31st August 2009 - Ribs and rework

It's been slow progress over the last few days but there are now 7 ribs completely finished and one with glue setting before the gussets are installed on the second side. I've also made a jig for the two root ribs and the first root rib has been constructed, glued, and is setting in it. For the root rib jig I've just pinned blocks of wood to locate the rib structure to a piece of polythene over the full size plan as there only two ribs to make so the jig does not need to be too durable.
I was intending to have a first go at covering starting with the rudder which is the smallest and simplest structure but when working out how to fix the fabric I realised that it was going to be difficult to get a good seal round the rudder horn. In order to give somewhere to glue I welded a small plate either side of the front rudder spar round the horn similar to those installed previously around the hinges. Then this needed the priming touching up where it had been sanded or burnt off so it's another seven days for the paint to completely harden before this is ready to cover.

23rd August 2009 - Priming Complete

Finally the priming is completed, actually the priming itself isn't too bad but cleaning the parts with the Deoxidine is fairly unpleasant. This is basically a phosphoric acid solution which dissolves the aluminium oxide and etches into the aluminium. It does produce a very clean surface for the paint to adhere to but smells terrible and is messy to use particularly on big structures like the fuel tank and combing.

Painting is not my strong point and I usually end up with the surface covered in runs and marks but this time I've invested in a new type of paint gun - LVLP. This stands for low volume, low pressure. Low pressure has been around for some time and has the advantage that the overspray is greatly reduced. Low volume means that the amount of air used is also greatly reduced. I'm spraying using a 1.5HP 50 litre compressor which is not sufficient for conventional guns but works fine with the LVLP gun which uses only 6.5cfm at 22psi. The gun is, predictably, Chinese made but a beautiful piece of engineering and good value - http://www.auarita.com

The rib making has taken something of a back seat recently so still only 4 complete and 1 half done.

19th August 2009 - More ribs and primer

The process of making ribs continues slowly, four complete and one gluing. Similarly the priming seems endless especially as I left out the fuel tank and the panel from the list last time. However, the end is getting nearer. All items except the combing and the fuel tank have been cleaned and at least partially painted so another couple of days should see the priming complete. The primer takes 7 days to completely set so once all the priming is complete I can then start applying top coat to those items where it is needed and that have had the requisite drying time. This is a subset of the items where they are visible or where the better wear resistance of the top coat is useful.

16th August 2009 - Ribs and primer

The first rib was completed today other than tidying up the edges which will wait until all the ribs are complete so that they can be done together to ensure they have exactly the same profile. The second rib was built in the jig and the gussets stapled to the first side. Then it was back to priming. I think my estimate of 2/3rds done yesterday was overly optimistic - perhaps it's 2/3rds now. I still have the stringers, the seat bottoms, the seat backs, the coming, the cowl cheeks and the baggage compartment floor to clean and paint and one side of the doors and outer floor panel to paint.

15th August 2009 - Rib gussets

Yesterday I carried on with the priming in the morning and went for a fly in my RV9A in the afternoon. Today it was more priming to start with - I think I'm about 2/3rds of the way through. Then I sorted out an approach to cutting the rib gussets from the 1/16" mahogany plywood called for in the plans. The 8' x 4' sheets of ply are very unwieldy to work with so I cut a small piece off and made the first set of gussets as per the full size rib plan. Then I laid these out on the plywood and established that a 5" x 13" piece was sufficient to make a half set (one side of the rib). I then cut five 13" strips off the main sheet which should be enough for 45 sets ( I need 44). The tip rib and the root rib are fully sheeted and there are 11 standard ribs in between each side. The master set of gussets were then used to draw round and the 5" strip with the outlines cut off. The gussets were then cut out on the bandsaw using a fine tooth blade running at medium speed. Rather than mass produce these I think I will make two sets each day to cater for the one daily rib. Finally I glued up the first rib using staples to hold the gussets in place while the glue sets. As per LAA requirements I also made a test piece with the batch of glue which will be inspected (destructively) by my LAA inspector to satisfy himself that the glue batch is satisfactory. I'm using T88 epoxy for gluing the ribs.

13th August 2009 - Fuselage Painted

I collected the fuselage from being sandblasted and primed today. The company I used is called AirBlast and work out of a disused airfield at Gosfield. They were recommended because they have experience with the sort of thin wall tubing used in aircraft - too much enthusiasm with the grit gun can blow holes in thin tubing!

The airframe now looks smart and clean in it's coat of white epoxy primer and will temporarily be stored in the hangar at the airfield where my LAA inspector is chief engineer.

12th August 2009 - Starting the wing rib production line

Actually the production line really started a couple of days ago when I sealed up one end of a piece of plastic pipe and filled it with hot water to soak overnight the first two 1/2" x 1/4" spruce strips that form the top and bottom structure of the ribs. Yesterday these were then clamped to wooden formers to form the bends which shape the nose section of the ribs and allowed to dry overnight. At the same time the next pair of strips were put in to soak. So today I had a pair of dry shaped strips that could be inserted into the wing rib jig, a pair drying in the former, and put the next pair into soak. The rib construction jig is a piece of MDF onto which the outline of the rib was copied from the full size wing rib plan. This was done by fastening the plan to the board and then pricking through the outline and internal structure with a compass point. Then small blocks of wood were pinned and glued to the board around the outlines of the various rib structures. Finally, at each point at which the rib structures are glued, 3/4" holes were drilled through the MDF so that the glue used to make the rib won't also bond it to the jig.
With the top and bottom strips in place, the internal strips could then be cut to length and fitted. The seven upright strips and front and back blocks were then mass produced (24 of each) to cater for the full requirement. This was done using the bandsaw with its mitre guide to cut the correct angles top and bottom. Finally, two off of the 5 diagonal braces were produced. These have to be finished individually using the disc sander so each day I will use the extra set as a template for that days rib. Next job is to fabricate the gussets that glue over the joints to support them. 48 each of these needed (one either side of the 24 ribs) so I'll try and find a convenient way of mass producing them as well.

11th August 2009 - Priming the aluminium parts

The fuselage and empennage are ready to pick up having been sandblasted and primed with Epibond epoxy primer. That's a job for later in the week so today I made a start on priming the aluminium parts. My system is as follows:
First each part is immersed in a solution of Deoxidine 624 and scrubbed with a scotchbrite pad. Deoxidine 624 is a liquid cleaner for aluminium and its alloys to remove oils and oxides prior to painting or anodising.
Then each part is washed with clean water and hung up to dry making sure not to touch them with anything that might result in contamination (e.g. bare hands).
Finally once completely dry the parts are laid out on a mesh table and sprayed with the Epibond. This takes 7 days to fully harden so each part will then be stored for at least that long before topcoating with Ranthane polyurethane where applicable.
Surprisingly, unless I've miscounted, there are 53 separate aluminium parts that need spraying including large panels such as the floors, doors, and cowl cheeks. This is going to take some time to complete and is weather dependent as I will be spraying outside. Anyway at least I've made a start with 12 of the smaller parts cleaned and spayed on one side. This will be a background job at the same time as building the wing ribs - see tomorrow's post.