6th November 2011 - Carburettor heat control

One more little job completed today. A semi-circular shaped hole was cut out in the top of the airbox and one half of a piece of hinge match drilled to its straight forward edge. Then an aluminium flap was created to completely fill the normal entrance to the airbox when at right angles to the airbox top. This took lots of iterations of filing and testing to exactly fit the shape of the fibre-glass bottom of the airbox. Once this was a good fit it was match drilled to the other side of the hinge. The holes were then deburred and dimpled to take countersunk rivets. These were set so that the flush surface is inside the airbox to provide minimal disturbance to the airflow when in the normal open position. Then an actuator arm was rivetted to the top of the flap and drilled for a cable connection. The top of the airbox was then bolted to the carburettor and the actuator cable measured and cut. The system is designed so that the cable pull holds the flap open against the airflow when carb heat is required. In the normal closed position the control is fully forward and the cable is assisted by the airflow to keep the flap tight to the top of the airbox and allow the cold air into the carburettor. The hot air intake is mounted over the semi-circular cut out and is spaced off it to allow the heated air to spill into the cowl when carb heat is not required. When heat is required the suction of the carburettor will ensure hot air enter the airbox. The six tabs on the underside of the airbox top-plate hold the K&N filter in position.

4th November 2011 - Lower cowl nearly complete

It has been slow progress over the last few days. The weather has been poor so I haven't been able to get the fuselage outside and I'm spending time waiting for resin to cure. Finally though the airscoop is fully bonded to the cowl and the air intake created and lined up with the airbox. The process for creating the air intake is to cut the hole in the airscoop to match the intake to the airbox then shape and insert a foam plug that projects into the airscoop. Glass cloth is then laid up around this plug to create a tube on the inside of the airscoop that matches the airbox. The airbox will then have a rubber seal riveted around the intake that fits over the tube in the airscoop that has been fabricated. This ensures that outside air is rammed into the airbox by the propeller and speed of the aircraft increasing the effective air pressure at the carburettor and therefore the engine power. I just need to wrap one final layer of glass round the lips of the air intake to protect them and final fill and sand then the lower cowl will be finally ready for priming.

1st November 2011 - Brakes and cowl

The first job today was to complete the installation of the brakes. The top end of the master cylinder pistons were connected to the brake bars on the rudder pedals. Then the fluid intakes were connected to the "T" junction on the fluid reservoir. Finally, the fluid outlets were connected to the AN fittings screwed through the floor. These will then connect to the brake lines running down inside the leg fairings. Next the front cheek panels were covered on the inside with the same self-adhesive felt fabric as the baggage compartment walls. These were then clecoed into place ready for riveting to the firewall.
The posting on the 26th October shows how I had had to cut the airscoop in half horizontally in order to increase its depth. Yesterday, I had put a first layer of glass on the inside of the gap to join the two halves and put a slurry of resin and microballoons on the outside to level up the surface. I had also put a first layer of glass over the joint between the top section of the airscoop and the cowl proper. Today, the joints were sanded to create a key and two extra layers of glass were glued into place over both the joints. The three layers should be enough for a final result but I'll check it tomorrow to see if I think it needs one extra layer. Then the cowl was inverted and a slurry of resin and microballoons used to filet the intersection between the airbox and cowl. This can be easily sanded once set to get a clean smooth joint. Any resin left over from each layup is mixed with some white pigment and painted onto the inside of the cowl. Once completed properly this will seal the inside of the cowl and allow any drips from the engine to be easily seen. Finally three layers of glass were applied to the joint in the airbox. Once this is set I will filet the inside of the joint to make sure that the air can flow smoothly into the filter.

31st October 2011 - Spraying the underside

It was good weather today so the aircraft was tipped on its nose once more to spray the underside with the white EkoPoly topcoat. The paint has gone on pretty well with no runs or other serious blemishes. However the edges of the finishing tapes are very obvious. Before I do any more painting I'm going to have to make sure these are really stuck down and lie as flat as possible. However, this sort of learning experience is one of the advantages of doing the bottom first. This is not a view that is going to be routinely seen!

While the paint was drying I made a start fibre-glassing the cowl and airbox with the vinyl-ester resin that arrived this morning. Pictures of this tomorrow. Once the paint was properly dry the brake master cylinders were installed on their pivot and the front lower skin was positioned and clecoed and screwed into place. The fitting to the rear left of the skin is the fuel tank breather inlet and there is a hole to the rear right which will take the transponder antenna. I'm not fitting this yet as they are very vunerable and there is a high likelyhood I would break it off before ever flying. In order to fit this later I've drilled a 1" access hole in the inner front floor which will be filled with a rubber bung but will allow the transponder antenna to be installed and also, if required, serviced or replaced once the aircraft is in service.

30th October 2011 - Dzus fasteners

I decided to use Dzus fastners to fasten the cowl to the mount strips. These are not the completely flush types (which are silly money!) but appear as a flat screw head on the outside. They take a quarter turn with a screwdriver to fasten and unfasten. The cowl mounting strips were removed and the cowl mounting pilot holes drilled out to 7/16" to take the raised surround of the Dzus "nut". Then 1/8" holes were drilled for the mounting rivets. The mounting strips and the fasteners were dimpled to accept countersunk rivets. AN426AD4-4 rivets were inserted and set using the pneumatic squeezer. Then the holes in the cowl were drilled out to take the Dzus "screws". The mounting strips were then clecoed back into place and the cowl replaced and checked for fit. Then the front inner floor was also installed and screwed into place and the rudder system installed.

28th October 2011 - Starting painting

I want to rivet the forward fuselage cheeks and forward outer floor to the firewall but...
I can't do that until I install the rudder pedals and brakes but...
I can't do that until I install the forward inside floor but...
I can't do that until I install the forward outer floor but...
I can't do that until I have painted the underside of the fuselage so...
Today I set to to do that. I brief trial proved that painting the underside with the EkoFill primer/UV blocker was not going to be possible lying on the floor. However, without the tail feathers the airframe is currently pretty much neutrally balanced when in flying attitude and the centre of balance moves forward as the tail lifts. So the wheels were chocked and a cable attached to the horizontal stabiliser carry through and very carefully the aircraft was allowed to tip forward until the engine rested on some foam padding. This allowed enough access to the underside to work and get access with the spray gun.
The process is first to clean the fabric with some special cleaner that Stewart supply and then to wash off the detergent leaving the fabric damp. Then the first coat of EkoFill is brushed on with a foam brush. Once this is dry a second coat was brushed on using the brush at right angles to the first coat. Painting the tail while standing on a step ladder was slightly bizarre and the passing local traffic seemed distracted! While this coat was drying I decided to make a first attempt at using the Stewart EkoPoly top coat. I had previously prepared the spinner so this was an ideal test subject. The paint was mixed with the catalyst and then thinned with distilled water and then 4 coats were sprayed on alternating in direction about 10 minutes apart. The first coat came out as tiny globules of paint rather than a mist. This was diagnosed as having too little gas pressure so once this was corrected the painting was much more even. There is a little bit of an orange peel effect but this should polish out and was probably caused by the first coat. After 3 hours the fuselage seemed dry and some 320 grade open coat sandpaper was used dry to remove any blemishes. Then the paint gun was prepared for 4 coats of the primer (2 coats in each direction). These were applied as per instructions about 10 minutes apart and resulted in an even light-proof covering of the fabric. This is critical as the fabric is degraded by ultra-violet light and left outside unprotected will loose 85% of its strength in a year. The fuselage was then gently returned to a more normal attitude and returned to the workshop where the paint can harden overnight.

27th October 2011 - Main gear leg fairings

It is an unpleasant day, rainy and cold, so I needed a task that could be accomplished inside with the aircraft in the workshop. I had acquired the blanks for a pair of the old style aluminium Vans gear leg fairings so fitting these seemed like and ideal job. First the fairing were cut to size to fit between the fuselage and the wheel. The fairings are joined at the back by inserting the pin in a length of aluminium hinge. The key to a neat job is to have the hinge positioned so that when the fairing is flexed around the gear leg it pulls the trailing edge of the fairing together precisely. Pieces of scrap steel tube were used to simulate the ends of the gear legs and with the rear edge of the fairings taped together the correct position of the sides of the hinges marked. The hinge pin was then removed. The ends of the hinge were match drilled to the fairing and then a rivet fan spacing tool was used to get an even line of rivets. In theory you are not supposed to drill through the fan to avoid opening up the holes, just use them to mark, but I'm sure I'm not alone in ignoring this advice. Once all the holes were drilled they were dimpled to accept countersunk rivets. With the thin aluminium and the thin hinges this could be done through the two together which ensures a very good fit. Then the rivets were set using the pneumatic squeezer - it is great to have these tools left over from the RV build. The result is a exactly spaced set of perfect rivets - this is one of the most satisfying jobs when it comes out well. The fairings were then wrapped round the gear leg and the natural position of the top of the legs in the fairing established. This was marked and then slots cut in the top of the fairings stop drilled at their bottom ends. Stainless steel jubilee clips were then used through the slots to fasten the fairings to the leg. Before flight they need very accurately aligning fore and aft with weight off the wheels as if misaligned they act as mini rudders and can put the aircraft out of balance.