Fuselage top skin fit up, starting on rudder fittings and engine re-work quote (aka what is the price of your dreams?)
Another productive day in the shop yesterday. Continuing my work on the fuselage, soon to be taken apart again for debur, prime, reassembly then final rivets. I have some plumbing of wire to do from the front cabin are to the tail section and I've got fit up the rear cabin windows before I close everything up.
Like the bottom fuselage skin, the top skin tapers towards the rear. The large hole in this picture still needs to be flanged, but it is the passthrough for the upper elevator control cable. The hole is covered by the horizontal tail assembly and fairings once the are mounted.
Finished trimming the front upper edge of the top skin at the longeron corners and trimmed the skin across the blue line. With this properly fit, the forward end of the longeron can now be drilled and clecoed. Eventually the rear edge of the cabin skylight window will attach to this front skin edge.
Reaching the top of the cabin was tricky, but there is actually just enough room to stand on the workbench to drill, trim and debur holes and edges.
I've bought a 90 degree aircraft air drill which I will use to back drill the wing mounting plates at the top corners of the rear cabin, just waiting for it to arrive this week. I'll post pictures when I get it, but think of the shape of a large dentist drill and you'll be close. For now I'm holding the wing plates in place with C clamps to check fit as I square up the cabin.
The fuselage currently sits on the bench in a tipped back position, so I needed a way to extend the centreline of the top of the fuselage in order to plumb bob that centre relative to the bottom of the fuselage. I cleco clamped a strip of 093 aluminum extended forwards along the top centreline and strung a plumb bob weight downwards:
I know the fuselage cabin is slightly out of square (leaning very slightly to the pilot side without the other cabin structure in place yet). To adjust the square of the cabin, I borrowed one of Ron's turnbuckles and strung it passenger bottom corner to pilot top corner of the cabin. Tightening the turnbuckle pulls the cabin square. It didn't take much to bring it into line, maybe two or three turns.
For the plumb bob, I used the pipe reaming tool head. It is heavy enough to quickly dampen any swaying of the plumb bob line, but not so heavy as to pull down on the fuselage cabin roof. As added bonuses the reamer can be tied and centred on the plumb line easily AND it has a pointy end for really accurate line up with the centre line of the lower cabin skin.
Here is the original square of the cabin - surprisingly close considering nothing else of the cabin structure is connected yet:
After a couple of turns of the turnbuckle:
Obviously string and turnbuckles won't be what holds it all officially square, I'll bolster it more externally when the time comes to tighten things up. But this gets it in position to measure the cockpit side walls and floor and where it attaches.
Also with the cabin squared up, I finished drilling the top skin to the upper longerons from cabin back to tail. I found it helpful to use a ratchet strap lightly around the fuselage to pull the longerons inwards to line up with the skin edges as I work towards the tail. It's this tension that gives the fuselage it's rigidity once riveted.
Every 3rd rivet hole on the top longerons drilled to A3. Next will all the holes aft of the baggage area up to A4. The picture below really captures how tapered the fuselage actually is. The tail is clamped for now to ensure the longerons maintain their taper curve until I figure out order of operations for the balance of the rivet holes and the bolts that hold the fuselage side rudder attachment plates. The longerons need to be trimmed to match the side skins. The small hole just in front of the clamp is the front edge of a passage slot for the lower elevator cable that runs between the hole and the tail end of the top skin hold for the lower elevator cable. It will be slotted soon:
Super stoked to see the fuselage coming together and that it is almost perfectly square as it sits!
Rough placement of the upper rudder hinge plate - this was one of my earliest pieces I cut from 0.125 aluminum plate using the early cardstock templates. I know I'm on the right track as it fits exactly where it should on the tail:
All four of these longeron ends get trimmed to match the side skins:
A look inside the tail looking forward through the tail bulkheads. This large area gets covered by an aluminum fairing that is attached to the rudder and pivots inside this spot:
I marked where the top, side and bottom skins ends meet the longerons, marked them for trimming then peeled back the skins a bit to facilitate trimming with the Dremel (just like the front ones):
Looks like the top skin is a bit short? It matches at the front edge correctly, so I know that is right, so what's going on here.
I remeasured the entire length of side and bottom skins and they are in correct relative position too. But once I remeasured the top skin, I seems I cut the tail end 10mm too short! Everything else on the top skin including the cross members, the upper doublers, the passage holes - all correct. Thankfully this 10mm shortage has no impact on the function of the tail or the rudder attachment structure. It would have much worse at the front end where the main spar channels are or if I'd cut the longerons too short. Still not sure where I made the mistake, but glad it didn't require replacing the entire top skin, that would have been a major set-back (and expensive!)
As more of this enormous project comes together, more intersections of items to complete start to cross on my list of things to do.
Back in September 2018, I travelled to Mexico Missouri for the Zenith factory Open House Weekend (full 6 part blog story about my trip)
One of the prime reasons to travel all that way was to meet with other builders, get some airframe parts that I couldn't fabricate/bend myself direct from the factory and most importantly have some of my Corvair motor parts assessed by the Corvair aircraft engine authority William Wynne who was also in attendance that weekend (he hasn't missed one since they've been doing them)
William had a look at my cores and offered to take them to his shop in Florida for re-work and at the time my plan was to start that process in parallel with my build. Of course that didn't happen for a number of reasons, cost being one of the them.
Fast forward to last week when I contacted them to inquire of my cores were still available in their warehouse as now I was ready to proceed with the work - four + years of them holding them for me was a lot to ask. Thankfully despite my tardiness in getting them moving through their processes, my cores were in fact still available and sitting in storage awaiting my decision.
I received a quote last week for the required work and in discussion via phone with William I now have a solid plan to get the engine work rolling. It's expensive work, but the value in having the recognized expert and his associates do the required work is great value in having a solid engine to fly behind.
Work includes deep cleaning the cylinder heads and piston chambers, new valves, new valve seats, exhaust value rotators and welding on intake pipes. The engine case I sent unfortunately doesn't make the cut and requires too much work to make it viable, so I'll need to replace that with another core (they are easy to obtain). The core crankshaft I had was too rusty to be ground, so they will supply the core which will heat treated (nitride process), stress relieved, the journals be ground/radiused, bearing surfaces polished, new crank gear welded on and the crank will threaded for the propeller hub safety shaft. When that is done, a 5th bearing is added to the crank, ground concentric and shipped back to me with a 5th bearing housing.
All this work is being done by experts and gets me past the half way point of having a ready to bolt on engine. Again well worth it.
William is a great writer. He often reminds people that none of this is possible if you aren't in the arena. I am in the arena and I continue to participate. It can be an expensive undertaking, but ask yourself honestly if you can put a price on your dreams what would it be?
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.