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 :)
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.