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Old 01-24-2013, 10:58 PM   #420 (permalink)
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The Truck - '02 Nissan GU Patrol ST
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Originally Posted by Sven7 View Post

Updated Patrol templates... hopefully these are correct

Ideal Wagon Form by Tyler Linner, on Flickr
That's what I was thinking,
And thanks for the pic, saved both versions.

I am not trying to manipulate the concept to get a shorter tail, just trying to work out what is most right.
Aerohead has mentioned a number of times, longer is safer as skin friction is minimal, so we know the outer limit is the taper predicted by the larger dimension, usually height, if this is applied to the sides as well then we get a longer tail that should maintain attachment, but becomes impractical for real life application, except as a basis for a Kamm back.

The side rule predicts a shorter tail with the vertical fin finish, but this all works fine from top and side, just becomes an issue when you hit the corners.
You can't leave them sharp as this will lead to vortex issues, but if you merge with a good radius, then this leads to a sharper finish over the top, resulting in more than 22* when viewed from the side.

We are after something like the centre image below, I think??.
Originally Posted by Sven7 View Post
Yes, it will end in a much more prevalent fin shape in the rear, and I think this is also correct. You would want to continue the natural top-to-side (of the truck) radius along the edge of the boattail. If you change it to a larger radius the angles will be altered.

So, imagine the right form here, with radii on the edges and the sides brought together enough to form that fin.
Looking at that centre image, because it is squareish the diagonal measurement of the max camber is greater than the vertical measure, this means that the path length along that corner from tip to tail is longer than that when measured over the top, so that means the angles over the corner must be greater than those over the top.
So should the template profile be applied to the diagonal dimension which is greater than either top or side?
Is it ok to have a greater degree of curvature along the corners, because we are filling it with air from two sources, both above and from the side?,

The more I think about it the more I think this is how it should be for a basic square form profile.

A round profile like the image 1 must maintain the template curvature because it's entire surface has equal competition for the air, but the square profile has an excess, so to speak on the flatter side & top surfaces, which should allow for, and need greater curvature on the corners to give minimal turbulance.

Sorry to all, for thinking out loud, am just exploring and testing the principles as I understand them.

I am sure the template needs to be applied in three dimensions, we have length and height or length and width, I'm just trying to merge all three with the limited tools I have at my disposal.

Last edited by Tesla; 01-25-2013 at 12:00 AM..
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