Tuesday, 30 August 2011

21 foot wing, 18 foot garage.

I knew the wing would not fit easily in my garage, basic math told me that, but now that it is in 3 dimension form, it becomes alarmingly clear just how much room it takes up.
I continued to build the the top wing ribs through early July, and also started to work on the spar center splice joints. I had not been looking forward to these splice joints, as for an 1 1/2 thick spar, at a 15-1 ratio splice, the joint would be 22 inches long. This is a large splice.
So I built a router jig to cut the splices in each board.
I got the idea for this jig and the method of cutting from Dave Binkley, who is building a beautiful 1932 Monocoupe 110, the restoration of which is nicely decribed on his site;
Dave does beautiful work, and it was really handy to see how he had worked out this splice method.
(thanks again Dave)
I spent a day building up the router jig, and testing it with a short length of spar.
The main points to note,
The spar has to be held completely secure, if there is any movement, it will affect the taper joint, and this is especially true as it gets to the end, which decreases to a feather edge.
It is very important to limit each pass cut depth to less than a 1/16th of an inch, any more and the router will be working too hard,and could move the spar or dig in.
Make sure via a solid base, the router cannot tip.
Go slow, methodically, and do not cut with the gyroscopic rotation. (huh?)
this means that as the router bit turns, do not try to cut into the rotation, this will let the bit wander and run away, you should always be pulling the router against the rotation. This is probably easier to do than explain, but it is pretty important.
I left the spar 3 inches long in at the end of the jig, to allow me to screw it down, then as each pass is made the jig cuts deeper into the end, and eventually, after about 30-40 passes, you have a 22 inch perfect taper.
I have a 1/2 inch shaft Makita router, which is a pretty heavy duty unit, I would not want to try this splice with a 1/4 inch shaft router, as I am not sure it would be rigid enough, I guess it would work, but it would probably require a great many more passes, as the cut depth would be so slight, as well a 1/2 inch straight bit only requires 50% as many passes to cover the same width and length.
So after a few rather nerve wracking hours, I had completed the 4 required splices to create two main spars.
and as usual, my capable assistant, displaying the appropriate safety equipment, was with me every step of the way.
Once the splices were complete, next step is to glue them, not an overly complex step, but I did make sure that when I made up the joint, first I spread normal mixed T88 on both surfaces, let this soak in for about 10 minutes, and then mixed micro balloons into the remaining epoxy and re spread over the joint surfaces, I did this to ensure that the glue would stay in the joint and not migrate out under pressure.
(note the seemingly never ending process of rib construction in the background)
Once both spars had been joined at the center, I marked out all rib locations, and also cut the various plywood doublers which are at fitting attach points.
When I was building the ribs, I had to keep adjusting my rib fixtures to allow for the various thickness plywood which the ribs must fit over, and in some cases different thickness at the front and rear spar points, this all takes time, but it worked out well, and each rib fit nicely over the planned plywood plates.
Now that all ribs are done, all 72 of them, I can honestly say I have had enough of building ribs!! I worked out I have about 800 hours into the ribs alone, this covers the parts cutting, and preparation, the various jigs and assembly fixtures, and all of the assembly. I think I could have built an RV6 start to finish in about the same time as the ribs have taken.
Here is a simple little tool I made to check the spar centers as I went along. The Super Solution spars sit at 20 inches from front to back, at the center, so to accurately measure this, I lathe turned two short sections of 3/16th stainless rod to a point at one end, and threaded the other ends with a 1032 die.
I drilled a section of aluminum angle at exactly 20 inch centers, and it becomes a handy center checking tool. This replaces the expensive trammel sets which can be used here as well, but this costs next to nothing.
By using a longer aluminum section and routing a channel at one end, this can be used as an adjustable trammel set to true the drag / anti drag wire bays.

I had to halt production for a family holiday in Thailand, we left mid July, and spend 3 weeks in Hua Hin, south of Bangkok, a beautiful beach resort.
The holiday was fantastic! but I was back home in Dubai early August for work, and production resumed. My family stayed in Thailand an additional 3 weeks, so I had the house, and more importantly, the garage to myself, which made for some very productive days.

I wanted to complete all of the wing woodwork, which meant I had to laminate the two tip bows, build the three tapered ribs, and also the leading edge boards.
After the lower wing tip bow disasters, I got smart, and asked David Oviatt to please send "full size" templates of the tip bow, and the three tapered end ribs. He had already worked all of this out in CAD, so he was able to produce and send these drawings.
What an incredible difference, no guessing, I was able to take the full size drawings, build a table for the tip bow (the wing was now taking up the entire bench) and in short order build two perfect tip bows, both identical, and the corrrect shape, the first time!
It is amazing to see how effective CAD can be, when an expert such as David uses it.
also by modifying my existing full size rib jigs, I was able to build the smaller versions of the truss and compression ribs.
With all of the structural woodwork now complete, I decided to take the wings outside for a group photo, the first time they have left the garage, and been outside.

The next step will now be to make all of the metal fittings for the top wings, and there are alot! over 50 separate parts, so much cutting, drilling and welding to go. I am a little more realistic after the lower wings, and I expect the metal parts will take me about a month and a half.
I will be able to now accurately measure the drag / anti drag wires, as there is such little room for error, and order them from Russ, at Vintage Aero in New Zealand. They will take a couple months to produce.
Then it is a a matter of assembling all together, at this point none of the ribs are glued in the top wing, as the spars still need drilling once the fittings are made.
However, I can now see the end in sight for the wings, and I am already looking forward to switching gears onto the fuselage, the tubing for which has been patiently hanging on the wall for a year now.