Ok, her goes todays work. I will post pics and try to explain. I started out building a section to give people a idea of what I had in mind. This is the shell of the root area that will go into the fuselage. It is 1/8 med balsa shear webbs 4 1/4" tall and 1/4x1/4 med balsa supports for the 1/4x1/4 carbon fiber trusses.

This is the carbon trusses in place. The trusses are hollow 1/4" x 1/4" carbon. I glued the balsa supports in with thin ca without the carbon in place. This piece will be sandwiched between two sets of 1/8 shear webbs.

The caps that are on the previous post are 1/8" thick x 1/2" wide carbon fiber. There is a 1/4"x 1/4" spacer on the outside.

This is the other shear webb on top.

Here I mocked up the wing length. I planned on running shear webb full length of the wing on both sides. I also planned on running the carbon trusses all the way to the tip. I have figured nine ribs for seven open bays in the wing plus the 14" straight (no taper)spar to feed into the fusalage and motor box. I had planned on wrapping the spar at least 1/2 way with something (glass cloth, tow, or grafite?)I hope someone will chime in. Now here is my questions and problems. The carbon 1/8"x1/2" spars are 76 1/2"long they weigh .026 lbs each. Do I need two spars that thick? A spar 1/16" thick would cut the weight in half. The two together equals .52 lbs. it looks like overkill to me but remember I am no engineer. (help please!) I figured all the lenghths of the 1/4"x 1/4" carbon trusses and they will weigh .26 lbs for each wing. I figured the weight of the shear webb full lenght on both sides for a total of .40 lbs. last but not least I figured the 1/4" x 1/4"balsa truss supports at .12 lbs per wing. That makes the total without glue and something wrapped around it to 1.302 lbs per wing. I know I have some options (1/16 spars, I could stop the 1/4 x 1/4 carbon trusses part way out on the wing, could I use light balsa for truss supports? The trusses will be totally enclosed in balsa.) I would sure like some guidence here. Remember my other wings are 13.2 lbs complete (for the two)with the 2 1/2" wing tube. Can I finish these wings under 4 lbs? If so that would be 5 of the 10 lbs I am looking for in this airplane.
Please don,t be afraid to post your opinions here I am drawing my conclusions from others expertise.
Mike

Mike I do have a question.
I see you installed some carbon on the side of the spar structure, I'm not sure, but I think you will not get much help from the carbon in this area, as the carbon will work better if laminated on the top side and bottom side, to work in tension. Don't forget, this is just an opinion...

Roger

I called DA today and ask about a 2 1/2' carbon spar and was told it could take six months I did not call back to see what there supplier actually said. I will call them back tommorow.
Mike

Mike,
You mention a full lenght spar and you also mention a tube.

Are you doing a full length spar as you have shown here or is this with the tube??

I'm finding interesting in this type of spar, since I will want to go this way for another project, a large war plane.

Roger

Roger,
I am not understanding your post please explain you wont hurt my feelings.
Basically the spar is flat on its side in the photos. It will be stood up to run vertical in the wing. Or are you saying my 1/2 X 1/8 should be stood up? not laid flat? It is definatly stronger standing up but I thought the trusses once all was glued together would make like a bridge support. It is not to late to change anything this is a mockup to get others opinions.
Thanks for looking and help me understand.
Mike

Originally Posted by mike chandley

Roger,
I am not understanding your post please explain you wont hurt my feelings.
Basically the spar is flat on its side in the photos. It will be stood up to run vertical in the wing. Or are you saying my 1/2 X 1/8 should be stood up? not laid flat? It is definatly stronger standing up but I thought the trusses once all was glued together would make like a bridge support. It is not to late to change anything this is a mockup to get others opinions.
Thanks for looking and help me understand.
Mike

No, your bridge structure looks good to me, I was only asking about the carbon you have on the side of it instead of on top.

Roger

Roger,
This is designed to replace a tube. the first 14" of the root will be straight not tapered so they will slide straight into the fuselage and motor box. The two spars will cross inside the fuse like paffys I just added my thinking to the wing mounting and made the root straight. I feel like the carbon trusses will strengthen the spar and all the balsa in there will help hold everything in place and give alot of glue surface area. Where the fusalage meets the root rib the spar will taper from 4 3/8 down to 1 3/4" at the tip of the wing.
Mike

Here is what I meant, I just drew up a quick sketch with solid works

The one with the carbonon top is what I meant rather then the one on the side

Roger

Different angles.

Ahhhhh, I do see the carbon part on top , I think , if so then that is what I meant , cool stuff..

I see your point. Yes yours looks better, when I ask if the 1/8 X 1/2 should be standing up on its side that is the one I meant. When I saw paffys spar I thought it was laying flat like mine. with the shear webb running vertical. That spar is a whole lot stiffer standing up like in your photo. I can adjust anything at this time. All I would need to do is stand the spar vertical and buildup to the 1/2 inch thick with balsa. Keep info comming I am listening.
Thanks
Mike