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.
