Good work Phil,

I would only say that 8gs is 8gs -- its a severe loading that your aircraft will NEVER see; so, if something supports all of the weight regardless if it twists a bit, it should be fine. To keep the weight down it doesn't have to be perfect under loading, just doesn't have to fail. Also, I think it's worth investigating the use of lighter-weight glass and carbon unidirectional tape. The carbon is actually a bit heavy in some locations. If someone had an electronic (CAD) model, I'd be willing to do some FE modeling of some ribs etc. to optimize the weight.





Also, I wasn't perfectly understanding your first rib (I didn't realize your flanges were so wide) the calculation I made was based on web only, not the whole rib. That's why I was thinking to optimize the weight, and unidirectional tape combined with very thin glass might, in the end, result in some lower weight ribs as well as in some other areas.




Kenny


--- On Fri, 3/2/12, Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


From: Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Subject: RE: [Carbondragonbuildersandpilots] Composite Rib Construction & Load Testing
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Date: Friday, March 2, 2012, 7:47 PM




Well now, that's the $64 question! The specific gravity of spruce is around 0.38 (24 lbs/cu-ft) and going on the quick calculation I did for the weight of a spruce root rib (and the measured weight of my CF rib) I reckon the CF version should be about equal weight - possibly slightly lighter given that the CF appears to be considerably stronger than the spruce and therefore the structural dimensions can be reduced in places. Ultimately only time will tell! My interest is in building an all-carbon dragon and eliminating wood from the build entirely. If it's lighter, then woo-hoo! If it's heavier, then boo-hoo... but at least it will be considerably stronger and won't warp in the rain!

Phil.

Thanks Rick - I figure on cutting my teeth perfecting my resin infusion technique on the smaller parts before tackling the main wing spars (I'll be doing both spars together to save consumables.) I've constructed a 24-foot long work table from three lengths of 2' x 8' x 3/4" white melamine covered chipboard. The melamine takes a nice wax finish and releases the cured parts very nicely, but I'm a little concerned (after looking at your rather expensive 'show-and-tell' spar!) about getting a perfect, vacuum-proof join where the ends of the sheets join each other. I figure I can probably get a good seal by pumping the joins with epoxy resin using a syringe a couple of times and then covering the joins with a wide, heavy duty packing tape. Needless to say... I'll be doing a thorough vacuum integrity test before I open the resin infusion valve!

Phil.

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From: This email address is being protected from spambots. You need JavaScript enabled to view it. [This email address is being protected from spambots. You need JavaScript enabled to view it.] On Behalf Of Rick Mullins
Sent: 03 March 2012 01:15
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: Re: [Carbondragonbuildersandpilots] Composite Rib Construction & Load Testing




Great write up Phil.


I played around with vacuum infusion when I built my spar. It sure is beautiful when the fabric is ls pulled down into all the corners and it looks exactly how you want it to. In my case though the bag for a 23 foot spar with 16 holes for vacuum and resin lines was very difficult to seal. My first spar I couldn't use because I had a small hole underneath and the vacuum pulled air through the spar while I was waiting for the resin to set. The second attempt worked better but there was a lot of set up time and lots of waste materials. The third time I just did a normal hand layup and was very careful about controlling the resin. I have a friend that has done a lot of composite work tell me that if you are careful applying the resin, vacuum bagging doesn't save that much weight. I was skeptical but in my case the infusion spar weighed 6 pounds 7 ounces, the hand layup was 7 pounds 3 ounces and was much less work and used much less (expensive) resin. I'm certainly no expert, this was my first attempt at it. But if I build another spar I would probably just do the hand layup. For smaller jobs like the ribs though, I can see how it would give you excellent results.

I'm not sure many of us would survive 8g without passing out in a rush of blood to the feet! No, if you're flying at 8g you've already lost the plot!!

I'm more concerned with the instantaneous shock loading that the glider might experience during take-off, landing or clumsy ground handling.

As I am now the proud owner of a 105m roll of non-cosmetic CF cloth (it was cheaper than the 60-odd meters I need if I went for a cosmetic grade CF cloth!) I'll probably use that throughout... for this build. If I'm super enthusiastic (and can find a buyer for my first one(!!) I'll use the lessons learned and try to construct an even lighter one!

My rib experements so far have been trial and error jobs... with a little informed guesswork when it came to reducing the structural dimensions. I do think that the resulting ribs are probably far stronger and a little heavier than they really need to be, so if you find yourself overcome by the need to indulge in a little FEM I'd be delighted to see the results and knock up a couple more test pieces to do a reality check on your numbers!

Phil.

PS - the non-cosmetic CF cloth simply has a thin red tracer running across the 1m wide cloth every 100mm (you can't even see it after curing!) - otherwise it's exactly the same as any other twill cloth.

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From: This email address is being protected from spambots. You need JavaScript enabled to view it. [This email address is being protected from spambots. You need JavaScript enabled to view it.] On Behalf Of Kenny Andersen
Sent: 03 March 2012 02:03
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: RE: [Carbondragonbuildersandpilots] Composite Rib Construction & Load Testing

Good work Phil,

I would only say that 8gs is 8gs -- its a severe loading that your aircraft will NEVER see; so, if something supports all of the weight regardless if it twists a bit, it should be fine. To keep the weight down it doesn't have to be perfect under loading, just doesn't have to fail. Also, I think it's worth investigating the use of lighter-weight glass and carbon unidirectional tape. The carbon is actually a bit heavy in some locations. If someone had an electronic (CAD) model, I'd be willing to do some FE modeling of some ribs etc. to optimize the weight.





Also, I wasn't perfectly understanding your first rib (I didn't realize your flanges were so wide) the calculation I made was based on web only, not the whole rib. That's why I was thinking to optimize the weight, and unidirectional tape combined with very thin glass might, in the end, result in some lower weight ribs as well as in some other areas.




Kenny