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Chuck and Ryan's Carbon Cub Build Blog

Nice looking parts and wing. You guys are strong...no way I can squeeze rivets and take a picture at the same time.
 
Even your squeeze riveter is just awesome!

It's really nice seing a nice CubCrafter product taking shape. Thanks for the pics.

Keep up the good work
 
Really nice looking wings. I can tell by picture #2 you don't live in MN. Them are nice looking squeezers, which ones are them?
 
Really nice looking wings. I can tell by picture #2 you don't live in MN. Them are nice looking squeezers, which ones are them?

Larry:

The rivet squeezers are from Avery. We ordered the Carbon Cub tool kit since, I am embarrassed to say, I had virtually none of the included tools needed to build the plane.

Indeed, we are not in MN. Southern Illinois, south of St Louis.

Chuck
 
Fuel tank straps

After the center ribs are riveted in place the next step, per the manual, is placement of the fuel tank straps: four lower and four upper for extended tanks, after which the drag wires are installed. After the first wing we decided to defer installing the fuel tank straps until just before the forward skins are installed. The straps tend to get in the way when installing the drag wires and other details. We will install them just before the forward cover is installed.

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When the straps are installed, note that the bolts on the forward spar are installed backwards. In other words, instead of the bolt head facing forward it faces the fuel tank. This is shown in the manual but defies the usual convention, so it is worth noting here.

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Foregoing pictures taken looking at the forward spar, showing the heads of the bolts facing backwards.
 

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Chuck, if you're going with the 44 gallon tanks, two tanks per side, check the continuity between the tanks for grounding purposes. Perhaps they've changed things a bit now and added a grounding lug on the second tank but if not, I placed a copper wire under the tank straps from one tank to the other making direct contact with the tanks so both are grounded.
 
Chuck

Looks great and thanks for posting all the photos and info. Greatly appreciated.

Bill
 
Should be a grounding lug on each tank...mine did. I was missing two of the four wires however and had Mitch send them out. Making great progress.
Jake
 
Spinner and Jake:

Yes, the current kit has separate ground connections for each of the four tanks, two on each side.

Chuck
 
Drag Wires

The drag wires affect the alignment of the wing in two primary dimensions: (1) leading and trailing spars perpendicular to the root of the wing, and (2) leading and trailing spars straight. The drag wires are tightened to a specified tension (14 pounds with half inch deflection) to accomplish those goals. The process requires a lot of adjustment and readjustment.

A string tied from one end to the other end of the leading spar provides a reference for maintaining a straight spar. We were able to keep the leading edge within 1/16” of the reference string for its entire length. When checking this alignment place a straight edge on the leading surface of the spar and note its position from the string. Place the straight edge at or near the compression tube fittings. I was amazed how precise an alignment could be achieved by adjusting the tension on the drag wires. The straight edge just barely “kissed” the string at each compression tube location.

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A modified carpenters square is used to confirm that the spars are perpendicular to the compression tubes. But as the drag wires are tightened the compression tubes flex ever so slightly. We found that there were slight discrepancies from one compression tube to another, some in opposite directions, but never more than a 1/16” over the 24 length of the square. Since the variation went both ways on different tubes and all were less than 1/16”, we are quite comfortable that perpendicularity has been preserved.

The tension on the drag wires needs to be adjusted so that a digital fish scale will show 13 to 15 pounds with a half inch of distortion at the mid-point. The manual suggests holding a ruler as one pulls on the fish scale; a bit cumbersome. We instead used a carpenter’s square to make a mark on the lower wire a half inch from where the wires crossed. A small ‘flag’ was placed at this point, made from masking tape. When the fish scale was used to tension the wire, it was simply pulled until it touched the ‘flag’ and the pounds noted. Only the upper wire was measured per bay (The tension on both lines should be equal in a given bay).

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When finished one can ‘pluck’ the drag wires and listen for the note. They likely won’t be the same, but should be similar in tone. With repeated checks and rechecks, the drag wires were all within six ounces of 14 pounds when finished.
 

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I like your flag idea I will have to remember that one. Keep it coming looking very nice.
 
Rear Spar Reinforcement

This is about a really small detail that in the final analysis makes no difference. But if one is fanatical about holes lining up, or shall I say one hole lining up, I will pass the information along.

A long flat reinforcing strip is riveted to the aft spar to reinforce it, hence the name “rear spar reinforcement.” It is a husky strip with lots of holes. Near the center of this strip a pulley bracket is mounted, after the reinforcing strip is securely riveted in place. The manual gives very precise dimensions on locating the reinforcing strip, but then adds to the dimension “+ 1/16, -3/16”. Now I am not a math major, but that looks like a quarter inch of variation, so how do you decide where to place it?

I will give you the answer.

First, put the pulley together (temporarily) and set it in its appropriate location on the aft spar, with a guide string that will run perfectly parallel to the aileron center support. (You are essentially skipping ahead a few steps in the manual, but don’t worry, we will get back to the reinforcement strip).

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(This picture shows the reinforcement strip already installed. Just pretend it isn't there for now).

Second, note the directions clearly state that one of the holes should NOT be drilled through the reinforcement strip and riveted to the spar. Put a nice black (or the color of your choice) “X” on that hole.

Third, set the reinforcement strip in place under the pulley bracket, lining up the hole in the pulley bracket that is “match drilled” with the hole in the reinforcement strip that you just marked with the “X”. Make sure you keep the guide string exactly parallel to the aileron support.

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(Look closely and you will see the "x" on the hole. That is what lines up with the pulley bracket hole)

You now have the correct location for the reinforcement strip. Clamp it in place before it can get away. If you now measure per the directions I suspect you will find the spar reinforcement is at the minus 3/16 range of the specified dimension. Now you can go back to all the drilling and riveting per the instructions. Just don’t drill the bulb on the spar. (Inside joke for CC builders).

If, like me, you just used the reference dimension and did not realize the significance of what was to come several steps later with aligning the pulley bracket, don’t despair. It just means you won’t be match drilling that hole but will have to drill a new hole. There is enough space to do it and no one will ever know. At least no one would have known if I had not done this post.
 

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Landing Light

Assembling the landing light is a straight forward project. A total of eight nut plates have to be riveted in place: two pairs of three each and two individually holding the light in place. Of course when three nut plates are in a row they need to be precisely aligned so when the screws holding the clear plastic lens in place are installed both the rivets and screws will be in a nice straight line.

The manual shows a template being used to correctly align the holes to be drilled. I spent some time looking for that guide plate in all those boxes to no avail. It finally occurred to me that the dimensions in the manual were so the builder could make his own pattern. I am a bit fanatical about patterns. It is nice to lay something out on a pattern, full size, and make sure everything is properly placed before pieces are cut or holes drilled.

A really useful product is poster grid board. It is essentially poster board but has shadow grid lines at half inch intervals. Get it at Staples. When making patterns it really helps keeping all the reference points lined up I keep several sheets around just in case. Assembling the lights was a good chance to make just such a pattern to assure perfect matching alignment of the nut plate holes on both top and bottom.
 

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Skins: Twelve Tips

Reading various posts, the manual, and watching videos, it seems there are as many different techniques and tricks as there are Cubs for installing the forward wing skins. Here are my twelve tips.

1. Mark the pattern provided for locating the two upper attachment holes with two additional holes 1.75” from the top. These holes are used instead of the top holes on the inboard section between ribs 1 and 3 where the fuel tank sets. (Extended fuel, can’t comment on standard fuel tanks).


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2. Mark a line along the center of each rib about six inches from the top down with a fine point Sharpie.

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3. Set the skins in place, using clamps and/or duct tape to hold them temporarily to the spar, starting from outboard to inboard. Make sure the aft edge of the skins are tight against the inside edge of the spar.

4. Using the provided pattern, mark the holes. Note that the primary ribs get a top rivet and a second rivet per the pattern, but the intermediate ribs omit the top rivet.

5. Mark the rivet locations at the top of ribs 1, 3 and 5 with a distinctive mark so they won’t be inadvertently riveted.6. Now remove the skins and take them to your bench. Using a #40 bit, drill and de-burr the holes.
7 Put the skins back in place. Line up the top hole with the vertical line previously placed on the ribs. Match drill with a #30 and cleco in place. Now line up the next lower hole with that line, drill and cleco. Then take the skins off again and de-burr the holes you just drilled in the ribs.

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8. Replace the skins and cleco in place. Now starting at the outboard end attach the clamps and tighten down the skin, starting at the center of each skin and working your way outward. I placed the clamps midway between the ribs. It takes a bit of creativity to get the clamps secure in some locations due to the drag wires and compression tubes. We used spacer blocks only on the web of the spar, not the spar caps. That permits the bar to pivot a bit at the center point as it is tightened which permits the clamp to find there ‘natural’ location around the skin. Before securely tightening the clamps, rivet the first and second row of rivets (except the two that join the next adjoining skin). Then tighten the clamps until they are snug, with no gaps, but only finger tight.

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9. Make a simple pattern to mark the location of the lower rivets. It sure beats trying to use a caliper lying on your back to mark each bottom rivet. Check to make sure the ribs are within the vertical opening of the skin at the bottom rear of the skin. We had to trim a couple that were too close to the ribs. Drill starting in the middle, cleco, and work your way out, left and right. Then rivet. Before putting that first bottom rivet in place take a flashlight and look inside to make sure the leading ribs are still properly aligned and not distorted.


10. Get the Avery jig for drilling the top leading edge of the skins to the spar. It makes drilling those holes go much faster and there is no question about properly alignment to avoid hitting a spar bulb.


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11. We wiped down the skins with acetone to remove the marks. Running a finger down the leading edge we could feel the ribs so we are confident it is nice and tight. The seams are all flush. There is no ‘tin canning’ affect


12.. Admire your work. Take the rest of the day off. Have a beer.
 

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I wish they had that jig when I did my wings. That would have sped things up a bit. I measured, marked, then used a center punch before drilling. Depending on your lighting, I used a blue sharpie instead of black because it showed up better. Hope it warms up soon so I can start covering mine.

Looking good guys,

Jake


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Wish they had that jig when I built mine. Would have save a bunch of time measuring, remeasuring marking, rechecking the mark, using a center punch, then drilling. Looks good guys.

Jake


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Sorry for the repost, taptalk said it didn't go thru the first time.


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Jake:

The blue marker is a good idea. Had not had any problems with the black but will keep that in mind.

The drilling jig is handy. A couple more tips for those using it.


1. When drilling, pull the bit out a time or two and get rid of the metal chips. With the drill stop in place the chips can’t get out and the bit won’t bite unless one clears it a time or two on each hole.

2. Set the drill stop so it just barely clears. When it pushes through the spar web the spring depresses slightly and you can breathe a sigh of relief: no damage to the spar bulb. On the other hand if it does not reach a point where the spring gives and it seems to not be drilling anymore, do the following:
a. Sit down.
b. Get out your check book
c. Pick up the phone and call Mitch. Make sure you are still sitting per (a) above.

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When drilling with the jig, the stop will obviously have to be set longer, but you get the idea

 

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Wing Wiring

The wire harnesses are set in place along the lower forward spar in the groove by the spar bulb, after which a bead of silicone is used to secure them at intervals.We found that a small wire tie would permit the harness to ‘snap’ in place and hold it securely.

This trick was used at tension points: at the start and end points, where the landing light wires branch off, and where the stall warning wires branch off. We still used the silicone, but the wire ties give a bit of mechanical support, and can be adjusted in place.
 

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Chuck, I just met you last weekend, you were a joy to converse with. As your tailwheel instructor I think I get dibs on about the 5th flight! Seriously, I am heading out somewhere Sunday - can I stop by for a viewing?
 
Chuck, I just met you last weekend, you were a joy to converse with. As your tailwheel instructor I think I get dibs on about the 5th flight! Seriously, I am heading out somewhere Sunday - can I stop by for a viewing?

Yes! Sent an e mail.
 
CherryMAX Rivets

Stainless steel pull rivets, squeeze rivets and CherryMAX rivets are used on the wings. The first two did not create any issues but the third did. The CherryMAX rivets have to be pulled perpendicular to the surface or they will not seat properly. What makes this problematic is one can pull a CherryMAX, the stem pops off in the usual manner, and looks like all is well. But it may not be seated properly.

The first clue there is a problem is to check carefully to see if the stem extends to the surface of the hole. The better clue is to look at the back side. If there is a stem sticking out you have a problem and it did not seat properly. So how to you see the back side of a rivet in a tight place such as the web of the spar? Those little round mirrors on a rod work well. Like a dentist would use.

The CherryMAX rivets placed on the upper holes on the inboard and outboard aileron supports are a challenge because the angle of the supports makes it nearly impossible to get a squeeze riveter perpendicular to the surface. Here are a couple of tricks.


First, start grinding. A ten dollar riveter from Rural King was the starting point. A power grinder was used to cut away material until the riveter would fit in close to perpendicular. So much material was removed that the fact it could still pull a rivet was a bit surprising.


Second adding a spacer between the rivet head and the riveter may help. An aluminum wire stop works perfectly. It may need to be filed down a bit so that there is enough of the rivet stem to catch the teeth in the riveter.

If the rivet does not seat properly there likely won’t be a stem visible in the center. The good news is it is easy to drill out without that pesky stem at the surface of the rivet head. Drill just deep enough to pop off the head of the rivet and then use a punch the same size as the hole to push the remaining rivet out. Done right the next rivet should fit tight.

 

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Rib caps #1 and #3

When you install the Rib Caps on ribs #1 and #3 you know you are getting close to the end of the wing build.

1. Locating the cap on rib #1 is no problem since the aft end is pushed all the way aft. But the cap on rib #3 [extended fuel] does not have an obvious alignment point. So where should it be located?


Both rib caps are pre drilled for the nut plates. I wanted the nut plates on the two rib caps to line up, left to right. Run a straight edge from corresponding nut plate holes on the two caps and measure from a reference point, left to right. Bingo. You got it lined up.

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2. Check the ribs on the bottom side of the location where the nut plates will go. Several will be fluted. Mark the center point of those nut plates, remove the rib cap, then use the rivet squeezer to flatten the locations where the nut plates will go.

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Fuel Tanks

The extended fuel tank option consists of two tanks per wing, connected with two large and one small diameter hose. To install them one simply bolts together eight straps with a two inch bolt and locking nut. What could be easier?

Turns out this was one of the more challenging parts of the wing assembly. When the straps are pulled tightly together they are just barely close enough to get the nut in place. Problem is that whatever is used to pull them together gets in the way of the bolt. Therein lies the dilemma.

We used a longer hardware store nut and bolt to temporarily tighten the straps down and then ran a wire around the two connections, twisted it tightly together, and then removed the hardware store nut and bolt. With the wire holding the straps in place the bolt was then inserted. Once the nut was started the wire was cut loose.

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This worked just fine for six of the eight but the two bolts holding the inboard tank on the left wing simply would not go. The bolts were about one tenth of an inch too short. Not wanting to deviate from the plans we fiddled with those last two connections for about five hours before giving up. Called Wayne the next day and described the dilemma. His solution: use a longer bolt. We ordered a bolt one tenth inch longer and it quickly came together.

Moral of the story: Quit fiddling and call.

Once the nuts are in place DO NOT tighten them down. At least not yet. The fuel tanks must be properly located first. So how do you determine if the fuel tanks are correctly positioned?
Find the fuel tank covers and set them in place. The outboard edge of the fuel tank cover should be even with the outboard cap strap. The fuel filler must be centered within the opening. Only after it is centered should the nuts be tightened.

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Great write ups on your build. I'm enjoying following your progress.

I thought getting these bolts in place was the hardest part of the entire kit.

Are your tank lids not oversize? Mine were by a couple of inches each direction and I trimmed the edges in a shear afterwards and punched the holes to match the nut plates after centering the filler hole opening.
 
Are your tank lids not oversize? Mine were by a couple of inches each direction and I trimmed the edges in a shear afterwards and punched the holes to match the nut plates after centering the filler hole opening.

Your question answered a question I had. Why didn't the manual mention the importance of making sure the filler lined up with the hole in the cover? I was wondering why the manual simply stated " . . The tank must be centered . . . Adjust the tank fore and aft, left and right as necessary to achieve the guidelines . . ." with no mention of using the tank cover as a reference. Now I know why.

Yes indeed, the tank cover is cut to size and it has a nicely beveled edge all the way around. I suspect that change was made and the manual not yet updated.

I bet Wayne will update the manual before the ink dries on the post.

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Wing done!

Moving the wings from the saw horses to a stand for storage is a bit like a right of passage. Sort of like graduating from eighth grade or learning to drive a stick shift. A milestone marking the end of a phase and now time to move on to something else. So after 150 hours spread over two months we can announce that the WINGS ARE DONE!

With the wings completed we really wanted to get them off the saw horses and onto a stand so we could make room in the hanger/garage for the fuselage assembly. We spent a day designing and building the stands with about $80 in materials, including casters. The center support is 48” high and the base is 36” long. The carpet support is 14” wide. Simple but works well.


Here is the cool part. The wings are built with a 1” block under the outboard trailing edge to set the washout. As we were building the wings they seemed to have a lot of ‘flex’ making me wonder what the point of that 1” block would be. Only after the wing tips were securely in place and the fuel tanks tightened down, did the wings seem to develop a bit of rigidity.When we placed the wings on the stands the inboard ends fit nice and snug in the carpet ‘sling.’ But the outboard ends had about a 1” gap between the trailing edge and the carpet support. So there is something to be said for building that bit of washout in as the wings are assembled! A short section of rolled up carpet was added on each side to fill the gap.
 

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Super nice wing dolly...makes mine look pretty sad. It is a great feeling getting the wings done. How much faster did the second one go? Without the landing light and the steep learning curve on the left wing, I took half the time building the second wing. Finished covering the tail feathers today after a seven month break.

Jake


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Jake

Second wing definitely faster but probably not a lot. I had both going at the same time once I got to the leading edge skins, fuel tanks, tips, etc. so the time sort of melded together.

i did learn that finishing up both wings together has the benefit of making sure both are symmetrical, like fine tuning the wing tips.

I am looking forward to the fuselage. A bit less repetition than the wings. Got the pedals assembled last night.

So why the seven month break? After OSH in January figured you would have it covered by now!

Tail feathers go okay?

Chuck
 
Chuck,

7 month delay due to weather.....Unheated hanger and record cold and snow on the north shore of lake Superior. my portable heater adds about 20F to the hanger. last winter, no problem with the sheet metal work on the wings. Plenty of days in the 20s and 30s and I could get the hanger up to 45-55. This winter, -15 to -30 EVERY time I made plans to head up to the hanger. (two hour drive) Poly Fiber says it should be 75F for their two part body filler for the Fuselage and the poly tack should be used around 55 or warmer. (it was 46 last week and the leaves are now just starting to come out) I got the first stab rib laced today. Girlfriends dad is in hospice in Florida, so I am heading back down there for a few days or more I fear.

Be extra careful with the gluing of stringers and such with the fuselage, I had a drip or two I didn't notice until days later and it is a pain to get that stuff off. When you glue up the extended cargo, leave some gaps in the glue on the cross bars for putting zip ties on the fuel lines.

It did get above 70 this week.

Jake
 
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