As I work away on the repair of the 701 wing I'm caught in a bit of a conundrum.
The spar cap repair I'm ready to rivet is all fit and ready to go, but in order to solid rivet the spar cap inside the nose skin, I need to take that nose skin off in order to have the room required for the rivet gun. Not a huge deal and not difficult to do, but as with everything else in this repair, we're scared to discover more of the original builders follies.
The other side of the coin however is do we want to take that chance? Forego opening the nose skin section and we might miss something important, but we can't leave it in place if we expect to complete the spar cap repair. Eventually the MDRA inspector will need to see inside the wings anyhow, so off it comes.
First steps, drill out all the nose skin rivets on the bottom edge and rib noses:
Gently unroll the nose skin which can very easily be creased when not secure:
Thankfully it came apart very easy. It actually looks decent and proper inside. Some minor issues with rivet lines on the nose ribs, but certainly better than what we've seen so far.
With the nose open, I finished solid riveting the spar root doubler. Nice to see this part close to being done - really happy how it turned out, the solid rivets are not too difficult to set:
I also finish riveted the spar cap repair. It too turned out real nice:
While all this has been going on, I've been working on printing and cutting out the templates I need to make my forming blocks and shaped aluminum blanks for my 750 build. It was lot of work but now I can start cutting and bending metal for my project!
Next up, continue the 701 wing repair (almost there!) and start tracing out the parts for my 750 horizontal stabilizer.
One of the new skills I'm learning is how to "buck" rivets.
Bucked rivets, also referred to as driven or solid rivets, have been used as the primary fastener type in the construction of aircraft for decades. These solid rivets are light-weight, strong and inexpensive fasteners. That’s why they and pulled rivets were chosen for aluminum aircraft construction.
A bucked rivet is a round fastener that attaches two or more pieces of metal together. The rivet is driven by a pneumatic rivet "gun" with an attached rivet "set" shaped according to the shape of the manufactured head of the rivet. The rivet's "tail" (blunt end) is backed up by a "bucking bar" that acts as an anvil while the rivet gun and set are acting as a hammer.
As rivets are driven the tail of the rivet is transformed (technically called “upset”) and two things are accomplished. First, the rivet shortens in length and the exposed tail bulges outward to morph into what is called the shop head. Secondly, the shank diameter swells in the hole to fill it entirely. A bucked rivet holds the metal pieces in compression (like your thumb and forefinger holding two pieces of paper together) and in shear (does not allow the pieces of metal to slide around in relationship to each other. Typically multiple rivets are used to hold objects together and the combined strength of all of the rivets have tremendous holding power. Although riveted construction is permanent in nature, it can be easily repaired by drilling the existing rivets out, making any necessary repairs and re-riveting with the same or a slightly larger size of rivet.
Although it will take some time and practice to learn how to do this, it really isn’t a terribly difficult skill to acquire.
First thing is the rivet gun. The rivet gun is like a hand held pneumatic jack hammer for driving rivets and could easily be confused with an air hammer. However, there is a significant difference between these tools as the rivet gun’s impact can be controlled by varying the amount of squeeze on the trigger, whereas an air hammer is on full or off. The gun incorporates a removable coil spring that both holds and retains the rivet set securely to the rivet gun and acts as a return spring each time the rivet gun drives the rivet set outward:
The rivet set is the business end of the rivet gun. You can have one rivet gun and any number of rivet sets to accommodate the shape required for the contour of the manufactured head of the rivets being used. From what I can gather in the plans, the vast majority of bucked rivets in the Zenair aircraft are of the domed head type, so the rivet set I need looks like this:
The bucking bar is the other half of the equation. Just about anything of a hardened material can be used and like the rivets themselves they come in all shapes and sizes, allowing access into tight or blind spaces where required. The brass cylinder on the left in the photo above can be used as a bucking "bar", as can the red cylinder propping up the rivet gun for the photo. Sometimes they are a square block, it doesn't matter as long as it can be held firmly and flat against the tail of the rivet being driven.
Like any fastener, rivets come in any shape and size you desire, and the plans are very specific about the specs required at each location. Usually, the length is measured from the flat underside of the rivet head to the tail and is noted in sixteenths of an inch.
Sometimes, rivets that are too long can be trimmed to the correct length using a rivet cutter. A rivet cutter is like a scissor or shear that can cut rivets of various sizes to specific lengths. The 1/4'” length rivets cannot be cut any shorter with this tool as this the minimum length of cutting. However, the rivet cutter can cut longer rivets (like the 1/2” rivets) to 4/16” (AKA ¼”), 5/16”, 6/16” (or 3/8”) and 7/16”. The rivet cutter has a series of length setting spacers that can be rotated above the selected hole that is appropriate to the rivet diameter being cut. Then, tighten the knurled knob to keep the length setting you desire while cutting a number of rivets:
As with any new skill, practice makes sense. I took a couple of scrap pieces of aluminum, match drilled some holes and got right to bucking some practice rivets.
Because this is a two handed job (sometimes a two person job) it was impossible for me to get pictures of the rivet gun and bucking bar in action, and I forgot to get a picture of the after bucking. I'll post some soon, but I'm happy with my first attempts and Ron says my results are to an acceptable level for construction. Again, it's not a hard skill, but an important one to get right.
Setting aside the rivet gun for a bit, I focused on match drilling and fitting (and of course deburing) the ring root assembly in anticipation of final riveting (both pulled and bucked rivets).
With everything clamped temporarily in place, I noticed that the wing root rib upper flange wasn't matching up properly:
As always, when something doesn't look right, refer to the plans.
The plans sometimes don't describe things as well as they should. Part of that is on me as a new builder. In this case, the plans advise that the flange is only bent to 30 degrees at the front, gently increasing to 90 degrees towards the rear. This makes sense as the wing root skin that it supports curves in the same way. So I'll have to bend it back. Hammering it isn't an option, but using another of Ron's custom made tools is:
With a bit of gentle work and some minor trimming, the root rib now fits as expected:
Next step was figuring out how to drill the rib, spar web, web doubler and nose rib in prep for final riveting.
Much like the wing attach fitting, this involved back drilling the top hole through the web into the rib, cleco, drill the bottom hole, cleco and finally the middle hole, being very careful not to ruin the previous holes:
Remove the root rib, debur and repeat the process for the root nose rib, back drilling from behind the spar. Remove, debur and fit everything together again:
Final riveting of the root ribs will be done once the rear spar fitting is complete and test fitted. I made progress in this regard too by match drilling the rear spar doubler to the rear spar:
As I stated before, the vast majority of rivets used in Zenair aircraft designs are pulled rivets as the sheet metal construction fastener of choice. The spar web doubler was ready for final pulled rivet setting.
The larger A5 rivets are called out in the plans for this assembly. Although they can be pulled by a hand rivet tool, it is much easier and consistent to use the pneumatic rivet gun. It uses the same mechanics as the hand riveter, but is much quicker and completes the "pull" in one shot, alleviating potential issues with partially completed rivets (where the rivet isn't fully pulled before the mandrel breaks off).
The pneumatic rivet gun made short work of setting the A5 rivets:
Backside of spar web doubler - looks like a crop of mushrooms. It's pleasing to see how much rigidity this gives the structure, something ignored by the previous builder. If you look close you can also see the tails of some of the yet to be bucked solid rivets where they poke through the spar cap:
Progress... Bucking and pulling rivets is fun (that opinion may change after doing thousands of them). I'll post some pictures and maybe even some video when I get a chance. Stay tuned :)
Good day in the shop yesterday. I'm making great progress on the 701 wing repair and starting to see the parts I've been producing come (loosely) together.
With all the parts now made for the fuel tank bay and wing root section repair, it's time to start fitting them in place in preparation for match drilling (and the requisite deburring).
First I decided to drill the rear wing spar doubler/attach bracket. It fits inside the rear wing spar where it attaches to the fuselage. Accuracy here is important so I drew out the location of the rivet pattern followed by using a punch and hammer to gently mark the rivet hole centres. This helps prevent the drill bit from walking across the surfact of the aluminum:
I used the drill press to ensure accuracy, then deburred the holes. This will be back drilled and riveted onto the rear spar once the rear spar is placed on the wing (yet another part to assemble!)
Next I worked on the front wing attach fitting.
Like many things on this salvaged 701, the original builder skimped on this critical piece, opting for a much thinner gauge of aluminum than what is called out in the plans. What made them decide to risk this? I haven't the slightest clue. What I do know is that the correct gauge is substantially more stout:
First thing was to drill the main attach hole. It's critical that this is as accurate as possible to ensure wing alignment and symmetry. First, I measured out the centre of the hole and confirmed that centre using a math set divider:
Using the centre punch mark as a guide, the drill press makes it easy to create a clean and straight mounting bolt hole:
Next was deciding on how to match this new piece to the randomly measured holes in the spar cap made by the original builder while maintaining the integrity of the new spar doubler. Here is the original clecoed infront of the new spar doubler:
I wasn't comfortable back drilling through the spar cap, the spar web, the spar web doubler and the new bracket - just leaves too many layers susceptible to inadvertent damage (read elongated or crooked holes). Besides, without any other holes drilled in the new fittling, how would I attach it accurately?
Next I laughed at myself pretty hard after spending way to much time over analyzing what to do next. I had to figure out a way to drill the new holes so they exactly match the old ones. Should be simple, I'll just put the old and new brackets back to back. Only trouble was that the old one was bent - if I used it this way, there was no way the new holes would be straight:
Now, the answer should have been obvious but bear with me. As the simple answer part of my brain took a break, the overthinker part took over. I'll just bend the old bracket back to flat, that should solve it. Out comes the clamp and two steel bars:
That didn't work. As overthinking brain pondered what to do next, simple answer brain came back from coffee and slapped overthinker in the face. The answer was indeed simple.... invert the pieces! (This is where I started to laugh at myself)
Now the holes in the old piece can be reliably used as a guide to the new holes. I drilled two on the drill press then decided to cleco them together, further ensuring accuracy:
Next I could have gone two ways. I decided to drill out all the holes in the attach bracket on the drill press, instead of doing it while attached on the wing.
With the holes in the new attach bracket now properly matched drilled, I clecoed the new bracket in place on the wing. The it was a simple matter to carefully drill through the spar doubler and the existing holes of the spar web and spar cap:
I'm very happy with my learning curve so far and I'm encouraged that Ron seems pleased with my work.
A large number of the rivets for this part of the wing root and spar assembly are of the solid type instead of the more common pulled rivets used in this aircraft design. As I have no experience "bucking" rivets, Ron suggested practicing on some scrap material first to get the feel for it. Better to spend a few cents on wasted rivets than many dollars on wasting good parts and aluminum!
Up next, learning how to buck rivets.
Huh... just noticed my countdown timer is now less than 1000 days. Better get going!
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.
Got to the shop this morning for a couple of hours. Trying to squeeze in a bit of time here and there before going to sleep before nightshifts.
First thing I finished off was the fuel tank bay inboard wing rib cap repair. Finished deburring the holes, both the old bad ones and my new ones to prevent any further cracking. The new cap repair is really stout and should give a great surface to attach the wing skin back on compared to the original rib flange which was mangled by the previous builder:
The missing wing root doubler has been drilled according to the plans and is clecoed in place. I've yet to decide which order to rivet this in place, but I'm going to wait until we have all the other items (nose rib, root nose rib, root rib, wing attach bracket, etc) gathered so I can test assemble and measure everything. This took a lot of careful back drilling through the spar web to get it right, and I'm happy with it so far:
In a lot of places of any given airframe, the designers of light aircraft take advantage of the inherent structural strength of aluminum to lighten the overall structure of the aircraft (lighter is better). A common method is the use of lightening holes. You can see them (the large circles) in the spar web of the above picture.
Lightening holes serve a number of purposes besides weight reduction (obvious). Wiring, hydraulics and or fuel lines can be passed through these easily. It also provides an opening for inspection of control linkages that might be inside otherwise closed cavities without having to remove the skins. The most common place they are used is in wing ribs, including the replacement root wing rib I'm currently making for the 701.
Lightening holes are also flanged which provides even more rigidity to the part (more on this in a future post).
Making lightening holes is where the fly cutter tool really shines. Cutting perfectly round holes by hand is near impossible.
So what is a fly cutter?
I particularly like the quote from the machinist that it's like "running a lawn mower without the deck". After drilling my into my hand a week ago (I'm fine by the way), I'll take this as a warning!
The fly cutter I used is a single arm one. It's like a high speed compass that cuts metal:
Adjusted to the right radius/diameter required using the set screws and placed into the drill chuck. When spinning it clearly will hurt you if it's not respected! Here it is with the root rib:
The only safe way to use the fly cutter is to clamp the part being cut down to the drill press table and keep you hands well clear. Trying to stop a piece of spinning aluminum should the cutter jam would be foolhardy. I used wooden blocks to prevent marring the aluminum with the C-clamps. It was also important to make sure the clamps were clear of the rotating fly cutter arm (that also would be very bad):
The secret with any machine tool cutting is to go slow and steady and use lots of lubrication. Once lined up correctly, I began to make the cut, adding a little WD40 as I went. Here is the cut well into the process (yes, the drill was stopped for the picture):
As soon as the cutter breaks through, pressure is lifted to prevent a chance that the cutter tearing the remaining aluminum.
Re-position and cut two more holes without issue. It takes a bit of time and I'll have a ton to do for my 750 parts, but it's worth it to have nice clean holes. Here is the root rib with all three holes cut and the cut out discs. They are sharp, I wonder if that's how they make pizza cutting wheels for the kitchen!:
All cleaned up and waiting for deburring and flanges. Looks great!
Next up, flanges! Stay tuned and thanks for reading :)
Got into the shop for a couple of hours on Friday afternoon. Busy week working around the house and cabin now that the nice weather is here.
First order of business was to finish making the new wing root rib for the 701 wing repair. When I last left the shop, I'd prepared the aluminum rib cutout by placing it into the wood forms. Now it's time to bend! Tools of the day... workbench board, plastic dead-blow hammer and fluting pliers.
Ron has made many wing ribs over the years and has developed some great ideas to make the work easier. One of his ideas is a wooden two-by-four with a channel cut down the middle. This workbench board is screwed to the tabletop and gives a great surface to bend against from many angles.
Next tools needed are a plastic headed deadblow hammer and fluting pliers. The hammer is plastic coated to avoid damaging/scratching the aluminum and the deadblow properties (non bounce) prevent leaving tooling marks.
Fluting pliers are used to slightly crimp the rib edges to take up the extra aluminum that bunches up when corners are bent. Pliers can be bought at a tool supply shop, but Ron prefers to make his own from re-purposed tools.
So lets bend!
Forming aluminum around a form takes equal parts of patience, gentle hammering and finesse. Starting at one end I used the deadblow hammer to start bending the rib flanges over, a little at a time all the way along and back again.
As the flange starts to conform to the curve of the form, fluting pliers are used to "take up" the extra aluminum in strategic locations. This is more of a do as you go type of thing, adding a little crimp here and there. The fluting pliers are just the thing:
One nice thing about the Zenair plans is that they take some of the guesswork out of deciding where to place the crimps. It still takes some experimenting to decide how much is required for each bend.
Once all the flanges are bent, the rib is removed from the forms.
Looks great.... until I laid it on the flat table! That's not right.... hmm...
The cause? Crimping depth wasn't enough. Flipping the rib so the web side is face down and the flanges face up allows one to adjust the crimps slightly, completely flattening out the rib. Perfect!
This was great to practice with and a big step to getting the 701 wing repair complete. I'll have a ton of ribs and other formed parts to bend for my 750.
The next thing I managed to do was finish rivet the fuel bay rib cap repair. Real happy with how good the repair looks:
In the closing moments of the afternoon, I started drilling apart the damaged slat ribs and brackets. I wanted to get these done as they are the next repair up after the main wing.
The title of today's blog entry refers to finesse and a stupid move. I've covered the finesse part with the wing root rib creation. But no day is complete without a stupid move....
While drilling out the rivets on the damaged slat ribs, my smart brain apparently took a coffee break without the rest of my brain knowing. Holding onto one the slat ribs in my left hand and drilling with my right I managed to remove the rivets fairly easily. However, one of the rivets required more pressure on the drill. Well... too much pressure and yup... through the rivet, through the rib and into the palm of my hand.
Ouch! I immediately thought "oh-oh" but considering how much it hurt, there wasn't much needed to stop the bleeding. Two days later, after much consideration about a weekend trip to wait in the understaffed ER, my hand is finally starting to feel better and I'm getting the flexibility back in my index finger. Hopefully no permanent damage. No pictures either, too hard to hold the tablet camera and take the photo with only one hand!
Who knew building could be so much fun!
Where did March go?
Work, family vacation to Florida and a week away from home for a work conference left little time for any shop work. It was difficult to be away so much, but it was a much needed break and I'm making up good shop time again this past week.
Took an hour and started comparing my CAD drawings to the templates already made for the 701. Ron and I had previously sat down and compared drawings and it was a great exercise in determining the commonalities between the two aircraft.
For example, I pulled out Ron's form block for the 701 slat rib and compared it to my CAD drawing for the 750 slat rib form (top right CAD drawing in the picture above). It's a perfect match, which means that is one form I won't have to make for manufacturing my part:
Every form has a matching template for the aluminum that needs to be cut for the specific part (that's the slat rib template CAD drawing directly below the form in the picture above). So somewhere the template already exists for this part, another thing I won't have to create for myself.
On the same track, I pulled a good number of templates and compared them to my plans. Every template has a matching form (where a form is required). What an amazing amount of time and labour this is going to save me:
Next up, I worked towards finishing the fuel tank bay repairs on the 701 wing. As you may recall, I've been working on repairing the spar, rib and channel tops using a "L" doubler. Working inside the nose skin is a challenge!
I made a spar cap doubler repair and test fitted it along side the new spar root doubler:
The only way to get this tight to the existing spar cap is to remove the rivets holding the spar cap to the web. As I indicated, the room to work inside here is really tight and I don't want to remove the nose skin any further than it is and risk creasing the thin aluminum.
Right angle air drill to the rescue!
With the required spar cap rivets removed, I back drilled from the rear of the spar into the new spar cap doubler and clecoed it in place. Another parallel row of rivet holes will be drilled between where the clecos are and the lightening holes of the spar web. This will be very solid when rivetted later:
Finished off fitting and match drilling the rib repair caps as well. Other than some final drilling and riveting, the fuel bay repair is complete and waiting for the new fuel tank.
The next thing to do is replace the root rib with a brand new one. Like a lot of the other repairs needed, it has less to do with being bent from the crash and more to do with poor workmanship by the original builder. Holes that missed centre line, cracks from forgotten de-burring and the like.
Ron and I pulled out the root rib forms. Root ribs are the same length as the wing ribs, but much shallower in height as the wing chord narrows dramatically as it approaches the fuselage.
Forms are what are used to shape flat aluminum into ribs or other structural components. The flanges created by folding the aluminum edges over create rigidity in the part being formed. It starts with matching forms:
Between these, the aluminum that is cut from the matching template is placed:
Before fastening the two forms togther, it's important to check the forms are oriented the correct way. The forms have a beveled edge. This is too allow the aluminum to be bent past the 90 degree mark and spring back to 90 degrees once removed from the form. My first look at the orientation showed I had the forms backwards:
The next important thing is to remember which way the rib flange is to be bent. Often the same parts are bent either left or right, depending on what side of the airplane they are on. It's about symmetry. In this case I have the advantage of looking at the part being replaced and comparing. Then I make a note on the part which way to bend it in case I get sidetracked on something else and button it together with through bolts and wing nuts:
Also needing replaced is the wing root nose rib. The original builder cheaped out and used non standard aluminum and again wasn't very careful with the drill. I found the template for this piece and the form.
Comparing my 750 plans to the 701 plans indicates that this part is identical, so while making the new one for the 701 wing, it made sense to make my two at the same time. My first manufactured parts.... YAY!
So cool to make some parts for MY airplane. Many, many more to come :) Time to go buy some plywood for the remaining forms unique to the 750.
Oh look, my build time log has 1 hour for the wings!
Remember how I said I was manually entering all the drawings from my plans into CAD? I've completed most everything and very happy about what I've learned.
I spent several hours trying to figure out how I'm going to print these items to scale for templates which will be used to trace out my aluminum parts. It's a careful balance trying to print the items to scale and within the borders of what a printer will print on a 8.5 x 11 sheet of card stock. I haven't decided yet if the card stock will be sturdy enough, or that I might transfer the patterns from card stock to a light gauge aluminum like an eaves trough flashing. This will be particularly important on multiple pieces where repeatable results are key.
LibreCad is the free program I used to digitize my plans, but like anything free it has some drawbacks such as a limited ability to print to scale right from the program. It does however export to PDF. There doesn't however seem to be any rhyme or reason to what scale the drawing end up in when exported.
To solve this problem, I found an online program that takes DXF files (the LibraCad file type) and converts them to PDF. It automatically scales them to the best size paper, not 1:1 scale (which I need).
I figured out however, that if I print the PDFs as is and hand measure them, I can calculate the scale percentage I need to up or down scale the PDF. The it's just a matter of entering that percentage in the final print and voila! 32 Perfectly scaled 1:1 drawings printed direct to card stock!
I'll be limited to those templates that fit on letter or legal card stock for now. Most of the larger parts are strait cuts anyhow. I'm more concerned with the complex curves of nose and wing ribs and some of the smaller parts. Maybe I'll do some research and see what size I can get card stock I can get.
The other item I've been trying to determine is the specs on my Corvair crankshaft. I've mentioned before it will need to be magnaflux tested for cracks, heat treated (nitride) for strength and the rod journals ground for bigger should radii. I happy to see the crank I have is within a couple of thousandths of stock meaning there is lots to room to have it ground properly.
Progress. Back into the shop I go!
To make up time I missed last week, I did back to back days in the shop this week.
The next step in the rebuild of this 701 wing is making new aluminum caps to reinforce the damage done by the original builder to the tops of the two fuel tank ribs. As you can see here, the holes are kinda randomly spaced and most aren't even clean:
We'll be doing a cap along the front edge as well for the same reason. This will strengthen the upper spar cap angle and make a much cleaner (and stronger) assembly. Before doing this, I did a test fit of the infamously missing replacement wing root spar doubler before measuring it for the bending of the flanges, and I'm really happy with the result of the fit:
Or at least I thought I was until I remembered the small bend in the upper spar cap that needs to be repaired. Looking along the top of the spar cap angle you can see the "wow" (bend) I'm talking about. It's not enough to change the fit of the spar root doubler, but it will affect how squareness of the wing to fuselage join-up::
So, using a bit of my recently learned knowledge about how aluminum "springs back" some when bent, I had to come up with an easy way to take this bend out. First, I taped some mahogany shims on opposite side of the spar cap and to either side of and equidistant to the bend:
Once these were in place, I carefully clamped a 2x2 piece of wood to act as a surface to leverage against:
Unfortunately, you'll have to use your imagination to visualize the next step as I don't have a picture.
Another C-clamp placed directly of the centre of the bend is gently tightened drawing the bend towards the gap and slightly beyond. Once released, "spring-back" takes over and the spar cap returns to the straight position. It took a couple of tries to get it perfect, but it worked. This wouldn't work if the spar cap was broken or kinked - it would have to be replaced at that point, a very time consuming and expensive process. Here is a picture of the now straightened spar cap. Very pleased how this worked out:
Next up, bending the spar root doubler and installing the new caps around the edges of the fuel tank bay. Progress!
I had hoped to get to the shop last week, but an unseasonably warm weather forecast was causing me some concern at home. With all the snow we've had through January and early February, we had about 3 feet of accumulation on the roof. Rather than go to the shop, we thought it better to remove the bulk of snow before the positive temperatures arrive and make the snow weight too much for the roof. It took several hours, but I got it done. Didn't feel like going to the shop (ok, actually I couldn't lift my arms for a couple of days).
Back to the shop today. Got right to work creating two new wing root spar doublers. These will be installed where they should have been in the first place. Using a template, I traced out the rough shape on the 0.032 aluminum:
I cut out the shape in rough and used a file and the grinder to get the final shape exactly right:
I repeated the same steps for the second one. The process is fairly simple as you can see from the wing root attachment brackets below. From top to bottom, a finished piece from inventory, a rough cut piece to be ground and the template from the plans:
First you trace the template onto the stock, and use (in this case) a bandsaw to cut it out close to the line. Comparing the two after the bandsaw, use a sharpie marker to trace it again, leaving a line showing the remaining material to remove by sanding or grinding:
Next, use the grinder or file to remove the balance of the material as defined by the trace line:
Last step, hand sanding all the edges to a satin smooth finish. Here is the stack of eight I finished (two for this repair and 6 for inventory) and below that the stack of wing root doublers for inventory:
More rain tomorrow, so back to the shop to start working these items into the repair.... and find more things wrong with this wing..... probably :)
Time until takeoff
Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.