15th March 2009 - Fuselage top complete

First job today was to match drill aluminium angle supports to the steel plates to support the bottom of the fuel tank. First the fuel tank was installed and 2/3rds filled with water to weight it into position. Then the angles were clamped to the mounting plates and drilled for 3/16ths bolts. The angles will have rubber strips glued to them to cushion the tank edges and are only designed to really support the tank if the main straps gave way.
Next job was to braze the supports for the left and right top fuselage stringers. The middle ones having been installed previously - http://tailwindbuild.blogspot.com/2008/11/3rd-november-2008-tank-straps.html
Note the offset of the bottom of the rudder to the left of the aircraft compared to the centre stringer to counteract engine torque. In hindsight, for esthetic reasons, I should probably have also offset the central stringer but I don't suppose this is a view which will often be seen in the finished aircraft. Then the panel that closes the gap between the rear of the windscreen and the fabric of the fuselage top was match drilled to it's support tabs. Finally the windscreen was drilled for the tank filler cap using a holesaw through the jig made earlier http://tailwindbuild.blogspot.com/2008/11/5th-november-2008-installed-fuel-tank.html This was done in a slow turning hand drill and then the hole sanded smooth to ensure that there are no stress risers that can propogate cracks.
This means that the top surface of the aircraft from the firewall back is now structurally complete and ready for painting and covering. Next on to the sides.

14th March 2009 - Rudder cable lead-outs, engine decision

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

13th March 2009 - Autopilot servo

I was out of the country last week so no progress but I've got no excuses for the next few weeks. While I was away I started making a list of the tasks to complete the fuselage structure but when it got over 50 I gave up and decided it was more effective to just get on with building so today I did just that. First, I final welded the rear spar attach brackets. I've been puzzling whether to do these now as the plans suggest leaving them until the wings are attached in order to set the wing incidence. However, most people build the wings before the fuselage so need to do the adjustment at the attach brackets. I've decided to match the wings to the fuselage rather than the other way round. Once I'm ready to build the wings I'll level the fuselage precisely set out the spars supported as though built into the wing structure and then match drill the wing spars to the fuselage. I can use a laser level to set the spars before drilling. In this way I can both make sure the wing incidence is perfect and also make sure the flap torque tubes clear the upper longerons before the wings are built - that's the theory anyway! It was also easier doing this fairly tricky welding before the area gets any more cluttered.
Second job was to create the mount for the wing leveller autopilot servo. I'm using a Trio Ez Pilot, same as in my RV9A. This unit is fairly competitively priced and works superbly. What does an aircraft with no engine, propellor, wings, or covering need? an autopilot obviously. Actually it is convenient to do all these sorts of jobs while the internal structure is fully accessible. First a attach bracket fabricated from 0.071" 4130 plate was cut out, drilled, and welded to the aileron control horn. The three holes drilled in this will allow the sensitivity of the autopilot to be tuned. Tabs 240-243 were then welded to the rear of the lower cross member under the back of the seats and to the diagonal just behind this. Two pieces of 3/4" * 3/4" * 1/8" aluminium angle were then cut to sit on top of the cross member and diagonal and match drilled to the tabs. Next the autopilot servo was positioned to allow a straight linkage from the servo horn to the aileron horn and match drilled to the support angles. Finally the servo pushrod was fabricated from 1/2" aluminium tube as per the instructions for the autopilot. Note the large washers under the bolt heads that connect the ends. These ensure that even if the Heim joints fail, the pushrod will be retained on the bolts. The Trio instructions call for a control throw of 1.5-2.4". I've got 2" so that should work well.

27th February 2008 - Empennage metalwork complete!

Yesterday I welded the control horn onto the left elevator, cleaned up the flux residue from brazing and welded the elevator hinge support tubes to front of the rear spar of the left horizontal stabiliser. Then 120 degree arcs cut out of some 7/8" *0.058" tube were welded either side of the hinges on the elevator spar to locate the hinges and set the clearance between the elevator horn and the tip of the horizontal stabiliser.

Today, I fabricated the ribs for the left horizontal stabiliser (HS) out of the usual 0.019" thick 3/8" rectangular steel channel. These were tack welded onto the stabiliser and then brazed to complete the joints. I had just enough channel left to complete the job and even had to butt weld two short sections together to make the final lower tip rib. Once the horizontal stabiliser was cleaned of flux residue it was time to mount both stabilisers and elevators onto the airframe. I had previously drilled the right HS front mount plate for a range of incidences as recommended in the plans http://tailwindbuild.blogspot.com/2008/08/7th-august-2008-setting-up-hs-incidence.html. This time it was a case of drilling matching holes on the left side. This was done by bolting the right HS into each hole in turn, ensuring that the two HS leading and trailing edges were exactly aligned with the two elevator horns bolted together and then drilling the left mount plate. The proposed position of the HS for the first test flight is 1 degree of negative incidence. This will then be adjusted to obtain cruising flight with no elevator deflection and zero elevator trim force.

After checking that the elevators moved smoothly, without any binding and with the full control range of 30 degrees up and 25 degrees down they were then removed and the airframe returned to the workshop. Next job will be to complete the left fuselage side with stringers, aluminium cheeks and the over-door fill panels.

24th February 2008 - Left Elevator

It was warm enough to work without any heat today so a good opportunity to build the left elevator. First the elevator horn was welded up (top of the first picture) and partially filled with molten lead to balance the finished elevator. I used the same weight as in the right elevator which resulted in a slight nose heaviness which should be counteracted once the elevator is covered and painted. Then the structure was jigged on the building board using drills to set the centre of the spar 1/2" off the board to provide clearance for the hinges, 1/8" under the spar, 5/16" under the 3/8" tubing and 1/4" under the 1/2" tubing. With everything aligned the various components were then half welded to the spar. The frame was then turned over and the welds completed. Next the stainless steel trailing edge was brazed to the frame. The elevator has 4 ribs each made of two pieces of 3/8" rectangular 0.019" wall steel channel. I found a neat way of fabricating these. First the ends were tapered over a 2.5" length using the band saw. Next the forward ends were placed between two jig blocks 3/4" apart to set the spacing for the elevator spar. A nut which was 5/8" across the flats was then slid inside the channels and located about 2" from the jig blocks. A pair of grips was then used to clamp the tapered ends together. The nut inside holds the channels against the jig blocks and creates a gentle curve down to the end. The tapered ends were then welded together, my TIG machine creates a nice stable arc down to very low currents so welding this thin material is relatively painless. The forward ends spring open a bit when the rib is removed from the jig allowing the nut to fall out and when re-inserted in the jig the rib takes up the curve without the internal support. The front ends are then tack welded together. Finally, the front of the rib was cut to final length and shaped to fit the spar using a 3/4" holesaw in the notcher. Each rib was then brazed into place.
Next a datum line was drawn on the workbench and the two elevator spars aligned along it. Then the left elevator horn was bolted to the existing one on the right elevator. Tomorrow, the left horn can be welded into place and I can be sure that the two elevators will sit exactly parallel on their respective horizontal stabilisers.

23rd February 2009 - Panel Wired

I spent yesterday installing the instruments and avionics into the new panel. The concept behind the panel was to use modern avionics but in a panel sympathetic to the age of the aircraft's design. The left side of the panel and avionics are in their final locations, the right side will still be subject to change once a choice of engine has been made. The wiring is largely as per the Aeroelectric Connection Z11 layout. There are three main power buses, an unswitched battery bus, the main power bus, and an endurance bus. Individual fuses for all the electrical components (except those required to be pullable) are mounted on a power distribution tray mounted behind the switches and fuses on the right side of the panel. From left to right and bottom to top the various switches, sockets and gauges are as follows.

Red switch: Three position, off, master on, alternator on
Push Button: Starter relay engage
Socket: Microphone P1
2-1/4" cut out: Fuel level
2-1/4" cut out: Tacho
Socket: Headphone P1
3-1/8" cut out: Trio autopilot head unit
3-1/8" cut out: ASI
3-1/8" cut out: DI
3-1/8" cut out: AH
3-1/8" cut out: VSI
3-1/8" cut out: Altimeter
Avionics stack: Bendix-King KMD-150 GPS-Map
Avionics stack: Garmin SL30 Nav/Com
Rectangular Cutout: System Monitor Display
White Switch: Nav Lights
2-1/4" cut out: Intercom
2-1/4" cut out: Will be transponder, compass used to fill hole
Blue Switch: Strobes
Green Switch: Fuel Pump
Yellow Switch: TBD
2-1/4" cut out: TBD, manifold pressure gauge used to fill hole
2-1/4" cut out: Davtron M811, Clock, Flight timer, Stop Watch
Pullable breaker: Alternator
Pullable breaker: Starter Relay
Red Covered Switch: Emergency electrical power
Socket: Headphone P1
2-1/4" cut out: TBD, EGT gauge used to fill hole
Small switch: Speaker On/Off
Socket: Microphone P2
2-1/4" cut out: TBD, suction gauge used to fill hole

22nd February 2009 - Panel Cut Out

Finally, spring has sprung, or at least it's warm enough to get back into the garage. During the past month I'd been thinking about the panel mock up that I'd built (http://tailwindbuild.blogspot.com/2008/03/blog-post_22.html) and working out how to translate that into a final arrangement. There were two errors in the design that became apparent now that the panel mount is installed in the airframe. Firstly, the position of the radio needed to be higher to pass over the top of the tank but not too high to avoid running into the combing as it angles down towards the window. Secondly, the power distribution tray needed to sit above the lower panel support and be shorter to avoid hitting the front of the fuel tank. Once these design changes had been drafted up and checked it was time to cut the panel. 3-1/8" and 2-1/4" holesaws were used in the bench drill to cut out the holes for the instruments. Used carefully these produce a beautifully clean hole. The two rectangular holes for the instrument stack and for a homebuilt system monitor (more on this later) were cut out using a 1mm cutting disk in a 115mm angle grinder. This produces nice clean holes which are quick to clean up with a file. Then the mounting holes were drilled using homemade templates to position the holes. The templates were produced by cutting 3-1/8" and 2-1/4" holes in pieces of 0.063" steel plate and then drilling though the mount holes of a couple of old instruments into the plates to accurately locate the mounting holes. Next the holes for the switches, breakers and headphone sockets were drilled using a step drill. Finally the cutouts for the VSI and altimeter were shaped to fit round the adjust knobs. The bottom aluminium angle was then match drilled and riveted to the panel to provide additional stiffness.