T-405-L Fabricated
Got a little shop time in and was able to get the T-405 for the left tank cut complete and deburred. It was kind of cool to take a raw angle and a drawing and make a part appear that looked like a real airplane part. Now the challenge is to mirror it for the right hand tank. It was late so I called it a night.
Started Attach Brackets
Not a big progress night, but I started the brackets that support the tank at the inboard end tonight. I got this far and ran out of time. I will detail how I did them after they are done.
Right Tank Drilled and Sunk
I had a goal for the day. Get the drilling done on the right tank and get the Z brackets drilled on the left. I had match drilled the right tank skins and ribs earlier so all that remained was the rear baffle. I reamed all the holes in the skin to baffle and then set out to decide if I was going to countersink or dimple these. Vans tells you to countersink them to make installing the baffle easier when sealing the tank. I have read where others have successfully dimpled these, which is a stronger joint. I tossed the idea around and then decided to stick to the manual here. It does not seem right to countersink 0.032″ material, but it truly is the minimum you can. I tested a scrap piece with my countersink cage and once set, countersunk the holes. I had to remove the plastic to the point where my cage would sit flush to the skin.
Once done, I still was not liking the idea of the countersinks, but many a tank have been built this way and are flying fine. With these done, all that remained were the stiffeners to match drill.
Right Tank Stiffeners Drilled
I disassembled the tank and then clecoed on the stiffeners and match reamed them to the skin. Before removing them I marked their location so I could return them to the same place. With the stiffeners done, I then opened up the screw holes around the perimeter with a #19 bit. At this point the drilling is complete on the right tank [except for the fill cap and drain port]. I have a lot of prep to do for the capacitive senders and plumbing, but I will do those at the same time as the left tank parts.
Working on the Z Brackets on Left Tank
Now that I had all the clecos from the right tank, I assembled the left tank so I could drill the baffle Z brackets. Here you see the tank in place and strapped down. I had already drilled the inboard bracket and was about ready to remove the outboard leading edge to get to the inboard. I completed the outboard bracket and then took the skin and ribs off and drilled the rest of the brackets in short order.
Left Tank Brackets Drilled
With the brackets now drilled for both tanks, I will be able to get the tank prep done. The next time the brackets attach to the spars, it will be on a completed tank. Next up is match drilling the left tank, stiffeners, baffle, and then countersinking the skin to baffle holes. Then I will work on all the attachments to the tanks and start sealing away. I may have completed tanks by Christmas.
I had to get on the roof of the house to clear some objects the kids had tossed on it. While up there, I took an “aerial shot” of the factory. Enjoy!
Aerial View of Factory with New Yard
Right Tank Match Drilled, Stiffeners Deburred
Short night, but I was able to get the stiffeners deburred and rounded and the right tank match drilled (reamed) except for the top and bottom skin to baffle holes. Not much done, but some.
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.
