Got some time in the shop this past week. Here is the latest on the right wing.
Upper main skins, upper nose skins and top side trailing edges are sealed up for storage. This means two temporary rivets in each bay to hold everything together until I re-open it for inspection at a later date.
Also created and installed the curved attach angle for the upper root rib. You may recall from a previous post that the design changed in this area since my plans were issued, however I hadn't seen any update from Zenith. This meant creating a work-around with a curved L bracket, I pleased this will create a much better curved surface for attaching the root skins.
Flipped the wing over to access the lower skins and final rivet them:
The bottom of the wing is almost all final riveted closed, very happy how it looks, but still needs some cleaning and light wet sanding to remove some light scratches:
Jury strut attachment brackets are now firmly in place on the spars/ribs:
Here is the rear strut pickup and 3rd flapperon arm. This joint area really turned out nicely. Still need to rivet the trailing edge joint where they overlap:
I purposely left the lower outboard wing skin un-rivetted so I can have un-fettered access to the wing tip area for fit up and final attachment:
Measured up the rivet line for the front wingtip attach bracket and drilled out to A3:
Wing tip in place, with the lower outboard skin in place to check alignment:
With the wingtip in place, I discovered that the rear channel attach bracket wasn't sitting flush against the wingtip. I re-fabricated a new one to match correctly (pic is of original):
With the tip in place again and the lower skin removed, I marked the location of the rivet holes from inside through the spar and rear channel brackets. Then I removed the tip form the wing, back drilled at the marks up to A3. I added a strip of masking tape where the holes are to protect and prevent cracking of the plastic and placed the wingtip back in position and fastened with clecos:
Lower skin back on, drilled the outboard edge to A3 and cleco. I won't be final drilling these up to A4 until the wingtip lights and wiring are done, probably just before inspection. Trailing edge has since been trimmed to match since picture was taken:
At the root end of the wing, I started making up the template for the nose root skin. I had originally cut the actual skin from 016 based directly on the measurements in the plans. But noticed when I went to fit it, I had made a critical cutting mistake near the spar attachment and I wasn't happy with the overall fit anyhow, so it goes to the scrap bin for other small parts.
Making a cardstock template from the plans with a bit extra on the edges allows much easier fit up. with some masking tape backing on the edges, the template can actually be clecoed to the wing. Initial stages of fit-up are very promising, the final template will be transferred to a fresh piece of 016 for the final piece, once I trim it perfectly.
Almost there, many MANY small steps along the way. In the next week I should be able to put this wing into storage and start work on the left wing. Testing continues on lighting and fuel sensors.
Thanks for following along. Onwards.....
Some good hours in the shop this past week.
The wing tip inner liners came out really well:
Next up for the wingtip is final fitment and pilot drilling the rivet lines top and bottom of the wing and into the spar tip support L and rear channel L.
I decided to try my hand at brazing some aluminum in preparation to assemble the wing fuel tanks. I started with a couple of scraps of 025, the same aluminum the tank walls and body are made from. The goaI was to simulate a welded seam:
To accomplish a good brazed joint on any metal, the surfaces of both pieces need to be cleaned completely to take off any oxidation. I used the Dremel with a stainless steel wheel brush to clean both:
The shorter strip will be on top of the longer one and offset to simulate a lap joint, so I cleaned the centre of the longer one:
My choice for flame heat is MAPP gas - from what I'm told it is hotter and cleaner than propane:
Gently heat up the aluminum joint focusing on the seam where the brazing will be. It needs to be hot enough to flow the brazing rod into the joint. Anyone who has done soldering should be familiar with this. The brazing rod melts at a much lower temperature than the aluminum. Unfortunately it is difficult to capture the brazing rod melting into the joint.
My first attempt wasn't very good. I found it hard to flow the brazing rod into the seam evenly. The bending of the aluminum wasn't from the heat, but from tapping with hammer after it cooled. The "weld" held but not very well (it broke much easier than it should have) and appears to be full of pinholes - not good for sealing a fuel tank seam!
Another attempt with two circular scraps was even worse....
I did manage to get a very strong bead along the edge furthest from the vice. I think a big part of the issue is that the cast steel vise is acting as a very large heat sink, drawing the heat built up in the aluminum from the torch away and into the vice quicker than it should. I'll need to consider this when I have the tank pieces clamped together, but I clearly need more practice before I can trust this as a leak proof fuel tank.
I've decided I also need more time to test the pressure sensors before committing to using them in the tanks, so I'm going to put the tank assembly off until later and focus on finishing this wing and the other one.
I've added the root skin to the right wing:
The root skin goes from perfectly flat at the rear channel to very rounded over at the spar. The root nose skin closes up the front corner of the nose. It's going to be fun!
One issue I ran into is the upper root skin in proper position, won't sit flat on the spar root doubler. Forcing this convex skin flat to meet the doubler only serves to crinkle the skin, so I had to reach out to some fellow builders to see if they had this issue and how they dealt with it. I have an simple answer, more on that in my next blog.
This picture shows how much the upper root skin tapers down at the root. You can imagine the root nose skin shaped somewhat like a cone as it tapers both inboard from the nose rib to the root nose rib:
Getting very close and happy with my decision to put off making the wing tanks. I definately need more time with the torch and brazing rod in hand to make good consistent brazed joints. Like everything else it will come with practice so I'm not worried. This will also give me time to get some serious testing done on the pressure sensor set up which I still believe will work as I designed.
Thanks for reading along. Onwards....
My pressure sensors finally arrived! I'm stoked to experiment with these models as I believe they have the measurement resolution and electrical specs for my Arduino fuel gauge solution.
First up, unboxing and evaluation. First thing out of the box I was really surprised at how large they are. It didn't have any physical measurements on the ordering page, but I had the mistaken impression from the pictures online they would be somewhat smaller and lighter, similar to the 10psi sensor I ordered initially. the new one is larger, a bit heavier (not unreasonably so) and doesn't come with an integrated cable:
They will still fit my application space, but I'll probably need to consider some sort of mounting bracket to secure it with the fuel line. Overall build quality seems real good. Two sensors, exact same spec, just like I ordered - 1.5psi, 1/4 inch NPT thread connection, 0.5V to 4.5V output:
Looking closer at the electrical connection end, standard cable compression sleeve entry and what appears to be a small screw holding the cap on the top:
Backing out the screw I thought would allow the cap to come off to reveal the electrical connections inside.....
........but the cap is actually a full 4 prong indexed plug on it's own - the machine screw secures the cap/connector to the sensor body. I like that in the design!
Another nice design detail is the rubber gasket on the bottom of the connector, protecting the joint with the sensor.
The terminal block pops out of the cap to reveal good quality screw terminals which are numbered to co-incide with the pin outs on the lable of the sensor. #1 for 5V+, #2 for sensor circuit ground and #3 for output signal. There is a 4th terminal with a electrical ground symbol - I suspect this is for sensor body ground, but I'll need to test to be sure:
I do know I need a better and more scientific set up for true testing and calibration, but here's what I did tonight to try it out. I used the same poly tube and connections as I did the for 10psi sensor tested previously. I slowly added water to the tube (in the upright position) and monitored the sensor connected to the Arduino micro-controller. Using the same Arduino script as before, it is clear to me this sensor is not only much better suited range wise to what I need (1.5 psi vs 10psi), it also seems the output signal is much more stable. I suspect this output stability is part build quality and part correct range specific, but I'm happy where this experiment and my related theory is headed. The photo doesn't capture the graphed output on the laptop, sorry. I'll try and get some screen captures when my test method/system improves.
Still much testing to prove the effectiveness of this method for measuring fuel tank quantity to come. This is another example of stuff I'm learning on this journey :)
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 :)
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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.