PMA Tank size

[rjmech]

Does anyone have the dimensions of a new PMA 17or18 gal PA-12 RH fuel tank?
Do the drag brace wires run under or through it?
Also any tips for installing over/under tank straps on a wood spar wing?


Reason I as is I am restoring a J4A and need to install a wing tank.
I am in the process of collecting data for the approval and need to know where to install the #4 rib.
I have called Dakota and another tank vendor a few times but gotten nowhere with them.

Photos for reference only
Thanks!
Tad

 

[RVBottomly]

I don't know the J4 configuration, but I think in the PMA tanks you'll find that they have a tube through them to accommodate a drag tube instead of wires. It goes right through the middle on a diagonal.

I remember Farmer Hank on here had a pair of fuel tanks with tubes that allowed wire drag bracing to go through them.

 

[Farmer Hank]

I gave those tanks away. They were 16 gallons each with two in each wing. Because the drag wires crossed inside the tank, the first tank was in the middle of the first drag bay, and the second was in the middle of the second bay. The result was balance problems. I had to watch the clock carefully and switch tanks on a precise schedule. You would be better off putting a drag tube through the tank and keeping the tank adjacent to the butt rib.

 

[Gordon Misch]

In the PA-12, the drag / anti-drag wires run underneath the tanks.

 

[skywagon8a]

You are addressing two separate major alterations. Adding a fuel tank requires engineering approval. Changing the cross wires also would require engineering approval. Get in touch with a DER before you proceed further.

 

[KJC]

I just checked the FAA DRS and unfortunately I don’t see an STC for a wing tank in a J4. It’s a good idea but your going to spend huge money and time with a DER for this. I recommend putting it back together in the stock configuration. It will still fly just fine. ��

 

[skywagon8a]

Once upon a time a friend of mine wanted to increase the fuel capacity of his Widgeon. Just a tank (which we made) behind each engine which would drain into the main tank. A very simple modification without much in the way of alterations. The tank rested on the top of the wing with some straps holding it down. I had to go to the FAA regional office for meetings with the engineers. I had to supply them with some sketches and stress analysis. I'm not an engineer, but they bought what I supplied them. They had to come to inspect the installation. Then they issued me a one only STC. This was in the days when one could go to the FAA, they would talk and work with you and the chief of engineering was a friend of mine. Times have changed. I fear you have no clue as to what you have bitten off.

Do you know the difference between an auxiliary fuel tank and a supplemental fuel tank? Look it up, there are different regulations for each.

 

[rjmech]

Morning all, thanks for the input.
Unfortunately because my fuselage is from a J4E I need to install a wing tank to get back to a normal fuel system.
The current fuel system was 6 gal main tank and 9 gal aft aux tank, the J4A should have a 16 gallon main + the aux.

i have already started talking to the local FSDO about the approval and if I need to go to a DER we have one local.
I have not bought anything or made any permanent changes yet, nor will I until I get all the approvals.

Worse comes to worse I can always part the project out, I dont have a lot of $$ into it.

 

[Marty57]

Morning all, thanks for the input.
Unfortunately because my fuselage is from a J4E I need to install a wing tank to get back to a normal fuel system.
The current fuel system was 6 gal main tank and 9 gal aft aux tank, the J4A should have a 16 gallon main + the aux.

i have already started talking to the local FSDO about the approval and if I need to go to a DER we have one local.
I have not bought anything or made any permanent changes yet, nor will I until I get all the approvals.

Worse comes to worse I can always part the project out, I don't have a lot of $$ into it.

Not sure if this will help but here's an idea. I'm building a Wag Aero 2+2; essentially designed from the J4A. I built wood wings but, the plans allow for wood spars with metal ribs. The tanks they have available are designed with tubes inside for the drag, anti-drag wires to run through them. I didn't want to use that design so I put a shear plate under the tank bay (as per the certified 1946 Rearwin Skyranger 185) and eliminated the need to run stuff through the tank. I had a friend (engineer) run the numbers and the 1/8" ply took care of keeping the wing square in that area. I believe the Dakota Super Cub wing has the same set up for the tank bay. In my case, the tank cover will be structural in keeping that bay square with screws every 3" as per the engineering analysis. I used the tank hanging straps as per the 2+2 drawings and used custom built tanks, allowing me to run control cables in front of tank, inside the wing. Everything I changed on my wing was to match the 1946 Rewin Commonwealth Skyranger 185. I have about 10 pictures of the wing. Maybe you could use that information to get a one time STC to modify your wing using the Skyranger as acceptable data? Might be worth a shot. I'll attache a few pictures here and I can email you what info I have and pictures. Here's a Youtube video on the Skyranger that I found years ago when I was figuring out how to change my wing. https://www.youtube.com/watch?v=ObjitueZayU

Marty57

 

[rjmech]

Marty, thanks for the information. I have actually been watching your build for years. Very nice work indeed!
i have seen the use of ply sheer plates in the rib bays on a D-Vii replica.
My wing has all the needed compression struts and drag brace wires, i just need to lower them and change out a few end pieces so the bolts pass through the middle of the spar.

Ultimately right now i just need to know the dimensions of a PA12 17 gallon tank so i can finish up my data pack. Then start on the approval.

Tad

 

[Marty57]

Marty, thanks for the information. I have actually been watching your build for years. Very nice work indeed!
i have seen the use of ply sheer plates in the rib bays on a D-Vii replica.
My wing has all the needed compression struts and drag brace wires, i just need to lower them and change out a few end pieces so the bolts pass through the middle of the spar.

Ultimately right now i just need to know the dimensions of a PA12 17 gallon tank so i can finish up my data pack. Then start on the approval.

Tad

I had the wires crisscrossing the tank bay, as per the drawings. When I found the data for the Skyranger, I removed the wires after I glued the shear plate inplace. With that done, any tank would fit in the bay. I didn't want to de-rig the wing if I needed to remove the tank due to a leak. If you could get that accepted, your tank options increase dramatically.
Marty57

 

[RVBottomly]

I had the wires crisscrossing the tank bay, as per the drawings. When I found the data for the Skyranger, I removed the wires after I glued the shear plate inplace. With that done, any tank would fit in the bay. I didn't want to de-rig the wing if I needed to remove the tank due to a leak. If you could get that accepted, your tank options increase dramatically.
Marty57

Not to get too far sidetracked, Marty, my Wag 2+2 drawings have one drag tube through the fuel compartment, not cross wires. Still a hassle, true.

I noted with interest your use of the SkyRanger design, especially because I'm flying one right now.

 

[Marty57]

Not to get too far sidetracked, Marty, my Wag 2+2 drawings have one drag tube through the fuel compartment, not cross wires. Still a hassle, true.

I noted with interest your use of the SkyRanger design, especially because I'm flying one right now.

Yup, your are right. I hadn't looked at it in a while; there was just the one diagonal brace running through the tank and no crisscross of brace wires. My bay is now closer to the Skyranger; a good alternative to the J4A I would think.
Marty57