By slight I mean no more then one (1) degree. We seen even higher MPG figures after we crossed the divide on our way to Deming, NM (see second pic). At Deming the wind switched around to the SE and trashed our MPG's to Las Cruces, NM.

1: Filled up in Las Cruces, NM for the trip.

2: Filled up in Safford, AZ 22.081 gallons for 263.9 miles. It was actually only 205.2 miles to the park so 58.7 miles of this composite trip mileage was driving the truck without the trailer or 22.2%. Composite average 11.951 mpg.

3: Drove to Las Cruces by a slightly different route to I-10 in Lordsburg for a total of 202.5 miles using 17.93 gallons of gas for a composite average of 11.461 mpg. Only 6 miles of this leg was with the truck unhooked from the trailer or 2.9%.

4: Total miles 466.4 miles on 40.011 gallons of gas for a composite average of 11.656794 mpg. Total miles unhooked 64.7 miles or 13.8%.

Synopsis: My trailer towing mods were a qualified success. On level ground with no or little wind I seen 13+ MPG easily. Side winds, and up grade performance were usually impacted negatively with MPG figures as low as 8 MPG climbing grades. The truck's greater Peak HP and Torque output made traveling easier then my last tow vehicle which was a 270 HP 2011 model 4 Runner.

Conclusions are that a gap filler is in order to mitigate some of the crosswind effects as well as stopping the air on the sides of the truck from hitting the exposed frontal side areas of the trailer. I think I have a way to do this without using any intrusive fasteners on the trailer.

A two foot boat tail would be nice addition to this also. A faring to clean up the air around the AC unit on the roof would be a good idea also.

We are planning a trip to the Florida Keys in February 2016 which will be a plus 2,000 mile trip possibly as much as 4,400 miles in round trip trailer towing. Some kind of mods to improve the aerodynamics of this vehicle combination even further would be a good idea before this mega trip.

John Gilkison June 22nd, 2015

[slowmover]

I'm

Originally Posted by Hersbird

In order to get the king of crosswinds represented in those pictures wouldn't they have to be 40 mph or higher directly to the side? Seems at 60-65mph with a normal 15 mph wind hitting somewhere short of directly to the side would be much less drastic. Also I was looking at an article on train crosswind analysis that shows how a big crosswind is reduced closer to the ground depending on terrain https://www.google.com/url?sa=t&sour...Uk0dCgEYsDwY_w
We will be headed across eastern Montana in a few days to try out our new modded camper but hopefully will just face mild wind conditions.

A 3/4 crosswind is the worst for fuel economy. As winds aren't ever perfectly steady (let's call the use of cruise control the vehicular version of "perfect" speed control as the computer works from inputs formulaically) a vehicle at a perfectly steady speed on otherwise ideal road surface will have the combined steering inputs and engine fuel burn rate vary in both degree of force, and duration. In other words, it starts to upset itself on top of outside forces.

If a person wants an FE version of why to stop every two hours for a break, this is it. The hardest thing a driver resists is fatigue. Fine motor skill declines throughout the day. It cannot be denied, but it can be delayed.

Second, it is also the reason to use sat images or other for an RV'er to keep any extraneous steering and braking events to a minimum in re breaks and fuel stops. Planning these keeps the acceleration event tenths penalty at a higher minimum in re-entering roadway.

Crosswinds (let's call them unfavorable winds) and fatigue are unavoidable. So are a certain number of stops. With the latter planned, and the day broken into time & distance legs, the driver WILL exert more care over along day within these settings, these two-hour and hundred or so mile distances.

For example, if a group is traveling and has stopped for lunch, even if they use the restroom both at the beginning and the end of a one-hour fuel & food break, they WILL need to stop again within 1.25-hrs, not 2.0. Preferably just under an hour. This stop needs to be planned as well.

All of this is to help offset the effect of winds. They need not be strong. Add to them that with the exception of completely rebuilt Interstate, that the cross-wise undulations (the worst are ruts) of the road surface is part of steering resistance.

It would be helpful to see just how much farther per 1000-miles the vehicle travels on Interstates due to winds above the speed of X. Time lapse overhead would be pretty cool. And this figuring is part of determining road resurface, but is cited along with other factors. It is a known factor to those who advocate about roads and national oil imports. For an RVer it is pronounced in compassion to traveling solo. Closer to what a big truck experiences.

The tow vehicle travels farther, but the trailer travels even farther than it would (and always does). This doesn't seem like much, but change from a pickup with work gear steering on live axle front suspension (and the usual improper hitch lash up) and go to a truck with rack and pinion plus a VPP hitch (which locks the trailer to the tow vehicle) and the wind force plus road surface degradation has to go a lot worse that the driver can't more easily control the rig.

There is no way to offset the sail area of an RV except by initial design. Even the best trailer will travel farther over the day than the tow vehicle due to slowing, steering and winds. Those effects can be controlled, I've argued, better than they are in 99% of cases. Being painstaking and/or upgrading equipment establishes a better baseline.

So, yes, higher crosswinds are dramatic, but one is never quite free of winds. Night time is a basic exception. And one can try to offset them in planning stops, these planned deceleration and acceleration events inside a short daily leg, but they are a fact that those towing have to contend with

[slowmover]

Glad that 13+ showed up!!

On my rig, having seen that under repeatable instances I was at 15+, I am confident I will be able bring up my overall average after attending to a number of those details cited elsewhere. This combo is still new to me.

But seeing even higher instant averages (as you probably did) and the better cruise numbers overall, it's something fine to which to look forward.

I'd wager the trailer bow aero mods are worthwhile.

And what of side skirting?

I'll measure the ground clearance of the body of mine when I get home. Some of my neighbors with conventionals featuring slide outs that raze them by enough to look like lifted pickups compared to my "low rider" so those "rooms" can clear the tires. In Aeros photo above of side views of trailers, the ones shown all ride low in comparison to the ones of today

In other words, at what point does airflow under the trailer due to increased floor height become a concern worth solving?

.

[Hersbird]

I'm hopeful for 15's once I'm across the divide, I'm actually wanting 16's but I have a hard time even getting 19 not towing so I should be happy with the 14's I was getting before the mods.

[slowmover]

Clearance on mine, body to road, is 17". Walls are radiused down into full belly pan. Only axles are exposed. Comparatively long leaf springs with fairly sophisticated equalizer. Full set of shock absorbers. Cross members from spring attach points.

A representative mid 20' footer Shasta Flyte was 23". No pan. Everything exposed. No shocks, short springs and standard steel equalizer. No crossmember. Greater resistance, IOW, to crosswind pressures, not to mention larger volume of air under trailer in any situation.

[aerohead]

Here's a link to a wind tunnel test for an Airstream trailer.You can see the advantage of a tow vehicle of larger frontal area,shielding the trailer as in a NASCAR 2-car draft.
Nope,it won't allow the link.Wiind Tunnel Testing Photo by CF105 | Photobucket

[BamZipPow]

[aerostealth]

I have looked at the three foot boat tail for the travel trailer and it looks good. It could potentially reduce the rear wake area by 35%, that is from 59 sq ft to 39 sq ft. I am having a bit of trouble designing the front tapers for the trailer however. I would like the tapers from the edges steeper but to do it with one piece on each side the front would have to be too wide. Then the front could run into the truck in a tight turn. Looks like I may need a two piece/two angle side. I think this is doable but adds another complexity to the build.