Greetings,
There are several different ways to safety piano hinges, like the ones used on the Panther’s control surfaces, and on many other aircraft as well.
The goal, of course, is to prevent the hinge pin from migrating out. For two reasons: 1. To maintain the functional integrity of the hinge itself, and 2. To prevent a migrated hinge pin from interfering with adjacent structure and components, or jamming an adjacent control surface.
If you look at the aileron hinge pins on many later model Cessnas, you’ll often find a method where the hinge pin is cut about ¼” to 3/8” shorter than the total length of the hinge. Then the hinge eyelet on EACH end of the hinge is cross drilled with a VERY small diameter drill bit (1/16th inch or even smaller), and a very small cotter pin is installed in each end (safety wire could also be used). This effectively blocks the pin and prevents it from migrating out at either end. The upside is that it’s an easy & light way to safety the hinge pin. The down side is that because the pin is shorter than the hinge, there is nothing hanging out for you to grab on to with pliers or vice-grips if you want to pull the pin out later. With this arrangement, the pin has to be driven out using a small drift pin or a short length of scrap hinge pin. So that makes it slightly more difficult to remove the pin IF/When you ever want to remove a control surface for maintenance, repair, or to access something else.
You could also “crimp-closed” or “crush-closed” the end of ONE eyelet at one end of the hinge, and insert the pin from the other end, then use the cotter pin method above, or the bent “L” method below. I’ve seen this, and it’s easy to do, but also makes future removal for maintenance more difficult.
One slick way to secure the hinge pin is to leave it at least ¾” to 1 inch longer than the total length of the hinge, and bend it 90 degrees at the one end. Insert the pin in place, leaving the 90 degree “L” bend hanging out at one end. Then cut a short length of piano hinge from a scrap piece. Just cut off ONE eyelet (usually ½” long) from a length of scrap piano hinge material, and smooth the edges. This eyelet can be slid over the “L” portion of the hinge pin, and then the tab of that scrap piece can be drilled and mounted to the adjacent structure or skin with a small #6 or #8 machine screw and lock nut. If you really want to be a craftsman about it, you could even plan ahead and dimple the skin/spar to make the screw flush to the skin, or even install a nutplate instead of using a lock nut. It really just depends on the geometry of the location you’re working in. The advantage of this method is maintainability. It takes a little more time & planning during your build, but you’ll be pleased with yourself if / when you have to remove the control surface later. One disadvantage of this method however is that the “L” bend makes it impossible to “chuck” the pin in a drill motor to twist or spin it in or out. I’ve found that using a drill motor (at least initially) to “run-in” the longer hinge pins really helps in getting the pins installed & removed. Some very light lubricant like BoeLube or parafin wax on the pin can’t hurt either.
Finally, one variation of the above method is to install the hinge pin with an “L” bend at one end. Then find a convenient place right next to the “L” bend to drill a pair of very small holes. Then take some 0.020 or 0.025 safety-wire and wrap around the “L” bend once or twice, then run the safety-wire through the pair of holes and twist the safety wire like normal. The safety wire will restrain the pin and prevent it from migrating out. This method is easy to do and the safety-wire can easily be clipped to remove the pin / control surface for any maintenance later. So the advantage is a simple and lightweight solution. The disadvantage is that some folks may not like the aesthetics of drilling the two small holes in the skin, or seeing the little twist of exposed safety wire. And also, if the safety-wire is twisted “too” tight it might have a tendency to eventually cut into the edge of the small holes and then require some future repair work. This last method is the one that we used on our Panther, it was fast and simple and we can still remove our control surfaces if we have to. This is also an important inspection point for us on every pre-flight inspection!
Most of the Van’s RVs call for the use of piano hinges to secure their cowlings in place, especially along the longitudinal separation lines where the upper & lower halves of the cowling go together. It makes for a very smooth & clean looking finish for your cowling. And you can do this with your Panther cowling if you wanted to. I’ve seen a number of different ways used to secure these cowling hinge pins on RVs, including bending the end of the pin around into a loop and inserting a screw, or welding a tab onto the end of the pin and drilling the tab for a small screw to hold it in place. Although, I’ve read of at least one instance of a cowl hinge pin on an RV migrating out (forward) in flight and damaging the aft surface of a very expensive wooden propeller! We used screws and nutplates everywhere in our cowling. With “seasoned” nutplates & torx or hex head screws, a driver bit and good electric drill, you can have the cowling off pretty quickly.
I’m sure there are other methods that folks have used to secure these hinge pins, and feel free to be inventive with your own idea, but the above are some of the common methods I’ve seen & used.
I’d also recommend looking for related topics in the EAA “Hints for Homebuilders” videos if you haven’t already.
For example . . .
http://www.eaavideo.org/detail/video/14 ... ue&q=piano
These "Hints" videos are outstanding resources from the EAA, and they’re FREE!
Good Luck on your Panther Project!
Les Boatright
President EAA Chapter 866
Panther S/N 083 (co-builder & now test flyer)
Flying since 9/16/17 !