Europa #435 G-RODO Build Journal - 2010 12

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2 Collect Herga vacuum switch from Jane across the road - it was delivered yesterday but I wasn't in to sign for it. Looks fine and operates audibly on a gentle suck. Edit main circuit diagram to show vacuum switch for hourmeter. Looking at the MGL documentation, it seems the tacho input for the E-3 instrument comes from the ignition module, not the alternator where the UMA tacho connects. Think I need to get another (guarded?) switch for trim isolation. After looking again at Bob Nuckolls' discussion of the subject, decide I don't really need an avionics master switch, so take that out of the circuit diagram. Will need a 5A circuit-breaker for the crowbar circuit. Add the crowbar to the main circuit diagram and save as V3. Add fuses in alternator warning light wires. Could do with a good toggle switch for autopilot disconnect. Check out the stock of aluminium offcuts and find a piece of twin-channel extrusion from the old double-glazing that seems perfectly sized to guard the mag switches, and can be cut down for single switches such as autopilot and trim disconnect.
3 Order 5A breaker for crowbar plus some switches, terminals, etc from Parts For Aircraft. Add power outlet socket to circuit diagram.
6 Dorothy helps to check the squareness of the fuselage rear bulkhead, measuring from each side at the height of the piano-wire to the centre datum on the seat-back. Both measure 2407mm. The outside temperature is about -2C and the fuselage rear bulkhead is outside the insulated area of the garage. Will have to build a tent for the layup around it, but for today do some metalwork instead. Cut off about 30mm of the aluminium extrusion, cut off the unwanted flange at the back and square the ends on the mill. Check switch measurements again and note the contacts are rather close together if the switches are butted up. That would be at 19.5mm centres. Check the extrusion again and it should be OK to go to 20.5mm centres, allowing for a piece of paxolin or fibreglass between the switches. Mount the extrusion upside-down and make 12mm holes with a slot-drill in the milling machine. No need to mark out, just count in from the edges. Find a piece of 5mm aluminium plate for the starter switch adaptor. Drill 1/2" and open it out slightly to mount it on a 13mm milling arbour (with a sacrificial aluminium washer under the securing screw) on the rotating table and use a 10mm slot drill to trepan out the shape. Make a notch with a 3mm slot drill. Take it off the arbour and find it needs a little off the thickness, so put in the lathe and skim off about 1mm. Try for size in the mag-starter switch hole in the panel. A bit tight, so will need further fettling.
7 Order arrives from Parts For Aircraft. Check operation of switches with LED in toggle and they are fine. Slightly more robust-looking than the ones from Maplin. Check again the dimensions of the starter switch collar and the hole in the panel; seems I have made the boss slightly too large. Put it in the lathe and skim about 1mm off the diameter of the boss. Now it fits perfectly.

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