To make the finished aluminum ribs, I decided on drawing the final design using CAD software. In order to input the curves into the computer, I needed to make more accurate templates of the tilt shell where the ribs would be attached. There are four rib sections on each side, plus one transverse rib, for a total of nine rib sections.
Being that the tilt shell is very flimsy by itself, I built a raised jig which keeps the shell in the proper shape while I work on it. If left to lie on the floor, it will droop and the fiberglass will take a set. This also insures that the ribs will be made to the correct contour and also hold the shell in the correct shape when bolted up. After putting the shell in the jig, I took the opportunity to let it sit in the sun to warm up and let the fiberglass "relax" and get used to its final form.
I wanted the ribs stiff enough to keep the tilt shell supported, and also to be able to take the force of the linear actuators. I decided on a 3" deep rib, and started laying out the ribs in cardboard. The ribs will start at the front of the tilt shell and be parallel with each other in the hinge/grille/actuator area, and then flare out to follow the original hood line. They will continue rearward until just ahead of the firewall, where a transverse rib will run parallel to the firewall and tie together the two front-to-back ribs. These photos show the early rib layouts in cardboard. The third photo is with the tilt shell positioned back on the car to check the clearance for the transverse rib. The rib will be just forward of the firewall extension "horn". The electric suicide door latches that I installed in the firewall horn will protrude through the horn and into a corresponding hole in the rib. The latches, along with the linear actuators, will keep the tilt shell closed and locked.
I then opened the assembly to the point just short of the hinge being fully extended, and scribed another line at the actuator rod pivot point. The spot that the two arcs intersect is the pivot hole location for the actuator rod. The last two photos show the completed mock-up of the hinge/rib/actuator assembly in both open and closed positions. All of the area between the frame rails is reserved for the radiator and mounting brackets. Next job is to finalize the shape and location of all of the ribs that will support and stiffen the tilt shell.
The first two photos show the hinge/rib assembly in the half-open and full-open positions. The full open position was a little too far, so I decided on something less than full hinge travel. The total travel distance of the actuator, along with the mounting position of the actuator on the frame will also dictate how far the tilt will open.
After a lot of trial and error, I located a spot on the top of the frame rail that would be the attachment point for the actuator motor. The 10" stroke actuator turned out to be the correct length. These actuators work by being either fully open or fully closed, and the mounting points have to take that into consideration. Now that I found the mounting point on the frame, I needed to locate the pivot point on the rib. Last photo shows the actuator/hinge/rib in the fully closed position. I took a pencil, put it through the rod pivot hole and scribed an arc on the rib. I'll continue this on the next entry.