Fiber glass and carbon fiber?

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AfterBurners

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I wanted to ask a few questions about the different type of materials that used to build rockets. So when I make my next pruchase I can deicde what would best fit my needs. I guess to start off saying that I'm "assuming" that having a carbon fiber or fiberglass rocket will withstand more abuse that your most commonly known paper tube rockets and phenolic tube rockets?

Why do most people on here fiberglass paper tube rockets? I'm guessing it's because of strength and to reinforce it?

Wouldn't it just be easier to purchase a kit made of fiberglass or just purchase parts and scratch build a rocket?

Is it also popular to fiberglass phenolic tube rockets or just portions of the rocket where it tends to have more stress like the fin can area?

When you build or buy a carbon fiber rocket is this done mainly to withstand flight of Mach 1 or greater?

Does the carbon fiber help displace the heat better caused by the friction from the rocket traveling so fast based on the frontal diameter; the larger it is the more drag?

This must explain why most carbon fiber rockets are that of minium diameter?

What are some of the best practiced safety precautions when working with fiberglass?

What are the best methods for finishing and painting fiberglass rockets?

I know you use a coarser sand paper when sanding to bond the epoxy, what about sanding to prep for primer and paint?
 
Wow. quite a list. I'll take a shot, giving reasons why *I* use fiberglass. I don't use carbon fiber much.

Why do most people on here fiberglass paper tube rockets? I'm guessing it's because of strength and to reinforce it?
Yes. In some cases for flight strength for larger motors, but partly to protect from wear and dings in the car and hitting solid objects on the ground, even when recovery is nominal.

Wouldn't it just be easier to purchase a kit made of fiberglass or just purchase parts and scratch build a rocket?
Fiberglass kits are HEAVY. Glassing cardboard or phenolic makes for a bunch lighter rockets, but still very tough. Also I like the build process.

Is it also popular to fiberglass phenolic tube rockets or just portions of the rocket where it tends to have more stress like the fin can area?
I like to glass flexible-phenolic tubes the most. Its a great base for glass, and a good compromise on weight. On larger rockets, I'll also tip-tip the fins with glass across the body tube.

When you build or buy a carbon fiber rocket is this done mainly to withstand flight of Mach 1 or greater?
Not necessary for mach 1. I've flown LOC cardboard to > mach 1.

Does the carbon fiber help displace the heat better caused by the friction from the rocket traveling so fast based on the frontal diameter; the larger it is the more drag?

This must explain why most carbon fiber rockets are that of minium diameter?
Carbon fiber is all about weight. Its light for the strength you get. When you are trying to max out altitude, min diameter and carbon are your friends.

What are some of the best practiced safety precautions when working with fiberglass?
Gloves, safety glasses, dust mask. Skin covering for sanding as well.

What are the best methods for finishing and painting fiberglass rockets?
Same as others: sand-prime-repeat....paint-wetsand-repeat. A bonus is you can drop the tube in a bucket of water for wet sanding.

I know you use a coarser sand paper when sanding to bond the epoxy, what about sanding to prep for primer and paint?
I use 220 grit before primer, then you can use 220 after primer until you get close. I've used grits as fine as 400, but that is for wetsanding of color coats.
 
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AfterBurners,

In my humble opinion….

Fiberglass is an affordable material of durability. But there are differences among fiberglass components. Most of what’s offered is filament wound as opposed to convolute cloth wound. If you can find it the convolute stuff is superior to the filamentary material. It is viable in smaller wall thicknesses. It is most tolerant of drilling and machining. Quality inspection is easily achieved by backlighting. There is no risk to unraveling as has happen to me only once.

Carbon is an elite material when DESIGNED to the application. Personally I haven’t weighed a filament wound carbon component against a similar filament wound fiberglass component. My guess is they are within 5% the mass. And please don’t forget the matrix (epoxy) has significant bearing on the thermal performance of that material.

But would you listen to one who knows himself as Feckless?
 
When you build or buy a carbon fiber rocket is this done mainly to withstand flight of Mach 1 or greater?
Depends on a lot of factors. 90% of small MDs don't need a gram of CF to survive. Most of the time It's the weight savings that people are after, but most commercially available are built to the same specs as the fiberglass tubing, so weight savings arn't as great as they could be with custom tubing. The could be much thinner. (One of the reasons all of my CF stuff is homemade)

Does the carbon fiber help displace the heat better caused by the friction from the rocket traveling so fast based on the frontal diameter; the larger it is the more drag?
Ummm... No. Displacing heat isn't what CF is used for at all. In fact, you want to protect the CF from heat if anything.



This must explain why most carbon fiber rockets are that of minium diameter?
It's a waste if it's anything else IMHO.
Unless it's one of those PML ultra light tubes specifically for non-structural applications.

I know you use a coarser sand paper when sanding to bond the epoxy, what about sanding to prep for primer and paint?
For a better composite bond, you don't use coarse sandpaper. Read the epoxy bonding thread sticky in the HPR section.

Alex
 
Wouldn't it just be easier to purchase a kit made of fiberglass or just purchase parts and scratch build a rocket?

One thing that irks me is cardboard designs converted to fiberglass. They're so heavy. I fail to understand why you would take a strong fiberglass tube and cut it up for through-the-wall fins. I've never bought a fiberglass kit (so consider the source), but I would look for a kit that seemed to make good use of the properties of the materials.

Is it also popular to fiberglass phenolic tube rockets or just portions of the rocket where it tends to have more stress like the fin can area?

I have a couple of 3" rockets that are two layers of 6 oz fiberglass over PML phenolic. They've held up for years. I think this is a good approach.

What are some of the best practiced safety precautions when working with fiberglass?

Other than working with epoxy (you know about that, right?), the main issue with fiberglass or carbon is to avoid producing airborne fibers. I prefer to cover any piece I cut with masking tape and then cut it through the tape on a cutting board with an X-acto knife or a "pizza cutter". When I cut larger amounts of carbon, I have my wife follow along with me with the vacuum cleaner wand. I try never to cut with scissors unless the prior options are not possible, and the vacuum is a must when using scissors. I have had the opportunity to cut carbon with sunlight coming into the kitchen. It is interesting how many fibers can float up into the light if you're not careful. Only takes one of them to ruin your day.

Jim
 
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