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.
I wanted to get back to the 3D printer this week, but my time was better spent in the shop working on the slats. I did manage to get the 3D scanner to work, but more on those later.
Slats are aerodynamic lift assisting devices attached to the front edge of wings. There are many types of slats and methods to accomplish the same aerodynamic principles. Large commercial aircraft often have hydraulically activated slats that extend on command from the wing. Some aircraft have slats that automatically deploy when the right conditions exist for it to be beneficial. In both cases, these are overly complex to design and build and not very common in light aircraft. Slats benefit STOL aircraft because in normal cruise, the profile of the wing acts the same as a wing without slats. However, at higher angles of incidence, such as in climb or descent, the slat forces air from below to the top of the wing, increasing lift dramatically, allowing much slower stall speeds (and steeper climb/approaches typical of STOL aircraft).
On Zenith STOL aircraft, the slats look/work like this:
I've learned the importance of gathering all my parts/materials before starting to build a section, so I started by laying out all the parts I have made so far for the slats. There are four to build, 2 inboard and 2 outboard - just like the flaps. I just noticed in the picture below I'm missing one of the slat doublers.... hmmm. I'll have to double check my count.
With a good idea of what's needed and what I need to still make (skins), I had another look at the plans.
The slats are a fairly simple structure to make without too many parts - this keeps them very lightweight. Like the flaps, accuracy is important so that the pick-ups match the attach points on the wings. Also like the flaps, it took some sleuthing to deduce the "distance between slat supports" by flipping back and forth several times between the slats diagrams and the wing diagrams. Not sure why Zenith couldn't just place the measurement on both pages! Each of the drawings have different points of measure. If this was a match drilled hole kit, no issue but for a scratch builder it takes some figuring!
Next I started laying out the skins. The width of the skin for a completed slat is deceiving as it curves on both the top and the bottom around the ribs. As a result I was disappointed to find that I can't fit two slat skins on every sheet, it's about 20mm too wide.... argh! I'll use the remaining metal on other parts but it would have been much quicker and nice to get two skins from each sheet. While I had the rolls out, I got all four slat skins measured and cut to size.
Full size 4x12 foot sheets are cumbersom to work with, so I cleaned up the bench a bit in order to make room, which was long overdue anyhow.
Other parts I still needed to make were the slat support brackets for attaching to the wings. These are traced from my card stock template onto 040 aluminum and cut out roughly on the bandsaw. From there they get ground down to size and sanded smooth.
Here is a pic of the four skins rolled up and the slat support brackets all ready for their turn in assembly.
I put away the skins for now and started to formulate a plan to assembly the first inboard slat. The general construction of each slat consists of a 025 slat doubler angle, 3 slat ribs and 2 slat support brackets. The slat doubler is essentially the spar of the slat.
Each of the slat support brackets also has a doubler made from a bent piece of standard 025 "L" angle. I decided to make up all eight at thee same time, 4 left/4 right. It starts with a 120mm long piece of L angle.
Measure out 50 mm and 80 mm in the centre of the bend where the relief holes will be. Use a centre punch to make a dirll point:
This notched piece of hardwood makes an excellent backer for drilling the holes so the part doesn't wander:
Use snips to make relief cuts to the edges of the holes:
Next was trying to decide how to make all the support brackets consistent with the ribs. The plans call the back edge of the support bracket to be 140 mm from the nose of the rib and that the rear lower edge of the rib be 28 mm elevated. So I figured the best way was to layout a rough sketch of the dimension lines on a board and trace out where a rib sits in relation to the bracket. This should ensure consistency for each rib that needs a support bracket and doubler. At the top right you seen the curved doubler (more on this later).
I struggled for a couple of minutes to figure out how I was going to place rivet holes from the inside of the rib, through the support bracket and into the doubler on the opposite side. The I figured out if I used a right side doubler inside a left side rib (and vice versa) I could trace lines on the inside where the doubler would be approximately. Now I know the holes I'm drilling will mate up with the doubler.
I duplicated the same process for the opposite side slats. In order to keep parts together with their mates, I put a alphanumeric mark on each set of parts. Slat support "J" matches up with rib "J" and doubler "J"
here is a better look at a curved doubler as it would be oriented under the rib and slat support. The doubler provides extra skin support around the slot that will be cut for the slat bracket.
Each inboard and outboard slat has 3 ribs. The outers have attach brackets and support doublers, the middle rib is just a rib. I'm pondering adding a doubler to the middle ribs to further support the skin. They are real easy to make and attach and weigh nothing.
Here are the ribs for the inboard and outboard right side slats. The one in the foreground shows how the doubler creates the sandwich of the rib and support bracket go together. Again, I decided to complete all 8 at the same time as I had the layout and process readily available.
Next up I started figuring out how I was going to bend the skins. Slat skins from the factory come pre-bent and it's important to be accurate here. A few test strips of 016 measured out according to the plans, bent then adjusted and bent/tested again to correct errors had me in good shape. I documented where the bend lines are compared to the plans once the skin is actually bent.
With the lines laid out, I made sure to mark each line with an bend order number, where the bend setback would be and what radius.
Clamping the long straight edge down to the bench makes it easy to scribe the long bend lines.
The underside edge of the skin needs a corner relief cut at each end to allow the tip insert to fit correctly. Measured the required cut and corner drilled first to make a clean inside corner when cutting:
The first bend must be the middle one as the throat of the bender isn't deep enough to make the bend from the other end of the skin if I make the small (2nd/3rd) bends first. After measuring several times to confirm the first bend (everything counts on the first bend being correct) I placed it in the bender and used a long piece of 025 doubler as a forming shoe. It worked perfectly.
Placing the slat doubler inside the bend confirms the bend is correct and true. I pulled the slat doubler out past the skin to show the match in this picture.
The second bend adds the up angle on the lower part of the slat. Again the bend here needs to be exact - too narrow, the next flange will be too wide. Too wide and the next flange will be too narrow.
More double and triple checking and the 2nd bend turned out perfect.
Here is the skin back in the bender getting ready for bend number 3. This bender can bend aluminum sheet up to 025 easily, but is really designed for lighter/softer aluminum trim coil/flashing/soffit which is can be bent to sharp 90 degree corners. To adapt to bending smoother radii required of aircraft aluminum, we insert a pre-bent strip of aluminum called a "shoe" to help form the bending sheet around the shoe to create the correct radius. In this case, I use a "shoe" of 020 to bend the skin around, leaving a perfect 1/8" radius in the skin.
Careful measurment and planning leads to a perfect set of bends - very pleased how it turned out!
Next I needed to figure out how to lay out the rivet lines for the slat doubler that fits inside bend # 1 (the 90 degree corner). I placed the doubler on the edge of the bench and slid the skin over top. The goal here is to make the rivet lines line up with the centre of the slat doubler flanges. So measure the middle of the flange.....
..... then slide the mark on the doubler to the skin edge and mark the skin.
Do the same at both ends then connect the marks with the straight edge. Voila, a perfect rivet line.
The first rivet is placed 30 mm in from the edge of the skin which is also the centre line of the inboard rib. From there, the rivet spacing is 50 mm. Rivet locations marked with black marks along the rivet line. These continue across until meeting the location of the centre rib. Then the same process starts 30 mm in from the opposite end on 50 mm spacing towards the middle.
Next I'll flip the skin around the do the same layout for the other side of the flange of the skin/doubler.
Overall a productive couple of days in the shop. More coming soon!
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 :)
As I mentioned at the end of my last blog post, I want to scan some of the parts into 3D digital models.
I'm making almost everything from scratch on the build, including the small tip inserts for the slats and flapperons. Normally these come with a kit and are made of either fibreglass or more recently are blown plastic molds. I could just purchase these, but Ron has originals from a 701 which shares the same sie and shape of the 750 ones. Purchasing is easy but expensive and doesn't do anything for increasing my learning. Making my own may not be much cheaper in the long run, but certainly equal or less and making my own also means I can learn some practical skills that come from 3D modelling and printing.
First step in this process is to 3D scan the original tips. Again, I could just purchase a 3D scanner and get at it, but what fun would that be?
When Microsoft brought out the XBox gaming system, they shortly after released a sensor system that can detect player movements and translate that into interactive game play on the screen. I believe this was in response to the Nintendo Wii game system which had already broke ground and was first to market with this type of player interface. Microsoft took the best of what the Wii motion sensor did with infra-red (IR) and expanded it to include camera capable of sensing colour, faces and more refined depth of field. Enter the "Kinect".
In this past decade of electronic and programming experimentation, it wasn't long until someone (much smarter than me I'm certain) said "Hey, I wonder if there is a way to hack this XBox sensor and piggyback on what Microsoft developed for other things?" One of the first uses was for robotics control - robots that could see (sense) and recognize objects. This quickly led to 3D scanning for types of objects, both for item manipulation and avoidance (is the obstacle in my way too big to move or is it of a shape I can grab/push etc.)
These type of developments often branch out to other things, including 3D printing. Think about the possibilities! Being able to 3D scan a rare car part and print a replacement for example. Scanning and printing replacement bio-mechanical pieces (heart valves). Printing materials are also evolving - industry is now printing everything from concrete to rubber to aerospace alloys.
Like 3D scanning, 3D printing has come also come to the home/hobbyist workshop - makes sense, these home hobbyist are often on the leading edge of these things, at least initially. At thankfully for less knowledgeable people like me, they often share their knowledge online - thanks YouTube and Instructables.com!
So, where to get started. I picked up an XBox 360 Kinect sensor. It is the most current one being used by 3D scanning hobbyists and has wide ranging support.
The hack of the sensor requires 3 items. A 12 Volt power adapter (bottom left and middle), the male end of a USB cable (top) and the Kinect sensor itself (cable end on the right).
Normally the XBox console gets power and sensor data directly from the Kinect. As a result (and probably because Microsoft wants to control everything) the Kinect has a proprietary plug similar but not exactly like a USB end. The third party 3D scanning software runs on a Windows computer, so that requires a USB connection. So, my hack requires replacing the proprietary XBox connector with a USB and also injecting 12 Volt into the cable to replace the XBox console power.
I found this wiring diagram in one of the online tutorial videos. In this case, the author wanted to dual-purpose his Kinect sensor for 3D scanning and maintain it for gaming use. To do so, he added a switch in his diagram - I won't be doing this, I don't intend on reusing this for XBox, so I can eliminate the switch and the XBox end shown on the left:
First step was to clip off the unneeded end of the USB cable (the phone end in the case of my sacrificial USB cable) then strip off the outer jacket of the clipped end:
Strip back the outer shielding if there is some and the inner foil shield if there is some (cheap cables don't have these, that's why they are cheap!):
Trim away the two shields, leaving the traditional white (data -), green (data +), red (5V +) and black (ground) USB wires:
Repeat the process with the Kinect cable (cut off the proprietary plug and strip/trim the shielding:
First thing I noticed once the shielding was pulled back was an extra brown wire I wasn't expecting....hmmm.... I was expecting a gray wire. Wonder if the diagram is referring to the outer shield, it's kinda gray?
A little further reading in some of the comments on the YouTube videos and some of the instructables pages I quickly discovered that Mircosoft switched to a brown wire from gray at some point. Problem solved.
I tinned the wires first after stripping of the insulation - this makes soldering them together much easier when the time comes. I also added thin wall heat-shrink tubing to each connection which once I confirm everything is working, will be shrunk to tighten everything up. Next, solder white to white, green to green, red to red.
Next, add in the 12 Volt supply lines. Positive 12 Volt from the wall adapter to the brown wire (gray in the diagram). Lastly, black wire from the USB side, black wire from the Kinect side and Negative 12 Volt from the wall adapter (hard to see in the picture sorry).
Next, connecting to a computer and powering it all up - hopefully no smoke escapes! Unfortunately, my laptop doesn't have a graphics card that is supported by the 3D software, so I'll have to wait to get my home server back up and running to test this, but should be good!
Not much I like better than wiring projects, can't wait to do more of this on the airplane.
I'll file this in tools for now and get back to it soon. Want to get the 3D scanner working so I can scan the flapperon and slat parts I mentioned above then print them. Carbon fibre anyone? :)
Sunday was a good day in the shop, and both Ron and I can see the finish line with the 701 wing repair and extension. Just a few more small items to go.
As Ron gets close to covering his Aeronca Scout with fabric, we've been discussing his plans to make a fabric/pain rotisserie rig for the shop. You may recall from way back in this blog an engine stand I bought for my Corvair. With my engine parts in Florida for rework, we're going to modify my engine stand and Ron's engine stand to become the end pieces for the rotisserie. This rig will allow us to mount any fuselage, wing or other large parts for priming and painting and being able to rotate them will be very helpful.
The inboard nose skin is ready to be installed. I clamped the skin in place, lined up along the spar. To draw the nose skin tight, ratchet straps are used, pulling the skin tight across the ribs. It's important to place the straps directly over the nose ribs to prevent caving in the nose skin before it is riveted.
Straps are equally tightened until the nose skins lay tight against the nose ribs and spar:
Folded protectors distribute the force across the trailing edge, thin scraps of wood protect the surface skins from the ratchet and strap hooks.
Using the hole duplicator, I matched the new nose skin to the original spar holes on the upper side of the wing. These were drilled to final size, the nose ribs to A3 until final fitting. The 3rd rib is drilled, but missing clecos so I can fit the outboard nose skin where it will overlap the slat pickup.
Once measured up, the outoard skin needs to be slotted to allow the slat pickups to protrude through. The easiest way to do this is with a trim router and spiral up-flute milling bit. I laid the outboard skin out on the table and set clamped a straight edge in place as a guide. Two strips of plywood under the sheet on either side of where the slot will be cut support the thin aluminum sheet and are thick enough to raise the bit above the table
After cutting all 3 slots perfectly straight, a valuable lesson learned - even if you right down the measurement, that is no guarantee that what you wrote down is correct :(
I measured the first slot as 395mm from the inboard edge, but for some reason I wrote down 595mm. From that point on, every time I double checked before cutting the slot, I measured/checked it as 595mm. Bringing the sheet back to the wing, my error was immediately obvious.
After pacing around the shop wondering how I could have possibly messing up the measurement, Ron told me he could fix the error fairly easily with a simple patch - go ahead and cut the right slot. This is part of learning and too much sheet metal to start over.
With the correct slot cut, all the slots lined up perfectly with the slat pickups - minor crisis averted.
Before working on securing the top side of the outboard nose skin, we thought it best to finish securing the inboard nose skin, that would give us a solid reference point for the outboard skin. We flipped the wing over and end for end on the bench. To get the nose skin flat, a thin strip of wood is placed under the ratchet straps. Once lined up and tight against the ribs, I again duplicated the spar holes and drilled the ribs to A3 size. Everything lined up excellent.
Even this nose skin, as small as it is lengthwise makes the overall wing so much more rigid. A good sign.
While waiting to discuss my slotting error I also unrolled my 040 sheet and start marking out the 3 horizontal tail doublers I need. I was initially really surprised at the amount of tape Aircraft Spruce used to secure the roll, but quickly understood why! There is a bunch of pent up spring energy in that roll, and I had to be real careful about wrangling it onto the flat floor for measure/cutting. The longest piece I need from this sheet is 1440mm long, so it was safe to cut that length off the end of the 12 foot long sheet. I marked and rolled the balance back up (that was a task!) and put it back into storage.
Aircraft Spruce ships all their sheet aluminum with a protective plastic sheet coating on both sides. Depending on how long the sheet has been on the shelf, room temperature, and other factors determines how easy it is to remove this coating. I think next time I'll gently warm it with a heat gun or hair dryer - this stuff sticks too good. For now, I've only removed a few inches from the edge I'm cutting from.
Even cut down to length, this sheet is awkward to put in the bender for scoring, and it's thick enough to making scoring a very long process. Instead, Ron and I think we are going to try using the router we used on the nose skin slots to accomplish the long cuts. If this works as we think it will, we'll use the same process for the wing spars (032) and maybe the fuselage sides/tops - anywhere a long straight cut on a large piece of material is needed. As I said above the tool makes really clean cut edges that require little in the way of deburring.
One other thing I've been doing is adding some of the complex shapes from the plans into CAD. Like my smaller parts (ribs, plates, etc.), these will be printed out to provide templates. One example is the wing root nose skin. I use a free downloadable 2-D CAD program called LibreCAD - it is very simple and more importantly it will accept the X/Y co-ordinate system common in the Zenith plans:
If you like doing things in 2-D CAD, you can download a free copy of LibreCAD here.
For those that have been asking, my finger is healing up nicely :)
More soon, thanks for reading.
Back in the shop today.... a full day to get lots done.
Started the day by cleaning up some of the small details for the flap brackets and assorted attachments. Surprisingly, most of these are actually good (contrary to most of what we've found during this repair). All four original flapperon brackets are stripped of paint, final sanded (not done by original builder) and clecoed in place. Final riveting will happen when we align the flaperrons. The new fifth one is already for final rivets and paint.
As with the flapperons, the wing extension we've added will require the slats to be extended too, meaning an additional slat support will need to be added. But first, I had to assess the current ones for condition and fit.
It became very apparent that the slats were installed with the same random carelessness of everything else on this wing. I really think most of the holes drilled by the original builder were done blind.
Here is the first one I I looked at. Clearly not to plan specs. Don't think those two top rivets will hold much, do you?
Drilled them out and not surprising, the nose rib looks like swiss cheese. No way we'll leave it that way or try and drill new slat supports to match either.
We decided to add doublers on both sides of the ribs that require this (we replaced several damaged ones with new already) in order to sandwich things together and give us fresh material to anchor to:
Taking a closer look at the slat supports, we determined that these too were randomly sized. Stacking them shows this well, none of the holes align, let alone match the plans:
So, like a lot of other things, we are replacing these with new. This of course means making new bent strips that will support the nose skin and required slot for the slat support.
Making the bent strips was fairly straight forward and and glad they turned out well.
It's very important that all slat supports are aligned the same, both for aerodynamic reasons and alignment of the slats. To accomplish this, the plans show how to create a positioning jig that puts the slat support in the correct position and alignment for riveting.
The bent strip is added and pre-drilled for fit:
The whole thing is re-assembled back in the jig for final drilling:
Disassemble again, debur, re-assemble and final rivet:
Managed to to get two done in about an hour. The second one went easier now that I know the process. With the second in place, it's clear the efforts to do it right are paying off. There are five in total so three more to do.
A view from about mid wing looking out towards the tip. A closer look shows perfectly aligned slat supports - yes!
That was a good day of work. Next up is finishing the other three slat supports and prepping the nose skin.
Thanks for reading :)
The last week of summer has come and gone. We made a family mini vacation to southern Ontario and took in the Brantford Community Charity Airshow among other things. It was an awesome airshow with quite the collection of warbirds, aerobatics and of course the Canadian Forces Snowbirds!
Also located at the same airport is Aircraft Spruce, one of the biggest suppliers of aircraft parts, pilot gear and building supplies. I had placed an order the week before and was able to pick up 3 rolls of aluminum sheet to be used in my build. Ron and Donna were also at the airshow and were kind enough to bring the rolls back north with them to the shop, saving us having to drag them around on the rest of our family trip.
I also stopped at KBC Tools in Missisauga and picked up a couple of really handy items. First, I've been reading about how to cut long straight edges on aluminum sheet. Some of the spars and doublers I have to make for my airplane are too long to be easily cut by shears. Even local machine shops in my area are either unable to handle the widths or too expensive.
One of the solutions on the Zenair builder's forums caught my eye. It involves making a aluminum cutting knife out of a carbide machine shop grooving insert attached to a handle, in this case a old crescent wrench.
I found the grooving insert at KBC tools. It's expensive for it's size, but is able to make very thin cuts in aluminum. For a couple of dollars more, I opted for the Titanium nitride coated insert making it more durable:
For a donor handle, I used an old crescent wrench with a seized head. I cut the head off at a 110 degree angle at the narrowest part of the handle using the chop saw:
Cleaned it up on the grinder.....
Next I used a combination of Dremmel tools and hand files to carve a shallow groove in the handle for the insert to rest in:
I made a test cut on a scrap piece of aluminum and this tool cuts it nice, clean and straight and only requires a couple of passes to score the aluminum enough for breaking. MUCH faster than using a laminate blade like an Olfa.
The other tool I picked up at KBC Tools was a NOGA Rotodrive countersink/deburring tool:
This is a much quicker and simple way to deburr dril holes. It is a rotating "dog-leg" countersink and with a very light touch and two turns will remove drilling burs without countersinking the hole. Lightweight and fast, it will be super handy as I progress through building. Much better than rolling an oversize drill bit between the fingers.
I continued work on the wing tip extension. I fabricated two (one for each wing) spar web doublers out of 0.032 sheet on the bandsaw. These will be the bread of the sandwich where the tip extension and spar web meet:
Laid out the proper rivet spacing and matched drilled them together:
Mounted the assembly to the wing spar web and match drilled the par caps, then clecoed everything together to confirm alignment:
With the assembly temporarily in place, the next problem needs to be solved. How to match drill to the original holes in the spar web (inclunding the orginal outer wing rib) without any access inside this part of the wing? As you know, the previous builder just eyeballed things so measuring what is already there won't be accurate enough. I could pull more of the wing skins off and back drill through the new doubler, but there is an easier way!
Introducing the "rivet hole duplicator". This ingenious tool allows you to match drill to holes behind the sheet aluminum. It consists of two straps of spring steel, one with a hole locator and the other with a drill guide:
With this tool, it's simple to find the right spot to drill each pilot hole. The pin tang slides in behind the panel you are drilling and the guide lines right up to where your new pilot hole should be..... GENIOUS!
Duplicate holes on web spar (right side of joint centreline) are complete awaiting final rivets. We'll need to figure out what we are doing on the back side to extend the spar caps and sandwich everything together but for now, this should be easily repeatable on the second wing:
With that complete, I took some time to fabricate the wing slat ribs from some spare 0.016 sheet.
There are 12 of them required, 6 in each wing slat. So I traced them out from the template, trying to use up as little real estate as possible. This will become more important later on when cutting other multiple items from full sheets:
One of the lessons learned earlier when I was making tail ribs was to centre punch and drill the relief and tooling holes before cutting out the metal, so I did that here first:
I discovered that the elevator tip rib form I traced out was undersized by about 2%. So I corrected the form and made the tip ribs with the correct aluminum template. Glad I caught this now, not later when I begin assembly. Here they are awaiting bending:
Very please at the progress I'm making. Coming up this week, I'm going to the woodshop to final trim and sand my plywood form blocks and I'll start tracing out the longer spar and doubler pieces for the horizontal stabilizer and elevators. Then I can start the assembly process!
I made some excellent (small step) progress on my airplane build this past week.
Before I get into details, I want to share a bit of scrounging advice. Don't ever be afraid to ask around when you are looking for something, be it materials or tools.
While building, Ron and I often get to talking about ways to save on costs. One of the things that costs a bunch of money when getting it done by others is powder coating parts. Powder coating is a dry finishing process that gives various materials a durable coating that can be much tougher than paint alone. It's particularly good on non load bearing parts that may be handled regularly or exposed to friction. Control columns and rudder pedals come to mind.
Powder coatings are based on polymer resin systems, combined with curratives, pigments, and other additives and ground to a fine powder. A process called electrostatic spray deposition (ESD) is typically used to apply the resin to the metal substrate. The process uses a spray gun which applies an electrostatic charge to the powder particles which are attracted to the grounded part. After application of the powder coating, the parts enter a curing oven where, with the addition of heat, the coating chemically reacts to produce long molecular chains, resulting in high cross-link density.
That's the long way of saying "it sprays on and sticks really well after being cured in the oven".... ha!
Ron and I both figure the majority of the parts we might want powder coated should be able to be done ourselves. Ron has a source for the powder coating gun and resins, we just need an oven. Baking resins can generate a fair amount of unpleasant fumes, so we won't be using the kitchen!
I've been real fortunate over the course of the last few years to have several people I know come to me with leads on "airplane stuff" and I owe a bunch of that to talking to everyone I know about my project and plans. Opinions regarding my sanity range from "wow, that's cool" to "you are bat-s%$t crazy dude!" However, even if the vast majority consider me closer to the slightly crazy side of the scale, they do come to me when they hear of something.
In this case, when I mentioned that we were seeking an oven, Brenda noticed a Facebook post from a friend of a friend who was remodeling their kitchen. Turns out they were giving away a built in Jen-Air oven! Free! Brenda messaged them, I hopped in the truck and 10 minutes later, it was in our possession. We really don't need the stove top portion for baking parts so this is perfect:
We'll build a simple stand and wire it for power. It will require some calibration tests to ensure the temperature settings are accurate as they need to be for the powder coating. Not every oven is created equally as far as accuracy is concerned and oven temperature can drift as much as 25 to 50 degrees over time.
As for my airplane, I started to put the templates I made to use and traced out my first parts with them.
They worked real good. A thick Sharpie marker leaves a good line for rough cutting:
Before making the rough cuts of individual pieces from the sheet, now is the time to drill the corner relief holes where reuired. Here are some that I remembered to drill before cutting them out. Much easier to do this before hand I've learned!
Once the parts are rough cut out (thicker pieces on the bandsaw), further fine cuts are made using hand tools. By always leaving a bit of the thick marker line, we can see where the part will be trimmed down with the grinder, a file or hand sanding when taking of the burrs.
I made several parts over a couple of hours:
I took a good idea from Ron and taped the template to the parts when they were done. That way I don't have to write the part numbers on the aluminum. These completed parts will be stored until I need them later. I'm keeping a massive spreadsheet to track parts made, where they are stored and what inventory of materials I have on hand:
I know I have a TON of parts still to make, some simple, some complex.... but there is something so motivating about making these first parts for my 750 that makes me want to be in the shop full time. Unfortunately without spending at least some of my waking hours at my paying job, I can't afford the materials to make parts, so I guess I'll have to get back to the shop when I can.
Next up, further repairs to the 701 wing and I'll finish the sub assembly parts I need for the tail group on my 750!
So back to the shop on yesterday, looking forward to flanging the root rib lightening holes.
When I set the flanging die up on the bench, I noticed that although my lightening holes are cut to a perfect 65mm diameter as per the plans, the outside diameter of the flanging tool above the shoulder (the one on the left) is also exactly 65mm, making it too tight a fit in the hole, and impossible to work correctly:
This means the holes I cut in the rib will need to be expanded just slightly.
There are a couple of ways I could accomplish this. To sand/grind the aluminum away to make the hole bigger would be quicker, but next to impossible to maintain a perfectly round circle.
Going back now with the flycutter set slightly wider presents an issue because there isn't any metal in the middle of the hole to centre the flycutter on and there is an increased risk of tearing.
I really didn't like the idea of ruining the perfectly symetric holes by grinding and hand sanding would take forever. Flycutter it is then!
To make another cut, I needed to add a piece of scrap aluminum to the back of the rib. Luckily, I have just the piece left over from the damaged rear channel (always save stuff you might use later). Here the sacrificial piece is riveted in place on the back side of the rib:
With slow and careful application of the flycutter, the new diameters are cut, maintaining the centricity of the circles. Now I know to make the lightening holes slightly larger to fir the dies. I'm pleased it worked okay, I was real concerned removing such a small amount may lead to a tear in the rib:
A quick drill out of the attachment rivets and voila, one rib ready for deburring (again) and flanging:
Deburring the lightening holes is very time consuming. I think I'm going to investigate what 3M Scotchbrite wheels will work on them.
The process to flange the holes using a die is much quicker than working them by hand tools. First, set the rib on the male side of the die:
Place the female side of the die on top, making sure the flange will press out in the correct directions according to the plan (in this case the same as the outside edge flanges):
Although it would be much faster in a hydraulic press, enough force can be exerted using a C-clamp and the bench top edge to accomplish this. For this size die, one clamp is enough, but on larger dies, multiple clamps would be used:
Squeezing of the clamp leaves a wonderfully even and clean flange:
Now that understand the process, making the ribs for my 750 will be much quicker.
I finished the day by doing further final work on the missing wing root doubler. Lots of back drilling of pilot holes, final match drilling and thinking about what can be riveted ahead of other items etc. I'm to the point of having everything ready for final fitting. I flipped the wing over to get better access to the doubler. The wing attach fitting in the lower left is the bent original with the terrible out of round bolt hole. I've clecoed back in place as a guide for backdrilling out the web doubler and new wing attach bracket:
So far so good. I'm really getting a handle on what it means to pilot drill, cleco, match drill, cleco, take apart, deburr, cleco again and final drill.... just to take apart again for deburring, cleco and final rivet. All important steps that mean a well built airplane.... something that the previous builder didn't seem to understand.
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.