Jul 17, 2015
Aerodynamic Modifications potential to improver TT (Travel Trailer) performance. How decreasing the coefficient of drag for a box trailer could reduce fuel consumption when towing it.
As many of you know last September (2014) my wife and I bought a Ford F-150 PU with the idea in mind of buying a 5th wheel travel trailer in the near future because we wanted more room. In November of 2014 I traveled to Little Rock, Arkansas to buy a Brett Herndon Aerolid Camper Shell for the 6.5 foot bed of our new truck to improve the aerodynamics of the truck. At that time I also bought a boat tail for the Ford truck which fits into the receiver hitch of the truck for road trips.
Our current TT (travel trailer) is a 2011 Apex which we bought new. It became immediately obvious to me that the aerodynamic shape of my new tow vehicle was far from idea when I hooked up Apex to take it down to the local Propane Company to have a gas leak fixed in the switch over valve. The very act of bringing the air back together behind the truck to reduce drag increased the drag when towing my TT because this now focused air ran strait into the relatively flat front of Apex, increasing the drag of the trailer itself.
In June of this year we were planning a trip to Roper Lake State Park in Arizona, which is about 220 miles from our home in Radium Springs, New Mexico. Since the Aerolid has a large rather substantial lift gate I decided that the addition of some fixed struts to hold the lift gate up in the air so that it would be pointing at the top of the trailer. It would have the potential to reduce the drag problem of our trailer when used with our truck and Aerolid combination.
In late April 2014 I set out to fabricate aerodynamic modifications (mods) to my Aerolid.
After removing the regular gas struts I added two fixed struts to the lift gate which held it higher up in the air. Then I fabricated two triangular shaped panels to fill in the sides of the Aerolid to stop air from folding into the bed of the truck. I used 1/2 inch foil backed foam board as a substrate for fiberglass to make them more rigid. These panels were not only trapped by the lift gate but were also U bolted to the the struts to stabilize them. Then I added two more cross braces in the rear to stabilize things against lateral movement.
My aerodynamic mods were a qualified success. On out trip to Roper Lake we seen mpg figures of around 13.6 mpg under ideal conditions. By that I mean little or no winds and while traveling on level ground. Head winds of course reduced mileage and tail winds helped it. Truck/Trailer performance was very sensitive to not only the wind vector but to grades of course. What I did notice which I felt was significant however, was that even a modest wind that was quartering reduced performance more then you might think. Quartering or side winds were getting into the gap between the tow vehicle and the trailer and causing vortex shedding on the opposite side of the trailer inducing drag. Such winds would also would do this on the windward side of the rear of the trailer.
It was plainly obvious to me that modifications were needed to the the trailer to not only fix this problem but to reduce the drag of the trailer itself.
Two major problems need to be addressed. One, the gap between the truck and trailer is too large. The addition of a fascia to the front of the trailer would not only reduce this gap, but also could help guide the air around to the sides of the trailer not allowing the air to impact the front of the trailer itself. While the trailer is more inside the shadow of the truck then it was there were still two areas on each side of the truck where air could impact the front of the trailer. These areas were only about a foot wide but significant in inducing drag. Two, was to add a boat tail to the rear of the trailer to reduce the wake area of the trailer itself.
Other worthwhile projects would be to panel in the underside of the trailer and to fabricate a shroud to go around the AC Unit on the roof. The total frontal area of the trailer is 62 square feet which my planned modifications could reduce to 35 sq ft. This is less then the frontal area of the Ford F-150 truck itself which from the manufacturer amount to 36 sq ft.
We are planning a trip to Big Pine Key Florida in February 2016 to attend the Southern Cross Star Party held there every year. I wanted to see some of the southern stars and deep sky objects not available from my home in Southern New Mexico at 32 degrees latitude. At The Southern Cross Star Party we would be able to see 8 degrees more sky which would be very significant given we will have an ocean horizon there. While a dream trailer vacation for us the 4,240 mile round trip would consume over $1,000 worth of fuel at 10 mpg and $2.50 a gallon. At 15 mpg we would only consume $700 worth of fuel, if this were possible due to aerodynamic modifications.
This is my project in the coming months which I can devote around $300 to at a minimum. I will start this week by taking the Aerolid off the truck and hooking up Apex for a test run to determine the baseline performance of this truck towing my trailer with a open bed. This is after all how most truck owners would tow their trailers and this performance figure will be what I use to determine what my mods are really doing.
I have included links in the body of this article to the Ecomodder website so you may view pictures and text of the work I have already done and discussions of proposed trailer mods. I am budgeting $400 total for this project and need to have it done by January 2016.
The other thread you may want to look at is the discussion of why RV Manufacturers do not include these kinds of modifications to their trailers to improve their product performance? I do not know, but if amateur like me tinkering in his garage can improve the performance of their trailers by up to 33% spending less than 2% of the purchase price of the trailer, it really does beg the question of why don't they address these high drag form issues in their product.
I will be publishing more blogs on my progress in buildings these aerodynamic TT Mods in the near future so watch this space. We of course will not be able to post a results article for these mods until after our trip in February. We also plan on posting results on RV websites after we have something to report that can be useful.
One final note, the planned modifications should make travel easier simply by reducing fuel stops to once a day for my 36 gallon fuel capacity truck. If I want to travel over 400 miles a day to get to Florida in five days I would only be able to make 320 miles before refueling at 10 mpg. At 15 mpg I could make 480 miles before needing to refuel. This is a important issue for any RV'er. Watch this page for further reports as this should get interesting. P.S. No one has really made all these planned mods to a Box TT before so we will be in uncharted territory. TrailerTopia for sure, we are hoping.
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