Air Deflector Van + Cargo Trailer Fuel Improvement

[maurice-r]

This post is about my homebuilt air ramp or deflector and the fuel savings from it.

We are running a 2010 Chevy with 6.0 gasoline, 180k miles. Cargo trailer that I added a 9,000btu mini split, condenser mounted on front. Live in Indiana. Few years ago, step 1 was I built a "luggage rack" on the van, based on a commercial ladder rack that clips onto the gutter rail, but lowest possible to roof without paint damage.

Van not pulling a trailer gets about 13.5-14 MPG whether loaded or empty. All values as reported by Chevy dashboard, and backed up by occasional hand math from gas reciepts. Our first trip with van and cargo camper got us 6-7 MPG. About 70-75 MHP

Few years ago, we drove/towed to Yellowstone NP and Arches NP, with an 8' long air ramp made from OSB plywood and open sides. This got us about 7-8MPG and a few odd looks and questions.

This year I built an 8' long, 18" high to match the trailer, and enclosed sides air ramp, open at the back. We drove to San Deigo CA using the Flagstaff/ Yuma route. Going west empty, the best we got was 11.3 (dashboard). About 70-75 MPH. Going east, we were loaded with a family moving to Sommerset KY. From the picture, you might guess we were loaded heavy. For the eastbound trip, 65 MPH, we got 10.5 MPG.

The air ramp comes off with 6 bolts, and is stored in my barn.

My hope is that this info helps someone else. My numbers are not scientificly accurate.

[dodge_guy]

fj12ryder wrote:
FWIW, I've drafted on a bicycle behind a van, and as long as I was within about 3-4 feet of the van I was basically traveling in still air, but any further back than that, and lots of air resistance. That was up to 55 mph. That's what makes me pooh-pooh those deflectors that mount on most trucks: they're just too far away from the trailer to do much of anything, and they're at such a steep angle, they just act as another air stopper. They may throw the bugs over the top, but the wind is just going to curl back around and continue on into the front of the trailer.

IMO Maurice's air deflector looks like it would work because it ends close to the front of the trailer, and is a more gradual slope than most of those add-on wind deflectors. JMO anyway.

:R :S

[fj12ryder]

FWIW, I've drafted on a bicycle behind a van, and as long as I was within about 3-4 feet of the van I was basically traveling in still air, but any further back than that, and lots of air resistance. That was up to 55 mph. That's what makes me pooh-pooh those deflectors that mount on most trucks: they're just too far away from the trailer to do much of anything, and they're at such a steep angle, they just act as another air stopper. They may throw the bugs over the top, but the wind is just going to curl back around and continue on into the front of the trailer.

IMO Maurice's air deflector looks like it would work because it ends close to the front of the trailer, and is a more gradual slope than most of those add-on wind deflectors. JMO anyway.

[dodge_guy]

valhalla360 wrote:

maurice-r wrote:
I respect you guys who have driven tens of thousands of miles! I had not seen any air deflectors that were as gradual as the one I made. I wondered how effective the short but sharp angle style is. Such as two pictures that have been posted in this thread.

If I may ask for clarification? Of the comments of little milage difference, (both your experience and from hearing others report) are most of the air deflectors of the short length and sharp angles?

Could it be possible that a long shallow angle deflector might help milage better than a short sharp angle?

Our family members also drove a Ford F150 pulling a car hauler empty except for a small cargo trailer ON the car hauler - so top of small cargo stuck up at the 9' mark. His fuel milage was much lower than with no trailers. (I had offered to make a quick "camper shell-air defelctor" out of osb ply before we left but he said his bed cover prevented that.) He got better milage on the eastbound trip when he pulled the car hauler with a kia sedan on it and another family member drove his own F150 pulling the samll cargo.

Again I say, all of my information is from the dashboard computer, so it is not scientific.

The problem is it takes some science and testing to get something proven and effective (while not perfect, our dash readout matches pretty well when we check against hand calculations). A smooth transition is important but the biggest trick is getting the back of the wing as close as possible to the front of the trailer matching the height of the trailer front. A big gap or a drop after the cab (such as with a pickup) results in difficult to predict results.

Interestingly having done 5 east/west cross country trips over the last dozen years with different rigs, I've found eastbound typically gets better fuel economy looking at my records. When I look at the individual days runs, it correlates well with the winds conditions (most common winds in the lower 48 are from west to east). For example on the current trip we are just finishing up, we averaged 9.1MPG westbound and are at 9.9MPG eastbound. Same rig, same driving speed/style and similar terrain.

There is no question that aerodynamics can help but randomly sticking a wing on will result in random results.

Are you still trying to tell us that they don’t work. Sheesh, give it up.
We have done the trips with and without. No need to be a scientist to make the comparison.
And BTW, for some reason I have always found that traveling east always got me the same mileage as traveling west, sometimes a bit less.

[valhalla360]

maurice-r wrote:
I respect you guys who have driven tens of thousands of miles! I had not seen any air deflectors that were as gradual as the one I made. I wondered how effective the short but sharp angle style is. Such as two pictures that have been posted in this thread.

If I may ask for clarification? Of the comments of little milage difference, (both your experience and from hearing others report) are most of the air deflectors of the short length and sharp angles?

Could it be possible that a long shallow angle deflector might help milage better than a short sharp angle?

Our family members also drove a Ford F150 pulling a car hauler empty except for a small cargo trailer ON the car hauler - so top of small cargo stuck up at the 9' mark. His fuel milage was much lower than with no trailers. (I had offered to make a quick "camper shell-air defelctor" out of osb ply before we left but he said his bed cover prevented that.) He got better milage on the eastbound trip when he pulled the car hauler with a kia sedan on it and another family member drove his own F150 pulling the samll cargo.

Again I say, all of my information is from the dashboard computer, so it is not scientific.

The problem is it takes some science and testing to get something proven and effective (while not perfect, our dash readout matches pretty well when we check against hand calculations). A smooth transition is important but the biggest trick is getting the back of the wing as close as possible to the front of the trailer matching the height of the trailer front. A big gap or a drop after the cab (such as with a pickup) results in difficult to predict results.

Interestingly having done 5 east/west cross country trips over the last dozen years with different rigs, I've found eastbound typically gets better fuel economy looking at my records. When I look at the individual days runs, it correlates well with the winds conditions (most common winds in the lower 48 are from west to east). For example on the current trip we are just finishing up, we averaged 9.1MPG westbound and are at 9.9MPG eastbound. Same rig, same driving speed/style and similar terrain.

There is no question that aerodynamics can help but randomly sticking a wing on will result in random results.

[maurice-r]

I respect you guys who have driven tens of thousands of miles! I had not seen any air deflectors that were as gradual as the one I made. I wondered how effective the short but sharp angle style is. Such as two pictures that have been posted in this thread.

If I may ask for clarification? Of the comments of little milage difference, (both your experience and from hearing others report) are most of the air deflectors of the short length and sharp angles?

Could it be possible that a long shallow angle deflector might help milage better than a short sharp angle?

Our family members also drove a Ford F150 pulling a car hauler empty except for a small cargo trailer ON the car hauler - so top of small cargo stuck up at the 9' mark. His fuel milage was much lower than with no trailers. (I had offered to make a quick "camper shell-air defelctor" out of osb ply before we left but he said his bed cover prevented that.) He got better milage on the eastbound trip when he pulled the car hauler with a kia sedan on it and another family member drove his own F150 pulling the samll cargo.

Again I say, all of my information is from the dashboard computer, so it is not scientific.

[valhalla360]

dodge guy wrote:
Everyone saying that they have used one and got better mileage and you still don’t like the answer.

But not "everyone" is saying that. I know a couple of guys who added them...then a year or so later they got rid of them because it was more hassle mounting and demounting with no improved MPG to show for it.

As stated before, there is a huge amount of variability between RV configuarations and then claims with no attempt at consistent testing...if everyone got noticably better MPG, I'm sure you would see 90% of towing trucks with air deflectors...yet the exact opposite is true.

On the other hand near 100% of semis pulling standard box trailers use them. You can bet the trucking manufacturers and haul companies have tested and confirmed how to implement to get the maximum benefit but unlike RVs, it's a very standardized configuration, so easy to apply to the next truck they buy.

[LouLawrence]

If it only kept the bugs off the front of the trailer it would be worth the effort with no downside at all.

[JimK-NY]

Before going through the effort and expense, I would like to know if an air deflector was worth it. This discussion reminds me of the air whistles that are supposed to help avoid hitting deer. There have been lots and lots of studies that show no effect, but plenty of people still use them and believe they work.

I have done many tens of thousands of miles driving my RV and have recorded every drop of fuel I have used. My fuel mileage has been highly variable due to road delays and conditions, hills, speed, ambient temperature, wind speed and direction and who know what other factors. I would never notice a difference of a half mpg due to a deflector. It would take a controlled experiment with an accurate fuel consumption detector.

[maurice-r]

Admittedly, a Chevy Express van gets poor gas milage, but we enjoy our van. Our adult kids keep trying to get us to buy an SUV like them, but for some reason, they still ride with us in our 15 passenger van!

Our family did one trip with no deflector, and saw the fuel economy drop in half. I did some google searching, including here on RV.net. I saw a lot of negative comments, but a few positive. So I figured, what the hey, its just a hobby and my time; I'll try something. For us, it worked.

I was not and still am not prepared to do scientific studies. I am not selling any plans, just basically giving away my idea and example. If I have everything fastened down so that I do not present a hazard to someone else nor bring attention to our fine dedicated Highway Patrol, then why be so adamant that "it does not work"?

Thank you for allowing me a place to post my idea!

[fj12ryder]

Actually for RV's I think there are more studies that say they don't work than there are studies that say they do. So stop trying to make yourself believe it can happen!

You think they work, and I think they don't. We'll just have to agree to disagree. 🙂

[dodge_guy]

fj12ryder wrote:
"I could actually care less if you can't find the studies. If you don't believe it, don't do it. I doubt there are any truckers anywhere who have taken their wind deflectors off."

There's a very big difference between the placement of semi wind deflectors and RV wind deflectors, in fact it can be measure in feet. If you don't get the deflector close enough to the trailer, there isn't going to be much benefit. Of course if everyone agreed that they worked as well as you're suggesting, there wouldn't be a semi out there that didn't have them. But there are lots of them, so there must be a lot of delusional people out there. 🙂

And .5 mpg increase can be put down to many things, not the least being a unconscious desire to make sure the mileage is better, i.e., backing off just little bit, a little less acceleration, many things can show .5 mpg increase. A person could perhaps be delusional to think it has to be the results of a wind deflector. Sometimes the data is worked with to support the theory, rather than vice versa.

The lengths people will go through to make their point is ridiculous. Everyone saying that they have used one and got better mileage and you still don’t like the answer. Sorry, but they can and do work! Try it for yourself and see. But stop trying to make yourself believe it can’t happen!

[fj12ryder]

"I could actually care less if you can't find the studies. If you don't believe it, don't do it. I doubt there are any truckers anywhere who have taken their wind deflectors off."

There's a very big difference between the placement of semi wind deflectors and RV wind deflectors, in fact it can be measure in feet. If you don't get the deflector close enough to the trailer, there isn't going to be much benefit. Of course if everyone agreed that they worked as well as you're suggesting, there wouldn't be a semi out there that didn't have them. But there are lots of them, so there must be a lot of delusional people out there. 🙂

And .5 mpg increase can be put down to many things, not the least being a unconscious desire to make sure the mileage is better, i.e., backing off just little bit, a little less acceleration, many things can show .5 mpg increase. A person could perhaps be delusional to think it has to be the results of a wind deflector. Sometimes the data is worked with to support the theory, rather than vice versa.

[LouLawrence]

JimK-NY wrote:

LouLawrence wrote:

JimK-NY wrote:

LouLawrence wrote:
If anyone thinks that adding an air deflector DOES NOT help is delusional. Air going over a trailer vs. slamming into the top of the trailer is a real thing. How much? Can't say, but it's a reality.

How much? Got any data?

It's been working for tractor trailer drivers for years.

Again, where is the data? I could not find results of any studies.

I could actually care less if you can't find the studies. If you don't believe it, don't do it. I doubt there are any truckers anywhere who have taken their wind deflectors off.

[dodge_guy]

JimK-NY wrote:

dodge guy wrote:

JimK-NY wrote:

LouLawrence wrote:
If anyone thinks that adding an air deflector DOES NOT help is delusional. Air going over a trailer vs. slamming into the top of the trailer is a real thing. How much? Can't say, but it's a reality.

How much? Got any data?

No bug splatter on the front of the trailer means the air is being moved up and over the trailer. Also the .5 mpg improvement says it works as well!

I don't see how anyone could detect that small of a difference. It would take a precise fuel consumption measuring device and identical driving conditions. I see huge difference merely due to traffic, wind direction, etc.

Well 3 years and 20k towing miles after its use shows that it works. I did the same trips big before and after and there was always that .5 difference. Sure sometimes it may have been less, sometimes a bit more but it always averaged .5 better with it.