With both the wings into going into storage, I added the fuel tank drain/test ports. I need to make sure that nothing can get into the tanks while they sit in storage, and the any openings on the wings, like the lightening holes at the root have been covered up with tape and plastic to prevent bird or mouse nests!
First time in a very long time the bench has been completely clear of wing stuff! Time to start laying out the fuselage skins.
Had a couple of minutes one afternoon after work to finish one of the horizontal tail fuselage bulkhead frames need for the fuselage:
The plans are a bit deceiving when looking at the them when scaled down from full size. Close attention shows that the four corners of the fuselage aren't actually directly straight - the fuselage tapers very gently from the back of the cabin to the tail along all four longeron corners.
I've been pondering this for a while and when I was at the Zenair factory in Midland buying my longerons last month, I asked Nicholas Heintz (Chris' son) what would be an acceptable way for a scratchbuilder like me to make the correct tapered curve of the skins (the longerons curve to match the skins and are pre-cut in the kit versions).
Nicholas said the taper is very subtle and I should just connect the measured points out from the centre-line as shown in the plans. As long as the taper is equal on both sides of each of the four fuselage skins, all would be acceptable, but the taper is important as it provides some longitudinal rigidity to the fuselage..
Apparently that's not good enough for me! I wasn't confident that each 500mm point would give me enough points close enough together to draw through to make the gentle curve. So I grabbed the plans and entered them into CAD, like a lot of the templates I've made.
CAD has a great "spline" tool that is like using a draughtsman's French curve ruler to average out the points in the plans to establish a smooth curve. Then I used tools within CAD to section each of the 500mm sections on the plans into 100mm smaller sections, then measured where the points along the curve so I could transfer this onto the aluminum. Enough points along this curve means I can connect them with a real French curve ruler and have my taper drawn correctly on the aluminum sheet.
Here is a snapshot of the fuselage bottom skin, half way through the sectioning process in CAD:
The fuselage skins are all 0.020 thick, with several doublers between the longerons laterally and diagonally to stiffen everything up. The bottom skin is laid out on the table and I used the long straight edge to draw the centreline from which the edge points will be measured:
I measured out each of the sections lines along the centre-line, then used a square aligned with the long straightedge to plot the section lines out the edge of where the skin will be. I soon realized that Nicholas was probably right, curves based on the 500mm sections would probably be enough, so I decided to divide the sections into 250mm sections instead. This is a good compromise and accurate enough for me to make the taper correct using the French curve ruler we have.
This picture shows the lateral lines drawn out from the centre - the circles are where the curve of the edge of the skin will be and the lines from circle to circle are the skin edges which will be trimmed later. From there, I laid out the lower hatch door opening (often called the hell-hole) and some of the other lateral lines for the stiffeners, diagonal "L's" and torque tube bearing channel (supports the control torque tube):
A 10mm line scribed inboard from the edge skin is the rivet line where the skin will be fastened to the longeron once the skin sides are trimmed. This picture is the tail end of the lower fuse skin.
The lower fuse skin is actually too long to fit on a full 12 foot sheet of aluminum, even if I "tilt" the lower skin outline on the sheet, so a lower rear skin is added - it becomes part of the horizontal tail "box" and further strengthens this part of the fuselage to support the tail structure. Aligning it on the centre-line at the proper location ensures the lower skin is the correct length from the cabin to the rudder supports. Here it is temporarily clecoed in place:
Z-channels are added around the sides and rear of the lower hatch. These still need to be trimmed, I just wanted a rough idea where/how they interact with each other and how the rivet spacing should lay out. The square of cardstock is a quick cut out for me to use to visuallize where the flap motor will mount - again for rivet spacing, etc.:
Cutting out the access hatch was fairly easy. I used the fly-cutter to shape out the corners:
Then connected the edges of the circles and cut out the hatch. Some filing and sanding to take care of some rough edges and the access hole is done. I'll make the hatch cover from some of the left over 020 of the top skin.
I finished (for now) the bottom skin. All the rivet lines are laid out and drilled. Before I cut the bottom skin out, I've rolled it back up as as full 12x4 full sheet. Much easier to store.
Returning to CAD, I sketched out the two side skins and the top skin - this time with 250mm sections. It worked so well with the bottom skin, this will be the path to obtain the tapered curves for the other 3 sides of the fuselage (these are snapshots from CAD, not scaled together):
The top skin is somewhat shorter in length than the bottom skin, so I can comfortably "tilt" it on the aluminum sheet to save wasting some of the sheet.
Same layout method as the bottom skin. This skin has a flanged hole near the tail - this is where the elevator control cables will pass through the fuselage into the vertical tail assembly. Cut it out using the fly-cutter. I'll flange it later once the skin out cut out form the sheet so I can clamp the flanging dies easier (can't reach the hole now):
A second hole is cut near the tail end. This will form the round end of the channel as laid out by the lines drawn rearward from the circle to the rear skin edge:
Now onto the part that has been keeping me up at night.
We don't have the ability to bend complex shapes such as the upper top channel shown below. It's a slightly leaning C shaped channel, tapered at the ends that forms part of the wing spar carry-through on the top rear of the cabin. It is made of understandably stout 063 aluminum and both the shape and dimensions are critical to ensuring the wings mate to the fuselage at the right angle and location. So I ordered this from Zenith and picked it up the same day as the longerons.
Problem is, I hadn't thought it through and asked them to provide the channel pre-drilled, as they would in a kit. What I didn't consider is how to transfer the holes to the cover channel and doubler that make up the other sides of the top channel to form the spar carry though box.
I could order those pieces too, but when I spoke with them, they couldn't guarantee they the holes in the other 2 parts would be an exact match to mine as they drill them together at the time of manufacture, and mine was a one-of ordered part.
What to do. Start looking at order of operations and see if I can match drill the holes somehow, while respecting the bends yet to be made in the other two parts.
I can access some of the holes at the end of the top channel where it is cut diagonally to match the cabin uprights, so I placed the top channel in the proper position of on the top skin, drilled/clecoed the accessible holes form above into the skin. With that done and the channel secured to the skin in the right location I then duplicated the remainng holes along the bottom of the channel (actually the top when the skin is in place) onto the top skin because I can use the strap duplicator before the other pieces are added and drill from below the table level:
Unfortunately, as well as that worked, several of the holes on the channel are the bigger A6 river size rather than the standard A5 in the rest of the channel. Here is the channel lying on it's back. The 5 holes grouped close together are the ones I'm taking about. I don't know if an A6 duplicator is available, but we don't have one. These A6 holes are not accessible from inside the channel either.
Time to get creative.
I bent a matching piece of 016 to fit inside the channel and long enough to cover both the A6 holes, two inboard A5 and the A5 hole outboard holes and clamped it in place:
Back drilling through the channel into the 016 (using clecos in the three A5 holes to hold it together straight) and A6 size in the other holes gave me an excellent template to transfer to the skin that will match the channel holes:
Template added to skin, secured with clecos in the existing A5 holes, then A6 holes drilled through the skin:
I added more holes in the template from the forward facing A6 holes so once I have the doubler and channel angle bent, it too can be duplicated without having the access from inside the channel:
Fabricated and drilled the upper baggage area rear panel support angle to the upper skin:
This angle won't change once needed, so I finished all the river holes, deburred it and put it back into storage.
Next up was fitting and predrilling the upper fuselage top doublers. These doublers are almost like the shoulder blades of the wing/fuselage junction which transfers the loads back over the fuselage longerons and upper skin.
First I lined them up on the top skin and used extended lines from the top channel holes and the longeron rivet lines. Once in place, I traced those same river lines onto the doubler and laid out the rivet locations as per the plan. The doubler actually fits onto the outside of the fuselage, but laying it out this way allows me to see the lines before drilling through the doubler and the skin.
Once I was satisfied with the layout, I drilled pilot holes in the doubler on the drill press in the require locations, but not where the top channel lays. Then I back drilled through the doubler in 5 locations to secure it to the skin. The rest I'll drill once the longerons are in place:
Both doublers in place, secured enough for the next steps:
Shifted the doublers to their proper position on the outside of the fuselage skin (remember, I'm working on the inside of the skin and it's actually upside down on the table) and clecoede them in place from above. Then I placed the top channel back in place and secured it from below using the holes duplicated earlier in the skin:
I drilled the forst A5 hole and the two A6 holes I can access at the end of the top channel, then removed the channel and marked the others through the skin and into the top skin doubler:
Removing the top doubler and finishing the holes on the drill press, proves the matching worked (for some reason the picture below seems to show the holes are out of round, but it must be a shadow from the flash as they are actually perfectly matched):
I've also been scrounging a bit online on various marketplaces, classified listings and forums. Scratch building makes you keen to grab deals when they come up and I've been scoring well lately.
Both Ron and I want to make epoxy resin castings for our navigation light lenses and strobes. One of the tools needed to cast clear lenses is a vacuum chamber which is used to de-gas both the silicone molding mixture and the epoxy itself.
I spotted this complete set on Facebook from a seller not to far away. She wanted $125 for everything but I managed to get it for $100 just by asking. It's really brand new, she told me she'd only used it a couple of times but couldn't handle the fumes, so she was looking to sell it to someone who could use it. I looked it up after I bought it and there is easily $400 worth of stiff here, so I was a bit surpised she was willing to sell it for so little.
I brought it to the shop and tried it. Ah. It's not working, that's why.
The vacuum pump appeared to be pulling lots of pressure at the end of the vacuum line, but nothing was jhappening in the pot. Originally I thought maybe the valves were bad or something and I would have to replace them.
When I looked closer however, it looks like someone let the some casting epoxy get into the vacuum port on the pot lid, sealing it completely over! A quick drill and clean out of the port, freed up everything and it is working like new again. Score! We can also use this to de-gas paint for the planes too.
On the Zenith website classifieds, I spotted a suitable airspeed and altitude indicator. Used, but in excellent used condition, clearly taken care of by the previous owner. $200 USD for the pair - Score!
Another Facebook marketplace find were these cable turnbuckles, cable swivels, and throttle cable. Less than $200USD for everything - Score!
Ron continues to look for some parts for his Continental O-200 conversion for the Aeronca Scout rebuild. He bought a Cessna 140 for the engine, but it needed a new intake spider which was cracked.
These are getting very VERY hard to find as they often get damaged during prop strikes and need replacing. New ones are available, but cost north of $800USD!! I spotted one on Facebook marketplace, contacted the seller and managed to get this good used one and a box of other intake parts for $100USD shipped! - Score! I've given it to Ron as thanks for all his help with my build and his kindness in letting me use his shop. That's the kind of karma that I believe we need more of in this world :)
I'm getting close enough now that I need to consider what I need for my Corvair engine install with regards to firewall forward stuff.
I ordered my Corvair/Zenith installation manual as well as the MOP (Maintenance and Operations Procedures) manual.
They arrived in my hands and I sat on the dock the following morning looking through them. This build is always on my mind, even in the quiet times :)
More to come, thanks for reading along!
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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.