All in one compass mount and instrument panel access cover
When I started working on a customer’s instrument panel, I had a difficult time finding a location for the magnetic compass that was free from magnetic interference. I originally placed the compass above the engine monitor, but when I powered up the instrument panel and the other electrical systems for the first time; I wasn’t happy with the compass error. To correct this issue, I decided to place the compass as far away from the electrical wiring as possible. I mounted the compass on the glare shield in a carbon fiber mounting bracket. This bracket served a dual purpose. The carbon fiber compass mounting bracket cleverly disguised the instrument access panel. Since the rear of the Zodiac 601 instrument panel is nearly impossible to access without a removable glare shield or some other devised method, this dual-purpose compass mounting/instrument access panel served me well.
Here is the procedure that I used to fabricate the dual purpose compass mounting bracket. The carbon fiber layup procedure will help you fabricate or finish the few fiberglass pieces on the Zodiac 601, such as the tail tips or the engine cowling. A list of fiberglass supplies that will be needed for the project has been compiled at the end of the blog.
- Layout the instrument access panel- Temporarily Cleco the aluminum glare shield in place, use a ruler and a small tipped marker to mark out the instrument access panel cutout.
- Release tape- Add some release tape to the top of the instrument access panel, so that it extends well past the marked out area. Clear box tape is an excellent release tape.
- Wet layup- Cut out several layers of carbon fiber or fiberglass. Mix up a small cup of epoxy resin. Use a small, disposable paint brush to paint some epoxy on the top of the glare shield. Apply the cutout layers of fiberglass to the glare shield one at a time. Wet out one layer of fiberglass at a time until no more bubbles remain.
- Peel ply- Always finish a composite lay up with one layer of peel ply. Be sure to wet out the peel ply using the same procedure that you used to wet out the fiberglass. The peel ply should be “peeled off” from the top of the dried fiberglass. Peel ply provides a slightly rough, sandable surface. After the layup has dried, pry the instrument access panel from the top of the glare shield. Turn off the lights in your shop and quickly yank the peel ply from the top of your project for some entertainment. The build up of static electricity produces tiny sparks.
- Compass m
- Bonding the compass mount to the instrument access panel- After waiting for the lay ups to dry, sand both the instrument access panel cover and the compass mount to the desired shapes, cut out the compass viewing hole, and drill the compass mounting screws. Mix up a small batch of epoxy and enough flox until the consistency of the mixture resembles cooked oatmeal. Apply a small amount of flox to the bottom of the compass mount and stick it to the top of the instrument access panel. Apply enough pressure to squeeze out some of the flox. Use a gloved finger to spread the excess flox along the edges of the compass mount to form a radius. Remove all excess flox from the surface of the instrument access panel using an Acetone soaked cloth.
- Finishing- Sand the radius until you are happy with the look. Rough up the entire surface of the project to facilitate bonding of any filler. Mix up and apply filler where necessary in order to smooth over any imperfections. Allow the filler to dry, finish sand the project.
- Priming- A good quality, sandable primer that contains UV protection should be used to protect the fiberglass. The UV protection in the primer does not necessarily protect the fiberglass from UV rays; it protects the primer from breaking down. You will want to apply enough primer coats, so that the primer blocks all visible light from reaching the fiberglass.
- Aluminum cut out- Remove any remaining release tape from the top of the instrument access panel. Carefully cut out and debur the edges of the hole. Drill at least four mounting holes and rivet on nut plates where appropriate.
- Top coat- Apply a top coat over the primer to match the glare shield.
- Install compass and compass
Following this procedure will produce a beatiful, dual purpose product that should significantly reduce the magnetic interference that affects your compass.
Here is a list of fiberglass supplies that will be needed for this project:
□ Small, disposable paint brushes.
□ Small disposable mixing cups.
□ Tongue depressors (used for mixing).
□ Box of thin, disposable rubber gloves.
□ Acetone or similar solvent.
□ Good two part epoxy (can be purchased from Aircraft Spruce and Specialty).
□ Bag of flox.
□ Filler.
□ Good quality hand sanders.
i. 1 Small, soft, foam Velcro-backed hand sander.
ii. 1 Small, hard Velcro-backed hand sander.
iii. 1Long, large Velcro-backed hand sander.
□ Rotary air tool sander with various sized disks and cutoff wheels make composite work a synch (not required).
□ Roll of medium weight fiberglass or carbon fiber.
□ Roll of peel ply.
□ Roll of clear box tape.
□ Appropriately sized hole saw (hardware store).
□ Appropriately sized drill bits.
□ Good quality sandable primer that is compatible with the top coat paint of your choice (UV protection recommended).
□ Box of comfortable paper dust masks.
□ Nut plates.
□ Rivets (for the nut plates).
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Nick Helsper
Avionics Engineer
Airframe and Powerplant Mechanic
Experimental Aircraft Builder’s Assistant
http://nickhelsper.blogspot.com/
