Originally published June 1992
Before I get going on this month's topic, I'd like to pass along another material source to you. Woodworker's Supply, Inc. at 1-800-645-9292 has an outstanding collection of woodworking tools and supplies. The really interesting thing is the selection of sandpaper. From 4-1/2" width and 10 or 150 foot rolls to sanding belts up to 50" by 103", they seem to have it all. So, if you are sanding a wood or composite surface and want a REALLY BIG piece of sandpaper, then give them a call. The catalog I got says $2, but they will probably send you one if you call them. I'll bring the catalog to the next meeting for any of you who are interested.
What I have for you this month is a hinge. That may not sound like the most riveting topic, but once you see it I think you'll find it quite interesting. I found this hinge when I ordered some European style hidden hinges for the entertainment center I'm building. When I got the hinges and looked at them, I saw a great mechanism for the double slotted flaps I wanted to put on my airplane. I had given up on the idea after looking at other applications, like the Cirrus. The large aluminum flap tracks hanging out the bottom of the wing didn't appeal to me, both aesthetically and from a drag standpoint. I've included an drawing of the hinge and I'll try to explain what makes it work. As you can see, there are two mirror image sections to it. Each section contains a straight slot and a pivot point. The two sections are connected by links that are pinned together in the middle by another pivot point. In the drawing, the circles are the main pivot points. The dark squares in the slots represent a sliding and pivoting point that could be something as simple as a dowel in a slot. Also please note that the links don't have to be the shape that is shown. They are shown this way for clarity. They could be any shape that connects the required three points.
There are several interesting and exciting things about this hinge. One of the really unique things is that this hinge will continue opening up to 180 degrees. If you wanted a flush access door that opened up as far as possible, this would do it. The other nice thing about this arrangement is that it would be very simple to build. There are no curved tracks to machine, just a straight slot. The down side is that I don't know how the placement of the pivot points and length of the arms affects the motion of the parts. If you had a specific application, it would be best to make a mock up of the parts and adjust until you got the motion that you wanted.
A few more ideas for this hinge include Norm Howell's suggestion of a canopy hinge and my other thought of using it as a gear retraction mechanism. You should also note that you don't need the right hand part of the mechanism. The left hand slide and two pivots will give the link the same movement, although the right hand slide and pivot should contribute significant structural strength.
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 22 February 1997