Rate1

I have found this company building models upon request. Normaly the mfg mold the fuz of the airplane from glasfiber, but can at request use carbonfiber instead. My question to you guys is approx how much weight can be saved by chosing carbon instead of glafiber on a 71" wingspan Extra 300 (a rough est or percentage or qualified quess)???

drela

Ordinary carbon has a stiffness which is about 3x that of glass. So for the same shell stiffness, the carbon it can be made thinner by a factor of 1 / 3^0.333 = 0.7. But carbon is also 0.8x as dense as glass, so the weight/area of the carbon should be smaller by a factor of 0.7*0.8 = 0.56 .
So for example, if the original glass fuse was made with a total layup weight of 10 oz/yd^2, the structurally equivalent carbon layup should be 0.56*10 = 5.6 oz/yd^2. The weight saving is 44%.

Rate1

Thank you Drela for your answer. Using your figures the way I am think is if carbon is less dens than glass (80%) then one would have to use more material to achive the same density. Further to take into acount that carbon is 3 times stiffer than glass I would have to take this into my calculation as well.

The way I understand your information is; to achive the density of glass using carbon I have to increase the thickness of carbon compered to glass. Thus; 1 unit glass thickness = 1,25 unit carbon thickness (1unit/0,8density=1,25unit). Further, carbon is 3 times stiffer than glass. Hence; 1,25/3= 0,42 unit of carbon in comparison to achive the same strenght as original glassfiber design.

Have I understood your information correct?

Christian, Sweden

Rate1

I just realized that I am comparing appels with oranges...or...wait I lost myself again... In your example you described the weight savings (mass). In my example I was talking about volume... Eh, so if I want to use carbon instead of glassfiber I should follow my example and the result in aspect to weight will follow your example. Is that correct?

I just read your text for the 89th time. The way I should do, if I chose to use carbonfiber instead of glassfiber, is to ask the mfg to use carbon that is 56% thickness of his orginal glassfiber design. Thereby I will achive the same stenght as if the fuz where made of glassfiber, but with a much lower weight by using lighter and stronger carbonfiber material (44% weight saving).

I guess I should also ask, to confirm that I have understood this right, carbonfiber is 3 times stronger than glassfiber when the materials are compered with the same volum. Carbon has 80% density of glassfiber=80% weight of glassfiber.

In addition to this problem there is also the usage of resin when making the fuze, wich should have the same weigt regardless if I go for glassfiber or carbonfiber or...? The way I see it, resin is resin and you apply as much regardless if you are working with glass or carbon?
How much of the finished product weight could be assumed coming from resin?

Finally, is there any advantages using glassfiber instead of carbonfiber beside cost?

I am aware that I am asking loads of questions about this but I found it intresting. This as well as I want to know the benefits if I am going to spend that extra money on a fancy fuze.

Regards,

C.

drela

No. You ask the mfg to use carbon which is 56% of the weight of the glass. Composite cloth is specified by weight, not by thickness.

Carbon is 3x stiffer than glass, not 3x stronger. For a fuselage, shell stiffness is usually what's required, not strength.

Resin weight can add 40-100% to the weight of the cloth, depending on the weave, layup quality, compaction (vacuum bagged or not), etc etc. My numbers simply assume that the resin will add the same % weight for carbon and glass. [/quote]

A carbon fuselage may cause radio reception problems. It doesn't seem to cause much trouble on 72 MHz, and I and many US glider fliers put antennas inside carbon booms, with no reception loss. But carbon does seem to cause significant trouble with 30-35 MHz in Europe. You can always do a ground range check, and put the antenna outside, or in the wing if there are problems.

Rate1

Thank you Drela for a very informative answer. Amazing what a big resource this forum is.

I had the same question on the scrached build forum as well an recived as answer. For simplicity I will move this thread to this thread despite the fact that this topic is regarding composite.

http://www.rcuniverse.com/forum/m_4540368/tm.htm

Regards,

C.