By Jim Twamley
Just how effective are those RV wind deflectors you see on trucks pulling 5th wheels and travel trailers? Though somewhat technical (what you’d expect from a Professor of RVing), this information could save you some serious cash.
Trucks pulling trailers lose a majority of their energy at highway speeds through aerodynamic drag. Using computational fluid dynamics, scientists study airflow as it interacts with test models in a wind tunnel. These studies have determined that in order for an RV wind deflector to work efficiently it must be within a few feet of the trailer due to the fact air flow created by the deflector closes in within a few feet unless it’s conducted by another surface. Cab extension gap seals and side fairings will help to make this possible. (From the article “On the Aerodynamics of Tractor-Trailers,” by M. Hammache and F. Browand.)
According to these scholars, the best place for an air deflector is actually on the trailer itself because that’s where the majority of the drag occurs. When you place a rounded “nose cone” on the trailer, you eliminate the gap of a cab wind deflector and the aerodynamic drag is significantly reduced. So, if you’re looking to save a bunch of money by installing one of these over-the-cab deflectors, make sure it’s as close to the trailer as possible and also install gap seals. If you don’t do this you’re throwing money to the wind.
In fact, if the gap is too large, it will end up reducing your fuel economy because you’re actually increasing the drag. The bottom line is that trailers like the Titanium brand, made with an aerodynamic nose, are more fuel-efficient than any aftermarket cab-mounted wind deflector. The more aerodynamic the trailer, the better the fuel economy. —Preventing the money from blowing out of your wallet —Jim Twamley, Professor of RVing
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When your driving around without the trailer make sure to remove the wing as it will suck mileage.
If you look at the big rigs on the highway with the aerodynamic cab designs, cab top wind deflectors, fairings between the cab and the trailer, and now the wind deflectors below the trailer and in front of the trailer wheels, this stuff is making a difference. I don’t see any advantage in the ‘wings’ you see on pickup trucks. As mentioned in the article, if it’s not close to the trailer, it’s just making money for the wing manufacturer and nothing for your gas mileage. An aerodynamically designed nose cone on your trailer is a far better aid in mpg.
These aerodynamic improvements are working for the trucking industry, the problem with the RVs is the tow vehicles and the trailers are not designed with each one complimenting each other. The trucking industry designs the rear of the cab basically the same and by adding side fairings to shorten the gap between truck and trailer it eliminates a huge turbulence between the two. The gap between the pickup and 5th wheel or worse travel trailer is huge allowing air flow several feet between rear of cab and front of trailer to enter the area creating turbulence. The market is not large enough for truck and trailer manufacturers to combine designs that would compliment each other. I have noticed over the last several years RV manufacturers have designed the front cap with a more rounded shape abandoning the 8X8 square front of years past.
You also have to look at the economics. If you can save 0.1 mpg and something costs $100 dollars, how many miles do you have to drive to pay for it? Trucks drive 100,000 plus miles a year. How many do you drive?
My non scientific testing has me believing that when I tow with my canoe attached to the top of my truck I get slightly better milage that without. Not so much better that I take the canoe when I do not intend to use it though. Maybe half an MPG at best.
Try AIRTABS…vortex generators placed around rear of flat-back trailers. I’ve pulled travel trailers and flown aircraft 50 years. Glad to finally have them available for my trailer. They reduce trailer sway when trucks pass, eliminate pull against back side and increase fuel mileage
My last RV was a Class C Greyhawk’ Installing AIRTABS made a world of improvement on highway driving. The semi’s did not bother me anymore!!!
I put Air tabs on my fifth wheel about 3 years ago. I feel the tabs may help stabilize lighter weight trailers, but mine weighs 18,500 lbs going down the road & was already pretty stable, so I saw very little, if any difference. I also noticed virtually no increase in fuel mileage in our fulltime travel over several thousand miles.
“on the aerodynamics of tractor trailers”, sounds like fun reading. Where can we find this.
Mr. Twamley, as so many of us tow with pickup trucks, using your wind tunnel testing, which is more efficient, a camper shell on the pickup box, a cover over the pickup box or just an open bend with the tailgate down?
I have a 1-ton pickup. The manual states that it is aerodynamically designed to give best mileage with no cover and the tail gate closed. I wanted a toneau cover (security and weather protection for bed contents), but after reading that did not get one. So I don’t know whether it would have been a detriment or not. I do get very good mileage!
I would go ahead and get the cover for your bed. I doubt you’d even notice any loss of fuel mileage, but the peace of mind for stuff in your bed would be well worth it.
More pictures would have been helpful.
It keeps most bugs off the front of my trailer. That’s good enough for me.
Stan, that’s how you know when your “wing” is doing a good job of deflecting. You’ll get a line across the front of your RV telling you where the air is actually being deflected. If the line of bugs is too low, increase the angle of attack of the wing. You can over do this which would cause the air to go up and over the wing and then slam down into the box of a pick up. This you don’t want.
Ah, my HiLo trailer solves that for me. It’s no higher than my van (or my station wagon back in the day) and I only lose a little mileage compared to my “aerodynamic” box trailer. Wish they were still being made.
would like to see the side fairing, cab extension gap seal, Unsure of what they are? Where can I learn about a round nose cone for our toy hauler ? I do have a wing for my truck and I think it must be helping because I only have bugs on a little bit of the front cap on each side, I believe that is the same for air flow also. Bob