A really good couple of days in the shop this week.
With the first slat underway, I was time to begin the task of wrapping the top skin over the ribs. To make this easier, Ron has built a "slat box" as show below. Made from plywood, it is essentially a reverse or negative pattern of the top surface of the slats. Green painters tape is added to any contact point to prevent scratching the skins:
Before getting the slat mounted in the box, I had to tuck the underside into the folded over trailing edge. It's tight, and I used a thin piece of wood as a slide to get it tucked under. The resulting pinch of the trailing edge fold is enough to keep everything together for mounting in the box.
Now it fits in the box and can be strapped down to complete the final wrap over.
I used a piece of HSS tubing to act as my spreader across the rear of the slat.
A look inside the each end confirms things are close enough and I can begin drilling the top side rivet holes.
To access the top side (which faces down in the box) I tilted the box on it's side:
Strategically cut access holes in bottom of the slat box line up with the 3 internal ribs so I can get at least 3 rivet holes drilled through the skin into the ribs:
The fourth hole is to far down inside the box to drill it accurately, but that can wait until everything is out of the box.
Put the box back upright and added some more blocks. This allows the force of the straps to transfer down more vertically, tightening everything up and I can begin to drill and cleco the trailing edge down on the underside:
Take the assembly back out of the box again and finish the top side rivet holes I couldn't access before. The finger clamp holds down the rear curve of the skin to the double bend flange underneath:
Layout the rivet line across the top rear. These will be A4 rivets with 50mm spacing:
To ensure I had everything locked down where it needs to be, I flipped everything over and drilled out everything to A4 on the underside:
Back ipright again, drilling the topside rear rivet line, A3, then up to A4 on 50mm spacing. I also completed the front rivet holes in each of the nose ribs. Everything is tight and square.
And it all comes apart again for final debur and priming:
One of the challenges I'm facing is how to make the inside of the slat structure accessible for the inspector to see my workmanship. The fold-over design of the skin makes leaving it open like the flaps, elevator etc impossible. I discussed this with Ron and confirmed with Roger at Zenith that adding a lightening hole on the flap ribs was acceptable here. I'm not looking to save weight, just want an easy way to see inside. This viewing can be done with a scope.
I carefully added some small holes in the centre of the slat ribs using a step drill. This will allow a camera scope inside.
I flanged the hole slightly to add strength:
I scratched off some of the primer doing the holes, but they cleaned up nicely and I re-primed them.
The new access hole creates a new small problem. The skin support L now protrudes over the hole:
the quick solve for this is to trim the L a bit before riveting. I also trimmed it back a bit on the top of the bend flanges to ensure clearance for the top two rivets.
Primed the skin and once dry started the re-assembly which goes back together fairly quickly
With everything drilled out to A4 and clecoed, the slat skin is tight to the ribs and looks good for riveting. The access hole turned out really nice - there should be lots of room to look inside using a scope.
Very pleased how this turned out using the steps I came up with worked well, I'll be following the same order when I build the other three. Again, I'm rather surprised by the size these are, it gives a good impression about the wing dimensions.
One to the next one, it all starts with alying out the bends. Thankfully I wrote down the measurements and bend order from the first one - that will make the next three the same.
Very happy how the first slat turned out considering how complex and tight the bending that is expected of the skin. It's not a complicated structure, but "fun" to do.
Back in the shop soon to get the rest of the slats done. I'll be continuing work on the 3D scanning/printing project too, exciting things coming up. Thanks for reading.
A really productive day in the shop today. Managed to finish off the last flapperon (inboard right). A milestone part of my build is complete. Here is a family pic of them all together:
The opposite end shows the open ends of the outboard flaps (on the left below). This is where the aerodynamic tip inserts will go during final assembly:
With everything complete on the flaps, I stacked them up for wrapping in plastic sheet to protect them:
Once wrapped up tight, they go up in the barn for storage until needed back out for inspection and set-up on the wings. Stacked on some of my rolled aluminum, from botton to top, my completed assemblies are stabilizer, elevator then flaps.
One thing I want to try is 3D printing some of my parts and the aerodynamic flapperon tips are the ideal candidate for this technology.
I wrote previously in my blog about 3D scanning some original parts and using the 3D model from the scan to print them. I discovered that although my home server has enough processing power and memory for 3D scanning, the video card currently installed does not quite have enough chops for the job. A replacement I ordered arrived last week from Amazon and I set to the task of installing it. For some reason, the server will not power up (it has been sitting idle for a couple of months while I waited for the new video card). Bummer, I will have to investigate this further before I can start experimenting with 3D scanning.
Meanwhile, our local library allowed me to bring home their 3D printer. It broke several months ago and they have no money in the budget to repair it or hire someone to fiddle with it, so I offered to see if I could get it working. No idea at this point what it will take to get it working (it is an early model) but I told them in return for trying some prints from my 3D scans, I would both work on getting it working for them and pay for any parts that might be needed. From what they have told me, the extruder nozzle is clogged and the print bed may be damaged.
Very happy to have the flapperons done. Next on the build table will be the slats which I am led to believe is one of the more challenging sub-assemblies of the entire build. But that is what I got into this for - to learn :)
In an upcoming blog I document the 3D printer un-boxing, rebuild and repairs.
Thanks for following along.
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.
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.