Chuck and Ryan's Build Tips

[Daveembry]

WELCOME BACK. Good to see you are building another one. Thanks for all the great posts before.,....it helped a bunch of us!

On the Level.


A Carbon Cub EX2 is under way so I will start posting the occasional tip resurrecting my dormant build blog from the EX1. So much has been posted in the five years since my EX1 started flying that not much remains to be said, so I won’t say much. Just the finer details.

The first pages of the wing manual make clear the importance of locating the saw horses the correct distance apart and assuring they are level, both longitudinally and transversely. The real reason for this precision is to make sure the washout is correct. Here is a little tip for anal builders, like me.

Just before the drag wires are trammeled with the fish scale, use the digital level to confirm that the most inboard and most outboard drag tubes match before setting the aft rear corner on the one-inch block. They don’t have to be at zero degrees, just the same. A thin shim between the inboard spars and the saw horse may be needed. Then lift the outboard end and place it back on the one-inch block. You now have precisely one inch of wash out over the distance of 151 inches.

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I needed to add thin cardboard shims to get the ends within a tenth of a degree on the left wing. The right wing was within that tolerance without any shims.

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When the set up was done the difference in angle between the inboard and outboard drag tubes was 1.9 degrees. Makes me wonder if the design calls for 2 degrees of washout from wing root to wing tip.

[ceslaw]

Thanks Dave

After reading your amazing and detailed build information, I'm not sure there is much left to be said. I have made notes on some of your tips which I will be following. Thank you for all that work.

Chuck

[ceslaw]

Trammeling Fun

Trammeling the drag wires can be a frustrating experience. By the time we trammeled the fourth wing (two from the build six years ago) it became easier. Here is what we did.

Once the first bay is done the nuts for the remaining drag wires were left loose. Really loose. Using the yellow guideline noted in a previous post, we literally “jiggled” the wing to line it up. It was amazing how close it could be aligned this way. When reasonably close the nuts were then screwed down barely finger tight. Using this as a starting point and tightening a fourth to a half turn at a time, no more, it came together nicely.

I don’t fish. Seems a bit boring. So I have Cubcrafters to thank for making me the proud owner of a fish scale. Five years ago, I posted the little trick for placing a piece of masking tape at the half inch point to provide a visual reference when using that nifty fish scale. Now I also mark the end result on the piece of tape so I will remember having done that task. A good tip for the seasoned citizen builder.

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And another tip. When the final turns of the wrench are applied to the drag wires the wire will twist and must he held in place. I use a vice grip. But how do you know if it is twisting? A black line made with a Sharpie makes it easy.

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If that fish scale could talk it would report that an amazing number of fish between 13 and 14 pounds have been caught.

[ceslaw]

Guide Line

A string running parallel to the aft spar provided the reference for keeping the wing straight while trammeling the drag wires after the first bay is properly squared. The manual shows the line clamped with a scrap piece of wood. Sometime a few minutes spent making a simple tool makes life a bit better.

Two six-inch lengths of 1/16” aluminum, 1 ¼” wide, were cut. An 1/8” hole was drilled near the end after which a bright yellow string was inserted (after cutting to length with a soldering iron so it would not fray) and then a keeper knot tied. The two aluminum strips were clamped in place with cushioned clamps so the string was about an inch above the spar. This provided an easy reference for assuring all was square.

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With several hours’ time adjusting the drag wires, the left-wing string was no more than 3/32” out of square. No discernable out of square was visible on the right wing. Life is good.

[ceslaw]

Wing Alignment

The build manual requires that the ailerons be temporarily installed after the drag wires are trammeled but before the lock nuts and Loctite are applied to confirm they will fit. This required installing the machined ribs and center aileron support. Seems like a lot of work. But we did it and the ailerons lined up and moved freely.

Then we did the string test, which is a bit more satisfying. The machined ribs and center support must still be placed, but string is used instead of the ailerons to confirm alignment.

First, spacers are needed to center the string in the inner and outer ribs. We used cable stops, which have a 1/16 inside diameter and quarter inch outside diameter. Perfect size.

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Second, bright yellow nylon string is threaded through the spacers and the center support and clamped in place. Clamps are easier than knots. I always cut this string with a soldering iron so it 'cauterizes’ the end to prevent it from unraveling.

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Third, the location of the string through the center support is noted. As long as it does not touch the sides of the hole you have less than +/- an eighth inch tolerance; which I suspect is pretty good. If it is centered, it is even better. I got lucky; it was nearly perfectly centered.

Note that the string must be pulled pretty tight. If not, gravity may cause it to set deceptively lower.

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As the build progresses, I plan to repeat this ‘string’ test to confirm that the three machined ribs remain aligned.

[ceslaw]

Cherry Max Rivets

There are two cherry rivets on each wing that cause considerable consternation. Anyone that has built an EX knows exactly what I am talking about: the top rivets on the machined ribs. If the rivets are not pulled perfectly straight the stud snaps off prematurely and one gets to drill it out and do it all over again.

I have this lingering fear that there may be some Carbon Cub’s flying with these particular rivets not properly set. They seem to go in just fine, the stem breaks off, and the assumption is it is properly set. But if the stem is not visible and flush with the head of the rivet and the back stem is not pulled in, it is not correct and has to be done over. The problem is one has to look carefully to see if there is a problem and seeing the back side within the groove on the spar is difficult.

I did the surgical destruction of a standard pull riveter per the manual. It just doesn’t seem like a very elegant solution and one still needs something to keep the rivet stem straight.

To hold the stem straight while pulling at an angle I milled a tiny aluminum block – sort of a wedge shape. Took me three hours’ time (still learning to use the mill). The theory is that it would hold the stem straight even though the rivet puller is at an angle.

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Then I found a tool made specifically for this issue sold by Cleveland Aircraft Tools. It is called a Close Quarter Rivet Pulling Wedge. Pretty clever name! I ordered one, just in case my ‘wedge’ did not work. It costs about $20.

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Then I got really lucky. Before trying either of these ‘wedges’ I was able to barrow a proper Cherry Max Rivet side puller and it worked perfectly. With this $800 tool the job was done in about ten minutes. Using it felt like cheating, but I am already past the guilt.

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[PBY Catalina]

I'm using also the Cleveland Wedge, designed for VAN's, than I find very useful for the SS rivets. But I was still not satisfied with the results with the CherryMax rivets. It took me half a day, but I finally had a satisfactory result on the CherryMax, pulled on the machined rear ribs, with the "modified/almost destroyed" Marson HP-2 puller, as described in the manuals and by Dave.

[ceslaw]

Good point. The Cleveland Wedge does not replace the butchered rivet puller. One still has to grind that rivet puller to near non functional status.

[ceslaw]

Skin Clamps

The skin clamps being passed around have presumably been in circulation for a while and some may be showing their age. The ones I received were in pretty good shape but a bit of time fixing them up made for a more pleasant clamping experience.

First, the aft portion was replaced with freshly cut 1 ½ x ¾” stock and 5/16” holes added on a drill press to assure they remained straight and centered. A four-inch-long piece of the same stock which makes contact with the web of the spar was glued and screwed in place, avoiding the need to use separate spacer blocks.

Second, the tiny washers were replaced with 1 ½” fender washers to more evenly distribute the clamping forces. The tiny washers that had been used were digging into the wood and the threaded rods had become a bit distorted.

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Third, the fender washers on the aft portion were epoxied in place so one does not have to fiddle with placing a washer while setting the clamp. Double sided tape is another option.

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Finally the threaded rods were aligned so the spacing was identical on all four clamps, making the aft portions interchangeable.

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Hopefully these little upgrades will make life better for the next one to use these clamps. And don’t forget to sign and date the clamps after you finish! It is interesting to see where they have been.

[ceslaw]

Skins: Bottom rivet pattern.

Lying on your back looking up trying to locate the bottom rivet that holds the skin can be a bit awkward. We made a pattern to make the job easier before starting installation of the skins.

Each forward rib is held in place with two or three rivets. Cubcrafters provides a pattern for locating the two top rivets, which few will see since they are on top of the wing. The bottom rivets, however, will be visible to someone that is looking for rivets so lining them up is important. This pattern assured that they were all aligned without having to measure each rivet location.

A 3 ½ by 1 ¼ section was cut from a scrap of 24 gauge aluminum. (If I did it again, it would be wider, 1 ½” instead of 1 ¼”). A quarter inch from one end a ninety degree bend was made, then the center of the bend was slotted to match the width of the ribs and the tab bent straight.

The guide holes were drilled per the locations specified by Cubcrafters’ manual. So, you ask, why were two guide holes drilled? Cubcrafters added a reinforcing plate to hold the door latch in place which requires a second rivet. Good idea Cubcrafters!

The two black lines help visually align the pattern with the rib.The #40 holes were used to mark rivet locations with a sharpie. Holes were then drilled in the skin and rib, first with a #40, and next with a #30 bit, and then riveted.

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