Keep It Simple,Stupid. My Level 3 build

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SDramstad

SDramstad

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After years of talking about it, I am finally going for it. (Just in time for Covid to shut things down...) Hoping it will be ready for Mini Midwest Power at the end of May. This build is going to use the KISS principle. Not going for optimum any thing, just a good solid rocket that I can fly with out an extremely high waiver. Basic rocket is a hand rolled 6" carbon fiber airframe with a 48 inch lower section and a 24 inch payload bay, 4 to 1 ogive nose cone and 1/4 inch aircraft grade plywood fins. Overall length is 8 feet. Should weigh in at just over 25 lbs. Flying it on an Aerotech M1500 to around 7000 feet. So first things first. This is the largest tube I have ever rolled and that did present a few problems. Had to modify the way I hold the mandrell or the tube would be bouncing off of my bench. Also rolling 7.5 feet of material didn't allow me to just let the material drape over the side of the work bench. So I rolled the material around my 2.6" mandrel to keep it off of the floor then feeding the carbon fiber under my 6 inch mandrel and up over the top where I wet it out.

build 001.JPG

build 003.JPGbuild 019.JPG

build 008.JPG

Wetting it out and squeegeeing it all out took 2 full hours for the first tube and just over an hour and a half for the second one.

build 020.JPG

Both tubes turned out pretty well. Trimmed both ends a bit then one more thin coat of epoxy and they are ready for the next step. Will do the final polishing when the build is complete.
 
Sounds like an awesome project, I'll be following. What did you use for a mandrel? Some day I'd like to see some video or tutorial on how you make these awesome carbon fiber and fiberglass tubes.
 
I am using a 4 foot length of blue tube coupler tube as a mandrel. Had to wrap it with 3 layers of 5 mil mylar film to shim it up to the right size and to allow me to remove the airframe when it is set up. One thing I am going to change next time is not to use all thread to support the mandrel. That was a real PITA.... Need to use 1.5 inch or bigger steel pipe through the middle to support it next time. Will make it much more stable when you are wetting it out.
 
The biggest I have ever rolled. I usually have trouble matching the airframe diameter to couplers that I buy. This tube ended up perfectly sized. I could not have done better, its a perfect fit.
 
Next was to roll the motor mount tube. I will be using a 75mm motor for my cert but decided to put in a 4 inch motor mount. Will use the motor with a 75 to 98mm adaptor. The tube is 3 layers of 6 oz "E" fiberglass. Makes a nice strong tube. I have used that as an airframe for several of my rockets so am very comfortable with it.

build 022.JPG

Now the tube ends up just a touch small for the centering rings so where the rings go I epoxied in 2 wraps of 1 inch wide fiberglass tape then ground it down to where the centering rings fit well.

build 027.JPG

After that I mounted the middle and top centering rings.

build 028.JPG

Next was to cut out the fins and skin them with carbon fiber. I used 1/4 inch aircraft grade plywood fron Aircraft Spruce.

build 023.JPG

build 024.JPG

Bolted the fins together then finished the edges with a belt sander.

build 025.JPGbuild 026.JPGbuild 022.JPGbuild 027.JPGbuild 028.JPGbuild 023.JPGbuild 024.JPGbuild 025.JPGbuild 026.JPG

Placed a flat board over the top and piled on a bunch of weight to flatten them out.
 
HVArcas said:
Why carbon?

Not critiquing or objecting only curious.
Click to expand...
Carbon has a lot of advantages and a lot of drawbacks too. Its really hard to beat for strength, and stiffness. Its easy to get and prices have been dropping. Its harder then fiberglass to wet out. It blocks radio waves and is conductive. And look out for the splinters!! So thin and sharp that I drove one all the way through the webbing in my hand without even feeling it. I have used it on several rockets lately and it just seem natural to use it for this build. Thinking of using bigger and bigger motors after the cert flight just to see how well it holds up. That said the builds that I am thinking of after this will probably be "E" glass fiberglass minimum diameter rockets going for speed and altitude....
 
Nice. Yes I have been sticking to fiberglass for tubes and carbon for fins.
 
Absolutely smokin build Steve..
I'm a fan of scratch..
This isn't the next level,
it's the final level, lol..
Good for you man..
Really great build..

Teddy
 
Thanks Everyone. Next step was to install the motor mount assembly and fins.
I used a dremel tool with a cutting disk to cut the fin slots.
build 030.JPG

Doing this free hand but they turned out pretty well. I then installed the motor mount tube with the forward and middle centering ring in place using thickened West system epoxy. Will install the rear centering ring after the internal fillets are complete.

build 032.JPG

After the motor mount was installed I made sure the slots came all the way up to the centering ring and trimmed the slots as needed. Then test fit the fins and trimmed the slots until the fins fit correctly.
build 033.JPG

I also did an internal fillet on the forward centering ring. I had installed a small U bolt in the forward centering ring. I intend to attach the harness to an eye bolt in the forward closure of whatever motor I use but will have this mount if needed with motors that wont allow an eye bolt. Also I may use the U bolt to secure the eyebolt in the motor to keep it from accidentally unscrewing.

build 034.JPG


Now why is there 2 U bolts? Actually there is only 1. The larger one is actually a reflection of the first on the internal side of the airframe. Shiny!!


Next was to attach the fins to the motor mount tube using West epoxy. Thickened the epoxy with powdered fiberglass, double buttered the edges then installed the fins. I did 2 fins at a time and used clamps and a piece of 1/4 in plywood to keep them aligned. It takes hours for the epoxy to set up so waited until the next day to do the other pair.

build 036.JPG

build 037.JPGbuild 040.JPG

And everything lined up! Was quite pleased with how they turned out.
 
Last edited:
Next was internal and external fillets. I used West systems epoxy with a little bit of filler in it to keep it from being too runny. I did want it to flow into the cracks which is why I used it instead of my usual Rocketpoxy. Little tape dams to keep it from running out and a high tech tool to spread it out.

build 046.JPGbuild 047.JPG

While waiting for that to dry I did a set of external fillets. I taped off the area needed with blue painters tap and used a tongue depressor to spread out the Rocketpoxy. I added black pigment to the rocketpoxy while it was mixed. I don't plan on painting this rocket and the fillet looks a lot better black then its normal color.build 043.JPG
Some people say to wait after mixing the rocket poxy before applying it. I dont do that. I want it to flow as much as possible into any cracks there may be between the fin and body tube. Then 15 minutes after it is applied pull up the tape. After 15 minutes it is thick enough not to run. After all of the fillets have set I glued in the aft centering ring with a 98mm motor retainer attached.
build 051.JPG

Once that is set the next thing will be to apply carbon fiber across the trailing edge of the fins, then tip to tip the fins and then covering the leading edge with CF.

build 049.JPG
 
Before finishing the fins I went ahead and cut the payload bay tube to length. Was aiming for 24 inches so I made the rough cut at 26". Its a lot easier to make it shorter then longer. :) Then I needed to square up the tube ends. The fiberglass coupler that I got from Madcow was squared off nicely so I slid it all the way into the airframe and used it as a guide to square up the ends as much as I could freehand. To finish it off I used this.

build 056.JPG

On one end of the coupler I installed the 2 bulkheads (inner and outer) in the other end I installed the inner bulkhead, Inserted a large sheet of 180 grit sandpaper and then a flat piece of plywood. Slide that assy into the airframe. Set it upright on the floor then pushed down and twist the plywood with the sandpaper back and forth. It only took a few minutes of twisting to get a squared off edge.

build 052.JPGbuild 53.JPGbuild 054.JPG


It worked perfectly.


Repeated the process with both ends of the payload tube and then couldnt help but do a quick dry fit.

build 058.JPG

Hey, it looks like a rocket!!
 
You cant see it but the leading and trailing edges were rounded with a router. I think the radius is large enough to wrap with carbon fiber. Will do a 4 inch strip across the trailing edges then do tip to tip then another 4 inch strip across the leading edge. That way there are no exposed layers to catch the airflow. This will be a first for me so we shall see how it goes. Will then sand the sides of the fins flat. If I have to cut into some of the fiber to smooth things out it shouldnt affect the strength of the fins too badly.
 
This is really looking great, Steve. I can't wait to see it in person - better yet, in flight! Thanks for sharing the build.
 
Okay, next step is to apply carbon fiber across the trailing edges of the fins. Plywood fins have been known to de-laminate at high speeds and while not needed for my cert flight I have it in mind to push it pretty hard in the future. So the fins are 1/4 inch aircraft grade plywood. I needed to apply a 4 inch wide strip of carbon fiber material through 2 90 degree turns in the space of 1/4 inch. Carbon fiber material is fairly stiff and if I tried to apply if with an epoxy covered paintbrush it would just keep lifting up every time I went around the corner. Also the threads of carbon tend to come apart around the edges which on a small piece of material is a problem. So this is what I did. First I had to build this.

003.JPG
It is 3 pieces of 1/4 inch plywood that I will use to hold the material in place while it cures.

Take a piece of mylar and lay some peal ply material that is cut an inch or 2 larger then the carbon fiber is. Saturate the peal ply with epoxy.

001.JPG

Lay the carbon fiber on top of the peal ply and wet it out with epoxy.

002.JPG
Now I didnt have a free hand to take pictures of this but lay the mylar/peal ply/carbon across the trailing edge of the fin carbon side down, make sure you are butted up against the air-frame at one end, fold the whole thing over the edge and slide the jig over the top and push it all of the way down. Since the fin is wider then 1/4 inch with the carbon fiber and all over it I had to loosen the screws on the jig just a bit to be able to slide it in place.

004.JPGMake sure everything lines up properly then clamp the jig down tight to keep the carbon flat while it cures.

005.JPG

I waited 6 hours or so for everything to set up then removed the jig, mylar and peal ply.

006.JPG
Trimmed off the excess material and sanded the excess epoxy off and here it is.

008.JPG
I will be doing tip to tip next so am not too concerned about getting every trace of excess epoxy off.
So just repeat for the other 3 fins and we will do the tip to tip next.
 

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