PA-18 tanks in a PA-12 wing

[BES]

We are experiencing some difficulty fitting PA-18 tanks in my PA-12 wings. Could someone who has done it explain what needs to be changed?
From looking at the PA-18 parts manual, the wing drawing doesn't show drag wires in the tank bay, but a cross tube. Would I be correct in assuming that one needs to take out the drag wires and install the tube (through the channel in the tank, of course) in order to fit the tanks??

Bent

 

[gpepperd]

You are correct in your assumption concerning the removal of the drag & anti-drag wires in the tank bay. You then add a rib to reduce the larger 12 tank bay to the size of the cub or pa-20 tank. Lastly fabricate a diagonal tube to go through the tank and one shorter one to stiffen the smaller bay you have created by adding the rib. Out board of the original tank bay rib you use all the wires as they are. There is some pretty close fitting to get the fuel line past the inboard compression strut and a little filing to do on one of the gusset plates. It's well worth the effort, though, as ypu're both loosing weight and getting rid of a tank prone to leakage, cracks, and trapping water in the ribs.

 

[Dave Calkins]

What are you guys using for approval data?

I'm about ready to do a couple of these.

 

[gpepperd]

I did mine on a 337 field approval back in 1986 from the Anchorage office. It was for PA-20 tanks in my 12.

 

[BES]

There are several things that are still a mystery to me. Firstly because of the way the bracing wires are positioned in the PA-12 wing, ie. they are very low in the bay so there doesn't, without final positioning of the tank, appear to be a need to remove them anyway assuming the tank straps would hold the the tank off the two false ribs.

Secondly , and more importantly, there is a problem we seem
to have. That is that when the PA-18 tank is positioned in the fuel tank
bay because it is a fatter tank it sits on the main compression strut and
sits proud of the top profile of the wing by about 3-4 inches.

Without major surgery to the tank itself, and assuming I am not missing
something obvious, the PA-18 tanks will not fit in the wings.

What am I missing/doing wrong?

Bent

 

[fatcub]

See they fit just fine.

Scott..

 

[BES]

Nice pictures Scott,
Did you move the compression strut in order to make them fit??

Bent

 

[landesskis]

Dave Caulkins

Dave,
I put -18 tanks in my -12 and field approved them. Swing by the shop if you want a copy, you can also go out to my "T" hanger and look at the installation.

Gary

 

[Dave Calkins]

Thanks Gary,

I'm about tired of pulling fuel tanks every annual for leak check and inevitable repairs......

.......it's getting to where it doesn't even bother me to open the cabin door and smell avgas.