Back in the shop after a couple of nightshifts at work. The shop is definately where I like to be, working away on the airplane and away from the constant din of COVID doom and gloom. We are streaming music via a bluetooth speaker to avoid any outside news. The crazies that call 911 with stupid scenarios around social distancing rules are starting to really annoy me, but that is for someone to worry about right now while I'm on days off.
With everything on the flap assembly correctly drilled to correct size, it's pulled all apart again for deburring. I decided it was best to drill the flap pickups for the connector bolt while they are off the flap that way I can ensure consistent position of the hole. I noted these measurements in my plans (Zenith don't tell you the dimensions of the hole placement on the angle, just that it's an AN3 diameter bolt hole).
Placing the pick-ups back to back and clamping them together for drilling through makes for an easy way to make them consistent.
With everything deburred, I cleaned of the Sharpie markings off with acetone, scuffed up everything with a purple 3M Scotchbrite pad and wiped everything clean again. The aluminum sure looks clean now!
I was going to use Cortec primer again here, but decided interior pieces can be sprayed with green chromate based primer. I did any edge that would be in contact with other aluminum. Kind of wish I had done this with the elevator - much easier that the Cortec and easier to see coverage is complete. The outside surfaces of the flap pick-ups are done in grey paintable self-etching primer as they will be painted with the flaps later. For the flap spar, the outside of the flanges and the areas where ribs attach were also done.
I cleaned up the flap pick up holes as well using the same process. Green primer on the inside, grey on the outside. The grey primer looks thick in the picture, but it dried thin and smooth.
It doesn't take long for either primer to dry, so assembly can begin almost right away again. Kinda weird seeing everything in green but it will be inside the flap!
Here you can see the flap pickup angles painted primer grey.
A5 rivets here really tighten up this joint/structure. The entire weigh of the flap counts on this important interface.
With the entire inner flap skeleton now riveted, I added the skin back on and began riveting it all together again. This picture below shows the control horn and doubler in place, already primed and ready for riveting. It also shows the "toe-in" of the root rib and how the skin was trimmed to match. I took measurements and documented the rivet placement so I can match the other inboard flap.
Here is another close-up of the protruding flapperon pick-up angle. Really happy how the hole turned out. When prepping everything for final paint, I might consider filling the gap with some flexible putty or something to clean it up entirely. Not required but would prevent water or something getting in there.
From here, it's the process of riveting alternate holes on the bottom surface, working from the trailing edge forward towards the spar. Next, remove the remaining clecos, rivet any remaining holes and the bottom is complete.
Next time in the shop, I'll be flipping it over and drawing the nose skin down for temporary rivets across the top surface. It will be set aside and I can start the next one.
Only 3 more flaps to go. They should go much faster now.
Thanks for following along. Find your way to self isolate - make something!
So, a lot has been happening in the world in the last week or so.
The Novel Corona virus, better known now as COVID-19 has seen exponential spread across international borders from it's origins in China. Unless you have been living under a rock or are reading this blog in some distant, future archive (thanks by the way!), news and anxiousness is rampant about what is now officially declared a pandemic. People are scared, some more than they realistically need to be and world financial markets are feeling the squeeze.
Mandatory closures of schools, businesses and government facilities are becoming commonplace as we work to "social distance" ourselves from others. Large groups, social gatherings, events and meetings are highly discouraged if not outright banned Efforts are underway by people everywhere to prevent the spread of the virus and protect those who may not have the benefit of good health and the ability to fight off this particularly nasty bug - it can and has been shown to be fatal. Unfortunately there are those ignoring common sense which is leading to more anxiousness and unease. This has even lead to a very strange phenomenon of the panic buying bulk toilet paper!
I've said before how much my shop time is my happy time. It's my place to decompress from my emergency services job. While a good portion of society has been told to stay home from work, my colleagues and I continue to work shifts in a busy 9-1-1 communications centre and although the calls for service have yet to peak as I think they will, we are an essential service and will continue to come to work and answer the calls. It's scary but I think we'll come out the other side of this craziness better off as a society from the lessons learned.
So, what better way to practice "social distancing" and "flatten the infection rate curve" of COVID-19 ng than to get to the shop and work on my build! Here's what's happened since my last blog post.
A couple of weeks ago, I traveled south to visit Dad and made a side trip to Princess Auto and Aircraft Spruce for tools and hardware. I needed an inch/pound calibrated torque wrench and was happy to find a good quality one on sale - score!
I stopped at Aircraft Spruce and picked up my online order of the remaining aircraft hardware I need for the build, other than some back-ordered nut plates and stainless machine screws. Obviously this isn't everything I'll need (the interior will require some fabric fasteners etc), but what you see in the picture below is the lion's share of bolts, nuts, washers and cotter pins called for in the plans.
I've primed and final riveted the elevator outer hinge pins
With the elevator all closed up I started fitting the trim control rod and servo arm
Here is a good look at the servo arm and trim control rod. I'm not happy with how they fit together as there is too much slop or play between the pin and the arm, so I'll likely put some JBWeld metal epoxy in the arm hole and drill it out to match size the rod arm pin.
The rod as it comes from the hobby store is plenty stiff enough to work in this arrangement, but comes much too long. I attached the trailing rod end to the trim tab actuator bracket. With the elevator trim in the neutral position, I held the road alongside the rod end, trimmed the rod to length on the bandsaw and ground it smooth on the bench grinder.
I specifically left the rod long enough so that I can trim is shorter if needed. The plans call for the elevator to deflect 20 degrees up and 40 degrees down from neutral. Before I can set the system up, I'll have to thread the this end of the rod for the safety nut. I may change the "neutral" position of the servo arm to favour the 40 degree pull - it will take some playing around to get it just right. The servo programming is the easy part!!
Some final clean up of the stabilizer was completed and I temporarily closed it up with rivets, just like the elevator. The insides will have to be inspected by Tansport Canada before all the final rivets are done. Stabilizer fences are just temporarily attached for storage purposes and may need to come off to open it back up for inspection, but I may get lucky and they can stay on for final riveting.
The following pictures show the completed tail assembly with outer and centre hinge pins installed. It lined up perfectly and shows no signs of binding - very pleased! (it's sitting on the bench upside down compared to how it will be mounted on the plane - it just sits better that way).
So! The tail is now complete. I currently have roughly 150 hours of work into it. Once wrapped in heavy plastic it will join the rudder up in the storage barn. There's about another full day's work once it's cleared for final close up to complete, with a lot of that having to wait for fitting to the fuselage.
I feel so productive and safe from the world's dangers in the shop right now. With all the temporary closures, I couldn't think of a better place to stay safe from COVID-19 - working on the some temporary closures or my own :)
Thanks for following along. Next up flaps and slats!
A bit of time in the shop this week. Dismantled the elevator (again) and deburred the holes now that everything is drilled to right size. It's points like this in a project that make you feel both accomplished and behind at the same time. You realize all the work you've done to this point by the number of holes you've drilled, but taking it all apart for deburring seems like a backwards (but necessary none-the-less) step.
Deburring the trim tab after it is bent is problematic. The holes for the hinge can't be drilled without having it bent to shape first. How to debur the holes on the inside angles (see yellow arrows)? Make a tool!
Normally we'd use a rotary debur tool, but access is too tight. To get access, I came up with this idea.
1. Slot a piece of wood
2. Insert sandpaper
3. Slide onto flange
4. Gently and carefully slide back and forth along the length of the flange. The goal here is to remove the burrs, not to sand the flange. It worked really well!
A follower of the blog had asked me why the elevator skin looked wrinkled in the pictures on the bench and the look of wrinkles is due to the protective plastic coating on the sheet aluminum. I've now peeled that back anywhere there are rivet holes so I can properly debur them. I'm leaving the remaining plastic on the skins to help prevent scuffs and scratches as I work with them off the skeleton.
With the elevator skin off the spar, now is a good time to fit the trim servo. The bracket I made will work, but now that I'm fitting it I've discovered something I hadn't thought of. If I have to remove the servo for replacement or repair, orienting it this way (mounting screws are sideways in the bracket) means it will be painful if not impossible to remove it through the access hole!
I decided it best to create a new bracket similar to the one Ron is planning for his 701:
It took a couple of tries to get it right, but it turned out well!
I'll need to add a grommet or strain relief at the pass-though hole to prevent the servo wire from chafing:
The servo will sit on an angle, parallel to the inside of the skin surfaces - the more direct the push/pull rod can be to the trim tab control horn the better.
As I sit on nightshifts at work, I have some time to ponder what else I can do with the Arduino. The ideas are truly endless and easy to implement. One thing that really excites me is the ability to display data on little screens. For example, here is a picture from the internet where an Arduino programmer has an OLED (Organic LED) panel emulating a basic cell phone display. OLED displays are super cheap and highly customizable and some models are capable of displaying in different colours.
Here is another example of a development board with an OLED display connected to an Arduino mini exactly like the ones I'm using. They are very small in size, but can be used to display lots of things at really bright contrast and resolution.
Here's an animated guage from the interwebs being used for something someone was developing:
If animation can be done, animation in colour can't be much more difficult.
I'm pondering a small display like this on my instrument panel, with a custom display graphic. Perhaps a overhead drawing/graphic of my airplane with animated lights that blink in co-ordination with my navigation/strobe/wig-wag lights! How cool would that be? Here is a (very) rudimentary idea about what it might look like. I can't animate this picture, but I think you get the idea - the red/green nav/beacon/strobe lights would blink or in the case of the landing lights alternate back/forth when in wig-wag mode. Maybe I can animate the prop too hahahaha!:
Maybe instead of the bar graph LED showing elevator trim like I already have planned, I can integrate the bar graph onto an OLED display, either by itself or with the light display above:
My engine gauges will be traditional mechanical versions - much more robust. Everything I propose here is for non-critical indications.
I've got a long way to go before I have to worry about this stuff anyhow, but it is cool to think this is easily and cheaply within reach for a simple hobbyist like me!
Some my regular readers might have noticed I've removed the countdown timer from the right navigation bar of the blog. I originally intended this to be a motivator for me. I had set the goal of first flight to be my 50th birthday, but that is never going to happen. I got behind in my build with changes at work etc., so I'm removing it for now as it doesn't reflect reality. I'll continue to strive to get the build done.
Next up, priming the elevator pieces and reassembly for riveting!
Thanks for reading :)
Back in the shop tonight, finishing up some of the smaller details on the elevator.
Got the motivation to cut the trim tab slot out of the trailing edge of the elevator. The plans call for a slot for almost the full length of the trailing edge. This doesn't leave much of the trailing edge remaining done this way, so after some discussion with Ron, I decided to shorten the trim tab somewhat.
Cutting the skin is tricky - have to be real careful not to damage the trim tab spar. I decided to drill some pilot holes to work towards, then clean the edge up close using a Dremel tool. It took several assemble/disasemble cycles to get it just right but it turned out nice a square. A round file helped to round out the inside corners.
I've decided to add some trailing edge ribs on the rear elevator skin and inside the trim tab as well. This not only supports the skin where I changed the cut, it also looks nicer and will be cleaner aerodynamically.
It took a few tries to get it right - there is no template in the plans for these, I'm making my own. I'm happy with the fit and feel.
Next on my list of small details was drilling the trim actuator hole in the trim spar and elevtor lower skin. The step dill was again very handy for this:
Took the spar out of the elevator skeleton to drill the matching slot:
Back together for final fit. The slot stays the same as the plans. I think I might try and come up with some sort of flexible cover for the trim actuator rod hole to prevent bugs, dirt, snow or rain from getting in there.
Started the initial fit of the elevator nose skins. These need to be in place to confirm the correct spacing between the elevator and the stab. Happy with the fit but surprised how much of the nose skin tucks under the rear skins - but that's what the plans call for and my nose ribs are correct!
With both nose skins temporarily in place, I set the elevator against the stab again to confirm (again) the alignment of the upper and lower horns and centre hinge bracket - all good.
Forward and rear brackets drilled and added - this really stiffens up the elevator centre assembly!
All in all a productive night. I'm headed back to the shop in the morning to continue to knock off the small details - it all adds up!
July was a washout with regards to getting anything done in the shop, so not much available content for the blog....
A home project to replace the shingled roof on our house with metal took up 2 weeks of my July holidays and work travels took up a good portion of the rest of the month. Day trips with family need to happen too. This Monday to Friday temporary assignment I'm currently doing at work is good that the work is both challenging and really interesting, but it only leaves weekends to enjoy the summer. As of last week, I've been advised that I'll be returning to shift work at the end of September. I don't want to go back to the communications centre, but on the bright side, my schedule during the week gets freed up substantially (4 days off every week), allowing me more shop time.
Speaking of work travels, I had a chance to check out the Chapleau Ontario airport. Although there wasn't much to see (MNR fire base was quiet), I did notice this cool sign posted by the local flying club:
July and the beginning of August hasn't been a total loss I suppose. I did manage to get some work done on the elevator and horizontal stab.
When I fastened the skin to the stab skeleton, I marked out where I needed to trim the trailing edge. The extra was on purpose - it allowed for proper length and square fit. Now that fitting is complete and correct, I can trim it back:
With the trimming done, the rear slot is cut. This is where the elevator cables pass through the stab:
I notched back the spar doubler a small bit, leaving clearance for the rivet. Everything was deburred, cleaned up and primed after this photo was taken. Fortunately only had two places where this was an issue.
With the stab skeleton ready, I deburred the stab skin holes on inside and outside - there are a ton!
Cortec primer on the rivet lines was next. I really like how it applies - next to no smell, easy clean up and cures almost clear:
With the primer curing, I turned my attention to the elevator skeleton. Some final measurements to ensure it's built square and it is ready to taken apart again for final debur and prime.
The elevator skins are made of 016 aluminum sheet, folded at the trailing edge and fastened to the top and bottom of the spar. It consists of two sheets of equal length meeting a the centre:
To allow the rudder to move left and right, the skins are cut out at the centre box where the rudder hinges are. It's difficult to perceive in this picture, but once folded the cut out makes sense.
It's important to radius the corners of the cutout, so I started with a centre punch then a pilot hole and followed that up with a 3/8 drill hole.
Cut outs complete for the left elevator skin. Easier to see how this will look when folded. Round file and debur tool to clean things up. This is a exposed edge, so I final sanded it with 360 grit:
Careful use of the bending brake got the fold most of the way, then I used a small diameter aluminum rod to finish the fold to the 5 degree bend called for in the plans:
I used the same piece of pipe to curve the elevator nose skins that I had used for the horizontal stab - much easier this time.
By this point the primer has cured on the elevator skeleton. Re-assemble and check for square - all good to final rivet. I'll wait to final rivet the tip ribs once the skins are on and I can align the elevator and stab hinges:
With the prime cured on the stab skin, it is reinstalled for final riveting. I've decided to river the curved side (lower) and leave the flat side open for inspection. It's kind of weird order - first place the skin over the spar pick ups and cleco everything down tight:
Flip everything over and cleco down the flat (upper) side:
Flip it back over and complete the riveting on the curved (lower side). Really happy how everything is coming together and how straight everything looks :)
The stab is essentially complete at this point. Remaining items to be done are final rivet the hinge assembly (waiting elevator match up), cable pass-through slot in leading edge and fairleads (rub strips). I've also decided to add wing fences to the stab tips which have valuable aerodynamic benefits and really cleans everything up. More on the fences later.
Next up, get the elevator skins fitted up, then cut the trailing edge for the trim tab and install the servo.
Thanks for following along, more to come soon!
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!
Getting close enough to getting the 701 wing completed, it's time to start planning the rest of the tail group on my 750. That means ordering some aluminum!
I called the supplier (Aircraft Spruce Canada) and ordered all the 016 I need for the entire build, a sheet of 025 to replace what I've used from Ron and some elevator trim tab hinge. The plan was to go last weekend, but the huge storm that dumped on southern Ontario precluded the trip so instead we loaded up the truck and headed south this weekend.
We arrived in Brantford and convenient for the girls, an equestrian riding store is about a kilometer away from ACS. I dropped them off and headed to ACS to pick up my order and some items for Ron.
The staff at ACS are fantastic - I had asked them to roll the aluminum as small as possible in order to fit it under the tonneau cover of our truck and keep it out of the winter weather. They are masters!
In addition to stopping at ACS, I had been in contact with another 750STOL builder in Burlington - Ghazan Hieder. Ghazan has been slowly working on his kit for about 10 years and self admits that any upgrade that comes out from Zenair he buys, so when edition 3 cabin changes were announced, he bought the plans and updated parts, making some edition 2 parts available. He had advertised on the Zenair Builders website he was giving away an edition 2 cabin frame and windshield, so I made arrangements to meet up with him while down south to take possession of these two valuable items.
He was glad I called as he had hoped to find another builder who could use these items - and I was glad to take them off his hands. All the research I could find shows only minor modifications need to be made to the cabin frame and the windshield is another easy mod.
Ghazan also offered me an early edition nose wheel fork and nose strut - he'd replaced his with Viking steel spring mod, something I'm considering too. If I can't use the strut he gave me, it will work for one of Ron's 701 builds.
Brenda helped me load everything into the truck as best we could, but we decided to put the windshield in the back seat until we could work in the daylight the next morning.
With better lighting, it was easy to pack everything safe ans secure. I borrowed some moving blankets from a buddy and laid them out in a way to protect the plastic edges of the windshield and the sharp edges of the cabin frame.
Getting it home safely worked really well, thanks to Brenda's amazing packing skills!
Unpacking it all at the shop, here is a better look:
Needless to say, I am truly thankful to Ghazan for his generous donation. He could have just tossed these away (frankly I'm surprised no one else came forward to take them) but he didn't - he just wanted someone else to use them on an airplane. Estimates are hard to nail down because I have no idea what this stuff would cost to ship, but conservatively? I saved about $800+ by picking up these surplus (to another builder) parts!
One of the coolest things I've learned about the homebuilding community is how keenly interested everyone is in other people's builds and more importantly successes. I have or am learning the skills to make these work for my build and that works for me, whereas Ghazan is happy to build from a factory kit. Either way we share a common bond - dream, build, fly!
Thanks for reading!
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.