The Bede BD-4C is a nutty efficient airplane but, since it was designed in the 1960s, some aspects are a little dated. In particular, the plans call for the cabin to be fitted with just three seat belts: one for each front seat occupant and a single belt to be shared by the rear seat passengers. The original design had no provision whatsoever for shoulder belts though the current Bede BD-4C plans do show shoulder belt anchors, albeit less substantial than I wanted.
I updated the interior appointments, including four-point safety harnesses for each person in the plane. This blog post describes the seat belt anchors and shoulder belt anchors for both the front and back seats of my BD-4C airplane.
I started by drawing the anchors for the shoulder belts. Here is what I came up with for the front seats. I know that it’s not readable below because the lines are too thin; click on it to see a larger version.
When I showed that diagram to people and asked for feedback, universally, everyone suggested that I not use such sharp points. 🙂 I had to explain over and over again that I was simply lazy while doing the drawing and that the points would be nicely rounded off!
I drew the parts on steel and cut them out, just like arts and crafts from grade school but with steel and power tools instead of paper and blunt scissors.
Dave helped out on the sander. He is now a certified pro at rounding off the ends and cleaning up the edges. Through trial and error, he discovered that the optimal distance between his fingers and the sanding disc and he can tell you with great authority that it is more than zero inches.
When all the sanding was done, we had a dozen anchors. Here are four of them, sitting on the diagram for the rear seat shoulder belt diagram.
It was one thing to draw a shoulder belt anchor with four tabs nicely spaced apart. It was another to consider welding them permanently into position and then (possibly) discovering that the belts rubbed uncomfortably on a passenger’s neck. The solution was to sew up some webbing so that I could actually sit in the back seat. I used upholstery webbing and a sewing awl. All in all, it wasn’t too bad a job. (Sorry, I couldn’t resist.)
Once I had a single strap done, I sat in the back seat and used myself as a model for positioning the shoulder and seat belts.
At the end of this exercise, I had three of the four belts clamped into position (both shoulder belts and the outside end of the seat belt). From this, I was able to mark all of the steel for welding.
I repeated the process for the front seat shoulder belt anchor and here are the results.
With the shoulder belt anchors complete, I attacked the seat belt anchor for the back seat. This was the trickiest anchor because it runs across the bottom of the plane and “crosses” an diagonal angle brace. Nothing on this anchor is square since the fuselage tapers and the angle brace is off-center. It also has to run through the tunnel, beneath the rudder cables and the push-pull rod for the horizontal stabilator. The anchor isn’t perfect but I am pretty pleased with how it came out. Even more important, I am quite confident that it is strong.
Here is a close-up of the tricky part, the middle where the two halves of the anchor meet underneath the rudder cables and push-pull rod. The two halves of the anchor sandwich the diagonal fuselage brace.
As I said, the rear seat belt anchor did not come out perfectly. If you look closely at the outside end of the right half, you will seen that I needed a 0.25 inch spacer. I decided it was easier to “make the fuselage narrower” than to stretch the steel anchor.
Here is one last photo: all the steel outside the plane just before I cleaned the anchors up for painting.