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Carbon rod 12 Feb 2017 15:13 #1018


After 18 years beeing busy with other things I find myself building wingribs again. Soon I will start making the flapperon ribs and since I started a lot is changed, materialwise. F.i. carbon rod. does someone have experience in working with this material. Seems far better than laying fibers yourself, more consistent and straighter. Is there a special brand I have to look for, are there specific properties I have to look for?
In using rod in the sparcaps. At the wingroot, the spar is thickened in order to compensate for the boltholes. The lower fibres go around the holes. By using rod, the holes will be drilled through the fibers that are supposed to bring the force in the cap to the fitting. Is that a problem, or does the force spread through the entire block of carbon sort of evenly?

Has anyone experience in operating a CD under EU rules?

Thanx in advance,


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Carbon rod 14 Feb 2017 02:54 #1019

write Phil, he is the CD CF expert. also might check out :


extensive discussion about carbon rods.

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Carbon rod 14 Feb 2017 12:52 #1020

Hi Erik,

I purchased my pultruded carbon rod from Jim Marske in the US - good price and excellent service. You should also buy a copy of his Composite Design Manual if you are going to build a wing using carbon/kevlar/glass fiber and epoxy - it's an essential primer if you're new to this sort of thing. He includes a section on different methods of spar design and fabrication. I used Marske's formulae and method when I created my wing load/stress analysis spreadsheet. You will also discover how to design and fabricate tapered carbon load transfer bars to transfer the spar cap loads from the pultruded carbon rods to the metal wing connection fittings and bolts.

Study both the Design Manual and my spreadsheet to get a better understanding of the loads and stresses in the wing spar and how to calculate the amount of material (rods and twill cloth) needs to be used to carry those loads.

I designed my spar to take 10.5g simply because the materials could do this! All the spars in my wings/tail/rudder/H-stab/elevator are made from two layers of 195gsm twill carbon cloth with the pultruded carbon rods fully encapsulated between the two layers of cloth. Technically only one layer of twill cloth is required to carry the shear loads, but this makes for a very fragile spar web which can be easily damaged during the rest of the wing construction proess. Even with two layers of twill cloth, my spars are lighter than the plywood originals.

Be careful when choosing your carbon cloth - you want a cloth with a 'medium to high' modulous (stiffness). I made a number of test pieces with different grades of CF cloth, all with roughly the same gsm weight (grams per sq-meter) and was amazed at the difference in stiffness. Low modulous cloths (mostly uni or bi-axial) resulted in very bendy (not stiff) shear web and leading edge test sections. You could still use these cloths but you would need to use a 2mm sheet PU foam core between the two layers of cloth to add stiffness. It's simpler (and lighter) to use a higher modulous cloth.

Stiffness in your leading edge cloth is especially important - you don't want it flexing or deforming when you're flying at high speed!

Feel free to pick my brains - I'll give you all the help I can.

All the best,


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Last edit: by Phil Lardner.

Carbon rod 15 Feb 2017 21:08 #1021

Thank you very much, Dan and Phil!!

This is a lot of info at once and after a quick glance, your calculations are impressive Phil!, but I am sure I need some assistance understanding it all. In that your last sentence is very comforting. In essence, I am quite unadventurous. On the other hand the idea just gluing a rods in a slit in the wood instead of hassling with spools of carbon and messing with wet epoxy as per instructions is very tempting.

I found your videos on YoyTube Phil! I think watched all of them. Very impressive, but I think I am more a wood man than a carbon man, with all the protective clothing and all. I like the hotwire apparatus that is balanced in a mysterious way.

We keep in touch and for the next days there is a lot of study to do. The project starts to get alive in my head again.

Thanks again,


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Carbon rod 15 Feb 2017 23:35 #1022

I am not dealing with this with my plane but I did read the manual. The amount of CF tow is called out I seem to remember. Maybe you can get some help from Marske as to equivalent amount of rods and thereby keep it simple if you just want to sub rods for the tow called out. He is easy to talk to. That information might be in his manual, I do not know.... maybe Phil can tell you.

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