Fiber Glass Fuel Tank

[Vince Carucci]

Your right, it isn't an actual reproduction. The picture is intended to summarize the nature of the problem. There could be an X in every other bay, but if the inboard section has no support, it risks failing. 

It's just my 2 cents and I may be wrong. But I'd feel terrible if I didn't speak out when I should have.

[aeroplain2003]

Seems to me, it  has long been known, it(the wing) will only be as strong as the weakest part(the first bay)and that the loads will never have a chance to transfer to the "X". As someone who works in composites daily, I would acquire some glass tubing and install it into the tank in the needed area to brace the wing as it was intended to be built, but it's your hinnie.
as an aside, 4 longerons ? it's no longer a LE, just sayin.

Kent

[docmatt]

Murray,

That tank looks great.  You might think about attaching it solidly to the spars to make it a structural part.  It might need some additional material to lower the risk of cracking when stressed.  
I am thinking about putting both tanks in my DE in the right wing (first two bays).  It should give better left-right balance when flying solo or with a light passenger.  Does anyone have thoughts on dissadvantages?

[Tom H]

Murray, you said a couple posts up:
"Another change in my XL is to make a four longeron tube fuse rather than the design three tube fuse, with a steel tube X brace in the center section. This might add to the drag/antidrag capability.  Then I put thin nose ribs between each design nose rib to stiffen the D of the nose and that D contributes to the drag/antidrag capability."


I think of the fuselage as a comparatively rigid structure that the wing root is connected to.  I think your 4 longeron structure with X brace will be as rigid as original.  No problem there, but does not help the wing with drag/anti-drag issues.


Adding ribs in the nose will probably increase the drag resistance of the wing spar.  I don't know how much, and if it is adequate, though.


Some here will remember the big fuss of the DE wing as represented in the plans from a few years ago (at least in the plans sets during that time, don't know if they were updated).  The issue was that no compression struts were shown along the root end ribs.  This got debated back and forth as to whether the struts were required, since the spars were attached to the fuselage near that point.  The final answer came, I believe, from the engineer who designed the wing, who said that these struts were absolutely necessary.  I personally did not see the need, but, even though our wing was covered and painted, we cut it open and installed the struts at the root end.


Vince, with his loading diagram, summed it all up.  Is the tank a good structural replacement for the drag strut?  I think it would be prudent to do some further analysis.

[Murray Randall]

I did bite the bullet Tuesday night and went back to the computer and I'm pretty damn glad you guys, Tom, got me concerned enough to do it.  Thank you. Its not all done yet.  But it looks like the upshot, at least on a preliminary basis, will be that I add an additional spar cap to the back side of the rear spar in that first bay where I eliminated the drag strut.  The front spar is loafing but that rear spar works its little heart out.  In the XL also.  I loaded the model with 4G's vertical and 225 lbs drag (225 each wing) simultaneously.  I distributed the vertical loads 2/3 front spar and 1/3 rear spar, the drag loads applied on the front spar.  The model that I made has one wing with my mods and one wing per XL design.  I'll post pics of the model the model later.  For the structural mods I've made I've analyzed to be sure that I have the same or better strength than the design XL. XL's don't break and I don't want to either.  And that is the criteria I want to apply in this first bay no drag concept, mine equal to the XL.  This is a prelim talk here, more BS and fun pics later. Many many thanks guys for your very thoughtful insights.  Many thanks!   

[Murray Randall]

Attached is a pic of the finite element analysis model I used to compare my mod wing with the as designed XL wing.  The model did not include the solid 3/4" filler block shown on XL dwg 37.  If you used that full size filler block the spar stresses in that bay are not significant. I reduced the dim's of the block and will add rear spar cap compensate.  The shop rat wants to go build airplane now.