Aerodynamics

Think I hurt my knee by slapping my leg so hard.. :B

Is your goal to prevent bugs and dirt from landing on the trailer ? Or to improve fuel mileage ?

The tests I have seen for deflectors do little to help in either case.

Staying at 55MPH and using a light foot on the throttle helps to increase fuel mileage. A good wax job makes it easier to get rid of the bug guts....

the bear II wrote:
Is your goal to prevent bugs and dirt from landing on the trailer ? Or to improve fuel mileage ?

The tests I have seen for deflectors do little to help in either case.

Staying at 55MPH and using a light foot on the throttle helps to increase fuel mileage. A good wax job makes it easier to get rid of the bug guts....

Fuel mileage.

Altern wrote:
Think I hurt my knee by slapping my leg so hard.. :B

Laugh all you want, but the O.P. is right on the money....



Source

Thanks Francesca, that is the one I was looking at. Another had a scoop on the bottom of the trailer pushing air into the vacuum. Some 1/4" plywood and fiberglass resin? The bugs are not the problem, just an indication of where the air hits the trailer.

Altern, can I send you an ace bandage? LOL

The costs for truckers work out because they drive 200-250K per year.

The under skirts on trailers give 0.3 to 0.4 mpg improvement under 65 mph, about 0.1 to 0.2 mpg at 75 from what I read. If you put eight thousand dollars into a trailer, you might get 0.7 mpg improvement.

If you run 250,000 miles per year at 8.1 mpg vice 7.4 - you burn 2,919 fewer gallons of fuel @ $4 per gallon - you save $11,676 dollars per year. A trucker can also save about 0.25 to 0.3 mpg by going to wide fat rear tires rather than duals - at about $1,200 per axle.

If you tow 25,000 miles per year - a 0.7 mpg improvement is a savings near $1,676 per year.

Dropping your cruise speed from 70 to 60 will save about the same amount, to 55 another 0.6 to 0.7 mpg.

Good point PawPaw. But if I put one hundred dollars into a trailer instead of eight thousand, pulling 12k a year, would I expect to see the same .7 mpg resulting in $500.00+? I currently cruise @65 mph.

Any dollar we don't put into the pockets of the oil companies is golden!

From what my trucker friends have told me the goal is 1 mpg, and almost none have reached it. But one reason the trucks get better mpg is the things they use are engineered for minimum weight. The truck deals are tested in computer models and eventually wind tunnels to be able to document the airflow.

The problems that no matter what they do, they are still cutting a hole in the air 8 feet wide and 13 feet tall.

So are we.

$100 is small enough to play with. You might get 0.1 and you might get 0.5, or you might actually hurt your mpg because of not engineering the airflow correctly.

Aerodynamic improvements are very complicated to develop correctly.

All I can really say is try. At worst it will cost you $100 or so and a few hours work.

Then do some controlled testing - driving the same route under the same conditions with and without the aero mods.

I'd be very interested to hear your results.

My new Flagstaff has a 'straighter' fiberglass front cap than the somewhat rounded front of my Grey Wolf. I haven't seen any real decrease in fuel mileage with a trailer 2,800 lbs heavier and 14 inches higher, but I know there will be some. I guess I haven't pulled it enough to really compare. (I track every mile I tow, fuel usage, speed average, and costs.)

I'm looking at putting a trucker type wind deflector on top of my TV. I have been able to do some measuring of towing with a bare pickup bed, with a bed rail level cover and with a cab level topper. The cab level topper gives me about 0.5 better MPG than the bed level cover and 0.7 better than the bare pickup bed.

But as I mentioned above - I got almost 0.5 mpg improvement going from 64 mpg to 58 mpg as my 'cruise' speed.

My new trailer bottom is almost eight inches higher than my previous trailer. The bottom is fully enclosed and slick. That helps minimize the impact of the additional weight - but I wonder if trailer skirts would help. However a big reason for the trailer skirts is that the bottoms of trucker trailers are not clean - the bottoms of many RVs are very clean aero wise.

I also think the rear end of RVs - all types - are badly engineered to avoid parasitic drag. Just looking at how dirt collects on the back shows you that the airflow is not clean/ efficient.

My prediction is that in 20 years - trailers and MH will look quite different because of trucker developed aerodynamic lessons.

Pure science...I like it!