The First Booster

My hobby is high power rocketry, I first started in the hobby a few years ago before I got married. Marriage and kids put the hobby on hold until I was able to afford it again, for it is an expensive hobby for the types of rockets I would like to fly.

Last year, my beautiful wife, gifted me with a membership in the local rocketry club here in Kansas, KloudBusters. A link to their website I will post at the end of this blog. For the last few months I have been getting my rocket fleet back into flying condition. I had bought a PML Endeavour over ten years ago, being my first rocket I made many mistakes and never flew the rocket. Over the winter, fighting colder than normal temperatures here in Kansas, I was able to refurbish the rocket and build it better. The Endeavour I plan to fly later this year in a level 2 certification attempt.

Now my current project is the Russian KH-31 Krypton/Sunburn missile. Here is the pic of the original: The above missile is 15 feet in length, while possible to build it in full size, I have decided to approxiamate a 1/2 scale model of this missile. Why you ask? Good question, I like the design, and I like the challenge it presents. The real life missile works on a ramjet engine, here is a link that describes what a ramjet is:

Since I can not build a ramjet, a little beyond my mechanical and technical skills, I will facismilate the ramjet with a standard F or G class motor in the booster stage. Yes, this missile will have 5 motors, 4 29mm motors and 1 38 or 54mm motor as a main that airstarts after the 4 29mm motors burn out. The following is the process I used to build the first booster.

Here is the pic of the final product:

I know that I am showing you the chicken before the egg here, I decided to blog the entirety of the project after I completed this. Go figure. The booster was relatively simple to complete and was only maybe 5 hours of work, but only because the G10 fiberglass fins were a little tougher to cut then I expected. Knowing what I know now I can probably push one of these out in half the time, but would rather take my time and do it right.

I first started with a trip to the local rocketry store, the Science Education Center, here in Wichita KS is the main source of everything rocketry that I will buy. I don't like doing business like this online because I have a complex...I want it now, not 4 to 6 business days later! Plus, I hate to pay shipping.

Another thing I do, I don't measure everything I do! I eyeball a lot of what I do and it typically comes out right. I know the axiom, "measure twice, cut once," and when it truly matters the meausring tape is there, the t-square is out, along with a level. My fins are always measured out, but tend to come out different due to the way they were individually cut and sanded. My fins are probably never going to be the same up close, but they will work and they have flown successfully.

Now, back to the 1st booster of the Sunburn which is why some, all, or none of you are here to read about. The most obvious start to the project is to build the motor mount that goes in to the business end of the rocket. I took an old G rocket that I used from last rocket and measured it out so that I could make the mount to the approxiamate size, which was about 5.5 inches. I took the centering ring that I also bought at the SEC (Science Education Center) and sanded the outer edges so that it would fit down the 38mm tube. Now I looked and saw that the shock cord was right there and noticed I would more than likely not be able to attach it like I normally to the motor mount, usually an eyebolt, this time I would have to notch the inner side of the centering ring. Out comes my trusty Dremel with a nice round sanding bit. I notched the appropriate size "notch" inside the centerint ring. Okay with that done I put the rest inside the tube and dry fitted the motor mount. Oops...cracked a centering ring, the pressure from the shock cord and not enough wood cracked the centering ring. Oh well, nothing plenty of epoxy could not cure. Mixing up some epoxy I also thought, "how am I going to keep the shape?" On the floor of my shop, which can get quite dirty and catches alot of stuff, I see the smallest flash of light on metal. A hose clamp, and just the right size for what I needed! So, I put the hose clamp around the damaged centering ring, tightened to within a degree of breaking and left there for a few minutes so that the epoxy could cure. Well with that done I proceeded on to the next step, it is actually easier to show you then it would be to describe, so here is the pic.

Now the cut doesn't really mean anything until you see the end of the Sunburn rocket. It took a couple of passes through the scroll saw and a lot of attention making sure that the bottom and top of the tube were cutting at the same time. The result is quite nice after a few swipes of sanding paper. The reason I made this cut first was this, it was easier to line the through the wall fin cuts with this then it would have been the other way.

After this cut was made I brought out my jig that I made to make straight fin slot cuts. Unfortuanately I don't have pictures of this process but will have them at a later date. For now I will go on to the boosters nose cone.

In this pic you are looking straight down in to the mouth of the ramjet. I forget what nosecone it is, but will get the name of it again. You will also notice a bubbly substane around it at the base. This is a two part foam that I use sometimes to secure parts into place. In this instance I used a bit of the foam to secure the nosecone, I also used it to secure the three inches of the shock cord within the motor mount. The foam is light weight but hardens to epoxy like hold, when it dries you have to carve it wih a hobby knife. The next pic shows the opposite end of the nose cone where the top end of the shock cord is attached.

Here is just a standard bulkhead with in coupler sunk in an 1/8th of an inch and doused in epoxy. The eyebolt has a nut on both sides of the bulkhead and is also encased in the epoxy. Between here and the nose cone is nothing more than empty space.

Now comes the hard part, the fins. I have never cut G10 fiberglass before so I just went with it and put it through my scroll saw. Everything was going fine until I notced that my blade had three less teeth right where the G10 was being cut, for a while I think I was using heat to cut through the G10!

I looked around at the local hard ware store, hit most of them, but found no carbide cutting blades. Will have to order them from online, crap...shipping costs. Sigh. Anyways, I grabbed what I could to finish the cuts and got the fins cut. Then the sanding started, then more sanding, and a bit more. Test fit into the fin slots, a bit more sanding needs to be done. Caution: Fiberglass gets hot when you sand it vigorously. Ouch. More sanding. Finally able to get the fins epoxied into position. Masking tape helps here, line up your fin, put tape from one side of the tube to the other over the top of the fin, line it up again. Apply epoxy before or after this step, preferably after, the tape gets in the way and only really holds it in position while the epoxy sets. And then you should have something like this:

At this point I sanded the tube alot, the discoloration you see in the cardboard is where I tried to spread some of the epoxy in the swirls in the tube to see if it would fill them up. Somewhat worked, somewhat didn't, probably won't do it again, epoxy is a bit heavy. Now I only have three more of these to go! Plus the main body, which will not actually be all that difficuly. The most difficult part of this project will be to get the electronics portion to work correctly during flight.

Stay tuned for more on the Sunburn project!