J4A Restoration

[rjmech]

Morning all,
I am in the process of restoring a 1940 J4A.
I have been documenting and asking questions over on the J3 Cub Forum https://www.j3-cub.com/threads/j4a-restoration.31667/

I just found out my project came with a 7 gallon fuel header tank from a J4E, and not the correct 16 gallon oval tank.

Looking over at the Cub Club i see they offer a 337 for a PA-12 wing/header tank in a J4.
I know this is a long shot......
Has anyone ever seen this 337?
If so is it for a J4A or J4E?

I have an email into Cub Club asking to purchase the 337, but from what i read they may not respond.

Any help is appreciated!

 

[J4A]

If you get any traction on this let me know as I'd like to add some more fuel capacity whilst I rebuild my wings.

 

[rjmech]

[FONT=&quot]Nailing on the ribs today.[/FONT]
[FONT=&quot]Simple drill guide and a sharp 16” long #40 drill bit made it pretty easy. The nails are staggered from the front and back side of the spar.[/FONT]
[FONT=&quot]Next I’ll set the drag brace wires, probably have a few more ribs to notch out for them.[/FONT]

 

[cubdriver2]

Pictures of your 7 gl tank? Are you sure it's not the 9 gl rear aux tank that the J4A came with?

Glenn

 

[Charlie Longley]

OK just to be clear purchase of a 337 copy isn’t approval to do the modification on your airplane. You would probably be better served to connect with other J4 owners to try and get a copy. If you can figure out an N number of which J4 this was done to, order the CD from the FAA. Freedom of information but it still cost $10. Then you can work with an IA and the FAA to get it approved.

 

[rjmech]

I have both the 9 gallon aux tank from the J4A and a 7 gal front header tank from a J4E.

 

[rjmech]

Correct on the 337 unless it’s pre-1955, then it’s considered approved data.
Either was being able to show previous approval and accomplishment helps grease the skids for me with the DER.
Unfortunately the J4 community is small, I have asked around but gotten no where. I have tried to order the 337 from Cub Club but no response from them yet.
I think I have enough information now to substantiate a 17 gal PA12 wing tank install. I just need the tank dimensions and I can start building the data package.

 

[bob turner]

I got a field approval for a small Air Energy tank (no longer available). It had been installed with IA approval in the 1990s.

But you just reminded me - we discovered an aluminum wing tank that may be Piper size. I will get photos and dimensions and post here. I use the 11 gal Air Energy/Biplanes tanks, and prefer them.

 

[rjmech]

How did you handle the drag brace wires under the tank?
If you have photos i would love to see them.
Thanks
Tad

I got a field approval for a small Air Energy tank (no longer available). It had been installed with IA approval in the 1990s.

But you just reminded me - we discovered an aluminum wing tank that may be Piper size. I will get photos and dimensions and post here. I use the 11 gal Air Energy/Biplanes tanks, and prefer them.

 

[bob turner]

Here we go . light corrosion on outside, but really shiny inside. Your guess is as good as mine - too wide to be a J3 tank.

 

[rjmech]

[FONT=&quot]Progress being made.[/FONT]
[FONT=&quot]Fabricated a new bird cage / upper cabin area.[/FONT]
[FONT=&quot]Formed a set of 5 wing profiles out of 3/8 Piper U-Channel[/FONT]
[FONT=&quot]Made FWD and AFT spar stubs, mounted them to spare ribs, then mounted to the fuselage.[/FONT]
[FONT=&quot]Then started replacing the sections from the inside out.[/FONT]
[FONT=&quot]I leveled the outer forms with the ribs, then the middle forms level but higher, and then the center is the highest.[/FONT]
[FONT=&quot]Turned out nice and true[/FONT]
[FONT=&quot]I followed Pipers methodology of welding uprights to the frame and brazing all the light weight structure above that.










[/FONT]

 

[DanP]

Hi, I think that mystery gas tank in Bob's photo may be a 13 gal tank from an Aeronca Champ. I just had those installed in the Champ I co-own and they look very similar. I wish I'd have seen those photos months ago-- we had to look high and low to find the 13 gal tanks because Wag Aero did not have any.

In any case, I am looking forward to watching this J4 project take shape. Best of luck!

 

[Cub Builder]

Morning all,
I am in the process of restoring a 1940 J4A.
I have been documenting and asking questions over on the J3 Cub Forum https://www.j3-cub.com/threads/j4a-restoration.31667/

I just found out my project came with a 7 gallon fuel header tank from a J4E, and not the correct 16 gallon oval tank.

Looking over at the Cub Club i see they offer a 337 for a PA-12 wing/header tank in a J4.
I know this is a long shot......
Has anyone ever seen this 337?
If so is it for a J4A or J4E?

I have an email into Cub Club asking to purchase the 337, but from what i read they may not respond.

Any help is appreciated!
View attachment 59510

I would suggest calling the Cub Club. He doesn't seem to respond to letters and/or email, but when I called, I got an instant and positive response. The price for these 337s is primarily just to cover the cost of printing and mailing. He just emailed a copy to me as a .PDF and called it a day. No charge. In return, I sent a check and joined the Cub Club, but never got a response, newsletter or anything. But the phone response was great.

-Cub Builder

 

[rjmech]

Yeah I called the number at various times over a month or so then finally gave up.
I borrowed an original RH PA-12 fuel tank along with the fwd/aft spar mounts.
I mocked up everything on my J4 wing and it will work with lowering the compression struts and drag brace wires, then a few minor other changes.
At some point I’ll write everything up and start talking to the FAA/DER.

 

[skywagon8a]

I mocked up everything on my J4 wing and it will work with lowering the compression struts and drag brace wires, then a few minor other changes.
At some point I’ll write everything up and start talking to the FAA/DER.

Better to start with talking to the DER. Moving the compression struts and lowering the drag brace wires will change the structural load paths within the entire wing. This could involve conducting a stress analysis of the entire wing. Some fuel tanks have tubes passing through the tank to accommodate the cross brace wires. The least alterations to the wing you do, the better off you will be.

Check the regulations, you will likely find that alterations to the fuel system will require an STC not a Field Approval. You will likely find it will be easier, less expensive and less complicated to build your own gas tank to fit your wing than it will be to alter the wing to fit an existing gas tank. The tank itself only requires a 3 psi pressure check. The installation itself is something else.

Also check the differences between an auxiliary tank and a supplemental tank. There is a difference, and it makes a big difference which you call it from a certification perspective.

Look up the regulations under CAR 4a. Those are the regulations under which your plane is approved and you will need to follow.

I've done this with a tank which just sat on the top of a wing. A single use STC was issued. And, the manager of the FAA regional engineering office was a friend. There is no way I would have been able to supply a stress analysis on the wing in order to keep the FAA happy.

Are you aware of item 306 on the type certificate A-703? 9 gallon auxiliary tank.
306. (a) Auxiliary 9 gallon fuel tank installation +11 lbs. (+57) Placard fuel selector valve: "Use main tank for takeoff and landing. In level flight, use auxiliary tank before using main."

 

[rjmech]

Making progress
[FONT=&quot]Got the LH wing trammeled last week, and some parts in from Univair.[/FONT]
[FONT=&quot]Quick fit check this weekend and now the leading and trailing edges are going on.[/FONT]
[FONT=&quot]All trammeling and Leading Edge install is done with a 9/16“ block at the aft spar under the aileron OB rib.[/FONT]

 

[rjmech]

[FONT=&quot]Getting back to it.[/FONT]
[FONT=&quot]Working on the ailerons.[/FONT]
[FONT=&quot]The metal fittings were looking rough with rust and old paint/varnish.[/FONT]
[FONT=&quot]Unfortunately you pretty much have to disassemble the entire aileron to remove them.[/FONT]
[FONT=&quot]Once removed they were bead blasted, epoxy primed, then painted using PPG aircraft polyurethane.[/FONT]
[FONT=&quot]Hopefully they should last another 83 years.[/FONT]
[FONT=&quot]Interestingly the ailerons were assembled by Piper with all soft rivets, even for the hinge points. I see on the others Piper models with the larger control horns they used soft steel flat head rivets, but not here.[/FONT]

[FONT=&quot]I am still waiting on parts from Dakota Cub for the LH aileron, who knows ho long that will be.
[/FONT]

 

[rjmech]

Second wing is now completed and ready to store.
Aileron rebuild is not hard, but kind of tedious to get really straight.
Probably doesn't matter as it will shift after shrinking covering when the time comes.
On to jigging up the fuselage and replacing most everything from the production splices aft of the cabin back.

 

[J4A]

Looking spectacular as ever!

 

[brirobyg]

Hi, I just discovered your project on the forum.

Back in 1986 I completed the restoration of NC27857 J4A S/N 4-1077. I noticed in one of your pictures that there was an instrument panel sitting in plane, and I couldn't help noticing its likeness to that of a J4E panel. I spent a lot of time resurrecting the panel I had and I got it as close to original as I could at the time. From what I can see of your panel it appears to be fairly original and would be worth saving as is given that the E model is probably to most difficult to document in terms of originality. Even if you do modify it, please make sure to document it untouched as much as you can as I'm sure someone who really wants to bring their J4E back to original would be eternally grateful for that kind of information. I was fortunate to have most of an original panel for my airplane, and there are several out there that are original.

My most helpful guide during my restoration was having a parts catalog which covered both 1939 and 1940 models, which was pretty much everything excluding the 1941 J4E. There were many differences made over the 3 years of production, and even one notable change that was made to the doors during 1940 with the J4A. But that parts catalog was my greatest help with figuring out a lot of how things were put together and what was correct given that my project started out as a truckload of parts from 1 1/2 airplanes with boxes of stuff that I had to salvage what I could from and figure out how to put it all together.

The J4A in my opinion was really the best looking of the 3 years. I kept the A65 for power with a wooden prop, and it was adequate. I only had the 16 gallon main tank, but I managed fine. Out of all the planes of that era that I flew, I have to say the J4 was the nicest flying of them all. I've seen a lot of people say that it didn't fly that well, but it was really the most gentle and forgiving flying airplane. Just don't expect it to fly like a Super Cub and try not to use the brakes for anything other than doing a run-up, as it tends to be nose heavy with just one person in it, apparently that's why cowlings have become scarce.

Looks like you're doing a great job with it. I would love to do another one myself, there are many things I learned from that first one. I only flew mine a few years and 250 hours, and the restoration took me 3 years and I figured about 2000 hours, but it was the experience of a lifetime.

 

[rjmech]

Hey brirobyg,
Thanks for the note.
Yeah mine is officially a J4A, but in the 60's someone swapped a lot of J4E parts onto mine.
Yes my panel is pretty well unmolested, but unfortunately that will have to change because the front fuselage is getting converted from J4E to J4A. With the cabin tubes being replaced and the cockpit angle tubes added the two glove boxes will have to change.
I have all the Piper manuals for both the E and A models, so i cam pretty well covered.
Mine was delivered with the 9gal aux, so i will and up with 25gallons total.

I dont post a lot but i am still plugging away.
I just got done replacing all the tubes from the cockpit aft.
The tube liners are thick 4130 tube sections turned down for a tight fit. Interestingly the upper longeron was .035" and the lower was .028", i guess Piper used whatever they had on hand that day. The Dwg says they should both be .028".
Soon ill be putting back on all the upper and lower stringer formers.
It should be blasted and painted in spring.
Here are some pics of the fuse replacement:

 

[bob turner]

Are you installing the original 16 gal fuselage tank? Ours is stainless, and has been out twice for leak repair. It is time to get some aluminum tanks welded up, I think.

 

[rjmech]

Yes ill be putting a 16 gal up front to meet the TCDS.
I was planning on stainless since the original was steel.
I havnt done the research on CRES vs Alum tanks.
I am open to any input.
Thx!

 

[brirobyg]

As I'm sure you must be aware having gotten into the fuselage structure as deep as you have, don't forget holes drilling holes within all of the welded joints to allow for preservative to be able to get everywhere when you reach that point.

 

[bob turner]

Original is stainless - paper thin. Our welder said he found dozens of pinhole leaks. Second time through it was JB Weld, and as far as I can tell that is better than welding. The Wag J3 tank is an order of magnitude better than any steel tank I have seen.

 

[rjmech]

Its been a while, i have some people asking questions so here is an update on the rebuild.

Currently i am just about to media blast and paint the fuselage. I just finished repairing the elevator trim system and replacing some crude farm repairs on the tail feathers. I also made all new vertical stab and rudder using all 4130, work was done per the Piper DWGs and using the removed parts as patterns.

Here are some pics:

 

[rjmech]

Still plugging away, wasted a lot of summer time waiting for a few low humidity days, but finally got the fuselage blasted, then epoxy primed.
Just yesterday i got it painted with PPG polyurethane.
Should protect the fuse well until the next recover.
Finally time to start putting it back together.