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!
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.