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Old 01-26-2008, 11:06 AM   #35 (permalink)
bondo
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Thanks Chris D.,

Finding an existing camper shell to modify is a good idea. My first aero cap was done this way. I cut out the roof, except for about a foot of the forward section close to the cab roof, and then cut the sides at an angle. I include some pictures of it, one next to the clay model of my present lid. Study that picture. Notice the roof of white one, the one I made from a camper shell, has an abrupt change in angle from the roof of the cab down related to the roof of the early aero cap. This is because I used the roof of the camper I cut up for the roof of the aero cap. This made the roof too flat for an optimum aerodynamic shape, causing the air to separate from the surface of the modified aerolid too soon, causing drag. This resulted in only a slight improvement in fuel efficiency.

I want you to know this so when you make your lid, don't use the roof of the camper you plan to modify. Cut the sides of it down at an angle and then cover the open roof with 3/8 inch plywood built upon a framework which will cause the plywood to curve some so the airflow will be better for you. You want to construct it to where the perimeter of the ply wood roof is flush to the lower camper shell you have cut at an angle on the sides. You can then use 3M brand masking tape to fill the seams and gaps and then wax it all with a special wax you can get from fiberglass suppliers. Also mask and tape off the camper part underneath because you are about to lay up fiberglass and it will get all over it. Wax the plywood at least fours times, wax on wax off. Then paint or spray the waxed plywood with PVA which is available at fiberglass supplier. Allow this to dry completely.

If you are not familiar with fiberglass, see if you can find someone who is. It is not that hard to do but fiberglass can be very messy and dangerous. You them want to lay up 6 layers of 1.5 ounce fiberglass mat over the plywood. Do one layer at a time wetting it out and rolling out the air bubbles with rollers. Best to use 1/2 inch by three inch rollers avilable at fiberglass supplier. After fiberglass cures, brace it up with a plywood frame before you release it from the plywood roof you have just cast. Glass the plywood frame in place with strips of the 1.5oz fiberglass mat.

Next pull the new fiberglass cast off of the waxed plywood curved roof. This is your mold. From this you can cast your new aerodynamic roof for the modification of the camper shell. Be sure to wax the surface of the new mold several times and paint or spary on PVA and let it dry before you cast the roof which should be 4 layers of 1.5 oz mat or 2 layers 1.5 oz mat one layer coremat and one last layer of 1.5oz. Let cure and strengthen up roof by glassing in 1/2 inch thick urethane foam. This is best done by cutting a center strip of foam flanked by a right and left strip of foam which continiunes the full length of the roof in the inside. Stop the center section a bit sooner if you plan to install a rear window. After it is braced, pull the cured roof from the mold and cut to fit the lower camper part. Finish the top with bondo and surface prime and paint. You may want to install hinges so you can raise your roof. Hydraulic struts are good too, but you need to make sure they are mounted at the right point and there is suficient structure to handle the stored enery of the struts.

I know this sounds like an impossible task, but it can be done if a dumb old country boy like me can do it. It would be wise to enlist the help of someone who has done fiberglass and mold making if you yourself have limited experience.

I submit one last photo of a flow visualization test of my lid with tufts of yarn. It shows attached air all the way down the roof of the aero cap. This is what you want to accomplish. Your reward will be enjoying the fuel savings.

Best of luck to you and I hope this has been helpful.

Brett

PS - If anyone drives a 1997 to 2004 F-150 with a spacecab and a 6.5 foot bed, if you want the old aero cap I will give it to you, You'll just have to come get it in Arkansas.
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Last edited by bondo; 01-26-2008 at 11:15 AM..
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