Hat section for fuel tank cover

[Marty57]

I'm back working on my 2+2 / PA14 build after a long break ...... knee replacement and other issues. I need to do a few things before I cover my wings. I want to make and fit my fuel tank covers before I make my control cables. I bought some hat section a while back for the reinforcement on the tank covers. My plans don't call for any reinforcement but that seems contrary to Super Cub tank covers. Is there any way to form the proper airfoil curve in this hat section? Would I be better off making two pieces of 1/2" x 1/2" angle; shaping with a shrinker to the curve and riveting them together to form a stiffener? Is that over kill; maybe just two seperate pieces of 1/2" x 1/2" aluminum angle riveted to the tank cover? The drawing shows the two ideas if I make my own aluminum angle (not to scale)

Thanks,
Marty57

 

[skywagon8a]

Turn three wheels from a hard wood to match the shape of your finished product including flattening the edge flanges. Mount them on two pieces of wood so they can rotate easily. Hinge the two pieces of wood at one end. Place your hat section as in this picture. Adjust the tension with a clamp. Move your hat section by hand using a varying clamp pressure to control the amount of bend. Make the wheels of a large enough diameter to give a smooth bend. You could also place a handle on one of the wheels which will make it easier to control. It will be easier to control the exact location of the small bend if the two wheels are close together. Make a template board to match the shape of the top of the nearest wing rib. Since the angle of the curve changes all along the full length, this will be a tedious process, but satisfying in the end. Be careful not to overbend as each little bend also moves the far end. It may be easier to work from the trailing edge forward.

One question: How much space do you have between the cover and the tank? That hat section appears to be higher than necessary. Your rollers can also flatten the height.

You can also use this process to make a hat section from a flat strip of aluminum.

 

[tempdoug]

be careful of sharp edges between the tank and cover, and know how much room you have before you start, on a 18 theres not a lot of room, especially if you put a thin chaffe strip of some type on the tank. theres different hat section dimensions that are available. 1/2 inch sounds like a lot?

 

[Dan Gervae]

I modified some old tank covers I had for my home built Cub…I wish I could remember what they came off, but either way…the hat section stiffeners were much smaller and lower profile than the one you show. I’ll try to find pictures if I can.

 

[Farmer Hank]

Go to the Tools, jigs, fixtures thread and look at posts 852, 853, and 855.

 

[skywagon8a]

1/2 inch sounds like a lot?

Exactly.....A 1/8" bead would be sufficient. Made from something like this:

 

[Marty57]

Exactly.....A 1/8" bead would be sufficient. Made from something like this:

I think my hat section isn't going to work; the flange is pretty small and the height is taller than needed. I think that 1/8" bead would be the best; I may be able to do that with some wood blocks. Good ideas so far. Thanks

Marty57

 

[bcone1381]

I am building a Bearhawk and it has a hat section like this at the fuel tank too. I bought the kit and did not have to make this piece.

But, The instruction book says to place the aluminum hat section over the wing rib form block. (The form block is 3/4" thick piece of MDF that is the exact shape of the airfoil) Hold it down (clamp it down) tight to the form block then heat the entire piece up EVENLY with a propane torch.

 

[Steve Pierce]

I don't think Dakota Cub charges much for the formed channels.

 

[skywagon8a]

I don't think Dakota Cub charges much for the formed channels.

You could make a complete batch in five minutes.

 

[tempdoug]

I don't think Dakota Cub charges much for the formed channels.

there hat sections are about 3/16 of a inch high, 1 5/8ths total width when done, rivets spaced every inch. wonder if you can get the pieces pre drilled for the rivets? the riviting without a machine looks like it would require a ton of patience. or get the pieces and epoxy them on? me i would look into the chevrolet-3m body panel glue. im sure its done in a lot of different ways.

 

[tempdoug]

its just a thought is all. https://www.amazon.com/3M-38315-Pan...ocphy=9020859&hvtargid=pla-439727859270&psc=1

 

[bcone1381]

the riviting without a machine looks like it would require a ton of patience. or get the pieces and epoxy them on? me i would look into the chevrolet-3m body panel glue. im sure its done in a lot of different ways.

A novice can drive at least 6 rivets a minute once the trigger on the rivet gun is ready to be squeezed.

learning to rivet has barriers, but then Learning to build/restore has barriers. Tool acquisition is one of them. But you could learn on your own to drill, Deburr, dimple and drive a rivet in an afternoon, and know the repair meets industry standards. If you have a teacher/mentor cut that time in half. Then once it’s learned a whole new world opens up.

I do not see adhesives as generally approved as an acceptable technique, or a substitute for riveting in the FAA’s book of acceptable practices and techniques.. Cost, weight, shelf life are additional issues, but you may have experience and knowledge that gives a superior result with adhesives.

 

[Steve Pierce]

You could make a complete batch in five minutes.

But then you have to have does and roll the curve.

 

[Steve Pierce]

Several years ago one of my so called mechanics installed the 24 gallon Dakota Cub fuel tank cover on a set of wings we had rebuilt. Those covers don't come drilled for the filler neck or the attachment holes. He put it on backwards so the curve was on the back side. When my blood pressure came back down I got to thinking that DC uses a lot of CNC stuff. I drilled the hat channels off, turned them around 180 degrees and the dimpled rivet holes lined up perfectly. Shot the rivets and as good as new. Yea, he got fired shortly thereafter when he hogged out the hole in the tank bay rod on that same wing so he could get the bolt in. I think he delivers for Door Dash now.

 

[Marty57]

I don't think Dakota Cub charges much for the formed channels.

I'll check with Dakota cub tomorrow, thanks. I do have a C Frame and everything else I need to rivet so that part is not a big deal. Lots of riveting ahead on boot cowl and everything else up front.

Marty

 

[skywagon8a]

For what it's worth, I put my gas tank covers on without any reinforcement stiffeners. So far, there is no evidence of any need for them. If there was a need, I would expect to see some "smoking" around some of the attachment screws. There is none.

 

[DJ]

For what it's worth, I put my gas tank covers on without any reinforcement stiffeners. So far, there is no evidence of any need for them. If there was a need, I would expect to see some "smoking" around some of the attachment screws. There is none.

What screw spacing worked for you?

Mine are .032 T6 and are bulging between screws from the low pressure. The extended rib flanges they are screwed to seem to be flexing a lot and allowing the pressure to deform them.

Sent from my SM-G965U1 using SuperCub.Org mobile app

 

[skywagon8a]

What screw spacing worked for you?

Mine are .032 T6 and are bulging between screws from the low pressure. The extended rib flanges they are screwed to seem to be flexing a lot and allowing the pressure to deform them.

7" across the front. 6" along the outboard side. None on the inboard side. 4 screws along the trailing edge. No bulges noticed. I think it is 5052-T3 as most of the aluminum which came with the kit was 5052.

 

[Marty57]

After a few days with my grandson; I got around to calling Dakota Cub today about the tank lid stiffeners and the neck reinforcement. Great shout out to them on these parts! Just $15 each for the stiffeners and and just $5 for the reinforcement for the neck opening. It's not a regular catalog item so they had to figure out the prices for me and they called me right back. So yeah, I ordered the parts. They are throwing in the proper rivets for the stiffeners in the order. Thanks Melanie!

Marty57

 

[DJ]

The stiffeners are probably the way to go. My screw spacing was 9 inches on the sides of the cover. Too few screws for Javron ribs and covers without stiffeners. I added more screws and the problem is solved.

Sent from my SM-G965U1 using SuperCub.Org mobile app

 

[Marty57]

For whatever reason, Dakota Cub was not able to supply the parts. Seems shipping issues and now out of stock ......

Anyway, I decided to fool around with my 3 in 1 Harbor Freight Shear Press Brake to make the stiffeners. I had some scrap .040 aluminum to play with. My first attempt was with a 24" piece; I'll need about 28" for the actual parts. My break will do 30". These turned out to be real easy to make. I'll make a forming block for the curve in the ones I use but this one I just used my woodworking vise with wood jaws to make the curve. The flange is 1/2"; I'll check my dimple dies to see if that works ok.

This seemed to work out pretty nice for first try.

Marty57

 

[Marty57]

This has been a process to say the least. The 3-in-1 shear press brake from Harbor Freight that I have can only be called a "kit" rather than a ready to us tool. No instructions, many adjustments, some parts not included by HF. The only way to figure this thing out is to download the manual from Jet tools ...... same basic tool plus a few important parts. The brake is way too sharp for aircraft aluminum. Ya get what you pay for. Now, it's a good usable tool.

After figuring this out, I made the hat sections pretty easily. I made a jig to bend the curve and it was relatively easy to bend the curve by hand over the particle board jig. Drilling holes is next and then making the tank cover. Had these been available it would have been a lot quicker to buy them but now ..... I have a working 3-in-1 one for the rest of the sheet metal work ahead.

Marty57

 

[porcuypine]

Marty,
A little late to the game. Once upon a time I repaired big MD cowling, all metal bond with AL honeycomb core.

A common issue was the edge close, out basic z channel with a curve. We bent up the piece basically a 2” flange with a 1/2” joggle. Now here’s the magic part: we had these premade HDMW strips about 7/16 thick and as wide as the flange with a bevel along the length corresponding with the joggle angle one piece and one on the other and the whole thing wrapped in masking tape. Now we opened up the slip roller accordingly and rolled her until we had the proper radius.


I know you’re done but you could have ripped wood strips accordingly, a wedge for the middle and they beveled edges for each flange, wrap with strapping tape and roll accordingly. Harder to write then do



Rocket

 

[skywagon8a]

Most brakes come with sharp removeable dies. The easy way around it is to bend up a long strip of metal of the appropriate thickness, then tape/screw it to your die. Make up a set of these strips of the appropriate radiuses which you may need. Another way would be to get some steel flat stock and grind your desired radius. (Big job to get it right) The big commercial press brakes have a collection of different radius dies.

ALUMINUM - Recommended Minimum Bend Radius for maximum strength

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https://americanmachinetools.com/bend_radius.htm
https://daytonrogers.com/the-minimum-bend-radius-for-aluminum/

PS. That looks like a nice useful piece of machinery. Over time you will appreciate all you can do with it.

 

[Marty57]

Skywagon8a,
I discovered that about making a shoe for the break. I made one out of some .040 aluminum and one out of .016 SS. The .016 gave me a nice .080 radius for the hat section and didn’t restrict the angle too much. The .040 gives a pretty big radius and will be helpful for larger thicknesses. I also took out each die and filed it to .040 to get rid of the sharp edges on the die and it worked much better. I had to make some special washers shown on the Jet parts list that were not on the HF diagram. The cast iron is poor quality and the bolts for setting depth were tearing into the casting; with the proper spacer not a problem. Like I said, it’s a kit! I think it was a good buy at $450 and should be very helpful with all the sheet metal upfront.
Marty57

 

[skywagon8a]

Another tip: Polish the edges of the lower die so that when the sheet is drawn over it, it won't get scratched as much.
And another: Apiece of round steel is sometimes tack welded to the upper die to give it a permanent radius. That might not be good on yours as you have separate fingers.

 

[Marty57]

Another tip: Polish the edges of the lower die so that when the sheet is drawn over it, it won't get scratched as much.
And another: Apiece of round steel is sometimes tack welded to the upper die to give it a permanent radius. That might not be good on yours as you have separate fingers.

Thanks for all of the tips. The lower die was kind of rough in spots. I ran my sharpening stone across it to remove the imperfections. It’s a good machine; it just takes work to dial it in. The hat sections take me about 5 minutes to make in the flat state now; it was just a lot of work getting to the point of being able to just use the machine.

Marty57

 

[Marty57]

Progress and success on the hat sections and the tank covers. It took a while to dial in the 3-in-1 Shear but once it was working the pieces were not that hard to make. I back riveted the 4 pieces on the two covers and finished up today with the reinforcement rings (from Univair) on the fuel neck opening. The gasket on the neck makes a great seal into the ring. Next step is to cut a few holes for fuel lines, run some control cables, and it's covering time.

Marty57

 

[gdafoe]

Thank you Marty for these posts. I have followed along a bit and you are doing a great job building. Mine is done like Skywagon8a's and getting close to 1000 hours no problems yet that I can detect. I did not use a reinforcement ring on the neck opening. Maybe I should have. I have been trying to find that Univair part, so far unsuccessfully. If you wouldn't mind posting it I would love to have the number of that ring