Locating tanks

[Yadama]

Bearhawkers

I am having some trouble locating my tanks filler neck centrally in the hole I have cut in the top skin. It seems as I apply tension to the tank straps the tank wants to move back towards the rear spar. My aim is to have the filler neck central in the hole however I am having some trouble achieving this...

Has anyone else encountered similar, if so any tips or hints greatly appreciated...

Yadama

[marcusofcotton]

I was thinking about this possibility earlier. One thing I learned from a wise gentlemen years ago is to have things "happy" - his example was in knot tying, but I've applied it many other situations. Where does it want to be - is it happy. Your post actually made me think about this more (unfortunately may not help you at this point but may help others).

Thinking before final skinning I may mount the fuel tanks with perhaps freezer paper (can you tell I'm midway through cutting up venison) temporarily between tank and the rubber of mounting straps. Wiggle a bit to find where it is happy, then get all related holes, lines, etc. locations measured.

This principle can be applied in many other areas too to prevent stress issues. Everything and everyone works better and longer if happy and with less stress!

Mark J

[Battson]

Yes, I also found they wanted to move as you tighten the staps. I got lucky and noticed this before I started cutting the holes. Locating them is tricky.

It would be a helpful hint to record in the builder's manual: that the tanks will want to move a few 32's, as they are tightened up.

[John Rheney]

Even though I'm plans building and assembled my tanks, skins and filler necks in a different order to try to avoid this problem, I too had this occur. The tanks just seem to be very sensitive to the strap position and tightening sequence. A solution that worked for me was to use a lever (a 1 x 2 board between the tank and the rear spar)) to encourage (push) the tank to stay in the proper position as I tightened the straps. Seemed to work well as they are all 'Happy' now in their final position.

[Yadama]

Thanks Guys

The geometry of locating these tanks is really sensitive to any changes I have made numerous different length straps trying to make it work. I have now made the top strap on the Aux tank adjustable which seems to be making things somewhat better but i have yet to go for a final fit so Im hoping this will make things work. I will keep you informed.

Any other Bearhawkers with thoughts on how they made theirs "happy"

Yadama

[BTAZ]

I made my tanks without the top filler hole. I then put them in the wing and tightened the straps. With careful measuring, I then drilled a pilot hole through the wing skin and the top of the tank at the same time. Took out the tanks and used a hole saw to enlarge the skin opening as required. Also used a hole saw on the tank. I applied air pressure to the tank prior to drilling to keep most of the chips out while drilling. I basically left the sight gauge ports open and put a blow nozzle against one while the excess pressure was relieved through the other. Then welded the filler flange on and it seemed to all work out

[N3UW]

I was wondering if it would be possible to fit the tank inthe straps after the stiffening strips are fitted but before the top skin is riveted. Could possibly use a template and then transfer to skins.

[Yadama]

After a lot of playing around and making the top strap adjustable (I recommend this approach) it works....

http://www.mykitlog.com/users/display_log.php?user=yadama&project=2419&category=0&log=200205&row=1

Yadama

[marcusofcotton]

Very nice job!

[GeorgH]

This is how I did that. Mount the tanks with the straps. If they move a little... don't care. Make a wooden plug like the one here on the photo. ( it should not fall into the tank! So watch diameter) Use a dry wall screw with a sharp tip and place the screw in the center of that plug. Place the plug into the filler hole. Place the wing skin on top and give it a slight hit with a rubber hammer or push the skin with you hands onto the tip of that screw. It will show up through the skin. There you go! Thats the center of you filler neck hole.

[DesertBearhawk]

GeorgH That is BRILLIANT! I assume you can NOT have your top skin riveted in place for this to work???

[GeorgH]

Right! This has to be done before riveting the top skin!

[Battson]

If you don't have the skin riveted, which you typically wont at this stage if you've followed the BH instructions manual, you can simply put a little pen / graphite / grease / lipstick / whatever on the lip of the filler neck, and lower the skin onto it, in the same way Georg describes. I am pretty sure those instructions are in the manual.

The trick is, because the neck stands proud above the wing skin when fully assembled, the skin won't lay flat with the tank in the way before the hole is cut. So the indication of the hole's location is always slightly aft of the correct location. I moved my hole-centre 1mm - 2mm or so forward, to allow for that.