new fuel tank

As I said earlier in another thread (new vent install) I am now testing a fully welded tank. It is constructed of 5052 H32 .090 aluminum. I have mounted the sending unit door and of course the Moeller gage on the top skin. I have used Van's cork buna gaskets for all three mounting plates, and was hopeful that they would seal the fastening screws, but no way. The soap bubbled air freely. So I had to make a concession to the Flamemaster tank sealant for the screws. That appears to have done the job still using the cork gaskets. Should further testing indicate any air leaking I will remove the 3 plates and the cork gaskets and apply tank sealant directly to the 3 contact surfaces w/o the use of the gaskets. The good news is all the leaking air was associated with the 3 plates. There are no leaks in the heli-arc welds.
It's been a while since I have conducted the air test and would appreciate any thoughts from your own experiences as to how long the balloon should hold the air and what is an acceptable rate of shrinkage?
Upon completion of satisfactory leak testing I will install the tank and run/flight test it. Following a successful test period I will send photos and tell all who are interested about what I have learned in this process about tank making for the RV12.
Dick Seiders

Dick, as I understand it, the only purpose of the balloon is to pressurise the tank while you check for leaks using soapy water. It's immaterial how long it stays inflated, except that if you have leaks it will obviously deflate a lot faster.

Just did one - -

Put the balloon test in place, and spray a mixture of 50/50 dishwashing detergent and water on it right away - ALL OVER. You will know if you have ANY leaks. Works great. Wash it off once satisfied.

Correct.

The intent of the balloon is to only use it as a very sensitive pressure indicator so that people don't blow up their fuel tank.
The pressure is so low, that judging the existence on a leak by the appearance of the balloon is not a valid test. Ambient temp change can cause a big change in the appearance of the balloon. It could actually hide the existence of a leak, if the temp was climbing while the air was slowly leaking out.

You can confirm this your self. Pressurize the tank the same as for a leak test, with tank at room temp. (~70 deg F.). Put the tank in the shower and spray cold water on it... the balloon will go flat almost instantly.

Thanks for getting back. Van's tech agrees . The balloon is to limit pressure. However, if it's still inflated, albeit at a smaller size after 6 hrs or so you have a leak free tank. I have that result, and in addition submerged it in my pool to look for bubbles and there were none. On to the next step. Thanks.
Dick Seiders

Dick - -

Try the soap mix. You might be surprised. Will wash off easily. A tiny leak may not be seen in a few hours of sitting. Will not hurt anything, and you might be surprised.

New welded tank was installed last week. Have flown about 6 hrs since and there are no leaks, no fumes, no problems thus far. The Moller gage is a good fuel indicator once you have calibrated the gage by noting levels and needle position. It worked fine on a trip to FL. this past weekend. Also learned that the new vent is a positive FULL indicator when a little fuel drips out of the vent line. (wasteful maybe but a very accurate indication of full tank). I will attempt to get some pics posted if anyone is interested, and will be happy to answer any questions about the tank anyone cares to post, My initial re-action to the welded tank vs the original is roughly 10 times more positive at the very least.

Dick Seiders

Nice. I would love to see pictures. Thanks

dick seiders said:

New welded tank was installed last week. Have flown about 6 hrs since and there are no leaks, no fumes, no problems thus far. The Moller gage is a good fuel indicator once you have calibrated the gage by noting levels and needle position. It worked fine on a trip to FL. this past weekend. Also learned that the new vent is a positive FULL indicator when a little fuel drips out of the vent line. (wasteful maybe but a very accurate indication of full tank). I will attempt to get some pics posted if anyone is interested, and will be happy to answer any questions about the tank anyone cares to post, My initial re-action to the welded tank vs the original is roughly 10 times more positive at the very least.

Dick Seiders

Click to expand...

Dick, any possibility the tank will be sold commercially?
If so, any other possibility the capacity could be slightly increased, like maybe 5-7 gallons?

Ok here is a few questions that I'm sure guys are thinking of asking.

How much would it cost per welded tank?

How much does it weigh compared to Vans Tank?

Do you still have the access hole in the front with the resistance fuel tank indicator?

Does it still have the baffles in it and are they welded in?

Is the threaded hardware on the bottom of the tank now welded on?

And yes pics of everything would be great. Thanks

Lots of questions and it's a bit early, but will answer as best I can at this point.

1. Commercially? Don't know, but maybe.

2. Cost? To be determined.

3. 11 lbs more than riveted tank. The 5052 is .090" for added strength.

4. The sending unit is placed on the top of tank towards the rear. In this way the sending unit could be repaired/replaced w/o removing tank.

5. Yes to the baffles, the reinforcing doublers, and the return line brackets as well.

6. Coupling is welded on bottom for the feed fitting. A threaded block is welded inside the bottom to lock the return line fitting in place.

7. You didn't ask, but the flange for the fill line, and a coupling for the alum. tubing to vent line is also welded.

8. I am still working on sending photos.

note: tank sealant is required only on the sending unit and the T1209 door. the Moller gage, and the two fittings on the bottom.

Dick

Photos of Dicks Welded Tank

The photos show the details well. Please direct any questions to Dick:

Any updates?

Any updates as to cost and/or will these be available for purchase? Just finishing a new tank build using parts from the old "seeping" tank. Going new got rid of the sight window as well. Not a fan of sealant and rivets . ZENITH offers welded tanks..... Will VANS ever consider this? No idea.

Video shows a welded tank from Zenith.

http://www.eaavideo.org/video.aspx?v=3617603499001

Wrong thread...

I welded mine from 0.05 to keep it light.
Works well for 500 hours but it does not look so well as yours.
How did you prevent the heat buckling ? It looks perfectly straight

Usually tanks that size have beads rolled in the for rigidity and flange welds on the ends which give more rigidity. You can use geometry for strength rather than thicker material. This helps with the heat disortion. In WWII it was common to braze the fittings on to avoid distortion as the brazing temps are much lower than the melting point of the patent metal.

.09" is much heavier material than most fuel tanks in airplanes, but 5052 is a standard material for tanks because of its corrosion resistance and because it welds readily. This could be made from 0.050" material quite easily.

Kent White has written numerous articles on welded tank construction. A good one was in Home Shop Machinist a coule of years ago. He gas welds everything....old school.