Aircraft Circuit Breaker Subpanels
This page created 2/10/99
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Original equipment on the Stinson 108 included automatic resetting circuit breakers installed behind the panel. In addition to being 50 years old, these breakers do not offer the safety advantages of pilot resettable breakers. I decided to go with modern circuit breakers. I also wanted additional circuit breakers for new equipment: the GPS, Communications radio, transponder, intercom, and electric turn coordinator. Since my goal was a "nearly original" panel, I did not want to drill non-original holes in the main instrument panel for the circuit breakers. I made the choice to add a 2" deep subpanel below the main panel. I added one panel on the pilot side for switches, circuit breakers, and headphone jacks and a matching panel on the passenger side for the intercom, ELT annunciator, and headphone jacks.
The subpanels are formed from .032 2024T3 aluminum. A small bending brake is required for this job. Both subpanels are 11 inches long by two inches high. The lower flange is two inches deep and the upper flange that attaches to the main panel is 1.25 inches deep. The basic panel in cross section is, more or less, in the shape of a "Z." The subpanels sit far enough back to provide adequate knee clearance. To secure each subpanel, I have five attach points. Three 6-32 machine screws attach the subpanel to the main panel, and brackets at either end attach to the fuselage structure. The outboard bracket extends up to the same attach point used for the main panel. The inboard bracket extends forward to the main fuselage cross tube behind the panel and is attached with an Adel clamp. The support brackets are riveted to the subpanel on either end. On the pilot side subpanel I installed nine Potter & Brumfield W23X1A circuit breakers plus a switch for the turn coordinator, an avionics master switch, and headphone jacks. I have yet to do the wiring for the electrical system.
To label the panel, I purchased clear label stock (available in 8.5" by 11" sheets from an office supply store) and designed the labels using Microsoft Publisher Desktop publishing software. When printed on a laser printer, this offers an inexpensive yet professional looking solution to the panel placard dilemma. For a detailed article on this process, see the "Instrument Panel Layouts" by Steve Formhals in the September 1998 issue of Sport Aviation, page 87. The subpanel on the passenger side contains the intercom, the ELT annunciator, and the headphone jacks. If I decide to add strobe lights or other equipment later, there will be space in this subpanel for the appropriate breakers and switches.