Quote:
Originally Posted by hotrodf1
Sorry for the delay on the pics. They aren't great but do show the trailer and the start of my framework.
Aerohead - I didn't know that 50% was a less than ideal number. Got it from widipedia. Perhaps not a great source, but when I searched for Kamm back that's what came up first, so . . . .
I kind of thought it seemed "too easy" to get there. Was planning on making it deeper, but then at 50% cross section and 15 deg. it was only 44" deep on the hypotenuse.
Anyway,
The piece was going to start out with straight corners since the corners on the trailer are straight anyway. Does this make sense or not? Could have easily used the bender to make them 6" radius curves.
The rear of the tail was going to just use the curves that the bender produces (seen in photo). I guess that's probably not enough curvature to make the most of it.
Thanks for the heads up on the template. that's what I needed yesterday but I didn't know what to look for. I'll look at that before I go any further.
Let's see if these pics will show up from photobucket.
First the trailer
Then the rear section of frame.
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Wikipedia as a data source is way out ahead of nothing,but we've been able to go straight to the horses mouth through original publications.
The 50% 'thing' originates with a 'practical' length issue,when considering traffic and driveways,and parking.
Also,Koenig-Fachsenfeld's model (of which Kamm is given credit) would suffer a ground-strike exactly at the 50% point due to the 10-degree departure clearance angle.So he just lobbed off the tail there,and added an inflated boat tail to get it out to 80% when out of town.
If you look at the 'Template',you see that there's essentially very little curvature at all where the tail begins.This is essential for high performance.If you just jerk the body into an arbitrary angle, boundary layer separation will be triggered right there and you're basically screwed.
NASA did a relatively primitive boat tail behind a Ford Econoline but respected the subtle beginning curvature.There are images of it online and here at EcoModder somewhere.
If I were doing your trailer,I'd use the height as the layout parameter,since the trailer is wider than it is tall.the With the imaginary end-point 1.78X of the heigh behind the trailer.
Your 50% frontal area point would be at around 51% of that dimension. Kinda 'long.' This is why Don Burr started his curvature 'early' on his trailer so it wasn't all 'behind' the trailer.
The final length is something you'll have to determine.I would recommend a short but proper chopped-off tail section over an 'aggressive' but 'dirty' longer tail.
I use an EMT bender to make small incremental bends of large radius.
Harbor Freight has a nice entry-level tubing bender at reasonable price.If you have any awning companies in your area,they can do perfect curves and might take on your work at a reasonable fee.
If the lengths scare you off,let's talk about DR Miller's idea.