Howdy,
Since a picture is worth a thousand words, I don't have much to add other than this was a challenging project because this is not a true truncated cone. The 1/8 inch Baltic birch plywood facing does not like to bend in two directions at the same time. In retrospect, I would have made the spars out of 3/4 inch plywood and would have added one more rib.
Notice that I added scabs to the struts for glueing surface and stiffeners because the wind loading would cause the plywood to have excessive deflection.
Since the tow bubble is entirely closed, there is no accessibility for storage. The bubble is fastened to the adapter plate with coated deck screws after caulking the adjoining surfaces at the perimeters.
The bubble is supported by fir wood legs and tagged at the upper corners to the trailer sides. A space between the backside of the bubble and the front of the trailer is allowed to shed water.
Two coats of Woodlife, two coats of 1-2-3 Zinser primer, and three coats of Glidden polyurethane porch floor paint was used for weather protection.
The floor paint was virtually impossible to attain a smooth finish even with sanding between coats and thinning and using a painting pad.
The total cost of materials for the bubble was approximately $150.00 My goal is to increase towing efficiency by 2mpg and have better stability in towing.
Thank you for sharing this project with me.
Take care,
Maury
P.S. The plywood I beams are fabricated from one sheet of 4 x 8 Paranaply and coated with three coats of polyurethane. These make for an excellent adjustable surface and can be easily stored on a wall mounted rack.
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