Another three smaller jobs today. First was to create a pair of rudder lead outs. These will allow the rudder cables to exit the fuselage
but still ensure that the fabric covering can attach securely around the exit holes. Two lengths of 5/16" * 0.028" steel tubing were bent into shallow "S" curves. Then two steel plates were cut out from 0.040 steel sheet. The sheets were slotted to allow the tubes to pass through at a shallow angle and the tubes brazed into place. Then the plates were positioned on the rear fuselage side uprights in line with the run of the rudder cable and brazed into place. The 5/16" tubing is a perfect fit for flexible plastic brake pipe which will protect the rudder cables through the steel tubing. Note, I'm not going to use electrical earth cable for the rudder but it was convenient to use to line up the plates:-) Once the fuselage is covered, shaped plastic fairings will cover the external section of the lead-outs to create a neat finish. I still need to clean off the flux from brazing hence the scruffy appearance.Next job was to position and weld into place tabs 244 -247 which provide the mount for the strobe power pack. There will be strobe lights in both wingtips and possibly the tail (if the dollar exchange rate improves!). The power pack only weighs 1lb so won't impact weight and balance much. I positioned it just behind station 78 to keep any interference away from the radios and antenna.
The rudder cable will pass over the top of the strobe pack, but I added an additional cable guide, to the left of the picture, to make sure it can't possible touch.Final job today was to weld two plates to the fuselage diagonals just behind the firewall. These will be drilled to mount two sections of aluminium angle which will support the ends of the fuel tank. This isn't in the plans but it seemed to me that the stainless steel bands that support the tank might one day crack or the braze give way and a loose fuel tank could really spoil your day so a little belt and braces wouldn't be a bad thing.
The big decision of the last week is that I'm definitely going to go with a Lycoming O-235 engine. These are available mid-time at a sensible price, are rock-solid reliable, weigh the right amount to make the weight and balance work and as I've already installed a Lycoming in my Vans RV9A - I know what I'm doing with this make of engine. The various versions of the O-235 range from about 108 to 118hp which should give about a 150mph cruise in a Tailwind. I still can't build the engine mount until I find a specific engine as there are two types versions - straight mount, or dynafocal. The other engine considered include:
Continental O-200: 100hp, less available and overall more expensive: purchase cost, rebuild cost, TBO.
Continental O-300: 145hp, very heavy, mods to wing spars needed to meet LAA requirements, 6 cylinder so very expensive rebuild cost, reliability not as good as Lycoming
Jabiru 3300: 120hp, very light so may cause W+B problems, expensive as no significant second hand market, power developed at 3300rpm so difficult to prop to get maximum effect.
Rotax 912/914: 100-115hp, very light so may cause W+B problems, expensive as no significant second hand market, engine runs at high revs so uses a gearbox. Complex install, both air and water cooled.
Lycoming O-320: 150-160hp, mods to wing spars needed to meet LAA requirements, good value but inconsistent with my objective of building a light responsive Tailwind rather than one for out-and-out cruise performance
