Quote:
Originally Posted by turbothrush
Still wondering about the cabover length and will it affect the cd ?
I now have a copy of Hucho's book and I refer to his roof load info..Now it appears to me that if my camper overhangs the windshield even just a little as in #3 , it has a definite effect on the Cd. Attachment 10530
So since I don't have the major panels fiberglassed together yet I thought I could move the side panels rearward and fill in the rectangles behind the cab and live with a slightly narrower bunk... and at the same time try to get a 5 degree roof angle as Yugomodder suggested. In blue below
Attachment 10528
I may also incorporate a small molded-in 10 or 12 degree Kammback on the rear if the rear door permits ( I need a drip edge anyway )
On a side note since I hope more people use this glass/foam method . I am on my last big piece and I found you don't need any clamps at all ...just duct tape. It works great in shear. And I didn't even use the 3M stuff .What you do need is a dead flat table which you can make out of old recycled hollow core doors from Habitat Restore joined together with biscuits (no glue) Use gauge blocks or a long straight edge to keep them straight and winding sticks to remove all the twist. Mine was 13' long at one point and setup takes only minutes .Works like a charm Attachment 10529
Advice, comments and suggestions always welcome and thanks to all those who replied so far |
I'm very late to the party.Sorry!
With respect to the overhang,I suspect,that if you cantilever out beyond the windshield header,that the underside of the overhang will begin to act like an inverted splitter,directing some air under and to the sides rather than up the sloping nose of the camper.
Some of the centerline flow will displace far in advance of the shell/cab roof intersection and just go on up over the top.Streamlines below there will be directed sideways around the A-pillars and up into the void between roof and shell.
The hard edges as many members have mentioned,are sure to produce immediate separation.Hucho will have two formulas you could look at,one based on a single dimension (say width),the other,on the squre-root of the frontal area of the shell.
These would offer 'minimums' for attached flow at zero-yaw.You want as much radius as you can stand to build.In crosswinds,this is where you'll save big time.I realize it cuts into interior space so you're the boss of that.
If you do decide to push the camper out past the windshield,I would recommend that you 'soften' all the edges around the 'splitter' area.There's gonna be some wicked transverse flow,a lot of shear,a mixture of velocities attempting to marry one another,and it's a breeding ground for vorticity which may cause so much wind noise,the weather stripping and seals around windows will be overwhelmed,making a loud stressful driving environment.
If you absolutely must use the hard edges you might get some relief with VGs,used just to break macro eddies into micro eddies,altering the frequency to something you could live with inside the cab.
I used to drive a 35-ft moving van with cantilever box.You could clearly hear the sheet metal tin-canning as the turbulence was beating the s--- out of it above my head.Very stressful.
