29th September 2011 - Rivet holes and more tapes

The stringers along the top of the fuselage need drilling for the pop rivets which will keep the fabric attached. I'm using 48" lines of rivets at 2" spacing on the outer stringers and 54" of rivets at 2" spacing along the centre stringer as per advice from Jim Clement. So the challenge was to drill 70+ holes in the centre of the circular stringers accurately spaced out without the drill bit wandering off centre and wrecking the fabric! After a bit of thought I decided to make a jig which would align the drill along the centre of the stringer and provide the spacing. I used a semi-circular router bit in the CNC router to machine a shallow channel in a bit of scrap aluminium. Then the router bit was exchanged for a 1/8" drill bit and the router programmed to drill two holes exactly 2" apart in the centre of the channel. The channel accurately located the jig over the stringers. Once the first hole was drilled in a stringer a spare drill bit was inserted through the jig into the ready drilled hole and then the second hole drilled through the other hole in the jig. Then it was just a case of moving the jig one space, with the spare drill bit popped into each new hole in turn and drilling through the other hole. It took about 30 minutes to make the jig and less than 10 to then drill the holes. I also then applied the finishing tapes over the bottom stringers and those on the left side of the aircraft. I now need to wait for the rivets to arrive from ACS before I can finish up the top of the fuselage and also still need to do the finishing tapes along the bottom longerons. I've also run out of 2" finishing tape which I need to complete the horizontal stabilisers and will also need for the elevators, flaps and ailerons so an order went in for another 50yds of that as well.

27th September 2011 - Tapes

The next few days are going to be spent applying finishing tapes to the fuselage and vertical and horizontal stabilisers. I'm following to Stewart manual and videos precisely. Rib tapes are stuck at one end and the glue allowed to dry to a reasonably strong bond. Then the glue is applied along the rib until just before the other end. All excess glue is wiped off with a paper towel. The tape is pulled tight to cause it to conform to the shape of the covering and the glue again allowed to dry. Finally, the tapes are cut to length and the end glued. The joints between the fuselage sides and top and bottom will be reinforced with 3" finishing tape. In this case the tape is folded in half to get a centre line. The centre of the longeron is painted with a glue line which is allowed to get tacky. Then the tape can be positioned accurately over the longeron centre. The glueline is ironed to thermal soften the glue and bond the centre of the tape in place. Next the tape ironed flat against the top and side. Finally the edges of the tape are lifted and glue appled about a foot at a time with the excess wiped off. So far I've got the tapes completed for the vertical stabiliser, the top fuselage side joints, the right fuselage side stringers, and the horizontal stabiliser ribs. I've also applied the reinforcing tapes along the top stringers ready for the fabric attach rivets.

26th September 2011 - Rib Stitching

I needed to rib stitch the vertical stabiliser before I could apply the finishing tapes to it and the rest of the fuselage and I had also only got the covering of the horizontal stabilisers to the point of being stitched so that was the task for today. One of the tedious but exacting jobs in rib stitching is marking out and making the holes for the stitches. In order to speed this up I spent some time making a jig. I used the CNC router to create a pattern of holes spaced 1-1/2" apart lengthwise and 1/2" apart side to side in a piece of aluminium strip. Some additional holes were also drilled in the middle of the strip. The centre point of a rib was then marked on the stabiliser in a couple of places and these were lined up in the middle holes in the jig. Then I used a fine taper bit on the soldering iron to make holes for the stitches through the parallel rows of jig holes. The net result was a perfectly straight line of evenly spaced holes along the rib. Then it was a case of putting the stitches in. Luckily I had videoed the demo done in the fabric covering course I'd done so after a quick refresher I completed the stitching of the two horizontal stabilisers and the vertical stabiliser. Rotating the horizontal stabilisers on the spar carry through made it easy to work on them. This leaves just the elevators to be stitched but I need to do the basic covering of these first.

24th September 2011 - Right fuselage side covered

I attached the fabric on the right side of the fuselage today so the basic box is now covered. The fabric over the windows on both sides was cut out using a soldering iron which seals the edge of the fabric and cuts accurately along the line of the window opening. In addition it was used to pierce all the holes for the screws to attach the window to the frame. You can also see round the inside of the left window frame the black self adhesive neoprene strip which will create a watertight seal with the glazing. It is a bit scary having a hot soldering iron near the pristine fabric - one slip....
However, all went well so next job on the covering is to apply all the tapes to cover the seams and protect the fabric where it lies on the stringers.
The rear shot show the upright vertical stabiliser as viewed from the rear; contrast yesterday's photo.

23rd September 2011 - Top and left side covered

I've put in two very full days of work on the covering and have made good progress . First the inspection rings were glued into the Vertical stabiliser (VS) and floor. These are first attached to the inside of the fabric and then a patch 1" greater in radius in glued over the top, also on the inside. Finally the centre section will be cut out and the removable panel installed.
Next the right side of the VS was covered and the reinforcement tapes glued along the ribs ready for the rib stitching. The top of the fuselage was then covered. The tricky bit is getting the junction between the VS and the top skin. The top fabric was wrapped round the bottom tubes of the VS and into the VS itself. Then a finishing tape was applied to the outside to reinforce the joint.
Finally the left side was stuck in place. This has a cut out for the horizontal stabiliser spar carry through and for the rudder cable. Also it was glued to the plate for the static port. The picture of the right side of the fuselage shows the interior open for the last time until the right side skin is applied.

All of the fabric is shrunk with a domestic iron that has been calibrated at 250, 300, and 350F. The fabric is ironed twice or more at each temperature to slowly tighten it and remove any creases. The result is a smooth and taut surface ready for sealing and painting. The final picture shows the rather strange way in which rudder offset is created in the Wittman design to offset engine torque - this hadn't been obvious until the fabric was on. The VS main spar is perfectly upright and the top of the rudder is aligned exactly fore and aft, but the front spar is offset to the left at the bottom - you can see how it is out of line with the stringer which is centred. This creates the illusion that the whole VS is canted over which isn't the case.

Next job is obviously to close the right side and then it is on to finishing tapes over the seams and over the stringers. The fuselage itself in the design is a lifting body so the top surface will be under negative pressure in flight. To stop the top fabric ballooning off the frame it will be pop-riveted to the stringers.

21st September 2011 - Covering underway

Yesterday and today I've started covering the fuselage. First the bottom cover was glued to the outline of the floor. This goes all the way from the rear of the aircraft to the rear of the front bay so it is the longest piece of material needed. In order to make best use of the fabric I wrapped the front section round the sides and used it to cover the panel underneath the doors. In this way the side pieces will only need to go to the rear of the dor opening. I'm using the Stewart Systems covering which uses a water based glue that seems to be latex based and is a fetching shade of blue.
Then the left side of the vertical stabiliser (VS) was covered. This meets the top decking at a right angle. Many aircraft blend the top deck covering into the vertical stabiliser but the construction of the Tailwind has tubing specifically set to create a right angle joint. Next job is to glue access panels into the VS and the floor to allow the horizontal stabiliser bolts to be installed and to allow the elevator pushrod connection to be made to the elevator horns. Then the right side of the rudder can be completed.

19th September 2011 - Putting it all together

I've finished painting everything apart from the flaps and ailerons so it was time to put everything together and check all the controls work properly before starting the covering. First the strut brackets were final bolted onto the wing spars. In line with requirements from the LAA, the holes for the attach bolts had been bushed and the 1/16" ply reinforcement replaced with 1/4" 12 ply. This provides a very strong mount for the attach brackets and it was possible to torque the bolts to full tightness without any risk of crushing the mount. The wings were then bolted into position and the flaps and ailerons installed. Packing pieces were inserted between the flap and aileron hinges and the wings to simulate the thickness of the wing skins and ensure the mounts were in the correct place.

The interior photo shows how the flap and aileron pushrods pass through the windowsills in the baggage compartment. The edges of the holes are lined with Rayrim edging. This is ready glued and is installed with a heatgun neatly protecting the edges.

The biggest issue has been with rigging the ailerons. The seat back support fabricated as shown in the plans (the end is just showing at the bottom left of the interior picture) fouled the aileron pushrods when I did the first test fit some weeks ago. To solve this it was necessary to remove and re-weld this to the interior of the door upright rather than to the rear and to replace the diagonal section with a two part welding that moved the tubing forward and in away from the pushrod. This solved the issue and the aileron linkages now operated very freely and without touching any of the aircraft structure.

The test fit revealed two bits of rework. First the right flap was too close to the fuselage side when the thickness of the flap and fuselage covering was considered so the inner rib was cut off, the tubing smoothed where the original weld had been and the rib re-welded 1/4" further out. Also I've positioned the counterweight on the left aileron about 5 degrees above where it needs to be to fit neatly into the slot in the wing in the neutral aileron position. This will need to be reworked but that's a job for another day. The bottom picture shows the rear seat belt attach, the elevator pushrod passing through the centre support and the static pressure ports and piping.
Last job for the day was to set up a 8x4 workbench in the garage, remove the wheels, and carry the fuselage into the garage and put it on the bench ready for starting covering. I haven't weighed the fuselage in its current state but carrying it was just possible with two people and I can just about rotate it on the bench by myself.

15th September 2011 - Back from sand blasting

I collected the various bits of metalwork from the sandblasting today so next job is priming and painting. You can see from the photo the perfectly clean surface of the metal after cleaning. Compare this with the pictures of the flap and aileron a few days ago. Actually the cleaning is not done with sand or aluminium oxide which are both too fierce for the thin material used in building an aircraft. Instead, a fine glass bead is used which does the job without any damage. The only problem is that the metal now corrodes instantly if there is any moisture around. Just picking up a piece with bare hands will result in brown finger prints appearing within minutes. So the job over the next few days is to prime all the pieces and topcoat where necessary. The complete list to do includes both flaps and ailerons, both lift struts, the aileron pushrods, the flap and aileron horns, the strut attach brackets and the two parts of the elevator pushrod linkage. This will take me until mid next week weather permitting and then the final internal components can be installed in the fuselage (elevator and aileron pushrods) and the fuselage is ready to start covering. I've ordered and received the covering material which is Diatex 1500 - a direct replacement for Ceconite 102 but with a rather finer weave which is easier to fill with paint and can give a better finish. Also ordered from the US is the paint for the Stewart system that I will be using.

5th September 2011 - Baggage Compartment

I'm using lightweight plastic sign board for the walls of the baggage compartment. To trim this I've found some self adhesive felt fabric. So this was stuck in place and the baggage compartment walls screwed into place. The seat belts have also been installed as the bolts securing the centre cable and outer lap belt halves will be difficult to get at once the fuselage is covered. Finally the rear window frames were installed as the fabric covering will go over these. I'm waiting for the last components (struts, flaps, ailerons) to be returned from sandblasting then I will do one last trial fit of the wings and all control serfaces and if all is well the covering of the fuselage can then start. In the mean time I need to order the covering fabric so it will probably a week or so before I can get going.

2nd September 2011 - Plumbing the vacuum system and installing the coaming

The last system to be installed on the panel was the vacuum system for the Attitude indicator (AI) and direction indicator (DI). The system is completely conventional. The vacuum pump on the engine pulls air through the regulator mounted on the firewall which maintains a 5PSI pressure differential. The regulator has two inlets, one is connected to the VAC terminal on the AI and one to the VAC terminal on the DI (blue pipes). The AIR terminal on the DI is then connected directly to one of the outlets on the air filter. The other outlet on the air filter is connected both to the AIR terminal on the AI and also via a "T" connector to the AIR terminal on the vacuum gauge. The VAC terminal on the gauge is connected to the GAUGE terminal on the AI. The GAUGE terminal on the DI is blocked off. In this way the gauge measures precisely the pressure drop across the AI. So in summary the vacuum pump sucks air from the air filter via the AI and DI.

Up until today I've had a catch 22 which needed solving. The tank had to be installed before the coaming in order to complete the routing of all the cables, pipes, and tubes from the panel. However, the coaming had to be installed before the tank in order to get the tank neck through the hole in the coaming. The solution was to cut out a small section of the coaming around the fuel tank. The sides of this piece were then riveted to three strips of aluminium to act as support for the rest of the coaming. These were match drilled to the coaming and nutplates installed on the underside. This small section could then be screwed into position on the firewall together with the formed piece of aluminium which closes the gap to the lower edge of the windscreen. The remainder of the coaming was then slotted into position. The two formed strips which support the side windows were then inserted and the coaming screwed into place. Next all the screws that connect the panel to the combing and fuselage cross member were installed. Finally, a piece of glue lined edging strip was heatshrunk into place round the lip of the coaming to protect the edge and/or the pilot! So that is the panel absolutely complete and installed. Hopefully it won't need to come out again. The coaming is removable in case of future problems but in service this will also require removal of the windscreen - not difficult but a bit tedious. I'm very pleased with the way this has turned out. I wanted something in keeping with the type of aircraft but fully functional and ergonomically laid out - I think I have achieved this.

1st September 2011 - Terminating the rudder cables

The rudder cables had been terminated at the front when the basic cable routing had been laid out. Now that the floor panel which they pass through was in place it was possible to terminate the rear of the cable. First the rudder was installed, centred and and clamped into position. Then the rudder pedals were clamped together in a neutral position with the rudder horns precisely vertical. The rudder cables were then terminated using nicopress fittings around AN100 thimbles and AN111 rollers. Glue lined heatshrink tubing was applied over the nicopress fitting to exclude any moisture and protect against the sharp cable ends. The cables were cut so that the holes in the rollers were 4cm from the holes in the rudder horns. Two pairs of coupling plates were then fabricated from strips of 1/2" x 0.063" 4130 steel plate to join the cable ends to the rudder horns. These just need priming and painting and then the rudder system is ready for when the aircraft is assembled ready for flight.