Inboard diagonal question

[jrbirdman47]

Building the XL: Why is the inboard diagonal bolted to the rear spar instead of being glued to it like the other three? This requires a compound angle cut on the forward end and causes the diagonal to protrude into the space where a fuel tank would go. (The LE would be even worse because the wing attach fittings were at the top of the spar unlike the XL, which are located a couple of inches lower)

Any insight here is appreciated, as it seems to me that not using the metal bracket is lighter and not having to determine and cut a compound angle on the forward end would be nice.

Thanks!  Rick

[flymorrow]

Ribs and spars built,close to statring my wings was thinking the same thing, anyone?

[scottiniowa]

Building the XL: Why is the inboard diagonal bolted to the rear spar instead of being glued to it like the other three? This requires a compound angle cut on the forward end and causes the diagonal to protrude into the space where a fuel tank would go. (The LE would be even worse because the wing attach fittings were at the top of the spar unlike the XL, which are located a couple of inches lower)

Any insight here is appreciated, as it seems to me that not using the metal bracket is lighter and not having to determine and cut a compound angle on the forward end would be nice.

Thanks!  Rick

Rick, you almost answered your question.  Please observe this overhead view and picture the diagonal if it were exactly like the other three.  THEN- You would have LESS room for the tank.  Presently it does not protrude into the space for the fuel tank, but gives you MORE space as shown on your plans.

The tank you see was just an example  and is 4.5 gal.  You can see you could easily get 5 gal without needing to worry about the diagonal.   This is based on the fuel tank top being the same profile as the top of the wing, like Franks excellent example.

Hope this helps.
Scott
ps... I am not saying this is why it was done, just showing what it gives you if you do it. 
By the way, to cut the second cut or "compound angle cut" as you called it may take 30 seconds more. Often this can be sanded into shape for the perfect fit.  I would take the time to install all the little extra "tight" fill blocks as they tie the wing together very nicely.

[jrbirdman47]

Thanks Scott! Maybe I just think bout this stuff too much, but maybe you can help me with this as well: The metal bracket used to secure the diagonal to the rear spar looks to be bolted on flat, or horizontal, reference the spar, while the wood diagonal angles downward. Would this not place stress on the bracket and lead to cracking? Maybe the bracket is "twisted" so that it is pointed directly at the spot where the forward end is glued? Thanks again!

[scottiniowa]

Thanks Scott! Maybe I just think bout this stuff too much, but maybe you can help me with this as well: The metal bracket used to secure the diagonal to the rear spar looks to be bolted on flat, or horizontal, reference the spar, while the wood diagonal angles downward. Would this not place stress on the bracket and lead to cracking? Maybe the bracket is "twisted" so that it is pointed directly at the spot where the forward end is glued? Thanks again!

By actually cutting the steel square tube, to get the angle you need (want)  then rewelding, this works nicely. I think maybe you think this wood is making a larger angle change than it is...
I don't like to use "degrees of angle" for measurements on any plans-   but in this case- .2 to .3 angle or even 1-2 degrees- twist is so little that it would be hard to measure on something this short.

When you have this in place, you won't be having tension of any type -pushing/pulling or twisting.   
Always good to think things over though. 

We could go into all the strength calculations of the wood dia. vs the metal bracket, but in short the wood diagonal won't (or shouldn't) ever be able to exert enough pressure/stress (repeatedly) to cause stress cracking in your welded up bracket.
Best of success.

[jrbirdman47]

Wow! That is a very shallow angle. Thanks for the info! It's hard to "see" his in my head before putting it all together so you've really relieved my worries. OK, back to the shop!