Fiberglass vs. Carbon fiber

[RocketboyG80]

I am looking at the airframe tubing sold at Performance Rocketry and was wondering what the pros/cons of the two kinds of materials are. I can clearly see that the price of the carbon fiber tubing is more than double. Is carbon fiber significantly stronger? I know you can stand on the 29mm fiberglass tubing without it giving way, is it the same with CF? Also, is there a weight difference between the two? Thanks.

 

[daveyfire]

There are lots of different properties of the two materials: carbon is stiffer than glass, carbon is ligher than fiberglass, carbon looks cooler than fiberglass, etc.

Bottom line: carbon fiber offers a lot more strength at a lot less weight. It's very stiff, making it great for rocket stuff where flexibility is bad. But it's expensive, as you have seen. For most purposes, fiberglass will do ya just fine, but for extreme projects carbon is the way to go!

 

[RocketboyG80]

Thanks for that info Daveyfire. I may go with the carbon fiber tubing on a 29mm high speed/altitude rocket I'm working on. This is stupid question, but is CF as smooth as fiberglass?

 

[daveyfire]

A fabric's smoothness depends on the weight of the weave. 2 oz. glass is going to be a lot smoother than 6 oz. glass. Same deal with carbon, lighter weight = smoother surface. It's just a function of the fiber size and the weave tightness.

 

[Juerg]

There is one more difference between carbon and fiberglass:
Carbon fails like (window)glass (shatters to pieces), while fiberglass doesn't. The typical failure mode of glass is "breaking and getting limp, but staying in one piece".
This is not so much of a problem in flight, carbon is very strong, but it gets easily damaged upon landing.
You know Murphy: There is a stone where your rocket is going to land

Also you have to realize that the tube construction (fiber directions, quality of the layup) may have a big impact on overall strength, bigger than the material itself.
I.m.h.o. both materials will be by far stronger than what you need, it's up to your personal taste.

Juerg