Bro Charlie,
Well, manufacturing composites is certainly the hard part [for me]. I got a buddy that is bringing a new ultralight to market and he has been doing some RTM for his spar, which also uses the carbon rods (I have to check to see if he is using the same technique for the LE), which is a good way to go, but making all of the tooling, vacuums etc is the only part that is… a bit daunting. It would be REALLY good if there were someone willing to make the carbon spar and Leading edge – that's something I would pay to have done. The reason I asked whether the plans call for the whole wing to be covered is that you could make the outside surface (OML) the bag surface laying up the LE skins on a male tool which would be easier. The outside surface could be smoothed over with micro balloons etc just to get it smooth, but the fabric doesn't weigh much so covering the whole wing could save you some finishing work on the LE. But the best way of course would be to have a female tool which would give you a good outer surface, but the tooling is a bit more difficult… I'm not a manufacturing specialist – I'm quite sure we have some folks in the group who could address that better than me. Anyway, I think the goal would still be to get a bit more wing area so that the wing loading would keep it in the micro-lift realm with a heavier pilot. Think 200 Lb design weight is close enough?

Your comment about the wood/carbon mix is exactly correct. The carbon stiffness (Young's modulus), especially when you use the rods or unidirectional fabric (as opposed to PW (plain weave fabric)) is MUCH higher than the wood, so it loads up instead of the wood. Think of it as two springs that are operating in parallel – a really stiff on and a wimpy one. The wimpy one will pick up a little load, but the bulk of the load will be carried by the stiff one. So, if the spar web was made out of composite fabric laid out, again at 45 degree, it could roll around into a C section with the carbon rods attached to the caps. The flanges (caps) facing aft, and the LE is bonded to the upper and lower caps to close out the `D'. The wood should be kept to a minimum (if needed at all). My buddy has already tested his wing to 6 gs and his spar had no wood and was very light – I need to give his drawing a little closer look. I sized it for the number of rods (I'll have to look again to remember what the allowable we used was, but it was quite a bit less than Marske used. So, if you have good tooling, you can eliminate most if not all of the wood in the spar, but your point about the spar being the tooling is well taken and it's certainly a legitimate approach to the manufacturing.

I haven't completely given up on the LE either. It may be with some thin foam (as someone else mentioned) the skins might be made stiff enough that some of the intermediate ribs could be removed. I'll have to build an FE model of that so I can do some iterating to see what is ultimately the most robust/lightest combo – it's not always so obvious (especially in this really light-weight craft).

Your comment about hang gliding is interesting. I've just been doing some reading on it and was thinking that might be a good way to train for flying the CD!

I haven't started looking at the cockpit…
Kenny out

Go Kenny,

I like what you are doing and appreciate the difficulty. I was a long time (18 yr;550 hr;120 mi xc) hang glider pilot, met Jim M. in 1986? Stood in a cold hanger in Tehachapie SP CA and looked at the prototype Carbon Dragon.

As a manufacturing engineer working with advanced composite rocket motor cases (no wood there) I was greatly disappointed to see a wooden glider. The composite work was also very disappointing from a manufacturing point of view. I am also puzzled as to why the mixed materials.

It is my understanding that if the wood/carbon spar cap is loaded in tension or compression that the carbon will carry 100% of the load because of the modulus mismatch. The wood only serves to stabilize the carbon in compression buckling? Or is the wood just a convenient mold for the carbon fibers Jim was a high school shop teacher and was very comfortable working with wood. I do not think Irv cared what material as long as a homebuilder could work with it, hence the lack of titanium fittings.

I would love to have a real Carbon Dragon that would fly me in mountain soaring conditions 6'2" 206 lbs. I all ready fell out of the sky and really do not want to do it again. I personally think the cockpit is over done and a lot of weight could be taken out of that by going to a Swift like cage with fairings,

Love the approach, keep going. Wood is nice but nut the ultimate material for everything.