Rocketry Planet

Over the last few years, many people have asked me how I make my carbon fiber rockets. So when I had an opportunity to make a new fin can, I decided to document the process in detail.

The result of the build was the fin can shown below left and the "TooCarbYen Tutorial" presented in this article. Actually, tutorial isn't a particularly accurate name for the build since it implies instruction on the proper way to do something. This article isn't about the best way to build carbon fiber rockets, it's about how I build carbon fiber rockets, presented in enough detail to allow others to execute the process if they so choose.

GALLERY: The product of this article, Jim Jarvis has taken carbon construction to a zen-like art.

The product of this article, Jim Jarvis has taken carbon construction to a zen-like art.

The fin can is the bottom half of the sustainer of my TooCarbYen two-stage rocket. This 4" by 3" two-stager was to fly at BALLS18 on a minimum diameter N4000-to-M1450 combination to perhaps as high as 70,000 feet. The flight did happen, and for about 15 seconds things went exactly as planned.

Then, at 21,000 feet, and at a speed of Mach 2.6, something went wrong. I don't know for sure what happened, but I suspect that I used the wrong nose cone and pushed it a little too hard. The fin section, which is at the heart of the tutorial, survived the shred and the subsequent hard landing. It will fly again at some point, so I stand by that aspect of the construction.

"Naked" carbon fiber rockets aren't for everyone, but if you plan to give it a try, remember to build safely. Carbon fiber can be hazardous, along with many of the other materials we use. And please feel free to ask questions on anything that is not presented clearly.

Project Description
On October 22, 2008, I flew the TooCarbYen two-stager in Wayside, Texas. It was a beautiful flight to about 50,000 feet, except that the sustainer fin can became detached and was lost. So, it is time to build the replacement. This text and photo tutorial will document the rebuild in detail, including the fabrication of the airframe tube and the fin section.

The original fin can is shown in the next two photos. It was designed to hold the AMW 75-6000 motor case, which allowed the use of the M1350 motor for the sustainer. The airframe was rolled from 5 wraps of 5.9-oz carbon fiber. The core of the fins was G-10 fiberglass from PML (a slightly thicker versions of their Nimbus fins), and they were covered with 5 layers of carbon on each side. After attachment, the fins were covered with 2 layers of tip-to-tip carbon. The zipperless coupler was made from Performance Rocketry carbon coupler tubing and contained several fiberglass bulkhead rings for strength.

The original TooCarbYen sustainer fin can (sized around the AMW 75-6000 case).

The original (with Cotronics epoxy applied to the fin edges).

The new fin can will be longer, and will be designed around the AMW 75-7600 motor case. This adds about 10" to the booster length and makes the entire rocket about 16' long. In all other respects, the design and construction will be the same.

Since the intended use of the fin can is as a two-stage sustainer, there are some things that are not quite standard. Mainly, the motor is used as the interstage coupler and hangs out of the back of the rocket by about 4". If 3" of the zipperless coupler tube is glued inside the top of the airframe, and if the 7600 case is about 41" long, the total tube length needs to be 41-4+3=40". I will plan to make a 42" tube and trim it to length.

Order Supplies
The first step is to order supplies. Here is my list:

Mandrel - For my mandrel, I am going to use PML coupler tubing. Unfortunately, PML does not sell 3" coupler tubing in sections longer than 36" — and I need to make a 42" tube. Therefore, I will request a longer section from them or I will splice two sections of coupler tubing together. Detail: PML tends to not sand their longer coupler tube sections. However, they do sand the short sections that they sell. Since the sections need to be the same diameter, I will get two 36" sections to splice together rather than a 36" section and a shorter section. When I construct the mandrel, I will foam-in a length of conduit tube to act as an axle (see the next photo for an example). So, I'll get some 2-part foam from PML.

Filling the mandrel with foam to lock the “axle” in place.

Mylar - I use 0.005" Mylar (PET film) from McMaster Carr. As it happens, I have a piece of this I can use for the fin can. The idea will be to butt-seam a 42" piece of this around the phenolic mandrel.

Carbon - I use 5.9-oz, 2x2 twill from Applied Vehicle Technology (AVT). A 5-wrap, 3" tube can be made using this 50" wide material. Therefore, I need a little over a yard for the airframe, about a yard for the fin lamination and about a yard for the tip-to-tip pieces. So, a little over 3 running yards total. Since I have some scrap pieces, I'll order three yards (at about $32 a yard). I will also order peel ply from AVT. I'll need a piece of peel ply for the airframe and 3 pieces for the tip-to-tip sections. A few yards will be plenty. I use just the plain peel ply, but the Teflon coated material might work too. I'm also going to order an extra can of the TR-104 high-temperature wax from AVT. This is used to wax the mandrel and the Mylar.

Laminating epoxy - I use Aeropoxy for laminating tubes and also for laminating the fin carbon and tip-to-tip carbon. I use the 2032 resin and the 3665 SLOW hardener. I feel that the 3665 hardener is essential for providing the working time needed to make multiple-wrap tubes. It takes an oven to get this to set up. I have some leftover Aeropoxy, but I'll order another quart kit from AVT. I'll use some 3665 hardener too for making the fins.

High-temperature epoxy - I use Cotronics 4525 high-temperature epoxy for the fin attachment. I also use it to protect the leading edges of the fins and also other places where structure epoxy is needed (such as attaching the zipperless coupler). I am going to order of pint of it from Cotronics (this glue is a little expensive, so a group order is a good idea). I do not recommend using JB Weld.

Epoxy filler - An epoxy filler is used to form the fin fillets prior to the tip-to-tip carbon. I have used Superfil and Aeropoxy Light, and both work. As it turns out, I have enough Aeropoxy Light for this project (otherwise, I would order it from AVT).

Epoxy additives - I use three epoxy additives for this project. One is milled glass, which can be ordered from a number of places. This will be used with the Cotronics for the fin fillets and the fin leading edges. I also use the West Systems 404 high density adhesive filler and the West Systems graphite powder. Check with your local boat supply store for those. These are not essential, but I recommend them.

Everything else that is needed can be bought locally. This includes items such as chip brushes, foam rollers, parchment paper, blue tape, mixing containers, drop cloths, etc. It is rather essential to have a scale when working with the above epoxies, and the Cotronics in particular. The scale should weigh to the tenths of a gram.

The construction steps for making this rocket will include:

• Making the fins;
• Constructing the mandrel
• Making the airframe;
• Attaching the fins;
• Doing the tip-to-tip lamination; and
• Final finishing steps.