Trailer mods to improve function of aerolid mod

[ChazInMT]

OK, I see now where this might work on account of being long enough to allow air to reattach before falling off, and, the whole "stuff the wake" principle.

Aerostealth is only going 2 feet back which leads me to think his top panel is just going to ride along under any air tumbling off the roof when sloped to 25°. That's why I suggest a 15° angle with a curve cause if nothing else it will smoothly direct air down reducing the amount of turbulence in the wake area and shortening the turbulent area in drag behind the trailer.

I really think the length variable is significant on this application.

[aerostealth]

Two feet saves on cost. In any case I probably would want to come up short of 4 ft because although the panel is 4 ft long the slope in reduces the actual length. I think 3 ft might be easier to build.

I moved the spare over on the back of the trailer this morning. This gives me room to U Bolt a little giant ladder to the right rear of the trailer. I can use both for attachment points to brace the boat tail.

[aerohead]

Originally Posted by ChazInMT

OK, I see now where this might work on account of being long enough to allow air to reattach before falling off, and, the whole "stuff the wake" principle.

Aerostealth is only going 2 feet back which leads me to think his top panel is just going to ride along under any air tumbling off the roof when sloped to 25°. That's why I suggest a 15° angle with a curve cause if nothing else it will smoothly direct air down reducing the amount of turbulence in the wake area and shortening the turbulent area in drag behind the trailer.

I really think the length variable is significant on this application.

My intuition is to totally agree,but I've got no prima facie evidence to back it up.And I refuse to experiment on the other guy's nickel.
Scott Funderburk,who was doing this research for his Master's Thesis did test a truncated version of GM's boat tail.

I don't have the Thesis,so,so far,the information is classified with the exception of his comment about vorticity caused by sharp edges.(something NASA never got into).
It's plausible that if the tail is truncated to 2-feet,that it will behave with a linear,or monotonic performance curve,as Hucho talks about with some mods.
Again,I don't know.And I'd never build one of these,but I'm not the boss of this project.
It is interesting that GM is using something like the 25/10/10-degree tail,with the exception of the progressive edge radii.(FKFS says this radii is good for a 16% drag reduction)


It sucks not to be a gazillionaire!
Here's a link to Scott's US Patent for a drag reducing add-on
http://pdfpiw.uspto.gov/.piw?Docid=0...iew+first+page

[aerohead]

I GOOGLED Scott Funderburk Masters Thesis Texas Tech University
It's online as a PDF file.
I printed a copy (128-pages)
He and Professor Carver used edge radii for their patented boat tail design.
On the 1/12th-scale 18-wheeler model :
*simulated 5-foot = 6.7% drag reduction
*simulated 8-foot = 17.4 % drag reduction
If the trailer had been skirted and the tail was lower to the ground they would have registered better numbers.
For RV travel trailers,there's no reason why we can't do better than the big-rigs,as we aren't held to the same regulations.
But it looks like 3' may have only a limited impact.We'll have to wait 'n see.

[slowmover]

While a belly pan on a trailer makes sense, would it be reasonable to think that skirting and a limited boat tail together might not effect a good compromise?

[aerostealth]

One thought that comes to mind is that a 3 ft boat tail on a 19 ft trailer is functionaly longer if the whole rig was scaled up in sized as semi tractor trailer rigs are much larger and longer. Also the trailer is much closer to the ground already.

[aerohead]

Originally Posted by slowmover

While a belly pan on a trailer makes sense, would it be reasonable to think that skirting and a limited boat tail together might not effect a good compromise?

If one didn't want to go the full monty,it would have to help.
The lowest drag,concept rigs always have full belly pans under tractor and trailer,but only the individual can decide how much trouble they want to go to.
I would personally promote the bellies,if not only for the reduction of splash and spray in inclement weather which can make it extremely hazardous to motorist visibility operating near the rig.
Nobody needs to run their wipers behind me on a wet road.I've got to run mine behind everyone.

[aerohead]

Originally Posted by aerostealth

One thought that comes to mind is that a 3 ft boat tail on a 19 ft trailer is functionaly longer if the whole rig was scaled up in sized as semi tractor trailer rigs are much larger and longer. Also the trailer is much closer to the ground already.

Anything back there would have a shot at drag reduction,regardless of length.Since Federal regulations allow for 4-5-feet of boat tail length,the research has concentrated on these lengths.
Here are some drag tables showing effects of aft-body mods













The dark blue area behind the trailer almost 'designs' a proper boat tail

Which was not lost on Fachsenfeld in the 1930s

But 'Regulations' don't respect physics,and these shapes are the most challenging to fabricate.

[aerostealth]

Okay, it looks like the boat tail by itself is worth at least 6% mpg improvement. The redesigned nose and an AC fairing could easily get us to 8% or more. If 13.6 were the current baseline we could be flirting with 15 mpgs. Closing the gap is going to help the composite averages a lot.

[aerohead]

Was surfing for Travel Trailer aerodynamics and ran across this homemade nose by John P. Bridge
Here's a link to John P.Bridge.com/images
http://www.johnbridge.com/images/Res...f%20nose22.jpg