Size of forming block; how big?

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57Marty

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I'm building fuel tanks for my Wag 2+2. There aren't any drawings so I'm on my own. I built a wood mock-up that fits exactly how I want it when finished. I'll be welding the tank from 5052 .050 aluminum. I'm going to use a form block to shape the ends and baffles; basic rib construction. Problem is, how much undersized do I make the form block so it will produce the correct size tank? I know I need to subtract .100 for the thickness of the top and for the flange thickness I will be bending, how much more? Is the .100 enough or should I be closer to 3/16" all the way around?
Thanks,
Marty
 

steveair2

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Be careful. I thought I had the dimensions right on my tank. Now I'm having to lower my tank supports and the tank barely squeezes in from the length.
I'd build them a few fractions of an inch too small and plan on using some soft spacers between the structure. You will want to allow for expansion and contraction of the tank. Pops made some nice tanks for his bird. Check out his build thread for ideas.
 

Little Scrapper

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Don't read in to it too much. It's aluminum. Aluminum if easily shaped. Use a generous radius and allow a few degrees for springback. If it's not perfect hit it with a leather hammer.
 

Chris In Marshfield

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Is the tank dropped in from the top and screwed to the wing's top surface, or does it strap in from the bottom like the Bearhawk line? If from the bottom, make sure you leave enough room for the thickness of any anti-abrasion material you use (cork, rubber, etc.) as well.
 

Little Scrapper

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Have you ever seen how Taylorcraft mounted the wing tanks on a BC12d? It's a good, easy, smart way of doing it. Something you may want to research.
 

Pops

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On the SSSC the top of the tank had a large flange around the edges to form the structural skin of the wing. I will never do that again. When welding the aluminum tank its hard not to change the shape of the airfoil. Lots of extra work.

Joe (Rockeydog 2) did the same thing and also said he wouldn't do it again.
 

57Marty

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The tank is held in with straps from the top. There is a plywood shear plate under the bay. I attached a couple pictures; one of the finished bay and one of my tank mock-up in the straps. When I fitted the mock-up I had the straps finished out except for paint. They fit how I would like the finished tanks to fit. The control cables run along the inside of the tank bay at the front of the tank so I need to keep that clearance. I made sure I had good clearance so the cables would not hit when slack.
Marty

tank bay.jpg


tank mockup.jpg


Marty
 

Little Scrapper

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End results are what matters. I'm a cardboard guy myself, but that's a pretty cool mock up.
 

Armilite

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The tank is held in with straps from the top. There is a plywood shear plate under the bay. I attached a couple pictures; one of the finished bay and one of my tank mock-up in the straps. When I fitted the mock-up I had the straps finished out except for paint. They fit how I would like the finished tanks to fit. The control cables run along the inside of the tank bay at the front of the tank so I need to keep that clearance. I made sure I had good clearance so the cables would not hit when slack.
Marty

View attachment 54049


View attachment 54050


Marty
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There is a FREE Very Simple 2D Cad program from www.emachineshop.com that also let's you view your Part in 3D that might Help building parts. Can save File as DXF for a CNC Water Jet, CNC Laser, CNC PLasma, and a CNC Routers. Will save in other Formats aslo for 3D Printing.

Here is a thread on building Aluminium Gas Tanks.
http://weldingweb.com/showthread.php?307071-Help-with-Aluminum-Fuel-Tank

Some Fuel Tanks in Plastic
http://www.air-techinc.com/topic_no_cats.php?ptid=41&pmid=12

5 Gallon Seat Tank, make a good Reserve Tank!
http://www.ebay.com/itm/5-gallon-gas-tank-seat-for-ultralight-experimental-aircraft-trikes-PPG-PHG-/112104914259
 

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Armilite

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They say it weighs 27 lbs. No thanks.
===============================================

I wrote them to see if that's the right weight for their 20 Gallon Plastic Wing Tank, maybe a misprint. Their 17 Gallon Internal Aluminium Fuel Tank is 10lbs.

This 18 Gallon Aluminium Tank says 20lbs. So a 20 Gallon would Weigh around 22.2lbs.
http://www.air-techinc.com/product_detail.php?pid=1083
 

Armilite

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Spruce's answer to 27 Gallon Fuel Tank.

The total weight includes the two extra cross/ compression tubes, rivets, bolts, fuel line, gascolator/filter, top and bottom aluminum sheet. Everything. Deduct the entire weight of your current fuel tank and brackets and pan and hardware and you are actually adding about 12 pounds more.
 

57Marty

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Nice idea but won't fit in my wing. I'll do some forming tomorrow but I also found a very experienced old school fabricator who has been doing tanks for 30 years and may have him build them for me. His price was pretty darn good considering the learning curve I need to make a couple of tanks. I'm going to meet with him next week and in the mean time, I'll form up a side piece to see if the form block I made gives me the correct size. The welder would than use my form block and mock-up and build a couple tanks for me. I need to get this thing flying some day and the learning curve sometimes takes way too long We'll see how the form works tomorrow.
Marty
 
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