Quote:
Originally Posted by ChazInMT
Here is what you want to try and do. You'll want to radius the corners of the tail extension as much as possible to help you in a cross wind. My angle may be a bit too steep, you certainly would not want to go steeper, going at less of an angle would probably get nearly the same result.
Notice how the shape starts out "Blended" into your trailer? Then it slowly curves to an angle, this is what Aerohead meant, I believe, when he said you don't want flat sides creating an abrupt transition.
I have about a 13° overall change and the back of the shape is at about 21° before it cuts off there. FWIW
Here is a link to a bigger slightly more detailed version of the same drawing as below.
Bigger Pic Of Trailer Kamm Dwg
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Thanks for the illustration. That looks like the ticket - it's about what I was thinking I guess. I understand the importance of the tail curve being tangent to the vertical of the rear of the trailer. Makes sense. Gradual transition so as not to upset the flow so to speak.
So, the 2" drop at the top due to the lights- it sounds like this is not a huge deal breaker?
Just looking at the illustration - I wonder what kind of drag reduction that will be. Appears to be such a small cross section change but if that's enough to make a significant difference then I'll roll with it.
I guess at the end of the day longer is better, but how much would the difference be if I were to jump from 60" deep on the tail to a 90" or something.
That trailer sits pretty low actually in the rear and very rarely scrapes, so the length would only be a pain getting fuel, etc. I think. Mostly highway miles, so maybe not a huge disadvantage, other than more weight and more fab time?
If I get most of the benefit from the pictured above, and only an additional few % by extending, I would then say it's not worth making it really long.
So that brings me to this question: is there a rule of thumb for amount of effective drag reduction along the length direction? As in, at the first line on the template you get 50% benefit, next line is 70%, next line is 80%, next is 85, next is 89, so on, so on?? A sort of curve that nears 100% reduction as you get closer to the 1.78x dimension that Aerohead referred to as the end point?