I've been meaning to publish this edition of my blog since Monday, which was Halloween, but work commitments have kept me busy and I've also been in the shop getting stuff done!
With the lower fuselage skin almost ready for deburring and priming of the joining surfaces, I needed to get the lower fuselage access cover (the Hell Hole cover) final fit up done. I didn't time this to happen on Halloween, but it seems appropriate :)
Before taking the lower skin/longeron/diagonals apart for debur, I fitted the flap/controls mixer cross support by back drilling from the inside of the skin just forward of the hell hole. This cross member provides the rear support structure for the flight controls as they pass through the centre of the cabin space back to the flapperon mixer tube (more on this once completed) .
Also drilled out and deburred the control tube bearing hole in the centre support channel. This mounts centred on cross member to support the control tubes, but I'll wait until I have more of the rear baggage area complete to determine the correct vertical mounting position for it. Nothing in the plans shows a vertical measurement and I want to have it exactly correct so the controls don't bind. There are also some clearance holes to be made once mounted.
With all the diagonals and longerons removed, I laid the lower skin down flat and upside down on the table. The hell hole cover was placed into final position and squared to the hole, diamond bends facing out from the hole.
The goal here is to make the cover lay as flat as possible to the lower skin and use the tension created by the diamond bends to tighten the cover skin as it rebounds once attached. It isn't much, maybe 5mm of depth in the cover from corners to the peak where the diamond bends cross, but it certainly is an effective design by Zenith.
With the cover in position, I placed a bucket of clecos on the centre, which weighted down the panel flat. Then I drilled the cover down where rivnuts and screws will hold it in place, starting at the corners:
With all the holes drilled and fastened (not all shown in this picture) to the lower fuselage skin the cover maintains tension and stiffness once the weight in the middle was removed - excellent!
With everything match drilled to correct size where I can at this point, it was time to strip off the protective plastic and start deburring all the holes. I generally try to leave the plastic on as long as I can to help protect the finish of the aluminum from getting scratched - it's never perfect, but reduces the amount of scratches I'll need to remove before eventual prime and paint.
Once every hole is deburred (both sides of the skin), every inside surface of the skin that contacts another part gets a scuff with ScotchBrite, then a light spray of primer. Like all the other components I've assembled so far, grey self-etching primer in visible/outside areas, zinc-chromate green on inside surfaces.
The inside of the access hole gets the grey:
The rear inside of the fuselage and lower rear skin gets the green:
Had a couple of minutes down time while the primer cured, so I fabricated some nylon bushing plates that will be required for the flapperon mixer assembly. 40mm square, 1/8" thick.
Used a punch to centre a hole in each which eventually will be drilled out to 3/8". More on these later.
For now the lower fuselage skin gets rolled up and put back into storage so I can complete the diagonals and upper longerons for the side skins.
Laying out the right side fuselage skin on the table I needed to complete the cabin window cut-outs. I've been anxious about doing these as there is always a risk of tearing the thin fuselage skin which could render the entire skin un-useable and needing to be replaced. But like anything in this build so far, no risk = no reward, right?
Clamping the skin down to the table with a sacrificial backing board behind it and I used a bit of cutting oil to assist with the round corners:
The pilot holes I drilled previously are exactly the same on both fuselage side skins, but they are being cut individually. I was going to use the fly-cutter tool to form the corners of the cabin window cutouts, but it is too big to cut 25mm radius holes, forcing me to use a bi-metal hole saw. Much more aggressive cutting, but taking it slow and using the cutting oil worked very well.
Corner holes for the cabin window cutouts complete:
Inside hole cuts can be difficult, particularly in small areas as there is no way for the cut-away aluminum to curl out of the way of the shears as it is cut.
Getting metal shears into the 25mm radius holes effectively was too difficult, so I used a Dremel cut off wheel to first cut a relief line wide inside the window cut out. This freed up the tension in the aluminum and I could trim the outer edges of the windows smooth between the corners:
Next all cuts are deburred and sanded smooth. Eventually I'll flange the edges inwards just a little bit so the edges are tight against the Lexan windows. I'm looking into adding a silicone or rubber gasket as well which will keep out the rain and prevent any rubbing on the Lexan.
It took a couple of hours to complete the cabin window cutouts, but with a bit of patience and careful trimming, they both turned out great!
Window cutouts complete, time to start adding the vertical and diagonal stiffeners:
I've done the same as the bottom fuselage skin, adding additional opposite diagonals:
Once the diagonals are in place, flip the right side fuselage skin over and start fitting the longerons. A yet to be drilled longeron for the top edge and the lower right longeron from the bottom skin in place on the side skin for fit up. The lower one is only clamped in place at this time, it will be match drilled during assembly of each of the finished side skins to the bottom skins.
I still need to trim the forward edges of the fuselage side skins at the front cabin join location. I'll wait until later once I have the uprights and spar carry thorough channels fitted in place (just in front of the windows, better view in another picture further down):
Drilled out the upper right side longeron to A3, then alternatively to A4. A forest of clecos!
With the upper longeron final match drilled, the entire right side fuselage assembly is flipped back over and I can start to fit up some of the upright channels.
The baggage area back panel support channel shown here in rough location. I originally thought I should pilot hole fit this in place for future assembly, but I've decided to wait until the fuselage sides are mated to the fuselage bottom to see how everything fits best. Kit builders don't have these issues, they just cleco things together and right size the holes for rivets.
Test fit of other upright channels seems to confirm things will go together nicely when the time comes. The two channels at the left show where the fuselage side skin will be trimmed to match. The channel in the middle behind the first cabin window is one half of the flapperon control tube cover (more on these later).
Next up, everything comes apart for debur and priming. The repeat everything for the left side fuselage skin. With the left side done, I can start assembly of the fuselage and installation of some of the controls like the flap mixer and bearings. I'll likely be fitting the windows up as well, but the final install of the windows happens much later on in the build.
Very pleased with my progress so far on the fuselage. I got discouraged for a bit figuring out order of operations, but managed to get a process together that seems to work well so the left side should go much faster. Another bite of elephant consumed :)
Thanks for following along, more to come soon!
I stated before that the fuselage should go together relatively quick and so far so good.
More work on the lateral and diagonal stiffeners, drilling them out to A4 (final size). Now that the stiffeners are solidly in place, it's better in my case to drill from the exterior inwards, rather than taking a chance on rounding out an exterior facing hole. True kit builders have match drilled parts, and quick build kits all the riveting is done for them!
Same for the "Z" channels around the hell-hole. First all to A3 for accuracy, then right sized to A4:
With the lower skin facing exterior up, it's time to add the corner longerons to the lower skin. I've been looking forward to this as it really defines the shape of the rear fuselage. First, I added the lower rear skin at the tail and confirmed the overall lower skin is the correct length as per the plan:
The 4 corner longerons are custom extrusions (read expensive) that you can't buy anywhere else but through Zenith. As expensive as they are, they a a beautiful extrusion (on the left in the picture) perfectly matched to the fuselage skin edges:
As stout as they are, they are flexible enough to match the taper of the fuselage. To start, I clamped the extrusion to the skins at each end:
This picture really captures the taper, looking back from the cabin end of the fuselage. The secret I found was to drill and cleco front to back, through the pre-drilled holes in the skin that I laid out previously. Bending the longeron extrusion to match the taper was actually quite easy and I used clamps as I went to get the skin tight up against the outer radius of the longeron:
First one done (right side, skin is currently inverted on the bench, second one clamped and awaiting it's turn:
The longerons come a bit longer than required for the skin - they get trimmed later in the process:
Left side longeron pilot drilled:
Longerons, lateral and diagonal bracing complete up to A4 rivet size where required. I purposely left the section of A5 holes adjacent to and forward of the hell hole, as there are gussets to be installed there that will require back drilling from the inside:
The combo of the longerons and the stiffeners really squares everything up!
The lower fuselage skin gussets were next. I cut the 060 alumium to shape and then pre-drilled them as a stack to ensure they match for both sides of the lower forward fuselage skin where they are installed:
The gussets are not equilateraly triangle shapped and they go on the inside of the fuselage. They distribute and balance the load from the landing gear and cabin/fuselage mating point.
Time for the hell-hole access cover.
The cover is 540mm wide by 640mm long which allows for overlap of the hell hole. Cut the 020 aluminum to correct size and initially thought this wasn't going to be stiff enough a material over the hole once airborne. Trust the plans they say, so I continued to fabricate the cover, starting my radiuses on the corners (both cosmetic and functional):
Centre of the crossed lines represents a 5mm radius corner:
Turns out a bolt size template also works good for tracing the radius - an AN6 bolt diameter is close enough to 10mm to be used to scribe a 5mm radius:
Snips to trim the corner to roughly 5mm, then file and sand to make it perfect:
The plans call for "diamond bends" diagonally across the cover, so I laid out bending lines on the underside as the very faint bend needs to point outwards from the hole it covers:
Flipped back over after the diamond bends. Very surprising how much that stiffens to the whole sheet. I think it looks like the back-splash on a fish-and-chips kitchen, but this will be less apparent with paint and flattening when I secure it over the hole using riv-nuts.
From the top side, I laid out attachment pilot holes, 10mm in from the edge. These holes will be replicated onto the fuselage skin once in place, but I'm going to wait until I have the lower fuselage apart for debur, that way I can press it flat to the table as I position the riv-nut holes in the lower skin around the periphery of the hell-hole.
A few more things to do from the inside of the fuselage, namely the inside lower skin gussets and the front/rear horizontal tail framing.
First the gussets. They are installed over the inside surface of the longeron and but-up against the front edge of the lower fuselage skin. Using the pilot holes in the gusset, I matched the holes through the longeron and fuselage skin. The longerons also need to be eventually trimmed at the front to match, but having them long allows for a cleco clamp to hold the gusset in correct position for match drilling:
Eventually they get drilled up from A3 to A4 then to A5 (final size). Here is a festive Halloween colour photograph half way through the process:
All done with the gussets for now. The forward facing edge of the triangle will be done once the passenger cabin is attached and the landing gear channel is installed.
Next, the horizontal tail box bulkheads. The rear one wasn't to difficult to line up, using clamps as it the mounting flange is an open angle and easy to drill and cleco, up to A5:
The flange on the front HT bulkhead is more difficult as it is a closed angle:
To facilitate the drilling, pulled the lower skin assembly over the edge of the bench so I could drill from below, eventually up to A5. The precise angle of these bulkheads relative to the lower skin will be determined later when the side skins go on:
I mentioned in a previous blog that the 12 foot sheet of 020 used for the side skins isn't long enough to reach all the way back to the tail. So like the lower skin, there is an extension piece. I made these very early on in the build as it was a fairly simple flat shape to make. It was satisfying to clamp them in place on the lower skin assembly and see that they match!
Looking at this picture makes me think I have the rear side skins turned 90 degrees the wrong way, but that could be camera distortion. I'll double check that.
So pleased to see the lower fuselage skin coming together and some other parts fitting up too. Too bad it has to come all apart for debur, prep and prime of the mating surfaces :( The both fuselage sides need their vertical and diagonal stiffeners matched up, then they can go through their own prep (I wish they could do it themselves!) before adding them to the lower fuselage skin... phew, that's a lot of holes!
Oh well that is just part of #dreambuildfly! Thanks for following along, stay tuned for more.
With the wings in storage and the fuselage skins measured and laid out, I can start working on assembling the fuselage! It's been a long time coming, but so looking forward to this step. Big updates as follows.
First up I finished fabricating the last component parts of the fuselage that I can ahead of time. These baggage back support channels will be needed once the skins are together to start building out the baggage area in the rear area of the cabin.
I've said before how handy the CriCut Maker is for taking CAD drawings and cutting them out for use in the project. Here is the template I used for the top ends of the baggage back channels.
I orginally planned to use the crosshairs in the middle of the circle to mark where to bore the hole in the blanks, but I realized I cut the blanks to length first. No way to expand the hole to the correct size by drilling (step drill only works on full area, not edges).
Cut the circle portion away, then traced the curve on the blank.
Carefully cutting them out with the bandsaw and gently finishing with a round file worked fine. The baggage back channels bent up nice.
To measure out the side skins, I used the same method as the lower and upper fuselage skins. They too have a gentle taper curve from front to tail. I adapted the plans into CAD and added 250mm sections, to be measured out on the skins for better accuracy of the taper.
Another template I cut out after CAD entry is are the cut outs for the rear cabin windows.
Unlike the bottom and top fuselage skins, both side skins need to be mirror images of each other. To accomplish this, I stacked two full sheets of 020 and clamped them to the bench.
Then I proceeded to lay out the balance of the measurements on the side skins. To ensure both side skin sheets stayed aligned, I drilled and clecoed indexing holes at the corners together. These index holes are on part of the aluminum that will later be trimmed off. From this point on any holes drilled for windows, supports or other items will be exactly the same on each sheet.
The plans are somewhat difficult to interpret here with regards to where the windows actually are on the side skins. Great measurements if you are using a CNC machine to cut out the holes - not so much for a scratch builder! It took some time and several cross-checks to be sure but they are correct.
Drilled A3 pilot holes along the measured edges of the skin, through both sheets and 10mm in from the skin edges where the fuselage longerons attach:
Balance of pilot holes drilled and clecoed. My camera really distorts proportion on long lengths like this, the taper from front to back of the side skins is much greater than what is seen here (see the CAD diagram above):
Another challenge when scratch building is being sure of the best order of drilling holes - i.e. what will I need to pilot drill, from which side and what attaches here. You can see some notes on the skin in red reminding me to wait on these holes until later assembly as there are doublers here that need to be back drilled on later assembly steps:
Extended the lines on the window templates to confirm they match and line up with what's drawn on the skins:
Taped the templates down in the right locations, then drilled pilot/index holes through both sheets, at the corners of the windows. These pilot/index holes will eventually be widened out to 25mm radius in the skin - but both skins will be exactly the same, just like everything else.
A trace out of the template edges onto the aluminum sheet confirms window orientation to other cabin area components - perfect!
Like the lower skin, the overall dimensions of the side skins are too big for a 4x12 sheet of 020 aluminum, so it requires a extension on the tail end. This doubler skin extension also bolsters the "box structure" of the fuselage tail that supports the horizontal tail and rudder. These side skin extensions are some of the first pieces I made in this project, several years ago - glad to see them being put to use after taking space on the shelf!
Took a few minutes to finished sizing and sanding the rear wing pickups - eventually these plates will attach at the top front corners of the rear fuselage to be mount points for the wings - will be needed very soon, so wanted them done and available.
Unstacked the two side skin aluminum sheets and put the drilled but unmarked lower sheet aside. With the marked sheet back on the bench, I trimmed the edges to the correct shape using shears:
Hard to see in this picture due to camera proportion distortion, but the top edge of the side skin definately has a gentle curve from front to back:
This angle shows the side skin taper well. This is after I trimmed the bottom edge:
Re-stacked the skins again, re-indexing them using the same pilot holes I drilled as before. Then I traced the outer edges of the first skin (now cut to correct size) onto the second skin, making a perfect copy:
Removing the first side skin and returning it (rolled up) to storage, I replicated the layout lines on the second skin - this was easy as the pilot holes already exist where the support angles will be, then this exact copy was cut out using the traced lines from the first skin, then rolled up and put away for now into storage.
Next I got the top skin back on the bench an cut it out from the sheet. Once done, it too was rolled and put into storage.
Bottom skin, back on the bench for trimming to size. Here the pilot side has been trimmed away:
Again, camera distortion at work. Here is the trimmed to size lower skin looking from the tail to where it will join the cabin. It does show however show the curved taper of the fuselage sides. Very happy how this turned out:
It looks really lopsided in this picture - but dimensions between the edges and the access hole are completely equal and square - weird.
Next up, fitting the internal bracing around the access panel (affectionately called "hell hole"). It is supported on 3 sides by Z shaped channels:
The first Z fits laterally across the fuselage skin just aft of the hole. Then one on each side:
Z channel is called that, but it's a bit lopsided to be a true "Z"
Two more overlapping Z's fit laterally on each side, really stiffening up the lower skin:
Next up, the lateral L stiffeners and diagonal L's in each lower bay:
There are literally tonnes of discussions on various forums and websites about "oil canning" of Zenith fuselages. Oil canning is where the skin surfaces between the lateral stiffeners tends to drum a bit as rough air passes over them during certain aerodynamic situations. Some say it's not a Zenith unless it does this but I don't think it needs to be that way. I remember going for a demo flight in a very early model and couldn't believe the noise in the cabin on slow approaches or steep turns (where the airflow over the fuselage is turbulent or "dirty" as they say). Almost too much to endure.
When the original Zenith 701 came out to build it was a plans only design, built in a garage and to be absolutely the the lightest structure possible. Zenith intended it to be be flown as an ultralight on 65HP Rotax two-strokes - so I understand that less weight was important and made it easiest and cheapest for the average person. I guess the drumming of the skins was considered an acceptable trade off.
As the design evolved into what is now the 750 STOL (like mine), the 750 Cruzer, the 750 Super Duty and the 4 seat 801 which all use larger and heavier engines, the drumming remains. In my opinion, Zenith needs to update their designs in this regard. Current larger engine horsepower choices allow for more overall aircraft weight and by extension the reinforcement of these areas - the weight penalty is extremely small for what it resolves. Less drumming is better on pilot fatigue and more importantly airframe metal fatigue.
So to improve my airplane I'm adding additional diagonals to all fuselage skin bays. None of this additional weight is significant nor does it impede any further components form being installed or functioning - all it does is stiffen up the skins to reduce (or hopefully eliminate) skin drumming. Here are the first two bays in the lower fuselage skin with the additional bracing installed:
Next up, I'll finish adding the extra diagonals where needed, then start to prep the lower skin for the addition of the lower longerons. In the meantime, I'm headed to the Zenair/Midland Huronia Airport open house soon and will pick up a couple of more parts from them for the fuselage I can't make in house and some more stuff from Aircraft Spruce - exciting progress ahead.
Thanks for reading along!
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!
Been over a month since I've updated the blog, but that doesn't mean I haven't been very busy in the shop making tons of progress!
Second fuel tank went together very quickly. Using the 2 part sealant enough times now, I've become used to best methods of applying it.
Outboard side of 2nd wing tank. Rivets on the lower seam are held in place with masking tape. This allows me to apply the sealant bead, insert the tank wall and then squeeze the rivets in one (almost seamless) process:
With the edges closed up and rivets squeezed, another layer of sealant is applied to all outside edges and seams. I learned from the 1st tank to make things cleaner by masking off the edges:
Waited the required 6 days after the last of the sealant was applied before leak testing the tank with water. Like the 1st tank, a couple of small weaping leaks required some re-work of the seams and some more sealant.
While that cured (for another 6 days!), I got some work done on some of the smaller parts for the controls and fuselage.
Some of these templates are ones I created a few years ago using CAD, a PDF conversion program and then printed out on cardstock using a laser printer.
Lots and lots of small parts from aluminum plate and aluminum sheet:
More recently, I've been using the CriCut Maker machine more as it has the ability to not only cut my templates from card stock direct from the CAD file, but I can also print on the templates as well - handy for part numbers and drawing centre marks for holes etc.
Some of the last parts I needed were from 063 aluminum sheet.
Some templates don't need to be the full length either. For example, these flapperon control rod covers are 890mm in length, but the same width at both ends. A short template serves dual purpose for both end cut measurements:
I laid out several of the pieces I have made for the cabin and fuselage - including seat pans upper and lower fuselage doublers and more. Like I said, I've been very busy! Here they are in an animation using the online gif maker Kapwing. My animations skills won't have me working for Pixar!
With the tank sealant cured and tested again (this time no leaks!), I got it installed in the wing. Fuel line and fuel tank wiring is done:
Wing is sealed up again:
Fuel cap and filler neck fit perfectly! Wing is ready for storage!
Next I started final bending/fabrication on some of the parts I've been cutting out from sheet.
Seat pans require lightening holes, so I drilled those out:
Then I used the flanging dies and some large C-clamps to form the lightening holes:
Same for the seat pan supports:
Major milestone completed with both wings now complete and ready for storage. Next, we'll get this wing into the storage barn and start the process of laying out the rear fuselage.
Thanks for following along! More to come soon!
Delayed time getting into the shop this week. Couple of busy and long days at work left me no energy for plane building (shocker really), and then my first CoVid vaccine (Moderna) kicked my ass for a day and half. Back in the shop on Sunday, but limited energy so things moved kinda slow.
Started the day pulling off the upper skin and deburring all the ribs, triling edge skins and upper wing skins:
Let the nose skin back up a bit to deburr it as well:
Clecoed the skin back down and pulled the A4 rivets for the wing stiffeners. Taking the skin off for inspection later won't be an issue having these complete so got them done:
Primed the edge of the upper wing skin where the tank skin will join over top:
Primed the root support L - did it in grey primer as it will show through the join in the tank and root skins:
Rolled out the nose skin again and applied a bit more green primer that got scuffed up a bit when I was cutting and deburring the slat support slots:
I wanted to strengthen the wing tip plastic so that when it gets riveted to the wing the rivets tails won't pull through or worse crack the plastic. Several builders reinforce this area using 016 strips around the perimeter and I did the same. First though I wanted to back the area where the wing tip nav-lights mount for much the same reasons. I don't know at this point if the nav-light will be riveted or screwed through the plastic, so I made a doubler plate out of 025. Had to rough it out then use the bench sander to trim it down until it fit inside the form to lay completely flat:
Once I had the first one, I made a second one the same for the left wing:
Next up, I went about cutting some scrap 016 into strips to match the inside edge widths of the wing tips. This took some time and I had to break the perimeter into several manageable sections due to the complex curves of the nose section:
This is the hardest section. The inside edge not only narrows dramatically, but curves sharply inwards at the same time. I used a cardstock template clipped on to the edge area, tracing the outer inside edge first:
Carefully flipping it over, I then traced the outside edge (which is the inner edge inside the tip):
This very rough size cardstock template is what I ended up with:
Trimmed out with scissors, I continued to trim it down until I was satisfied with the fit when pinned to the inside curve of the wingtip:
Traced out on 016 scrap and the tail end was left purposely long as I can adjust the length of the next piece easier than fussing with this one:
All the edge pieces, deburred and edge sanded smooth. Inside surfaces scuffed up with 150 grit sandpaper and cleaned with lacquer thinner. More scuff than required for primer, something for the EkoBond adhesive to grab onto:
Being new at using this stuff, I decided to do the nav-light backing plate first. EkoBond on both surfaces after scuffing up both with 150 grit sandpaper:
You have to be careful as the grip is very strong once it starts to get tacky - not much room to re-position once in place, but I got it where I wanted first try:
In hindsight, I probably overdid it with the clamps, but happy with how it turned out:
Overnight curing and that plate isn't coming out!
Same process for each of the strips. I was smart enough to number them to match them up when the time came to place them. If you look close, you can see streaks of blue in the green on the lower left where the EkoBond is still setting up (turning green like the rest):
Started with the complex curves near the nose first then trimmed the long straight pieces at the trailing edge end where needed. Several binder clip, spring clamps and clothes pins keep everything clamped together while it cures:
Perimeter backing strips complete. When I return to the shop on Wednesday night this will be cured and ready for final fit up on the outboard end of the wing. Pulled rivets now have something to grab on:
Between steps (waiting for blue to go green), I got the inboard lower trailing edge trimmed using the Dremel and a cutoff wheel. It's becoming my favourite tool it seems!
Good progress despite feeling like a bag of dirt the last couple of days.
My new pressure sensors arrived in my work mailbox today, so I'll have them shortly for testing. I have high confidence in my theory of how they will work in the fuel system and how to read them using Arduino micro-controller and display.
Onwards... thanks for reading.
p.s. - I'd be wrong not to mention the passing of Chris Heintz, designer of Zenith Aircraft who passed away a couple of days ago, peacefully with his wife at his side. His legacy in aviation stretches from work on the Concorde (yes THAT Concorde) to starting a small aircraft plans business that has grown over 40 years to become the Zenith Aircraft Company, the makers of the aircraft design I am building. His contributions to this hobby and general aviation as a sport can not be overstated. Such a kind and humble soul.
Blue skies and tailwinds Chris - and thank you for making dreams possible for people like me :)
It's been a while since I posted, but progress continues on both wing spars. As I stated previously, I want both main spars complete and ready for ribs before starting to add the other wing structures. The wing takes up a substantial part of the work area, so the left spar when complete will go to storage while I build up the right wing. Once the right wing is skinned, it will swap into storage and I'll build up the left.
All the bucked rivets in the right wing spar are done, so it was time to final hole drill the left wing spar in prep for debur, prime and final reassembly.
This picture was taken around Halloween. The black A5 clecos and copper (orange) A4 clecos reminded me of the season!
Unfortunately, one of the holes in the spar web doubler came through very close to nicking the spar cap. Thankfully it didn't, but this will make it impossible to have enough clearance to drive the rivet with the bucking gun. Solution was to drive the rivet from the other side - not ideal, but perfectly acceptable according to the build standards.
With all the holes now complete, it comes all apart for debur, prime and reassembly.
When I was reviewing the drawings, the question of dissimilar metal corrosion (called a galvanic reaction) came to mind. Galvanic corrosion (also called bimetallic corrosion or dissimilar metal corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. The electrolyte in this case can simply be environmental humidity. Salt water exposure would be worst case scenario.
The aluminum spar attachments are made of aluminum. The connection points on the struts and front of the cabin frame are 4130 steel. I did some research on the forums and it seems most people just ensure they have good prime/paint on both parts and/or powder coating on the steel parts.
So what does the aerospace industry do? They anodize their parts.
Anodizing in the simplest of terms is a process of increasing the thickness of the natural oxide layer on the surface of a metal part. This thickened oxide layer renders the part non-conductive electrically, thereby preventing galvanic reaction with other metals. The anodized aluminium layer is grown by passing a direct current through an electrolytic solution, with the aluminium part serving as the anode (the positive electrode). The current releases hydrogen at the cathode (the negative electrode, either lead or aluminum) and oxygen at the surface of the aluminium anode, creating a build-up of aluminium oxide on the part.
This doesn't however change the dimensions of the part as the layer is nano-metres thin.
Sounds complicated, but is actually simple enough to do in the shop. There are literally dozens of YouTube videos online showing different methods for doing this. Many home hobbyists do this when making parts for their car, computer cases, flashlights etc.
I managed to find a good article in KitPlanes magazine which was simple enough I thought I'd give it a go for my strut pick-ups and spar attach brackets. In the end, if it it didn't work, I can always just prime and powder coat where necessary. The over-riding mantra of my build is to learn, so this is something worth trying.
There are several components needed for the home anodizing process, which I'll try and detail here in pictures.
I scored a small aquarium air pump at the thrift store - 2 bucks. A new piece of air tubing for $3 and a air-stone for making bubbles in the electrolyte $5 from the local pet store. The purpose is to agitate the electrolyte, essentially circulating the solution as the process happens.
Distilled water which makes up the majority of the electrolyte solution. A thrift store kettle for $5 - I should have bought a larger one as the parts once complete need to be boiled in distilled water for an hour to seal the anodizing coat (more on this later). Baking soda to neutralize the electrolyte bath acid and also to contain any spills.
The main electrolyte bath tub.
The main rinse/neutrailizing bath - warm distilled water/baking soda solution:
My electolyte bath is a 10% solution of Muriatic acid and distilled water. I followed the measurements closely and all the warnings of adding the acid to the water slowly. Never add water to acid - always acid to water. The thermal reaction is easier to control by adding acid a little at a time - it can be explosive if you do it the other way around! Pay attention closely to the instructions. Muriatic acid is nasty stuff, so wear gloves, goggles and breathing mask. Make sure to use a well ventilated area.
Before the parts can be anodized, all residual oils, markings and natural corrosion must be removed. The easiest was to do this is using household amonia. Again, proper gloves, googles and respirator mask - this stuff is hard on the eyes.
I proped everything up on some bent metal strips to allow full circulation around the parts. The parts sit in the bath for a while.
For the negative plate in the anodzing bath, I used a piece of scrap aluminum sheet that had too many dings/creases in it to be useful for anything else. I cleaned it with lacquer thinner and made sure it was completely dry before bending it to shape inside the acid tub. The more surface you can expose to the bath and parts the better, so it's bent up both sides of the bath.
Checking back on the ammonia bath, the parts are starting to bubble - a good sign that any contaminants on the surface are being lifted away. I don't have any pictures, but once I was satisfied they had soaked long enough (about 30 mins), I used a clean 3M scrub sponge to wipe them down, then a spray bottle of distilled water to rinse them off. A good indication that the part is completely clean is when the water spray refuses to stick to the aluminum and jut flows off. Water beading on the part means contaminants remain. Mine parts just flowed the water freely. It's important to not touch the parts at this point without clean gloves as any natural oils on your skin will contaminate the part again.
As the parts are left to air-dry, I prepared the anodizing tub. I connected the negative lead from the power supply to the aluminum plate in the tub (the cathode).
The process is hard to capture, but the next steps are to hang the parts in the electrolyte acid bath from aluminum wire. The parts need to hang freely, not touching the other parts or the cathode. The positive lead from the power supply is connected to the parts via the hanging wire. The circuit is now complete and the power supply is engergized. The airpump is also turned on. The following pictures are of the anodizing bath well underway. The electrolyte solution is fairly cloudy by this point, making it hard to see the parts.
The voltage and current applied is calculated with an online tool, using the total square area of the parts to be anodized and what thickness you want the anodized layer to be. This gives you the starting voltage and current and how long the circuit needs to run.
As the anodizing takes place and the oxide layer builds up, the current slowly diminishes to almost zero as the parts no longer can conduct the current. A good indicator other than the readings on the power supply is the distinct reduction of bubbles coming off the parts.
Very close to the time to shut off the circuit, the bubbles coming off the parts took a dramatic downturn as expected. I waited for the time to run out and stopped the power to the circuit and the air pump. The parts are carefully lifted out off the acid bath and immediately dunked in the soda bath to neutralize the acid on the parts. With gloves on, sloshing the parts around makes sure the acid is fully removed from the parts. Once satisfied the parts are "neutral" they get boiled in fresh distilled water to seal the oxide layer. It's at this step that some people add dye powders to the boil to colour their parts. Iwas thinking of doing this, but decided colour wasn't import as I was going to prime/paint the parts as well.
Overall the process of anodizing went ok and I learned a lot. In hindsight, I'm not sure it's worth all the effort when prime and paint will suffice. There is also anti-galvanic paint on coatings that they use in marine applications. I'll look into those as well. The complexity of the system and process turned out to be too big a distraction from acutally building. It would have probably been easier to send them out to an anodizing shop, so my foray into anodizing is over, but in the end I'm smarter about it now than I was.
With the left spar primed and reassembled, I finished bucking the last of the rivets in the spars.
The spar pick-ups have been primed at this point on top of the anodizing I did. I need to order some AN bolts to go with them and the strut pickups (should be here next week). They look fantastic!
With the spar now essentially complete, it is time to start lining things up to ensure the spacing of the ribs match the spacing of the slat and flapperon pickup brackets.
I stood the spar up and anchored it to the bench. I started to add the ribs temporarily using small clamps at the spar and masking tape:
With the ribs in place temporarily, I clamped the nose rib slat attach brackets. These are only in the lateral position for now to allow for lateral measurement. They actually sit up higher on the nose ribs when mounted.
I did the same for the flapperon brackets at the tail of the rear ribs. Preliminary measurements show that the slat and flapperon bracket positions are perfectly matched to the slats and flapperons. This allowed me to drill the pilot holes in the spar for the ribs.
Next up for assembly is the rear wing channels - an inboard and outboard.
I previously had these channels bent by a professional shop as we don't have a suitable bender available at this length. The inboard channel has a support angle across the top. I laid out the angle rivet spacing and drilled out to A3:
The inboard and outboard channels are joined by a splice channel at the rear strut pickup point.
I laid out the splice channel, drilled out the holes to A3 as per the plans.
With the holes complete through the splice channel and the rear channel, I laid out the rear strut pick up. The plans aren't completely clear on the placement, but with a little figuring I was able to confirm the placement.
I clamped the strut pickup in place to the splice channel and backdrilled through the splice channel, ensuring accurate line up of the holes for the entire assembly:
The rivet spacing is tight here and one of the holes is actually for an AN3 bolt. Before drilling the holes out to A5, I finished adding the strut pick-up AN6 bolt hole:
Moving the clecos to the underside, clears room to work with the drill to brig the holes up to A5 size. The far right row of rivets is where the tail end of a wing rib attaches through the channel and splice channel. I'm leaving them as A3 until I fit the rib. I'll have to decide if I want to debur, prime and rivet this section first, or wait until final fit up of the wing ribs.
I did the same at the root end of the rear channel. Lay out the rivet pattern, then back drill through the root plate (a .125 plate inside the channel) that supports the rear channel attachment to the cabin frame.
With the placement of the nose and rear ribs confirmed earlier, I could drill the remaining pilot holes in the rear channel for for the rear rib attach points. Until the wing ribs are in place, I'll wait to debur and prime everything before riveting. After this picture was taken, I drilled everything out to A5 size and trimmed the outboard end of the channel to length and taper (more on this later).
Before final layout of the wings, I decided it was probably best to confirm the work table was completely flat, so I cleaned it off completely. It still was very flat and required almost no adjustment. It was weird to see it so empty!
Making sure the spar is completely straight laterally, vertically and no twist is critical. This is accomplished by using the flat table as a reference. The right angle towers are placed at each end across the rear face of the spar and secured to the table. A tight string line between the outer uprights gives a straight line reference for the other uprights. My spar is straight in all dimensions.
The camera shot give the impression this is far from vertical. It is, confirmed by inclinometer - the view is an optical illusion.
With the spar completely vertical and straight, I started to add the rear ribs. I back drilled through the spar web and into the rear rib flange, using an upright bubble level to ensure the rib was square up and down.
Very happy how this is going. The ribs are a perfect match to the spar. Once I have all the rear ribs in place, I'll remove them one at a time and repeat the process for the nose ribs one at a time, back drilling them through the rear of the web.. This will ensure they too are lined up exactly correct.
Lots to go on the wings, but they are starting to come together. I'm back to Monday to Friday schedule at work, so I should be able to get to the shop more regularly, perhaps one or two nights a week and a full day on the weekend. Hopefully my blog will keep up!
Thanks for following along.
Another successful week in the shop.
I continued to work on forming and flanging wing parts. Last blog post I had started the forming of wing ribs, starting with the root ribs. Here they are out of the forms - I'm happy how they turned out and using the hardwood dowel to work the metal flanges into the flutes on the forms made forming the curvatures of the flanges much easier.
As I mentioned before, I'm using Ron's 701 nose ribs forms. The trick here was to pre-flute the blanks as the 701 forms don't have flute channels cut in them.
In the vice, I start by bending the flat trailing edge flange over as it is straight and does'n require any fluting. Then the bottom flange, working forward towards the nose.
as I got close to the nose, I carefully worked the nose flange over, drawing the aluminum across. The metal backing plate on the forms really helps in the this regard.
A little cleanup with a small tack hammer backed up by a body work anvil and some tweaking with the fluting pliers and the nose ribs are ready for lightening holes.
Six left and six right, enough for both wings
Lightening holes are cut on the drill press using the fly-cutter, set to the diameter of the flange dies (which are exactly to plans - in the case of the nose ribs is 115mm)
Lightening holes cut and deburred, awaiting flanges.
Next up, the wing ribs. I used the exact same process here as the root ribs with a couple of modifications. I stacked all the blanks together and drilled the pilot holes as a stack to ensure consistency in the forms. Each of the ribs has 3 lightening holes, however two of the blanks have no third hole, so I pilot drilled those separately from the rest, but using the same layout as the others.
First blank/form in the vice and from here the forming is the same as the root ribs - using a hardwood dowel to massage the flutes. All ribs are made from the same form, regardless of lightening hole requirements. I added a small clamp at the tail end of the form to keep the forms tight.
All my wing ribs formed and lightening holes cut awaiting debur and flanges. The two wing ribs on top are the two that only require front lightening holes, the rest underneath have three holes.
Took the day Thursday to travel to Sudbury and pick up a sheet of 063 aluminum and some flat stock needed for the wing and strut pickups. I also grabbed a small chunk of 0.188 plate for the fuselage pickups. This supplier is much cheaper than Aircraft Spruce and much closer to home.
I was pleasantly surprised to find the sheet came on a well strapped pallet which fits nicely in the back of our truck. Over packaged for a single sheet, but it didn't cost anything to me, so that's good!
When back at the shop Friday, I planned on cutting off the pieces I need immediately for the spar doublers. I laid out the rough dimensions while the sheet was still on the back of the truck. This allowed me to nest them a bit and save waste. All set to rough cut but unfortunately mother nature had other plans and a downpour forced me to abandon the plan and just unload the sheet off the truck for next time in the shop.
The flat stock is perfect for the spar and strut pickups, and the flat plate works for the rear wing/fuselage pickups.
I'm so fortunate to be able to use the tools and jigs and bending equipment of Ron's, it's saving me untold hundred of dollars. One of the best examples of this are the flanging dies Ron had custom made at a machine shop.
In the front of the picture below are the two halves of the 115mm diameter flange die - female side on the left, male on the right. It's easy to see the shoulder on both that creates the flange on the lightening holes.
The process is easy. Place the blank over the male side....
Invert the female side and place it on top (carefully - the dies are heavy tool steel and dropping them will permanently damage the blank and maybe the die as well!)
A shop press would work well here, but two large C clamps and the bench-top edge work just as well. Make sure to use two clamps the same so equal turns on the handles makes even clamping force on the dies. I did four turns on each at the same time, going about a half turn each time and it worked well.
The distance to compress the dies together isn't much. Top photo before compression, bottom photo at the end of travel.
Take the dies apart and the flange is complete - total time about 2 minutes each once I got into a rythym.
The process is repeated for the wing ribs, using the correct flange die size where appropriate.
The smallest flanging die only requires a single C clamp centered over the hole. Credit to my daughter Caitlyn for taking some of the following photos of me working!
After about 90 minutes, all the wing, wing tips, root and nose ribs for both my wings are now flanged and ready for fitting on their spars.
Something really cool looking about the symmetry of wing and nose ribs laid out side by side on the table
Next up, I'll get the 063 spar web doublers cut from the sheet I bought, bent and fit one to the spar. Then I can proceed to add the spar pick up, the strut angle and strut pickup. With everything fit, I'll drill/flange the lightening holes, begin drilling all the holes to correct A5 and A4 where needed. After that, disassemble, debur, prime and reasemble for final riveting. Just a few more steps!
Thanks for following along, it was a productive week indeed!
Busy couple of weeks since the last blog update, but lots to share.
I continue to assemble the wing spars and gather the remaining materials and make parts for the wings.
With the spar webs cut, it's time to layout the lightening hole locations along the web, and cut the spar cap angles. These form the top and bottom of the spar. It starts with a centre line along the length:
Measuring outboard from the root edge, I made a hatch mark for each of the lightening hole locations:
With the locations laid out, I stacked one spar web on top of the other, secured them with clamps and drilled pilot holes through both - this means all lightening holes in each spar are in exactly the same location.
Next up was cutting the bottom and top spar cap angles using the chop saw. I left them a couple of mm long to allow for filing and sanding the ends smooth as the chop saw cuts fairly rough..
Here are the first pair, roughly laid out on the right spar web. You can see in this picture I've marked up each of the webs with a Sharpie so that I keep everything straight as to which way is up/down/fore/aft and a rough idea of the lightening holes. This is important as I want to use the factory edge on each of the spar webs on the bottom edge of the spar and as my reference for measuring the height of each assembly.
With the lower spar cap lined up with the factory edge and clamped in place, I laid out the rivet lines on the spar cap angles. These holes will eventually be filled by A5 solid rivets. I measured and double/triple checked the layout to ensure everything matches the plans. It's easy to be off a couple of millimetres at the beginning that translates to being off several millimetres at the other. The rivet pitches also vary a bit near the middle of the spar too where the spar web doubler and strut pick-ups are located so those have to be carefully considered too.
Drilling all the A3 pilot holes in the spar caps left a LOT of swarf!
At the bottom of the spar at the root I only drilled one pilot hole to begin the process of lining up the spar cap angle. There are several holes and bolts needed here in the spar cap angle, but I have more components to add including the spar root doubler and the spar root pickup. It will be easier to back drill from the opposite side - pilot holes for spar root pickup will be laid out and drilled on the drill press for accuracy and ease.
To start the process of matching up the lower spar cap to the web, I used a straight steel block. The web sits on a board to back up the drill bit, tight against the block and under the spar cap angle. The spar cap angle is exactly even with the end of the web, forming a perfect corner. Drill through the pilot hole to A3 size - this hole will eventually drilled out and filled with an AN bolt.
I secured the inboard end of the lower spar cap with a cleco, then used the same steel block to line up the web and lower spar cap again moving outboard. A clamp kept everything straight as I drilled the next holes:
Every tenth pilot hole was drilled though the cap and web. A long piece of HSS square tube confirms everything is remaining straight as I go:
With the spar cab and web confirmed as straight and true, I finished drilling the rest of the holes between, checking for straightness each time:
I left the section un-drilled between each end of the spar web doubler location (shown as red angled lines). I'll wait to confirm fit of the doubler and the front strut pick up angle once they are made and fitted. I may back drill these like the spar root depending on how the fit up goes.
With the lower cap in place, i started to layout where the top spar cap will be on the web and the associated rivet lines. yes those are my red Crocs.... don't judge.
The upper spar cap is initially cut long enough to overhang the web where it tapers. This will be trimmed off later to match the doubler which gets added here at the root (more on that later). The rivet layout at this corner is non standard, so for my first hole, I chose the first standard rivet spaced on along the cap. I used a ruler underneath everything to make the spar height exactly 209mm as per the plans and secured it:
Pro Tip: Be careful your pilot hole isn't over top the ruler when you drill through the web! Better that than a finger I suppose!
With the spacing between spar caps confirmed and triple checked, I used a carefully cut wooden spacer to make each of the subsequent holes along the upper spar cap exactly parallel to the bottom one. I started with a wooden block close to the length needed to fit between the caps, squared the ends on the band saw, then slowly sanded each end until it fit snug but perfectly between the two.
I copied the process all the way along, doing every tenth rivet and double checking the spar height each time. The caps are perfectly parallel and the spar height is bang on 209 mm. I finished of the rest of the holes to A3, skipping over the section where the spar web doubler will be. All the holes, top and bottom are A3, eventually will be up sized to A5 for solid rivets. The whole spar assembly as it sits now is already very strong.
Flipping the whole assembly over, I checked the rivet lines and confirmed the spar height as correct. I also started to formulate a plan for the spar root assemblies, spar web doublers and how to trim the upper cap angle taper effectively.
Next up is the spar tips. Made from 025, I bent these a while back when I was working on some 025 sheet work. They too have lightening holes, which I laid out and completed with the fly-cutter on the drill press.
Both tips with lightening holes cut and ready to be flanged. These holes are exactly the same diameter as the ones that will be in the spar web, so I marked the cutter with a flag note stating it was already set. Once I get the spar lightening holes cut, I'll flange them at the same time as these.
To ensure the spar tips are perfectly square and parallel to the spar, I flipped the spar back over and clamped a spare piece of angle to the bottom spar cap angle, measured exactly where the tip should overlap the spar end and marked it for pilot holes.
The red line on the left is the rivet line for the spar tip where it attaches to the spar web. The red line on the right is the rivet line station for the outer wing and nose ribs. It has a different rivet spacing, so I'm leaving that alone until the ribs are ready for installation. This will allow a small adjustment to compensate for any variance on the pickups in the slats, which will be installed on the wings later.
Four A3 holes evenly spaced between the spar caps. These will eventually be A5 pulled rivet holes.
Flip the spar back over. Layout the rivet holes in the ends of the spar caps as per the plans. Clamp it all together. I found it helpful to extend the whole thing over the end of the bench for this.
Back drill through the spar caps through the spar tip and secure with clecos:
Extremely happy with everything so far. The spar is dead straight, dead on 209mm tall throughout it's length and distance from root to tip is exactly as in the plans. Straight and rigid enough to stand on it's own! I'm waiting to pick up some aluminum sheet and flat stock later this coming week to make the spar pick-ups, the spar web doublers and front upper strut fittings..
I had a couple of hours for the shop one morning, so I decided to start modifying my wing rib templates. I've had these made for many months and now that I'm ready to start forming wing ribs I wanted to re-visit their layout. I'd experienced some issues forming the slat ribs and thought I could address this on the Wing ribs. I marked the location of flute relief on both the left and right side templates. This will eventually make forming the curves on the bottom and top of the ribs easier.
I started cutting the flutes using a small drum sander on the Dremel tool. It worked really well (more on these later).
Back in the shop the next evening, I started to form up the 032 spar root doubler. It was relatively easy to make as I had experience from installing a missing one on the 701 wing repair (click here for that part of my story).
It starts with bending a flange on the outboard end, then trimming the doubler to match the taper of the spar web, leaving enough width to bend a second flange to match the taper.
With the doubler bent correctly, I laid out the rivet lines for the upper perimeter and back drilled through the web out to A3, using the bottom spar cap angle as a guide to keep everything straight. (it's hard to see it here as it is underneath the inboard spar web):
Flip the spar over and lay out two rows of rivet lines, 5 rivets between spaced between the spar caps:
With the spar doubler drilled, clecoed and and confirmed as correctly positioned as in the plans, I removed it again in order to better see where I need to trim the upper spar cap angle. I marked a line on the angle using the web as my guide.
The next part was quite challenging - using the chop saw to make the accurate angle cut on such a long and un-wieldly piece of angle. I managed to get it close enough, but boy the chop saw makes ugly work of the cut:
The black line represents everything actually left to trim back for a perfect match to the spar taper. I used an angle grinder to gently remove more material using the spar doubler as a guide until it was perfect:
As I got close, I switched to a hand file, taking it down until it was perfectly level. Some final sanding to round off the sharp edges and it is complete:
Putting it all back together, I began laying out the rest of the root doubler rivets and drilling them out to A3. The plans here are kind of lacking about the spacing, but I believe I got it close to what is intended. These will be A5 rivets and the spacing I've left between them it well withing tolerances. I've written what I've used for measurements on my plans so it will be the same on the left spar.
I upsized these to A4 with the exception of the 3 at the tip. I'll leave these as A3 until I can align the inboard root rib and nose rib. This assembly will only get stronger with the addition of the root attachment plate.
As per the plans, I added two standard L angles on the back of the spar at the required location. These add more torsional rigidity to the spar assembly as a whole.
First I marked the centre line of where the angle attaches at each location on the spar:
I cut and deburred two pieces of L to 209 mm long, then used the rivet holes in the spar tip as a guide as they are the same layout (4 rivets between the spar caps):
It doesn't show here, but I drilled pilot holes in each of the L pieces, then used the layout line on the web to align the L in each of the spots and drilled it out to A3. They too will become A5 eventually.
Ron had a look at the flutes I cut in my rib forms and suggested I widen and soften the edges a bit. To do this I used a hand file.
The file was very effective but left the flutes a bit rough.
A little hand sanding of each and they cleaned up nicely.
Both the wing and the root rib bottoms taper slightly up from the front bottom corner. In order to lay out the lightening hole and tooling hole locations correctly, I set up one of the forms on the bench and used a scrap of angle and a carpenters square as a straight edge for measuring against. As this is my first go at using these forms, I decided to do the two root ribs first in case I discover procedural issues. Better to change plans now if needed, but I think this will work.
The four vertical lines measured laterally from the square end. The tooling hole locations measured vertically up from the straight edge provided by the angle. I drilled the four holes out to 15/64ths diameter, same as the bolts I will use to clamp the forms together when bending the blanks into ribs. Left to right, the first 3 holes are also the centre of the lightening holes, the fourth is a tooling (bolt only) hole:
Flip the stack over, clamp the forms together straight and use the new holes to back drill though the other half of the forms, ensuring both left and right rib consistency.
With the forms and templates ready, I start to stack them and a blank together. From top to bottom in the picture below - right side form, left side form and wing root rib blanks. The blanks don't have holes yet and the stack is now pointing in the opposite direction (left to right - tooling hole, and 3 lightening hole centres).
Line up the root rib blank on one side of the form......
.... followed by the other form, lined up directly over top the other. Normally this alignment is accomplished via the bolts and holes. My blanks don't have tooling holes as I wanted the holes to first match on both forms otherwise what's the point?
With everything lined up exactly where it should be, I clamped the sandwich to the table and using the form holes drilled pilot holes through the blank:
This results in perfectly located holes - all four will initially be bolt holes for forming the rib.
With both root rib blanks having their tooling holes complete, I can bolt it all together and put it in the vise for forming:
Gentle and firm blows with the dead blow hammer, bends the flange over the sides of the form. A piece of hardwood dowel rod helps direct the forming blows, massaging the aluminum into the flutes, taking up the extra aluminum from the curve of the form and creating the desired shape across the top and bottom of the rib:
The flutes really help make the rib nice and straight, but it also make is tougher to remove the form. Not bad enough to avoid the flute work! Once out of the form, fluting pliers can be sued for final adjustment. Once flat and out of the form, the 3 forward bolt holes become pilot holes for the fly cutter.
Knowing the procedure works as I intended with the root rib, I repeated the hole alignment procedure for the wing ribs and it turned out perfectly. I'll get to pilot holing the rib banks soon in preparation to form the ribs..
The nose ribs of the 701 and 750 are close enough that I can use Ron's forms. I remembered this while looking for my nose rib forms - that's why I didn't make them for myself! Ron and two other builders were making their nose ribs at the same time, so they bolstered their form with a metal plate close to the nose. This absorbs and backs the small tinsmith hammer blows required to get the thin nose flange rolled over much better than the wood alone.
Ron's forms are already drilled for tooling and lightening hole centre, so the process changes only slightly. This time, I laid a nose rib blank on the drill backing board and centred the form on the blank.
With it clamped in place, I drilled out the holes, using the form as a guide. Then I repeated this step 11 more times for a total of 6 left and 6 right rib blanks.
Ron's forms do not have flutes cut in them, but Ron says they had no issues forming their ribs without flutes. I will need to know where the flutes need to be crimped using fluting pliers, so I marked out 6 left and 6 right for future forming:
A couple of parts I've yet to make are the front upper strut fitting and the spar root fitting (2 of each, one set for each wing). These are substantially thick pieces of aluminum, each a 1/4 inch thick.
One challenge scratch builders have is a good reference of materials needed for a build. Kits come with everything already cut and mostly bent. To make scratch building affordable, one needs to purchase materials in complete sheets then cut them down to size. Buying in bulk saves major bucks.
Thankfully, I received a really good spreadsheet from another scratch builder early on in my build process, which has been invaluable in giving me some idea of the materials needed.
I've been following along pretty closely to the spread sheet of material, but it sometimes has a bit discrepancy compared to the plans. But as we all know, the plans are king.
My spreadsheet states the spar root fitting is 38mm wide by 240mm long - this coincides nicely with the spreadsheet and can be made from 1-1/2 inch x 12 thick aluminum bar stock perfectly (38mm is 1.49606 inches, close enough for me!)
My spreadsheet also states the front upper strut fitting is 40mm wide by 203mm long. This means I'd need bar stock just over 1-1/2 inches wide (1.5748 inches). This sucks because the next width in bar stock is 2 inches, meaning a bunch of wasted material if I have to cut it to width.
I spent too many hours thinking about this and trying to figure out if maybe I'd be better to order some 1/4 inch plate and cut them all out from that, which means more work and chance for error. It was then I looked again at the plans and realized the spreadsheet is wrong. Both are 38 mm wide, meaning I can make all four from a single strip of 1-1/12 wide bar stock. Cool! (I've adjusted my spreadsheet!)
So the 1-1/2 inch bar stock has been ordered along with some 063 to make the spar web doubler and some 0.188 plate for the wing attach brackets on the cabin/fuselage. It pays to shop around, these materials are about a quarter of the total cost ordering it from Aircraft Spruce and 8 hours closer too! I'll pick it up this week from the supplier. I'll probably get them to quote some 020 that I still need for the wings and fuselage skins.
One material that is cheaper to get at ACS are aircraft grade hard rivets. What you see below is way more than I need, but it's good to have extras. $68 something including tax and the time to go get them. I was going that way anyhow to pick up something for Ron, so it saved us both a little on shipping too. The picture below is what I got for the money. The writing on the label is the weight in pounds, not the cost per rivet.
Another consideration I've been pondering is fuel capacity and what that means for my build. Will the standard size fuel tanks be adequate for my expected fuel burn and range? I need to think about this as it affects how and where the fuel tanks get installed in the wing.
I reached out to William Wynne, the Corvair guy and he advises I can expect to flight plan for an average of 6 gallons per hour fuel burn at normal cruise speeds. Looking at the specs from the Zenith website, standard dual wing tanks are 24 US Gallons (2 x 12 gal.) - meaning not including unusable fuel in the lines and any reserve I can expect about a 4 hour range on average.
The extended tank option from Zenith (plans sold separately?!) increases this to a total of 30 US Gallons (2 x 15 gal.) - an increase of about an hour of endurance. The tanks are essentially a little bigger but still fir in the same wing bay.
Some have added a second standard tank in each wing, meaning a total fuel capacity of 48 Gallons!
That sounds great, but there are some serious pros/cons to consider. Extra range and fuel is always a good thing. But how long do I want to a leg to be - i.e. will I need to stretch/pee/eat before 4 hours? It also costs more to make larger or dual tanks, and it complicates the plumbing of the fuel quite substantially. There is also the consideration it may decrease the usefull load (how much can I take in baggage and gear - fuel weighs a lot) and that it costs fuel to haul fuel.
I'm all for the extra range - it never hurts to have more fuel than I need. I'm just not sure it meets my mission and if I eventually plan to put the plane on floats, then what? That has impacts on gross/empty weight on it's own, without considering the extra weight of fuel.
I don't have to decide yet, but will have to soon. Maybe I'll reach out to Jeff Moores in NewFoundland - he has a 705 Cruzer on floats and see what his experiences are. I'm leaning towards the middle option for a slight increase in range without complicating the plumbing.
So.... long blog today. I hope you are enjoying following along. More to come soon including some decisions on fuel tank size.
It has been almost a month since my last blog post, but work continued on the slats over that time. No real need to blog about it as the process was the same for all four with the exception that the outboard slats were slightly longer externally. The internal skeleton and assembly steps were the same.
A pciture of the last slat on the bench awaiting trailing edge bend before debur, prime and rivet.
Also in the last couple of weeks I played a bit more with the 3D printer. It seems I've run into an issue with the filament jamming in the extruder. Very frustrating stepping away to do other things while the printer works on something, just to come back and find nothing coming from the nozzle!
I took the extruder apart and it was clear it wasn't feeding correctly as evidenced by the "knot" of melted filament between the extruder and the hot end.
I spoke to a work colleague who is very invested in 3D printing as a side business and showed him some pictures. There are two things that most commonly cause this are a gap between the hot end feeder tube and the extruder, or worn extruder parts. As the extruder parts are 3D parts themselves from the manufacturer, his suggestion was to spend some money to upgrade to an all metal extruder and hot-end.
Looking further into this, I decided to not to proceed any further with using this printer. The printer is not mine (it belongs to the local library) and I'm not quite ready to invest the time or money to upgrade something that is already esentially obsolete. I still plan on printing parts for the airplane eventually, but this printer is has become a bit of a distraction from the airplane itself. Also, newer model printers are getting cheaper by the minute and easier to use with built in functionality that makes printing exactly what I need more sense, so I'll look at investing in one of my own eventually. I've accomplished what I set out to do - proof of concept and making it functional again for the library. 3D scanning is also functionally feasible, but it too needs more time to getting it working the way I want it so it too will be shelved for the meantime.
A question came up from another builder on the forum on how I've managed to bend the trailing edges so cleanly. The entire procedure of assembling the slats can be seen on a previous blog post but for the sake of explanation, I used a small diameter rod along the inside of the fold held in place with some spacers Ron and I came up with. The are scrap strips of 0.016 aluminum with a a small curled up end.
I used wide painters tape to hold the strips in place, the curl of the strip against the rod. The picture make sit look like the curl is taller than the rod, but it is not. If it were, it would leave a mark on the inside of the skin so caution is warranted here
Strips and tape are cheap, good to have several across the entire width of the slat skin:
The inboard slats (the shorter ones) eventually tuck inside the outboard slat enough to be riveted together once they are mounted on the wings. Here they are back to back and upside down on the bench lined up but not yet tucked together - this really gives the idea how long and wide the wings will be!
Looking at my "completed sections" drawing, I'm pleased to be "mostly done" the control surfaces.....
.... and happy to see an empty bench, even for a few minutes! Now to begin one of the bigger sections both in size and number of parts - the WINGS!
I brought a fresh roll of 0.032 (on the bench) and 0.042 (coiled beside the bench) down from the storage barn, to start laying out the components for the wings. Like everything else, I want all the parts made and ready to use in assembly to minimize the time on the bench.
First up, the wing spar webs from 0.032. The two spar webs are almost a full length section of a sheet and requires accurate cutting so the spar assembly is straight and true. They make up the centre part of the spar between to 6061-T6 angles on the top and bottom (more on later).
I cut the first web using a plunge saw with metal cutting wheel and it turned out fairly decently. The saw isn't as accurate or clean cutting as I would like leaving me some extra work with a hand file to clean up the cut edge by hand before deburring and sanding smooth. With a bit of work, it eventually cleaned up nice and straight. I cut the second spar web by hand using the large hand shears - it took longer to cut, but I found that if I was careful I could be more accurate cutting by hand and it took a lot less time to debur and clean up the cut. I used each side of the factory edges of the sheet to be and edge for each spar web giving me a perfect factory edge to measure from..
With the spar webs cut to size, I measured and cut out the tapers at the inboard ends of the spars where they will meet the wing (the bottom of the spar web faces the ruler in the picture below)
The thickness of the 0.032 and 0.040 sheet make them awkward to roll/unroll, so it makes sense to cut the other pieces out while the sheet is on the bench.
In the picture below you can see the remaining 0.032 sheet after cutting out the spar webs (coiled at top of picture), the spar root doublers (bottom of picture) and the four rear spar channel blanks (middle of picture). The two thinner strips on the right at 0.040 blanks that will be bent into angles as inboard rear channel doublers.
The 0.032 rear spar channels and the 0.040 doublers are too long to bend at our shop, so I've taken them to the same shop who bent the flapperon spars for me previously. I'll get them back this week.
I also needed to cut out the left and right 0.063 strut support brackets (bottom right in photo below). So while I had the sheet on the bench I also cut out some of the other 0.063 parts for the fuselage - the fuselage parts will be put into storage until I need them, but at least they are done. I ran out of space on the 0.063 sheet I had to layout/cut the spar web doublers, so I'll have to get some more from storage to get these done.
So despite no blog updates, I have been working away. Control surfaces are "done" and work on the wings is underway. Looking at the completed parts picture I posted above I'm very pleased how far I've come since starting. I'm not sure I can put a concrete answer on how much I've got done, but of the approximately 275 aluminum parts to make, I've got about 145 done which is very roughly 53%. Understand that's just parts made, not bent, assembled, drilled, debured, primed, riveted.
As always, thanks for following 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.