1st July 2009, 05:54 AM
Difference between fiberglass and G10?
This is probably a dumb question but I tried looking it up on the internet and couldn't find and answer. Thanks!
1st July 2009, 06:08 AM
G-10 is fiberglass that is sold as a pre-cured sheet rather than cloth. Many use it for fin and centering ring stock for larger and Mach+ high-power birds. There's also a form of it called Waferglass that is used for competition rocket fins.
1st July 2009, 06:27 AM
I found that G-10 is an epoxy/fiberglass laminate that is heat cured under pressure.
1st July 2009, 07:54 AM
Yep, and it's stronger than just about any kind of fiberglass laminate you could make yourself (heavier too though).
NAR #84281 L3
TRA #11233 L3
1st July 2009, 07:30 PM
G10 is simply a specification for a grade of fiberglass laminate composite made as commercial sheets, rods and tubes.
G10 FR4 laminate grades are produced by inserting continuous glass woven fabric impregnated with an epoxy resin binder while forming the sheet under high pressure. This material is used extensively in the electronics industry because its water absorption is extremely minimal and the G10 line of materials is not electrically conductive. The G10 FR4 is most commonly used in PCB (Printed Circuit Boards) applications. G10 exhibits superior mechanical and dimensional stability and doesn't shrink. Temperature ratings of 180 degrees C. In addition to these properties, G10/FR4 has excellent dielectric loss properties, and great electrical strength. The difference between Grades G10 and FR4 is that FR4 is a fire retardant grade of G10. FR4 (also known as Garolite) can be substituted where G10 is specified; G10 can never be substituted for FR4. G10 is also known as Micarta and Garolite and can be used for structural supports, buss bars, mechanical insulation, gears, test fixtures, washers, spacers and tight tolerance machined parts for electromechanical assemblies. http://www.jjorly.com/g10_fr4_sheets_fabricator.htm
Commercial laminates are denser than most of their home made composite equivalents because the commercial processes do a better job of minimizing the epoxy fraction in the laminate which adds weight but not strength to the composite.
Last edited by bobkrech; 1st July 2009 at 07:33 PM.
Reason: additional comment on density
1st July 2009, 08:29 PM
weight difference understood, strength?
Good answer Bob, but it brings me to my question. How much strength is lost by not getting the epoxy ratio as low as possible - or perhaps more accurately, by not getting the glass fibers as close together as possible.
Here's where I'm at. I built a rocket with tip to tip glass and I simply used those rubber spatula things to press the glass down and squeeze out the excess epoxy. It came out eat and clean and it survived Mac 1.5 on a Kosdon L1900 or some such thing. Now I'm building another rocket with tip to tip glass on the fins. I own a nice vacuum pump and I could get the supplies and learn the techniques to vacuum the tip to tip on the new rocket. This would give me the tightest pack on the glass and the best glass to epoxy ratio that a garage shop is capable of. But I kinda just want to build the rocket - I can lay it up by hand and work the epoxy the same way I did the other rocket.
Can you convince me that I need to build a jig and get release film and bag material and bag sealant and etc and etc and learn to vacuum bag? Are we talking 10% more strength or 50% more strength.
I do read the Composite Rockets yahoo group, but I think I know what their answer would be and, if you couldn't tell, I'm looking for an excuse to build the rocket sooner and simpler.
2nd July 2009, 12:52 AM
I wouldn't try to convince you that you have to do anything different than what you currently doing because it's not necessary. Your methods work for how you fly so my recommendation is to just build rockets the way you built the first one and you'll be fine.
Military rockets by nature have to be extremely efficient and the structures have to be very strong but very light because they have a mission to perform that usually end up with a big bang so the majority of the weight is warhead and propellant. A certain minimum warhead weight is required for a given type of mission, and having more propellant gives a greater range, stand-off distance and/or speed which reduces time to target.
In any composite, the strength is derived from the fibers and the epoxy is simply a matrix material that holds the fibers in place. Extra epoxy does not weaken the rocket, it just adds weight and since the ultimate in performance is not an issue, who cares. Hobby rocket aren't weapons. They don't carry warheads and don't require extreme range or speed. The weight of the structure is much less of an issue.
Compared with military rockets, the stresses in hobby rockets are low. Our rockets are unguided and we're not pulling 50 G turns, so the structural airframe loads are much less than in military rockets. Hobby rocket motors in general have lower thrust than most military motors and have lower peak velocities as well.
Truth be told, the composite materials used in the early day of rocketry, fiberboard tubing and plywood, are plenty strong for most rocketry applications. Sonotube, aka paperboard or fiberboard tubing, is strong stuff (it can support the weight of a 20' tall column of wet concrete) and about half the density of fiberglass tubing. Plywood too is half the density of commercial fiberglass.
Many rocket failures are not caused by lack of strength, but lack of stiffness. Airframe buckling and fin flutter are two examples of this. An alternative to fiberglassing an airframe is to use thicker wall fiberboard tubing or doubling the thickness with a full length coupler. This makes the airframe 4 times stiffer. Similarly if you double the thickness of a plywood fin, you double the weight, but it becomes 4 times stiffer and the resonant frequency also doubles so you effectively increase the resistance to flutter by a factor of 8. A 1/4" thick sheet of G10 weighs the same as a 1/2" thick piece of plywood, but is more expensive and harder to work with than plywood. A 1/2" thick of Baltic birch plywood is really stiff and I doubt you could get it to fail in flutter.
The bottom line is there's a ton of ways to build hobby rockets, and the right way is whatever works for you.
2nd July 2009, 07:36 PM
Thank-you, Bob. That's really good advice. I have the day off tomorrow and just might have to do some fiberglassing.
Originally Posted by bobkrech
I do have to take exception to the idea that hobbyists don't fly warheads. After I added lead to "Probable Shred"'s nose to get to optimum weight I would say it had a warhead. It's really important to get launch angles right so that a ballistic recovery only drills a hole in the desert and doesn't get a chance to pierce something more valuable.
2nd July 2009, 10:52 PM
Care should be taken when using vacuum on the fin can. Unlike a flat panel a tube will crush under vacuum as will a foam core of composite fins. a controlled leak is the easiest way to go. Fancy 300$ vacuum pump for a/c work are great, but a vacuum cleaner works just as well. Unless you want to spend 500$ for a vacuum regulator, it is time to go to the rocket building department of home depot.
A controlled leak is the easy way to keep everything under control. While i have all of the good gear to vacuum work, for composites i have found that one to two pounds work great. Those little needle valves for your ice maker water line are good for some pumps and PVC ball vales are great for the shop vac.
A large bore manometer can also serve as a vacuum regulator. Caution here as it must be installed on the vacuum side of the bag and large flows can dry out the fluid.
2nd July 2009, 11:37 PM
True enough, however a velocity of kinetic energy warhead needs to exceed ~10,000 fps to have the same energy equivalent per kg as TNT, however since in the real world you have to encase you HE, the effective number is closer to 5,500-6,500 fps.
Originally Posted by mparker59
It's an interesting field to work in.