20th October 2008 - Windscreen mounts, tabs 161-194

I bought some more Argon this morning, so first job was to complete the weld across the back of the channel that will support the rear of the windscreen. This and the channel on top of the rear spar carry through were then drilled for screws to fasten the aluminium panel which will close the gap between the windscreen and the top fabric. This will sit on a neoprene seal to ensure that the joint is watertight. Next I welded tabs 161 -194 onto the side and front windscreen bows. These were then drilled with an 1/8" drill as was the centre windscreen bow. The windscreen was then positioned into the rear channel and starting from the back was match drilled onto the tabs with a cleco positioned into each hole as it was drilled. The drill used was a special version for drilling acrylic. This has a much steeper angle on the point and does not grab the plastic in the way a normally ground drill can. Finally, the windscreen was clecoed into position front to back. Next job is to trim the edges back to the windscreen bows but this will have to wait for a bit as I'm probably not going to get anything done over the next week or so but normal service should be resumed first week in November.

19th October 2008 - Left side window frame

I started today by jigging and tack welding into place strips of stainless steel behind the channel that supports the back of the windscreen. Then started final welding this into place when my Argon ran out when about a third of the way across so the rest will have to wait for another day. With no welding possible there was no option but to bend some aluminium so I started on the framing for the left side window. This sits on the outside of the fuselage butting against the window bows at the top and the stub longerons at the bottom. First job was to create a section of angle to support the bottom of the window from the inside. This will screw onto the tabs already in place to support the side of the combing. The outside of the window at the bottom will be supported by the aluminium skin that cover the first 18" of the fuselage. Next the two sections of angle that surround the top front door post were fabricated. the rear one is a U section that will screw to the outside of the window; the internal dimension of the U has to be equal to the diameter of the door post (3/4") plus the thickness of the window (2mm). The front one is a "step" shape that forms the support on the inside of the window; in this case the thickness of the step needs to be exactly 3/4". A 2mm spacer was sawn out of wood to mimic the thickness of the windscreen and can be seen clecoed between the two sections. It took two goes to bend the rear section to exactly the correct width but the front one worked first time. The front/back dimension of the box created around the door frame by the two sections is about 1-1/8" to allow room to duct the cables and pitot tube up to the wing root from behind the panel.

18th October 2008 - Windscreen

I started work today by installing the piece of stainless steel channel that forms the top of the fuselage over the rear spar carry through. This has the front edge of the top fabric wrapped round it and a section of spruce inserted into the bottom to anchor the fabric. Then a section of aluminium sheet screws through the section and into the spruce to close the gap to the back of the windscreen. This sheet will also provide a suitable mounting for the GPS aerial. Next the windscreen itself was clamped into position using a piece of wood to keep the rear edge flat. The windscreen is a sheet of 4mm acrylic (perspex). The centre windscreen bow was then shaped to fit against the natural curve of the windscreen. This took quite a few iterations but eventually there was a good fit from front to back. The windscreen was then removed and a suitably sized stand-off fabricated for where the centre bow passes over the front spar carry through. Then the centre bow was welded into place; front, back and to the stand-off. I was unconvi9nced that the aluminium sheet would provide a neat rear edge to the windscreen which wants to bow and the sheet would probably not be strong enough to fully prevent this so I welded a second piece of stainless steel channel on edge to capture the rear of the windscreen, keep it in a straight line and anchor it against the three windscreen bows. This works very well as can be seen in the picture. Next I need to weld 30 or so tabs to the outside windscreen bows and across the top of the firewall. The windscreen will be match drilled to these and then cut to final shape. I've have made work for myself by using the channel at the back of the windscreen as to create a seal to the aluminium top panel I will need to weld a ledge to the back of it across the entire width to create a weather seal rather than just using tabs.

17th October 2008 - Left windscreen bow and wing attach brackets

My TIG welding machine will only do DC welding whereas you need AC for aluminium so yesterday I took the completed fuel tank to the local aluminium welding guru to be finished. Today was another beautiful autumn day so Paul and I took the Vans from Andrewsfield (pictured) to Old Buckenham for lunch. We flew along the east coast before cutting inland and the third picture is of Southwold, one of the most picturesque Suffolk villages. I did get a bit of work done later in the day and welded the left front spar attach bracket and left windscreen bow to the fuselage.

14th October 2008 - Rear spar carry through tie rods, left wing attach brackets

Now that the position of the rear spar carry through has been established fairly accurately the last couple of tubes that form the main fuselage structure could be added. The right one welds between the rear spar carry through and the upper fuselage diagonal just in front of station 78. The left welds back to the top fuselage cross member at the station. Later plates that form the upper seat belt mounts will be welded between the rear of these tubes and the longerons. Next the wing attach brackets for the left side of the fuselage were fabricated. Again it took much longer to make these than seems reasonable but it is critical to get the dimensions exact to fit inside the spar attach brackets.

13th October 2008 - Right side door

As previously noted the left side door had been made too tall and would not have opened under the wing. To get this correct for the right door I made a template of the bottom half of the main wing rib. This was attached to the root rib template referenced via the cord line. A straight edged piece of scrap timber was then clamped to the fuelage stretching horizontally across the door opening to define the position of the top of the door opening. This was set 3/8" lower than the bottom of the main rib template to allow for the door panel to overlap and create a good seal. Then the right door was fabricated in the same way as the left. See http://tailwindbuild.blogspot.com/2008/08/14th-august-2008-left-door.html , http://tailwindbuild.blogspot.com/2008/08/17th-august-2008-seat-bottoms.html , and http://tailwindbuild.blogspot.com/2008/08/18th-august-2008-left-door-latch.html for details. Finally the left hand door was shortened to the same dimensions as the right so it should now open!

10th October 2008 - Windscreen support bows

With the root rib template accurately positioned it was now possible to shape and install the lengths of 1/2" * 0.035 stainless steel channel that will form the outer edges of the main windscreen. Two lengths were shaped to identical curves matching as closely as possible the profile of the root rib and braised onto the two short supporting tubes. The windscreen also has a central bow but this will be fabricated once the windscreen is in place to follow precisely the actual curve of the acrylic material to be used as the shape of the top of the firewall means that the centre of the windscreen will not follow exactly the same curve as the edges. Once both outer bows were finished one of them was jigged onto the right hand side of the fuselage flush with the outside of the main tubing (to allow the side screens to lie flat) and tack welded into place. The jigs were then removed and the right hand bow was then final welded. Next job while the fuselage is in the workshop nose in is to fabricate the right door, then I can reverse the fuselage to install the left hand wing brackets and window bow. Also, I can then shorten the left hand door to fit under the wing as it is currently too high.

9th October 2008 - Root rib template

Just a short day today as the weather is beautiful so I'm going flying the Vans. I constructed a root rib template with a dummy flap torque tube and overheight cut outs for the spar attach brackets. The fuselage was then levelled on the bench and the template positioned over the attach brackets with 1/8" clearance from the torque tube to the top longeron and the bottom of the template horizontal as called for in the plans. The rear spar mount and spar carry through tube were then positioned to put the spar attach bracket in the centre of the spar as it passes through the root rib and the position marked on the template and the bracket and carry through tube tack welded to the fuselage. The position of the front spar attach bracket was then also marked on the template. Next the root template will be referenced to a template for a main rib using the cord line drawn on the plans. This will give the exact positions of the spar attach brackets from the bottom of the spars before they start tapering towards the root rib . It will also allow for the upper part of the door to be finished to final size and the root rib gap seal to be fabricated. This should allow the complete fuselage and tail sections of the aircraft to be finished before starting on the wings - I need to adopt this approach as I haven't got room to store the fuselage and build the wings (building in a single garage) so once the fuselage is complete it can be taken to the airport for safe storage.

8th October 2008 - Right wing attach brackets

It was a full day today although it doesn't look like it. I'm waiting on some all aluminium pop rivets to secure the baffle in the tank and also some aluminium tube which will be welded through the tank to take the engine controls from the panel to the firewall. After a lot of sheet metal work recently I decided to get down to some welding and fabricate the brackets which are welded to the fuselage and bolt to the spar attach brackets on the wings. These are tricky little fittings as they must fit perfectly inside the spar attach brackets and some close quarters welding is needed. The front one was fabricated and welded to the fuselage in line with the front spar carry through tube. The rear one slots over the rear door post and will be welded to the upright together with the rear spar carry though once the correct position for the carry through is established. The requirement is to get the correct wing incidence and also to ensure that the flap torque tube clears the upper longeron. The torque tube clearance seems to be a generic problem with tailwinds with some builders having to compromise the wing incidence to get clearance. I'm going to be radical in setting this up by making a dummy root rib with a dummy flap torque tube and then using this to establish the best position of the spar attach brackets on the two spars and the best position of the rear carry through tube. Once this is done I will weld the rear bracket into place and then build the wing to fit the fuselage mounts.

5th October 2008 - Tank sump and filler tube

Carrying on with the tank, next jobs were to create a sump in the bottom which will take the fuel outlet and to install the filler tube. The sump was created by cutting a 6" diameter hole in a piece of 3/4" particle board, springing open the tank and then hammering. This seemed a little crude so I tried it on a scrap piece of the same sheet first and it worked well creating a smooth depression about 1/2" deep in the centre. So the exercise was repeated on the real thing with the same result. Then the tank was temporarily fastened into the fuselage to establish the location and angle for the filler tube 35 degrees from vertical and 4 inches from the front and right side of the tank seemed to work well so the tube was cut to the correct angle and used as a template to mark the hole to cut. A small cutting disk on the Dremel cut the hole reasonably accurately and the end of the pipe was cut into a turret shape to create four tabs which were bent over and match drilled to the top of the tank to support the tube ready for welding. Then it was a case of deburring and trimming the edges of the tank wrap. Next its just a case of mounting the fuel level sender and the tank outlet and the tank is ready for welding. I haven't tried to make the tank the maximum possible size but was interested to know what it should hold - but how to measure it before welding? Inspiration was at hand and I weighed the form block used to make the central baffle. I then weighed a square piece of the same wood. Using the ratio of the weights and the measured area of the square section gave me the cross sectional area of the tank - 1201 sq cm. Multiplying this by the length gives a volume of 106339 cc or 106 litres or 28 USG or 23.4 Imperial gallons. This will give me a duration of about 5 hours to empty with for example a Jabiru 3300 engine - that should do OK.

4th October 2008 - Fuel Tank

It was miserable weather today so I did a full days work on the plane and decided to tackle one of the jobs that seemed likely to be tricky - the fabrication of the fuel tank. First job was to cut out form blocks to shape the end panels of the tank and the centre baffle. First a paper template was made to fit into the space under the combing from the firewall back to the tank support cross member. The vertical dimension of the tank is determined by the need to get the pilot's feet onto the rudder pedals with good clearance - which needs about 12" from the floor to the bottom of the tank. Then the template was glued to one piece of particle board which was then bolted to a second. The two pieces were then cut to the template on the bandsaw. Next two blank end panels were cut from 0.050" thick 5052 alumium - each 1/2" bigger than the form block in each dimension. 5052 is a fairly soft material which can be successfully welded unlike some of the other aluminium alloys used in aircraft construction. Drill holes in the blanks were made at each of the the corners of the form block and at 1" centres along the curve of the shape and filets of material removed to allow the flanges to bend round the form block. The blanks were then thoroughly deburred. Then the first blank was bolted between the two form blocks and the flanges hammered down against the block. Once removed the top edge was folded to 45 degrees to create a relief in the shape of the top of the tank visible in the last picture to clear the engine mount bolts. The second blank was then shaped to form the opposite end of the tank.
Then started the process of forming the skin of the tank. A flange was folded at right angles where the horizontal join in the skin will take place - visible in the third picture, using the bending brake. Then the curve of the tank was created using small bends every 1/2". Every few bends the skin was drilled and clecoed to the end panels to check fit and make sure that the position of each bend was correct. The third picture shows the tank with just the last two bends waiting completion. Once the final bends were made the final section of the skin was trimmed to fit in behind the flange created at the beginning. Next the top of the form blocks were trimmed to fit the final tank shape ( taking into account the impact of the 45 degree bend) and a third blank prepared and folded. This fits in the centre of the tank and is drilled with 7 off 3/4" holes three at the bottom and four 2" up. This piece forms a centre baffle to stop the fuel surging in the tank as the aircraft banks. A centre line was drawn on the flanges of the baffle and holes drilled in the skin around its centre line in the same position as the end plates. Then it was a question of manouevering the baffle into position centering the line through the holes and match drilling and using clecos to fasten it into position. Finally we have the world's largest bread bin.

2nd October 2008 - Firewall top section

No work yesterday as I spent the day playing with my new camera - a Panasonic FZ28. Today I started the installation of the channel that will form the mount for the windscreen. The first section forms the curve at the top of the firewall. This was welded to the frame at the corners and to a 1-1/2" section of tubing in the centre to support the curve. I've decided to mount this piece parallel with the line of the window which means there will need to be a small bend in the very top of the firewall to match. With this in place it was then possible to fabricate a section of alumium angle to fill the gap between the combing and the line of the what will be the cowl. This finishes the whole panel/combing assembly and looks neat. The combing will eventually be covered in a matt black vinyl material to ensure there are no reflections in the windscreen and a protective edge will be attached to the front lip to protect the crew from the sharp edge of the aluminium.

30th September 2008 - Tabs and nutplates

Bit of a slog day today installing tabs 144-160 and the 33 nutplates to mount the combing and to secure the panel to the combing and mount tubing. All easy enough but takes time - the first picture shows the jigging of just one of the combing mounting tabs and the second the panel and combing mounted into place