No pictures, but I was able to get the z-brackets bolted to the spar on the left wing in prep for the “Checkoway” method on that tank. I may not get to it for a bit, but they are ready.
Nothing Big, but Progress
Progress has slowed a little. Life has a way of getting busy at times. I was able to spend a little time out in the shop tonight. I cut the stiffeners for the right tank, cut out the innards of the reinforcement rings and deburred them, and cleaned up the nose reinforcement plates for the tanks. That was about all I had time for so I called it good enough for the day.
Ready for Drilling
With the tank now on the wing, I made sure that everything lined up correctly. To pull the skins tight together, I used a couple tie-down straps and carefully cinched the tank down. This insures that the tank will not move once aligned and makes sure all the parts are in close formation before match drilling.
Tank/Leading Edge Joint
Here you see the joint of the tank and the leading edge. Nice and tight, ready to match drill the splice strip.
Inboard Bracket Drilled
With the tank completely in place and strapped down it was time to match drill the inboard bracket. I used my 12″ #30 bit with a drill stop on it and knocked out the 5 holes for the bracket and clecoed the tank down. I did not attempt the four holes outboard of the bracket ends for fear of nicking the spar bars.
Drilled Joint Plate
Next was to match drill the joiner strip to the tank end with a #19 bit. I started from the top down and clecoed them together. Looks great.
Removed Leading Edge
Once the inboard bracket and the joiner strip are drilled, the next task in the “Checkoway” method is to remove the leading edge assembly from the wing exposing the outboard bracket for match drilling. Here you see it removed from the wing.
Drilled Outboard Bracket
I drilled all the outboard holes to full size. You can see here that the outboard bracket is right where it needs to be to line up. At this point, the “Checkoway” method is essentially complete. The baffle is now match drilled on the inboard and outboard ends, perfectly aligned and where it should be. Next you take the skin/ribs off the wing and leave the baffle and the inboard and outboard ribs in place.
Removed Tank Skin
With the skin removed, you can now match drill all the baffle to z-bracket holes. I took care of these and clecoed them down. If I did my math right, I should be in good shape on all the brackets.
Brackets Drilled for Right Tank
Once I removed the baffle, I was delighted to see that all the brackets looked just like this one. At this point, the brackets are complete for the right tank. I need to repeat the process for the left tank. Thanks to all the sites for documenting the “Checkoway” method. This makes much better sense than the manual method and produces a perfect result. I closed up the shop for the night and likely for the weekend. I have a Scout Camporee with my son tonight and tomorrow in the Utah desert, it is my birthday Sunday, and I have a young cousin who just passed away, so work will be on hold for a few days at least. Once back at it, I will be taking care of the left tank brackets.
Nutplate Locations Primed
I took some time tonight prepping and then priming the z-brackets. I decided to only prime the face of the brackets that 1. would have the nutplates attached to them, and 2. would be difficult to prime once attached to the tank. I may prime the outside of the tanks once the brackets are permanently attached and the tank is leak free. I also wanted to be sure that I did not create a path for the ProSeal not to stick to on the surface that will eventually be attached to the baffle, so I left that surface un-primed.
Nutplates On and Bolted Down
Since the primer I use dries so fast, I was able to get nutplates installed on each bracket in short order. The precision of the tool I used to drill the nutplate holes showed here. I simply had to cleco one ear of the nutplate and set the rivet in the other with my squeezer. Then I simply set the rivet in the other hole. All the bolts lined right up in the spar. I then bolted the brackets onto the spar for the left wing.
Right Tank On
Once the brackets were bolted on, I set the assembled right tank skin and ribs onto the right wing in preparation to drill the baffle side holes for the tank. You can see here that my bracket is spot on at the inboard location. Since I cannot see the outboard yet, I can only hope it is.
Looking Like a Wing
Here you see the tank on the wing. It is starting to look like something airplane like. It was late as you can see from the outside of the shop, so I called it a night.
Set Screws for Tie Downs
I placed an order for some set screws to thread into the tie down blocks from McMaster-Carr. The theory is that that set screw sits inside the tie down blocks and remains there. Then as you insert the tie down rings, they hit the set screws and will stop. This allows you to tighten down the tie down rings without crushing the skin since there is a gap between the tie down block and the skin.
I ordered a pack of the above as one option. They are 3/8″ long with a self locking patch on them. This should help them from rotating out of the tie down blocks if I choose to leave the tie down rings out of the plane until needed.
Another Tie Down Option
Another option was to get some smaller set screws and use two of them as jamb screws against each other to keep them from vibrating out. Both are stainless, just like the tie down rings. I have not decided which to use and when I do, I will likely offer the extras to other builders since I have many extras.
Nutplates in an Instant
Sorry for the lousy picture above, but I had to get a shot of the FANTASTIC tool I was able to use. Now that the Z brackets are drilled to the spar, the next task is to drill the nutplate holes and countersink them to accept the nutplates that are used to bolt the tanks to the spars. There are 36 holes that need nutplates. This means 72 holes to drill and countersink.
Typically, you would use the nutplate as the drill guide for the #40 rivet holes. Some do this by bolting a nuplate to the bracket from the underside and then using a block of wood that has a relief in it for the bolt head, drill a hole in one wing of the nutplate through the bracket into the wood, insert a cleco in that hole, and then drill the other. Then you have to repeat for each hole in each bracket. Once done, you then have to countersink the aft side of the bracket to accept flush rivets as this face sits against the spar. They do make drill jigs to speed this process up, but they are a bit pricey. It eliminates the need to bolt the nuplate to the part, but still requires the holes to be drilled one at a time, flip the jig and drill the other.
I was not looking forward to doing these. The time it takes is simply ridiculous. I sent a text to a friend that I know that works in aircraft assembly and asked if he had at least a nutplate jig. After a few messages back and forth, he said, “I have a better way. Meet me tonight.” Boy did he ever.
Basically, he had a pneumatic tool made specifically for doing nutplates. It uses a center pilot the size of the bolt hole that when engaged, it acts like a cleco, pulling the part to the tool. It then has two drill bits on either side, exactly at the spacing for the nuplate rivet holes, that plunge simultaneously to drill the #40 holes. Wait, that is not all. The bits also have countersinks on them. So at the end of the drilling, it also countersinks the holes. In one trigger pull, you get perfectly aligned rivet holes, that are countersunk all in about 10 seconds. Most of that is inserting the pilot and lining up the part to the tool.
Needless to say, I knocked out all 36 nutplate locations in less than 20 minutes and was left with parts that only needed the backside of the countersunk holes deburred. I could hardly believe my eyes. It is certainly true what they say about the right tool for the job.
Nutplate Holes Ready in a Flash
Here you see the result. I did this bracket in 30 seconds. Some of the nutplates will little askew, but they are nutplates you will never see…and it was due to me not being quite aligned with the part on the tool. No biggy, they are close enough. Needless to say…that was the coolest tool I have ever used. Next up, I will prime these (sans the flange that will attach to the tank) and then rivet the nutplates on with a squeezer. Then I will bolt them to the spars and continue with the “Checkoway” method in the next few days.
The time has come to start the fuel tanks. First up are the infamous “Z” brackets. The manual procedure is pretty universally accepted as worthless. The more acceptable and best result creating method is typically referred to as the “Checkoway” method, named after the Dan Checkoway that documented the process really well, though credits another for the actual idea. Dan has since retired his website, so builders are left to discern from other builder sites the actual process. Several sites that I used to get the general idea were Bruce Swayze’s, Jason Beaver’s, Brad Oliver’s, and a couple others found on VAF when searching “Checkoway.”
[ed. Dan has given full credit to Steve Hurlbut for the idea. Original description can be found here.]
Once I felt I had enough information, I began. I hit all the edges of each of the brackets on the Scotchbrite wheel. Essentially, the “Hurlbut/Checkoway” method is offsetting from center the Z brackets to make it easier to get a wrench on the inboard brackets and to give more room for the pop rivet gun for the outboard ones. It also allows the tank to be perfectly aligned with the wing and the leading edge assembly before drilling the baffle to bracket holes. This eliminates the need for possibly elongating the holes in the brackets to be able to position the tank in the right place. In reality, it is just a better way of doing it.
Inboard Offset Away
First thing to do is to offset the inboard bracket holes away from the web. I measured several different distances and finally settled on 1/4″ from the outside edge for the inboard brackets. This about 1/16″ out from center (as viewed from the aft of the bracket). This gives just enough room to allow a socket to fit over the head of the bolt that will be used on the inboard of the tank. You then find the exact center of the bracket. Once I did that, I center punched the hole. I then drilled the hole with a #12 bit. I repeated the process for a second bracket.
Bolted and Ready for Match Drilling
Once the center hole was drilled, I used some scrap AN3-4A bolts and nuts and bolted the bracket to the spar. As you can see above, the bolt is slightly offset from center on the flange. The reason you use bolts is because clecos will allow some movement where bolts will not. You square the bracket to the spar and then match drill the holes remaining using the spar as a guide.
Hey, Math Works!
As you can see from this shot, once the bracket is square, it should be aligned with the holes in the spar along your drill line. I drilled one of the holes through the spar, then inserted another bolt and secured it with a nut, then drilled the remaining hole in each bracket. This insured each was perfectly aligned.
Squaring to Spar
Here is how I squared the brackets. The contrast between the spar, bracket, and the square made it easy to see if they were off. I simply looked to see if the gold was shining through between the square and the bracket. To be double sure, I flipped the square and checked against the other spar bar. Every bracket was spot on.
For the outboard brackets, I changed the offset to 5/16″ from the edge of the flange. Some have gone more, but I figured it was a good compromise. 5/16″ is actually the center of the flange on the aft side but offset in towards the web. This will move the rivets on the other side out from the web. I may still have to get a cheap pop rivet gun to grind down the head to still set these, but not nearly as much as I would have.
I set up my drill press to replicate the center holes on each of the remaining 12 brackets and then bolted them in place on the spar. Then I match drilled them to the spar.
Right Brackets Drilled
Here you see the brackets all drilled and in location for the right wing.
Left Brackets Drilled
Same for the left. These are now ready for the nutplates that will be riveted to each of these brackets. I then installed the three nutplates on each spar for the inboard brackets. It was very late so I called it a night. I hope to borrow a nutplate jig from a friend to make drilling the 72 holes needed a little quicker. Stay tuned for the rest of the procedure next.
Right Tanks Works Begins
I was able to get the tank ribs deburred completely and started assembling the right tank in preparation for the “Checkoway” method of completing the baffle brackets. (More specifics to come as I complete them.) It was a short night and I need to get some hardware in order to do the brackets anyway, so after I clecoed the right tank together, I called it a night. Some progress is better than no progress.
As with the leading edge assemblies, I did not have any trouble getting the ribs in the skins. Everything lined right up. I guess I just got a good kit.
Joint Plates Complete
I had more 3/32″ clecos arrive this week, so I could now continue on the leading edges. I assembled the right leading edge parts and set them on the spar. Once on, it was time to tackle the joint plates that are sandwiched in between the inboard rib and the skin. This will tie the tanks and the leading edge assemblies together for a nice transition. I set the rib in place and using some 0.032″ shims made from scratch, centered and clamped the rib into the inboard end. Once in position, I match drilled the flange that attaches to the spar and then clecoed it. Next, I took the joint plate strip and marked a line 1/2″ in from one side. This line should line up with the rivet holes in the skin and leave 11/16″ protruding from the skin for a flange that the tank skins to use as a backer. It took some muscling into place, but I was finally able to get it and the rib where they needed to be. I then drilled the plate and the rib, using the skin as template. Above you can see both done, drilled, and in place.
I then match drilled (actually reamed) all the skin to rib/spars to full size. There are a lot of holes in these wings and I am not even to the tanks yet.
Enlarged the Tie Down Holes
Once all the match reaming was complete, I tackled enlarging the holes for the tie down rings. This means I had to reinstall the large bottom skin to get my previously marked reference lines for the center of the tie down block. This took about a minute to do. Both were just a hair off from the pre-punched reference hole, but Van’s states this is possible and to simply file the hole in the right direction and then enlarge with a unibit. I did just that. This one above on the right wing seems pretty darn close. The left was a hair off, but looking at it, you will never know. If you are looking that close to my plane, you better be a mechanic hired to look at it. 😉
Tie Down Ring Test Fit
Remember those fancy tie-down rings I bought from Cleavland Tool and polished to a mirror shine? I figured now was as good of a time as any to test the fit with the skin. I like it! I will need to buy some threaded inserts from McMaster Carr to set the stop depth of the rings in the tie down blocks like another builder I have seen, but for now…they are looking great!
Both Leading Edges Drilled
By then end of the night, I had both leading edges match drilled.
Next up, Fuel Tanks…yipee! I hear this is the most favorite task of the wings…NOT!
I got the tank parts sorted and on the bench, cleaned up shop, and called it good for the day.
Cradle Fabricated
I got home from work and quickly ran over to my neighbor who has a nice table saw and cut down a 2′ x 4′ x 1/2″ sheet of plywood I picked up last Saturday. I ripped it down to 13″ and then cut four 2 1/2″ strips to use as base rails. I then cut the 13″ piece into three 15″ sections (one just in case I messed up). I then traced a leading edge rib and added about 5/16″ to allow for the foam pipe insulation I wanted to use as padding. Once the trace was done I was able to run over to my jig saw and cut out the shape. Per Van’s, I did not worry about making the shape perfect, just close.
I then drilled and screwed the parts together and lined the cradle with the foam pipe insulation. All done, you get what you see above. I was a little concerned about the lower bracing I added to keep the cradle ends upright as it could get in the way of clecoing. Turns out my concerns were unfounded. I had no issues.
Left Leading Edge in Cradle
Here you see the cradle in use. Worked great. I have read that some have had real issues getting the ribs into the leading edge skin. I have even seen some extravagant setups to push the ribs in. I do not know if they have improved the kits or if I was simply lucky, but I had absolutely no issues getting the ribs into the skin. All the holes lined up and looked good. Once I got to this point, it was time to head into the house for dinner and family night.
I did have one issue with the ribs. The nose ribs have several little tabs that help support the skin near the nose. Where the flange near the front ends and the tabs begin on the top in particular, it seems that the transition is not very smooth and when inserted in the skin, causes some little bumps to appear. I read up on VAF on others who had similar problems and their solutions. Basically it comes down to hitting the corners with the scotchbrite wheel and then radiusing the relief notches to eliminate the thin corners that appear after the scotchbriting. I will take some pictures when I get to assembling the right leading edge.
After dinner and family night, I ran back out to the shop, disassembled the left leading edge parts, employed my dressing technique above for adjusting the nose of the ribs. I still had little bulges in the skin where the ribs were a problem. I will likely have a friend of mine that can massage them out come over at some point, but for now, they look much better. The right leading edge should be better.
Left Leading Edge Together
I ran out of clecos after setting the leading edge on the spar. So…I guess that means I am done for the night. I believe that my order to Brown Tool will arrive tomorrow with 200 more 3/32″ clecos and some more #30 and #40 drill bits. That should let me keep going. Before calling it a night, I was able to get the Stall Warner bracket cut from the kit and deburred. I then stole some of the clecos from the wing skins and got it clecoed in place in the nose of the left leading edge. As you see in the above picture, the inspection hole for the Stall Warner system is already cut in the skin. I also clecoed the skin doubler for the inspection hole as well.
I did have some visitors to the shop tonight. A good flying buddy, his son, and dad stopped by. We chatted at bit while I was able to slip the W-408-1L into place, mark the location of the holes, flute, and then slip in back in ready for the W-423 Joint Plate that is to come. I cleaned up the shop and gathered together the other things related to the leading edges (AOA kit, landing light kits) and set them out so I would not forget. It was late, so I called it a night.
Top Left Skins Drilled
The weekend has arrived and a mix of honey do’s and RV tasks awaited me. I had hung some plumb bobs off the left wing main spar at the inboard and outboard ends the night before. When I went out to the shop in the morning, they were not moving at all. It was time to anchor the rear spar to the newly finished anchor points I had fabricated. I was surprised to see that the distances were only about a 1/16″ off from each other. Not bad. I found an equidistant measurement and anchored each end of the rear spar to that point and checked the level of the main spar again. I then removed and reinstalled the top skins to relieve any pressures caused by the twist removal.
I then hung the plumb bobs on the right wing to repeat the process. Once hung, I headed out to take care of some honey do’s and let the bobs settle. Once done with my list of chores I returned and anchored the right wing.
I then set out to drill the wing skins on both wings. Not much to say other than there are a ton of holes in these wings. I started with the top, then the bottom of the left. I hit each with a #40 chucking reamer.
Bottom Left Skins Match Drilled
On the right wing, I started with the bottom and finished with the top. After that, my back was done for the night. I removed the bottom skins on both wings and set the skins aside. I cleaned up the shop and the chips from the wing structures and then called it a night.
Next up is the outboard leading edge assemblies. I need to make a cradle and debur the ribs a little more. Perhaps that will get done this week. I also realized that I needed more 3/32″ clecos. Those were ordered last week and hopefully will arrive soon.
Fabricated Lower Inboard Hard-points
Since I was able to get the top skins on last night, the wing skeleton was essentially squared up to itself. The pre-punched holes are simply amazing on accuracy and how it lines everything up. With the skeleton now squared up, it was time to make the bottom stand hard points so I can anchor the rear spar in the fixture to take out any twist.
Above is the inboard mount. I used some 2″ angle. Since the distance was a little too much, I had to add a chunk of 3/4″ oak I had laying around. As you can see, it worked out well. Now I can clamp the rear solid at the inboard end.
Fabricated Lower Outboard Hard-points
Now for the outboard end. I used some 1 1/2″ angle. It was too wide to clear the skins protruding from the ribs so I cut some clearance out with the bandsaw. After a little time on the scotchbrite wheel I was able to attach it to the stand.
Nice Little Level
Once the hard points were done, I rechecked the level of the main spars. I picked up this digital level at Home Depot Aviation supply. Between the bubble and the digital scale, I think I have these pretty well zeroed in. The level was pretty well priced for the feature set compared to others out there. Seems pretty accurate.
Time to Square Up and Anchor…Then Drill Away!
Next up, I need to hang some plumb bobs from the main spar and then insure the distance from the string/bob is the same at each end at the rear spar and then anchor the rear spars solid. I think I will then remove the skins to relieve any pressure from the twist removal and then re-attach and start match drilling all the holes.
Setting up the Doubler for Drilling
I decided to get the wing walk doubler sheets knocked out. For some reason, Van’s ships two 10″ x 48″ x 0.025″ sheets to make these wing walk doublers from. It seems strange that they want you to cut these down to 9 3/8″ x 26″ and then match drill them. Perhaps this contributes to the 51% required to be completed by the builder, or maybe, they just did not feel the need to punch these. Either way, it has to be done. I have read that some builders simply cut the sheets to the 26″ lengths and leave them 10″ wide. I thought about this, but I figured that I would stick to the plan dimensions.
The next question was how to trim these. I called a couple of friends that work with people that do sheet metal work to see if they had a metal shear. After a little more thought, I figured I could just use my shears and cut them close. That is what I ended up doing. I simply measured out the cut marks, sheared them close, and then filed to the line. It took me about three minutes for each of the doublers. I probably saved three or four ounces trimming off the 5/8″ down the side, but every ounce counts…right?
Once the sheets were cut to size, I lined them up per the plans. I then taped them to the underside of the wing skins. It was time to flip and drill. I pulled over my bench that I used to match drill the rudder stiffeners and began to do the same for these holes.
Doubler(s) Drilled
Here you see the end result of the match drilling. It went pretty quick and painless. They are now ready for mounting. Despite being late, I decided to get the doubler and top skins clecoed on to the spars/ribs. Once the skins were on, I cleaned up the shop and called it a night.
