Mitch,
As discussed earlier today, here’s a progress report on my boot cowl piano hinge installation.
I am using the same piano hinge that Van uses on RV-4 and RV-7 between the fuselage and the fiberglass cowl ( I know because I’ve built both of these airplanes). The piano hinge is listed in Van’s catalog with the old AN number AN257-P4. The hinge is listed in Wicks and Aircraft Spruce catalogs with the new MS number MS20257P4. These are the rolled hinges, not the extruded ones. I used this hinge because I had enough of it on hand to do the job. You could also use MS20001P4 which is the “closed” extruded version of the same hinge. All of these hinges have an open width of 1.5 inches (that’s a complete hinge with the wire holding the two halves together). Some of these hinges are supplied with aluminum hinge wire. Van recommends replacing the aluminum wire with stainless wire. The diameter of the wire used in these hinges is 0.118” Stainless piano hinge wire is available from the three suppliers previously mentioned.
A special note about using piano hinges in places where it must follow a curve: It may be necessary to file a bevel on the hinge loops so they will fit together around the curve. Also, if the curve is severe enough, as it was on the RV-4 and the RV-7, you may need to install a smaller diameter wire, 0.089” It helps to grind a beveled point on the tip of the wire so you can push it through the hinge loops without catching on the edge of a loop.
Attached is a photo of my boot cowl on the fuselage with the piano hinge installed. I used a spacer between the hinge and the boot cowl same Cub Crafters dose when they use a screw plate. You can see where I have used four sections of piano hinge. At the seam on top of the boot cowl there is a space between the two top hinge sections. This is where I intend to put an access opening in the top carbon fiber engine cowl. This access opening will be about 2.5” wide and 1” wide held in place by two screws. With the access plate removed, you will be able to insert or remove the wires that attach the top engine cowl to the boot cowl. At the left and right side of the boot cowl you will see a gap in the piano hinges. This is where the joint between the top and bottom halves of the engine cowl meet the boot cowl. I am not giving you the dimensions of this yet because I think they can refined for a better fit after my installation is completed. Okay, mine will be what it is, but the next one could perhaps be a little better.
More to follow…..
When I have it done I’ll write a complete explanation.
BTW…I did receive the engine cowl without any screw holes, just the way I asked for it.
Dennis
Boot Cowl 1.jpg