Dodge Tank Installation Question in PA12

[rsmarch]

The Dodge tanks require adding a drag strut just outside the tank area. In a 12, all of the original single drag struts with right angle brackets on the end are very nearly parallel. The new drag strut for this tank installation is significantly non-parallel to the others. The front of the strut, which secures the drag tube through the tank, is lowered relative to others by about 5/8", the rear of the strut is raised relative to others by about 1/8". Because of the right angle brackets on the drag strut, this installation puts a lot of stress on the spar and nearby ribs and doesn't feel right.

Has anyone run into this problem or have any suggestions?

I'm inclined to lower it so that it is parallel with the other drag struts. This would require trimming the angle bracket on the end of the strut or turning it over. There's also the complication that I already drilled the hole in the spar web and I don't want to weaken the spar.

Would two 5/16" holes in the spar web 3/4" apart significantly weaken the spar?

 

[cubunltd]

I've installed these tanks in 2 PA12's recently with no problem. Email me and I'll talk to you about it. It's too long to explain here. I'm looking for my copy of the instructions so I can refer to them. cubsunlimited@verizon.net.

John

 

[Gordon Misch]

I encountered the exact same situation. The hole location on the rear spar is just plain wrong as far as I can figure out. I called Atlee this morn, and he insists that the drawing is right, but at the same time I didn't get the feeling that I was making myself fully understood. I finally moved the rear hole, after double-checking quite a few times. The strut is now in there straight with the hole 1 15/16" from the bottom of the spar.

I encountered a couple other dimensional errors also, including the thickness of the spacer at the lower #1 compression strut. The dwg calls out 17/32, but 15/32 is required to be flush with the face of the rear butt hinge extrusion. I'll have to check the wing attach point fitting spacing on the fuselage to be absolutely certain, but the spars are 1/16 farther apart at the butt than anywhere else on the wing.

What this means to me is I darn well better fit things up to check dimensions before cutting or drilling!

 

[rsmarch]

Geezer - This is encouraging news for me.

I encountered a couple other dimensional rrors also, including the thickness of the spacer at the lower #1 compression strut. The dwg calls out 17/32, but 15/32 is required to be flush with the face of the rear butt hinge extrusion. I'll have to check the wing attach point fitting spacing on the fuselage to be absolutely certain, but the spars are 1/16 farther apart at the butt than anywhere else on the wing.

I ran into this one also. I agree the lower #1 compression strut spacer should be 15/32" and along with this when you shorten the compression strut, be sure to cut off only 15/32" instead of the 17/32" the drawings show. And as you say, when you are done cutting off the #1 compression strut and adding spacers, be sure that the wing root attachment points are spaced to fit on the fuselage, if I remember correctly, the seperation is 31" center to center.

It is discouraging that an STC as old as this one hasn't been corrected, so that you can trust the numbers in it.

The STC also tells you to move rib #4 (I think) outward until it rests agains the new added drag (compression) strut. But if you do this it ends up further out than the actual wing station that it is suppose to be at which is listed later in some of the drawings.

I also don't like the shape of the front spar joggle strip (I think its called) that fits over a wood spacer and supports the front of the tank. It isn't really bent properly to lie on the wood spacer and distribute the load evenly on the wood and it doesn't really blend in with the airfoil either, it kind of sticks up. So I'm thinking of re-shape the wood spacer so that it actually supports the joggle strip.

 

[StewartB]

My 12 recently got Dodge tanks and the issues you guys have weren't a problem. The diagonal drag tubes are stock Supercub. The instructions were correct. The one variation was that we rigged the washout with the wings on the plane before installing the tanks. Washout rigging is easy to do wrong, and even easier to do wrong on sawhorses. On that point, Atlee's instructions are not the best.

Are you guys sure you have 12 tanks? There is a bit of twist in 12 tanks that isn't there in 18 tanks.

SB

 

[Crash]

Dodge Tanks

When I did the Atlee Dodge tank installation on my PA-14 I had the wings on and off the fuselage twice and rigged right on the money before shimming the joggle strips so the tanks would not rock when set down into their mounts.

Fast forward, the plane is done but flys one wing low. Adjust the left wing rear strut fork a turn and it flys level. One year later the tank in that wing cracks and leaks like a sieve. Pull the tank out an take it to Atlee to get it welded. Go to install it and notice he welded the wrong end of the tank. Take it back and they weld the correct end and hand deliver it to my business (good service, no one's perfect). I set it down into the wing and put 25 lbs of dive weights on top of the tank to weigh it down. I take a feeler gauge around the tank (between the lip and joggle strip) and come up with one corner .020 high. I had glued the shim strips in place so two hours of screwing around I got the old strips out (.065) fashioned new ones (.045) and the tank sets tight to the wing all the way around.

One thing to check for on these tanks is the welded seam around the tank lid that supports the tank needs to be inspected for "weld knobs" that will make the tank set up and ride on the knob. Take a file and dress the knobs down so the bottom support edge is nice and flat without compromising the weld. Crash

 

[Gordon Misch]

Now I'm wondering if RSMarch and I got PA-12 drawings?!! The error is that the compression strut is not even close to square with the spars when located as shown.

Thanks for the heads-up on the joggle strip supports and weld dressing, guys.

Gordon

 

[Crash]

Tanks

The one thing I don't like about these tanks is if the plane needs some fine tuning to the rigging after you get it flying. Then all the time you spent shimming and getting the tanks to set flat in the mounts is out the window. After re-rigging you really should loosen the hold down brackets, with some weight holding the tank down, take a feeler guage around the tank. If you have a gap on one corner, then you have to remove the tank and re-shim (what a pain).

As a test, I took the rear lift strut fork in and out 1/2 turn from the "factory" washout where I had set it originally. The tank started to rock in its mounts with only 1/2 turn of the fork. Too critical for my taste. Crash