I'm finding it more and more difficult to keep my blog up to date - I've accomplished much in the last few weeks. A lot of it has been routine fitting, drilling, cleco stuff so I haven't been taking many pictures. There are a few updates to share though.
With the one side partly secured with clecos, I moved the stab to the other bench. A large square steel tube was placed on the top to gently bend the skin partially into position before we tightened the ratchet straps to pull the skin down tight around the nose and upper surface.
Long strips of wood help spread the strap loads across the length allowing for fine adjustment. You have to be real careful here, too tight and the skin can collapse at the nose, leading to damaging kinks.
With the fit confirmed, I made a few reference marks, then it all comes apart and I can start the process of measuring the skin for holes. This is the only way to make sure the skin rivets are centered on the ribs as I don't have the luxury of pre-drilled skins.
Measure twice and then twice again, using the stab skeleton as a reference.
Again, I don't have any photos of the assembly, but the process is the same as above - weigh down the skin with the metal tube, use the straps to draw the skin down tight. The only thing that's different this time is drilling through the skin holes and into the structure below. I worked from the nose back to the rear edge (right to left in the photo) and from centre section out to the tips. Each hole gets a cleco until the rear most holes, ensuring a tight and bubble free fit.
Spar lines front and rear are drawn and rivet holes drilled. These don't have to be done with the skin off as the spar is a straight line and on this side the spar isn't pre-drilled. Again, measure 3 times - it's important the spar holes are centred on the spar flange:
I'm happy with how this turned out. Next step was using the template I made earlier to start laying out the slots for the horizontal stab brackets
This cutting is very delicate. The skin needs to be trimmed to be flush with the spar so the brackets sit flat and vertical against the spar. Cutting the skin is fairly easy, but any damage to the spar will be fatal!
I traced out the approximate location of the slots using the template and confirming with the plans started a pilot hole
I used a Dremel tool and rotary burl bit to slowly expand the hole enough so i could see where the rivet holes in the spar for the bracket are:
With a confirmed visual and measured slot location, I redrew the hole on the skin and slowly used the burr and some gentle hand filing to get it to the correct shape and location, ever mindful not to cut or mark the spar. Round files make a perfect corner:
Eventually with patience, the stab bracket fits nice and straight in the hole and perfectly vertical and flush with the spar underneath (it's sitting a little low inside the stab here as I couldn't hold it and take a photo at the same time!)
With that experience, the second slot went well too. I cleaned up the ragged edges a bit using a Dremel sanding/cutoff disc. The slots still have to be deburred properly, but that will come when the skin is off for full deburring:
On another note, Dad and I travelled to St. Hubert airport outisde of Montreal to attend the first flight of a C47/DC3 know as C-FDTD. We've been following the epic journey of Mikey McBryan (of Ice Pilots fame) and his Plane Savers team as they restore to flight a WW2 D-day survivor - a DC3 that dropped paratroopers over Normandy on D-day and during operation Market Garden, and that was sitting derelict, falling victim to vandals and the passage of time being slowly destroyed by neglect.
Here are a few personal pics of that trip - motivational for sure! For a full experience and to see what an amazing accomplishment this is, checkout www.planesavers.ca - of particular interest, watch the YouTube segments from the beginning - awesome and well worth your time!
Here is a copy of the flyer they were handing out to guests:
What an honour to be there and share this with Dad and the thousands of others who followed the restoration was unbelievably amazing..... what a great feeling watching it take to the sky again! All I could think about were are brave young countrymen that participated in the D-Day invasion exactly 75 years prior - God bless them and thank you for our freedoms!
I was so happy to share this adventure with Dad. As I post this blog on Father's Day, I'm reminded how much influence Dad has had on my life, particularly a love for aviation history. Thanks Dad!
While in the Montreal area, I also picked up a left/right set of fibreglass wingtips for my 750. These retail for $160USD a piece and I grabbed this uncut pair for $100CAD. Steal!
So, it's been a productive couple of weeks. Next up, I'll finish the stab skin, get the stab brackets installed permanently and proceed to skin the elevator. Once I have it skinned, I begin the process to line them up together and drill the mount holes for the hinge points.
Thanks for reading, more to come :)
Got a chance for a few hours at the shop last night.
The plans call for the stabilizer skin to be pre-bent to 90 degrees prior to attaching it to the skeleton for drilling. Conventional wisdom from other scratch builders is that this can be a challenge to do right.... bending this incorrectly, either crooked or in the wrong spot on the skin can at minimum lead to challenges getting the skin to lay flat on the skeleton and at worst render this very large piece of 020 aluminum useless (kinks are easy to make in such thin skins). I been nervous approaching this step, but with a bit of prep and double/tripple checking everything it worked out well.
First step was to mark the skin with the bend line which represents the middle of nose curvature (done previously) and lay the stab skeleton in position to confirm alignment:
I had to find a long enough (10ft) length of hard wall pipe to use as the bending form, as Ron doesn't have anything long enough in the shop. I originally thought I'd need some schedule 40 iron pipe, but I managed to find this mild steel electrical conduit at Home Depot that will work fine:
To prevent the sheet from slipping, I used wooden blocks as clamps, screwed down to the table:
Some thought went into the placement of the pipe in relation to the line. The overall goal here is to pre-curve the aluminum leaving room to tighten the aluminum down, not to make the curve exactly the same as the nose ribs. The pipe gives the curved surface to bend against. So the pipe is not directly on the bend line, but where the bend begins. Once exactly straight, the pipe is secured at both ends with blocking screwed down and a strip placed in the end and screwed down to the table to prevent it from lifting:
It's hard to capture when both of us are lifting the skin and forming it around the pipe. We use a long piece of rigid steel tube to place even pressure across the width. It's bent a little at a time, readjusted under the pipe, bent again, shifted, bent until the 90 degree bend is complete. If you look closely at the end you can see the incremental marks we worked to:
The size/width of what will be the horizontal tail on my 750STOL is really evident when I stood the skin upright. At almost 9 feet across it almost touches the ceiling!
Placing the skin back on the bench and adding the stab skeleton confirms the bend is very close (enough) to make assembly move on to the next step.
In a previous post, I mentioned making a decision having to be made about which surface to fit first. While researching how to bend the skin, it became apparent most builders suggest easiest is attaching the flat side first and drawing the skin across the curved side, so that will be my plan too.
Another challenge faced by scratch builders is that nothing made by the builder comes pre-drilled. In my case this becomes compounded by the fact my factory spars have rivet holes already - so how am I going to match those blindly from outside the assembly?
First step was to drill though the existing spar holes to match the holes on the doubler from the outside - no problem, that part is easy.
Now how to proceed? I can't drill from inside the skeleton out through the skin, there isn't room for a drill inside the spar web that is big enough to drill straight and the strap duplicator won't reach that far.
I placed the stab skeleton back on the skin all squared up and marked some of the points on the skin where holes will have to be drilled. I really don't like this method as there is too much room for error if the skeleton shifts even the slightest over the length of the skin and there is no easy way to clamp it down.
Before drilling more than a couple of holes, I flipped things over on the bench, moved it to the edge where the top side can hang over the edge and secured the skin where the holes matched up at the one corner:
The trailing edge holes I can rivet from the outside and matching them up is easy with the duplicator. There isn't a good way to blindly drill holes in the forward spar that guarantees a tight fit of the skin and correct hole alignment - and no second chances.
This got me to thinking about a way to drill from inside like I want to. The only thing that I can come up with is buying a tool like this that will fit inside the spar, but man they are expensive and most require specialized drillbits:
I'll continue to ponder this until the next time at the shop and maybe Ron and I can come up with an alternative. Happy with how this stab is coming together so far and really glad the bending of the nose worked out so nicely.
Another thing that got done for each of the airplanes being built in the shop was the elevator hinge pins. Made form plate steel and a modified AN bolt, Ron put several hours into each of these. What you can't see from the picture is the tiny cotter pin hole drilled in the pin or the finite welding he did making these - excellent work. The black paint is a first coat of anti-corrosion primer:
Back to the shop this weekend for a whole day hopefully on Sunday. Got to keep moving this project forward :)
Thanks for reading
I worked this week on getting the elevator trim channel installed on the elevator skeleton. I went over the plans several times to visually ensure I was adding the trim to the correct side of the elevator (remember, I'm building it upside down to take advantage of the flat upper surface of the airfoil).
Again, the plans have to be interpreted correctly - in this case the position of the channel is determined relative to the trailing edge of the elevator. But, that can be difficult without the elevator skin installed as the fold of the skin at the trailing edge extends past the tail end of the elevator rear ribs.
To solve this, I made a small narrow strip of 020 aluminum and bent it exactly as the elevator skin would be - it looks rough but it is exactly the right length to simulate the trailing edge:
I placed the strip in position and clamped it with clecos to the spar as if it was a complete skin. Measuring back from this temporary trailing edge, gives me the position of where the elevator trim channel should be but gives me room to to see my work.
Even with the measurement confirmed, I was having a hard time getting the trim channel to fit correctly, until I got a look at the build pictures that come with the plans. Turns out the kit supplied channel has been joggled at the end, allowing it to sit inside the tip and inner elevator rib.
Once I joggled my channel (that sounds bad as I type it), it fit in the ribs where I needed it to. This automotive body panel air tool is very handy for this:
The middle elevator rib gets trimmed down to fit between the spar and the trim channel. It's attached to the trim channel by an appropriately sized L bracket.
With everything squared up thus far, a quick check of the elevator alignment to the horizontal stabilizer shows extremely close to the plans, so my measurements, cuts and bends are very good and accurate. Very, very happy.
Next step is to start cutting the skins. These are fairly large in size and the bench is pretty crowded at the moment, so I rolled out the 020 sheet and traced out the skin on the floor, leaving it a couple of millimetres wide and long - it can always be trimmed back once I have it fitted to the tail skeletons.
First up is the horizontal stab skin. Making it fit correctly is challenging as you have to make holes AND account for the curvature of the skin across the top (bottom) of the airfoil as well. A kit skin would already be trimmed and holes cut for the front and rear stab brackets. As a scratch builder, this isn't a luxury we benefit from, so we have to come up with a workaround. Time for a template!
First step I did was to mark the location of the front brackets on the spar:
In order to transfer these measurements to the skin, I made a template from scrap 020. I cut out the space needed for the rear bracket, keeping in mind the overlap that is required by the real skin past the spar (15mm):
I removed the front brackets and with the template now in place (clamped) where the skin will be including the curve, I drew a line with a straight edge to represent where the back of the spar is - the goal here is to simulate where the final skin will sit in relation to the brackets. It's better to make mistakes on the scrap than on the full skin!
Knowing where the brackets come through, I was able to measure-mark-create the matching holes in the template and gently open the holes a little at a time with a Dremel tool until the brackets can be reattached where they will protrude through the skin:
I'm very happy how this template fits and I'm very confident it will transfer the positions of the holes to the real skin. I'll use the template to cut the slot for the rear stab bracket before final fitting the skin, but for now I placed the skin across the stab skeleton to check the fit - perfect, nice and square with the outer tip ribs and has the correct overhang of the spar.
Now I've reached a decision point. Do I fit the skin on top first and tighten it down with straps across the flat bottom or vice versa? Both have advantages. I can work form the rear bracket at the spar, fit the skin over the front brackets and pull the skin tight across the nose. Or I can start at the spar on the flat side, secure it and draw the skin tight around the nose, over the curve of the top - essentially working in the opposite direction. I've read that drawing skins tight over a curve is easier, but that means fighting with the brackets.
Either way, the skin will need to be pre-bent at the line that defines the tightest curve first - at the nose with a 27mm radius. The plans show a 90 degree bend in the skin prior to wrapping it around, so I need to get that done first.
I flipped the skin over on the bench to mark the centre of the bend line as per the plans (checking very carefully to mark it in the right spot - right and square:
A long piece of factory edge aluminum clamped down with wood blocks makes a great straight edge:
With the scribed line, I slipped the sheet under the stab skeleton to where it overlaps behind the spar 15mm and the bend line coincides where it should.
The next step will be pre-bending the skin, but I'll need to obtain something close to 27mm radius and more than 8.5 feet long so I can clamp it to the bench. I was thinking a piece of 2 inch ABS plumbing pipe might work, but it may not be stiff enough laterally, so maybe a piece of steel pipe. Unfortunately, Ron doesn't have anything that long in house, so I guess I'm going shopping :)
Thanks for reading, more to come!
The next sub assembly to do is the elevator. This is the trailing edge of the tail and it's primary function is to control pitch movement for the aircraft in flight. The initial assembly of this structure is somewhat less complex than the horizontal stab, but as always just as critical to get straight and square.
The nose, tip and rear ribs I formed fit almost perfectly and with a bit of trimming squared up the spar really nicely.
Being able to interpret the plans is becoming more apparent as I progress through this build. One item missing on the plans is the distance from the elevator spar to the elevator rear support channel seen below. The builder is left to decide where this fits. From what I can determine, the placement is designed to be back far enough so the flanges on the support channel are equal in height to the inner rear ribs. This would make sense as the skin and elevator hinge assemblies attach here. Front to back spacing is held temporarily in place with tape, squaring the whole thing up proved to be a bit tricky but I got it done without too much issue.
I had some discussion with Ron at this point, as I wasn't happy with the rigidity of the elevator assembly. I know that things will square up and get stiffer once the skin is on, but the assembly seems a bit lacking in structure at the middle where all the force and weight is acting on the elevator in flight.
Ron suggested I make a small modification that he is doing on his 701 builds by adding a 016 gusset plate across the top and bottom of the elevator centre section, extended out to the spar.
I liked the idea and set out to make the suggested gusset plates. Even at 016 thickness this will strengthen the centre spar of the elevator without causing undue problems adding the elevator skins.
I've drilled them out to A3 and will wait for A4 holes once the skins are on. One on the lower side....
...... and one on the upper side:
The last pieces to be fit on the elevator spar skeleton are the tip ribs. It's a bit of a juggle to get them in the exact right position, but they fit perfectly. Figuring out the order to drill them and the attachment angles to the spar was fun, but I got it done. A pair of wide neck welder's vicegrips are excellent for holding things together for drilling (note the protective masking tape on the pads to avoid scratching the aluminum):
Here is a picture of the elevator tip rib clecoed into place. The final rivets here are four A5 rivets which also hold on the outboard elevator pivot pins. Ron and I are going to weld up enough sets for each airplane being built and the holes will be matched with the A3 pilot holes I've drilled here.
As mentioned in my previous blog post, I'm considering options for a system to control the elevator trim tab. The plans call for a Ray Allen trim actuator and digital trim position indicator for the cockpit. But at $400+ I'm exploring alternatives, including substituting in a giant scale RC servo.
The Ray Allen system is spec'd to provide 40 pounds of linear push/pull force. Current metal gear RC servos are more than capable of meeting or beating that spec and with a bit of microprocessor power and programming are an attractive alternative. The whole replacement system from front to back including servo, a cockpit indicator and voltage regulators will likely be less than $100. The question is how?
Welcome to the world of Arduino, a programmable microprocessor board based on the AT328 chipset. With a bit of time, I believe I can use the Arduino to not only control the trim servo but provide failover support and control correlation. In addition, I have many options for how I want it to display in the cockpit, from a simple bar graph LED to a more intuitive graphic display. Only imagination limits me here. I',m also considering an Arduino board for controlling LED navigation lights and LED strobes.
So what does an Arduino processor look like? There are several models of boards all with different strengths and weaknesses, but most of either are related to what the board is capable of providing. I want the board to be simple to use but small for space considerations behind the control panel. For my prototype and likely final design, I've settled on the smaller sized Arduino Nano for the trim system:
I went on Amazon and ordered the Arduino Nano board and the associated mounting pins. I was able to find a 3 pack that included the unsoldered breakout pins. My plan is to use one board to prototype the trim system, one board to make for the airplane (wire soldered to the board) and one spare (in case one decides to poof into blue smoke if I screw up). I also ordered a voltage step-down board (top of picture) - the trim servo operates on 6 volts, so i needed a way to power it from the 12 volt system:
The easiest way to prototype and learn how to use the Arduino board, is to mount the pins on the breadboard, then place the Arduino on the pins. From there careful soldering each pin of the Arduino:
The Arduino is supported by a large online community of programmers, experimenters, robotic designers, musicians and others. It's simple but powerful programming language is easy to learn and because it is "open source code" based, there are literally thousands of example projects to build from and modify. I won't get much more into it here, but if this interests you, check out https://www.arduino.cc/
After getting everything together, I powered up the Aruduino from the USB port of my laptop ..... IT'S ALIVE! (I guess it's a stretch to consider that this might count as the first "power" my aircraft has had - I'm such a geek!)
After a bit of fussing around with loading up the correct USB drivers so that the Arduino programming application on the laptop can talk to the board, I uploaded my first "sketch", (the Arduino name of a coded program that instructs the board what to do). In this case, I added an LED and used the basic "Blink" sketch which tells the board to blink it's on board LED light
Again, I know this sounds geeky, but it's really cool! I messed around with the sketch and changed the blink rate and patterns and uploaded it again to see the result. I've got a bunch of learning to do, but a work colleague sent me some links to YouTube instructional videos which I'll work through and learn what this board can do.
Well, that's it for tonight. Back to the shop Thursday night to work more on the elevator. Got to finish the centre section, the elevator upper/lower control horns and start looking at how the elevator trim gets mounted. Got some disassembly, deburring and priming to do as well.
Thanks for reading, more to come :)
You know that satisfaction of reaching an important milestone when working on a large project? The joy that is only tempered by the fact you know you still have a long way to go? That's what today felt like..... incredible :)
After deburing, cleaning and priming all the parts for the horizontal stab, everything was reassembled and checked for square - all good and ready for rivets!
My daughter came to the shop to capture the first rivet being pulled on my 750! I don't think I can wipe the grin off my face. All the work I've been doing to form parts from paper to CAD to cardboard to aluminum to bending - it all comes together here.
There it is - rivet # 1 of MANY more to come. Before I close up the stab, I'm thinking of somehow identifying this rivet - a small inscription or label or something. All small steps may seem to make the journey a long one, but progress is defined as forward motion towards a goal. Happy builder am I!
With the first one down, the rest are quick to follow....
The rear bracket riveted in nicely. I'm going to wait to final rivet the attach bracket and gusset until I have the elevator complete and can match them up to ensure the pivot holes lined up for drilling. Same with the front attach brackets, but that's more for aligning the skins.
Very happy how this is all coming together. Next up, I'm going to start building the elevator skeleton using the exact same processes. Drill, fit, debur, repeat. When both are complete, I'll start working on adding the outer skins. I'm also starting to think of a system for activating the elevator trim system that should be an improvement on the plans.
Thanks for reading.
With the 701 wing gone from the shop and into storage, the bench is now clear for my 750 tail group and I can get to building my airplane using the skills and knowledge I've learned. This blog post will try and capture several days of shop work over the past week - it's been busy and to the uninitiated observer looks like it's moving really fast, but there's a bunch of work that goes into this that pictures will never capture.
The factory tail spars come predrilled, with all the rivet spacing laid out - this saves a bunch of time on layout, but you still need to consider order of operations and keeping everything square. Slight imperfections in scratch built parts means measuring everything closely.
And here it is.... my 750's first drilled hole (back drill from rear spar hole to doubler) and cleco. This is the basic procedure and first step of everything to be assembled to come.
Each doubler is done the same way, A3 hole in the spar as guide, A3 drill through doubler and clecoed. I pleased my doublers fit as nice as they do.
With everything together, drill again, this time upsizing to A4 and again to A5 where needed and cleco. It's quite repetitive but this ensures nice clean and centred holes. The other thing we did was line both edges of the table with angle iron clamped to the edge. 2x2 HSS tubes laid perpendicular across the table provide a level reference point (flat table) to work with.
With the spars upright and referenced flat, I started to trial fit the rear and nose ribs. These to are back-drilled from the spar to the rib flange, then up drilled to A4 and clecoed. A quick measurement confirms my scratch built ribs are correctly sized and by default the spars are spaced correctly. Excellent!
Spars and inside ribs are drilled and clecoed in place, so next are the tip ribs. The key here is make sure they are square to the spars and the spars are square to the rest of the assembly. The front end of the tip rib is connected to the front spar (left side in picture) by a fabricated 025 "L" bracket. It takes a bit of ingenuity to make it all square and drill it, but not overly difficult - and certainly a TON easier that repairing the completely un-square 701!
To help square everything up before final drilling of the tip ribs, we added some uprights to the bench (there were eventually 4 of these, one at each spar end front and back).
The use of standard "L" around various parts of the airframe allows for small adjustments to square everything up as well. Kinda explains why I need so many of these (see this post).
Here is where the tiip rib attaches to the stabilizer spar. Drilling this takes some thinking about which order to do it first, but the uprights hold everything in place while the drilling is completed. Another check of measurements first, then final drilling to A4 size clecos.
With everything squared up, the horizontal stabilizer rear bracket assembly is prepped for installation. This 063 thick aluminum plate is fun to bend, but again if you think it through it isn't that difficult. The tabs are bent inwards to 98 dregrees from flat. This is an important measurement as these tabs are where the horizontal tail attach to the fuselage. I used a protractor and drew out an example angle on paper to confirm both tabs were correct before test fitting it on the rear spar.
Clamp the bracket in place and back drill from the pre-drilled spar holes.... all good.... right.... wait a minute... damn...did I just put this in upside down?!?!
This is where paying close attention to the plans was important. A traditional horizontal tail looks like a small wing - flat on bottom and curved on top. The Zenith STOL aircraft have inverted tail airfoils, where the flat side faces up. There are a number of reasons for this that I won't get into here, but what makes this confusing is that it goes against common thinking. Multiply that by the fact the plans for the ribs and forms are drawn with the ribs flat side down, it'e easy to get confused which way is up! I'm also building the horizontal stab flat side down to take advantage of the flat table to get everything square.
So, what saved my bacon? The predrilled factory holes! The fact that they are symmetrical and the bracket is centred on the spar horizontally means I just had to invert it before up drilling to A4 and eventually A5 holes. What could have been a nightmare was avoided, but I'll be much more careful next time!
With the bracket turned up to the correct orientation and DOUBLE CHECKED AGAIN before drilling, I worked on right sizing the holes and clecoing things in place. Another check and everything is now where it needs to be.
Next to go on is the centre elevator hing bracket, one of three attach points between the stabilizer and the elevator. The attach point is at the tip of the triangle and will be drilled later when we match up the elevator.
Supporting the hinge bracket is a support gusset, which was chaleging to bend correctly - again the plans give a somewhat confusing view, but a little figuring, fitting, and adjustments finally got things where they needed to be. It's getting crowded in this area with all the clecos!
Like the ribs, clecos can be moved inside the spar or to the other side of whatever it is attached to - clecos don't seem to care and that's a good thing :)
Making notes on the parts as you go through assembly helps to remind you in the future. Here you can see I wrote a note that an "AN-bolt", not a rivet goes in this spot - a reminder that the hole is drilled to a specific size that is slightly larger than an A5 rivet. Before anyone comments that my grammar sucks, the term "AN" stands for a particular type of fitting (in this case a bolt) used to connect flexible hoses and rigid metal structures. It is a US military-derived specification that dates back to World War II and stems from a joint standard agreed upon by the Army and Navy, hence AN.
The final parts to be added to the horizontal stabilizer being measure/confirmed and laid out for bending - accuracy here is critical to make sure all three attach points for the elevator and the two from attachment for the stabilizer to fuselage are correct. This will make rigging the plane easier at final assembly and a straight plane ALWAYS flies better!
I flipped the stabilizer over, making it easier to attach these brackets. Alignment bother vertically with the proper amount protruding above the spar and horizontally in relation to the centreline of the spar is critical for tail alignment. Looking at this picture is decieving, the brackets are perfectlyperpendicular to the spar - I know because I measured it 5 times and confirmed orientation 5 times.... no second chances here.
Next I measured up the stab/elevator hinge attachment brackets for rivet hole spacing and drilled them out. I thought I might drill them as a stack, but I was concerned about alignment so I did the individually. The plans are very clear here on where they attach to the rear spar and they installed accurately without issue. So nice working with newly made, undrilled parts!
So,with everything drilled correctly, together with clecos and measured as correct, it all comes apart for final deburring, cleaning and corrosion protection. Now was a good time to lable anything that might get confused when it goes back together for riveting.
Well, that's a lot of work done, approximately 14 hours in total. I'm updating my build time tracker on the right of the page as I go.
Next up, prime everything for corrosion protection. In hindsight, I think I'll wait to prime/corrosion protect parts until all the drilling/deburring is done - the drill and debur swarf tends to get stuck to anywhere the primer is already applied (it's somewhat sticky even after curing) which makes cleaning more time consuming when it doesn't have to be. After that reassembly of the entire horizontal stabilizer for final riveting - my first rivets on the 750 will be so satisfying :)
Thanks for reading, more to come!
After completing the 701 wing repair/extension, I'm anxious to get started on the 750 tail group. It will be really great starting to assemble the parts I've made and have been sitting patiently in boxes at my workshop.
Back in September, I was at the Zenith factory in Mexico, Missouri. I decided to buy the spars for the horizontal tail and elevator. I could have made these myself, but our shop bender isn't wide enough to bend them and I decided the price was worth the value of having factory accurate spars to build around. The wing spar is made differently and can be replicated easily in the shop, where these can not. The purchased tail spars have other distinct advantages which I will get to later.
You may recall from a previous blog, the spars come neatly wrapped from the factory in a very long paper package:
After what seemed forever, it was finally time to open up the package. The staff at Zenith sure do a great job wrapping!
All the spars come pre-drilled from the factory as these would normally be part of a complete kit. As I'll explain later, this makes assembly much easier!
Although 6061-T6 aircraft aluminum is already a very corrosion resistant alloy, most people including Zenith recommend addition corrosion protection be added anywhere metal parts join. It's not the metal part themselves that cause issues, but any moisture that accumulates or creeps it's way in between the parts (and it will!) that can cause issues. I'm particularly concerned about this as I want the plane to be robust against all weather conditions, particularly when it may have to reside outside. In addition, my plans are eventually to get the 750 on to floats, so operating on the water adds to the concern.
To accommodate this, I'll be painting all joints with Cortec latex primer. Cortec comes in traditional primer green or clear. I choose the clear, which paints on with foam brushes as a milky white colour and dries clear. It weighs next to nothing and offers huge advantages over more toxic and smelly spary on primers like Zinc Chromate.
It sounds like a bunch of work to prime all the mating surfaces, but I was able to complete all three spars in about 10 minutes and it cures fully in about 30 to 45 minutes.
While I waited for the primer to cure, I decided I just had to trial fit some ribs - I've been waiting for a long time to see if all the work I put into making the forms, cutting the blanks and bending the ribs was going to pay off.
Although they fit properly within the spar web flanges, something didn't seem quite right. That's when I remembered that I hadn't bent the last flange over where it would connect to the elevator spar. Fit first every time to confirm!
A quick look at the forms also showed me I hadn't yet cut back the end of the form to allow the bending of the spar attachment tab:
I was quickly able to fix the problem by measuring the correct length for the form and cutting it in the band saw.
With the right length on the form, it was then easy to make the rib have the correct spar attachment tab:
With that, all the ribs now fit correctly - very satisfying to know all the work I put into getting the plans from paper to CAD to card stock to forms paid off. Hoping other forms are this well done too.
Before I got to far into it, I decided it would be a good idea to get the spar doublers made - they are the last larger component that I need for the tail group. You may recall from a couple of blog posts back, I broke a rotary bit trying to cut the 040 aluminum sheet. I managed to find replacement bits on Amazon fairly cheap and now that I had them in hand, I could continue to try and use the rotary cutter to finish off these 4 parts.
I got everything lined up again on the bench and proceeded to make another attempt. Unfortunately although I didn't break another bit, the cutter really wasn't working that well with the 040 thickness. It would bind and the cutter would get gummed up with aluminum chips, rendering the cutter useless.
In the end, I abandoned cutting the other two doublers on the bench. It was just easier to use the band saw, even if that meant a little bit of waste cutting the larger 040 sheet down to a manageable size.
Well, that's today's update. More exciting things to come, thanks for reading!
It's finally "done", the 701 wing repair/extension was completed a couple of nghts ago, but I'm just getting to the blog now. Here's a quick update of what happened Thursday night to finish it off.
Off the table and to be prepped for storage. Ron and I will add some plastic sheeting wrap over the ends to keep any birds out while it's stored in the barn.
I'm so glad to be done this repair/extension, but I can't deny how much I've learned. Now the table is clear and I can focus can be on building my 750!
Stay tuned more to come!
There is a famous saying in homebuilt aircraft circles.... "95% done, 95% still to go".
I'm starting to understand that saying. I can see the finish line still on this 701 wing repair, but everytime I think today will be the day that we put it back into storage, something else gets remembered, discovered and repaired.
So here is a quick photo run down of what I've done in the last couple of trips to the shop:
Flipping the wing over (again) I started the fun process of creating the new wing root skin. I put the plan drawing dimensions into CAD on the computer, but struggled to find someone locally who could print it to scale accurately (at 1:1 scale, it's almost 1 metre long by 300mm wide). As it turns out, the plans are really only a guideline to how this will need to be cut thanks to the original builder not closely following the plans anyhow - so hand drawing them out was the better solution.
Next up, cutting the root skin as per the template I've drawn from the plans. I tried a trial fit with the bristol board and it's close but like everything else on this wing, it'll need some adjustment to match up with the original plans.
More to come soon!
Once again, I find myself disappointed that I haven't been keeping my blog up to date. Almost a month has gone by - if you've been following along, thanks for staying with me.
The last couple of weeks have been busy in the shop, I can honestly say I think we are coming to the end of the 701 wing repair/extension. It's been a very VERY long road, but worth every minute learning how to read Zenith blueprints, bend metal, plan ahead and correct mistakes (both my own and those of the original builder).
In my last blog post, I mentioned we were going to try using the router to cut the 040 thick aluminum sheet. I have to cut 3 strips that will be bent to make up the corner supports of the horizontal tail frame box, and using the bandsaw or scoring method would be difficult at best because of the size.
I laid out the 040 sheet on the table. Unfortunately, I didn't take any pictures of the set up, but essentially I planned to use the same method as I used for cutting the nose skin slots - a long straight edge to guide the router along.
What I didn't expect was the router bit to snap immediately on contact with the aluminum. Frustrating as I was very careful in set up, feed speed, etc. In the pics below you can see it snapped up close to the shank, not down by the tip where it contacted the aluminum. I'm guessing it can't handle the stiffness/thickness of the 040 despite cutting the 016 very easily:
I decided to put this testing away for now - I'm going to have to obtain a replacement bit anyhow. I'll do some more reading/research to see what I can do to improve my chances. I'll have to get back at it soon, I need these pieces for my tail, the first thing going on the bench when we're done this 701 wing.
Back to the wing.
Using the same method as the inboard nose skin, straps and wooden strips are used to bring the skin down tight to the spar and nose ribs. It actually wrapped a lot easier than I thought it would, but careful even tightening of the straps was key.
With the skin in position, I used the hole duplicator and matched the nose skin holes to the spar. Surprisingly, the rivet hole spacing is correct - at least the original builder got that part right.
With the bottom of the nose skin secured, we flipped the wing over to get at the top side. Same process here, straps, blocks and careful tightening.
If you look at the picture above, it's clear I need to trim the wingtip nose skin. It's a complicated curve, even more so than the upper and lower wing tip ends because it also curves from top to bottom to form the shape of the nose.
Adding to the challenge is that the original fiberglass wingtip can't be installed yet as we are using it as a template negative mold to make more.
So, how to cut the skin to match the wingtip nose, without actually installing the wingtip nose? There are a couple of things I can look at for reference.
First, the other wing for this 701 is in much better shape and the wingtip is still intact:
Unfortunately, I'm not going to take the nose skin off the good wing, just to make a template for the wing repair. We also can't assume it's correct - remember, it came from the same builder!
Second reference, the plans! Only problem here though is the plans reference measurements from the last wing rib to various points on the nose skin curve, where X is the distance from the spar line, and Ynose is the distance from the last rib to the point on the curve:
Seems simple enough, but we've added an extension and added two more ribs. So where to measure from, hmmmm.
With the skin in place, I marked the skin where it overlapped the upper spar cap - essentially this marks the end of the upper spar cap and is the X=0 point in the table above.
The nose skin was removed again - clecos from both sides, straps, blocks, and all (the skin had to be deburred anyhow). Now that I had a good X=0 point, I measured back from there 505mm, simulating where the outermost wing rib rib would have been. I made a scribe line from top to bottom at the 505mm mark, then marked out each of the X points. From these I could now mark each of the matching Ynose points on the curve.
To make the line a smooth curve, I connected the points with a french curve drawing ruler. Once i was satisfied I had the measurements correct and the curve was a smooth as possible, I used hand snips to carefully cut away the excess skin. I left it a bit long as it's always easier to trim it back once the fibreglass nose is in place.
Before putting the nose skin back on, I ran a pair of wires from the root to the tip, leaving enough to work with at both ends and correctly labelled. The wires are secured firmly (but not tightly) to the nose ribs by a dual wire tie standoffs.
The other thing we wanted to do before fastening the nose skin permanently, was to rivet in a backer plate behind the wrong slot I had cut. This backer will give us a surface to place body fill putty in the slot.. When it dries, the holding rivets will be ground flush and the nose skin sanded smooth.
The wing skins go back on, the straps are tightened again and the skin lines up perfectly. Clecos are added, and the final riveting is completed on the lower side of the nose skin. The wing finally looks substantially complete!
The next step to finish was to replace the damaged lift strut pickup support bracket. I made a new one out of 032 (the original builder used 025), drilled and clecoed for fit
So, what's left to do? Finish installing the fuel bay cover and rivet the upper side of the nose skin. The upper wing root skin will be done once the wings are installed and wing incidence/dihaedral is set (more on that later).
Very happy to see this wing going away for storage by the end of this week.
Next up, my horizontal tail. Here are the frames for two other 701's Ron is working on. I'm getting my parts gathered and will be building my tail alongside these ones:
A productive couple of weeks. Hopefully my followers here will finally get a chance to see me working on my airplane. I wouldn't be able to even begin without the skills I've learned here on the wing repair/extension. I'm very thankful for the opportunity to learn - that's what it's all been about :)
Time until takeoff
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.