38MD Carbon Sleeved Paper Build

dwightr · Jul 6, 2019

I've been flying and building for a while now but I've never done a build thread. I decided it was time to share what I'm working on and get some outside the box comments and suggestions. I did my L1 certification with an Apogee Zephyr on an Aerotech SU H135. I've since modified it for dual deployment and I plan to use it for an L2 attempt this fall when the high power season resumes in Eastern North Carolina. Right now I'm just enjoying low power flying in local fields with my kids.
I love building, probably more than flying, so I have decided it's time to try something a little more advanced both in terms of building skills and performance.
I'm planning to build a 38 mm minimum diameter rocket with carbon fiber sleeve over LOC paper tube, fiberglass nosecone, G10 fins with CF tip to tip. My design choices were influenced by (1) wanting to gain some experience with carbon fiber without breaking the bank (2) high performance for winter flying at Bayboro on 38mm 6 grain motor (3) light enough for waiver free summer flying with a 29mm adapter and a G80 motor.
I started to accumulate some of the building supplies and ordered 38mm LOC tube, 29mm tube and a fiberglass nosecone from Ken at Performance Hobbies.
My build plan is reversed from the way I've always done things. I'm planning to build the nose cone first. I'm installing 1000lb Kevlar for recovery and then a piece of 29mm tube inside the nosecone to house a GPS tracker, probably an Eggtimer. Next I'm going to build the avionics bay to house a RRC2+ altimeter. Then I'm going to epoxy laminate the carbon fiber sleeve on a full length piece of LOC body tube. Once these parts are fabricated I'll have accurate weights to put into Open Rocket to adjust fin size and parachute sizes. Then I'll get the chutes and protectors, pack them and determine the minimum lengths for the upper and lower body tubes. Once body tube length is finalized, back to open rocket to finalize fin design, a clipped delta shape made from 1/16" G10, based on my best estimates on the weight of fillets and tip to tip.
I'm planning on sizing the fins for 2.5 calibers of margin throughout the flight envelope.
Early simulations look like about M.55 and 3000' on an Aerotech SU G80.
Eventually working up to about M1.7 and 11,000' on a CTI J330.
Looking forward to everyone's thoughts and concerns.

Rail Dawg · Jul 7, 2019

dwightr said:
I've been flying and building for a while now but I've never done a build thread. I decided it was time to share what I'm working on and get some outside the box comments and suggestions. I did my L1 certification with an Apogee Zephyr on an Aerotech SU H135. I've since modified it for dual deployment and I plan to use it for an L2 attempt this fall when the high power season resumes in Eastern North Carolina. Right now I'm just enjoying low power flying in local fields with my kids.
I love building, probably more than flying, so I have decided it's time to try something a little more advanced both in terms of building skills and performance.
I'm planning to build a 38 mm minimum diameter rocket with carbon fiber sleeve over LOC paper tube, fiberglass nosecone, G10 fins with CF tip to tip. My design choices were influenced by (1) wanting to gain some experience with carbon fiber without breaking the bank (2) high performance for winter flying at Bayboro on 38mm 6 grain motor (3) light enough for waiver free summer flying with a 29mm adapter and a G80 motor.
I started to accumulate some of the building supplies and ordered 38mm LOC tube, 29mm tube and a fiberglass nosecone from Ken at Performance Hobbies.
My build plan is reversed from the way I've always done things. I'm planning to build the nose cone first. I'm installing 1000lb Kevlar for recovery and then a piece of 29mm tube inside the nosecone to house a GPS tracker, probably an Eggtimer. Next I'm going to build the avionics bay to house a RRC2+ altimeter. Then I'm going to epoxy laminate the carbon fiber sleeve on a full length piece of LOC body tube. Once these parts are fabricated I'll have accurate weights to put into Open Rocket to adjust fin size and parachute sizes. Then I'll get the chutes and protectors, pack them and determine the minimum lengths for the upper and lower body tubes. Once body tube length is finalized, back to open rocket to finalize fin design, a clipped delta shape made from 1/16" G10, based on my best estimates on the weight of fillets and tip to tip.
I'm planning on sizing the fins for 2.5 calibers of margin throughout the flight envelope.
Early simulations look like about M.55 and 3000' on an Aerotech SU G80.
Eventually working up to about M1.7 and 11,000' on a CTI J330.
Looking forward to everyone's thoughts and concerns.

Good luck with your project! It’s always great to track someone’s progress.

Chuck C.

dwightr · Jul 7, 2019

Thanks Chuck, I've been following your "R" build with envy.

dwightr · Jul 7, 2019

I've been working on a rough draft in Open Rocket.
Weights are just wild guesses.

cwbullet · Jul 7, 2019

This fall I am going to do a how to to make your own nose cones and tubing. I just need to finish my work shop.

dwightr · Jul 10, 2019

I've started assembling my nose cone tracker bay. I'm using a 5.5 to 1 VonKarmen Fiberglass nosecone from Performance Hobbies.

I started by epoxying a 24" loop of 1000 Lb Kevlar into the tip of the nosecone to use as an anchor point for the recovery harness.

Next I glued a 4 .25" piece of 29mm tube inside the cone with JB Weld.

Finally I made a couple of bulkheads from 3/32" plywood. One is sized to fit inside the tube and one is sized to match the OD of the tube.
Short pieces of 6-32 allthread were glued inside the tube with JB Weld, the two bulkheads were fastened together with CA, drilled to match
the allthread and finally installed with hex nuts. The center hole in the bulkhead was for holding them in the lathe, it will be plugged later.

Theory · Jul 12, 2019

cool deal and I will surly be following this one.

I have a fair amount of experience with composites, but have yet to apply much of it to rocketry. like you I anticipate that my first venture will be at a small scale as to learn at a reduced cost.

dwightr · Jul 20, 2019

I carbon fiber wrapped a piece of LOC paper tubing today. I used a some carbon fiber sleeve from Ebay. Slid the sleeve on the tube. Brushed on a light coat of 30 minute epoxy to hold it in place, then went back over it till the fiber completely wet out. Covered it with peel ply till the epoxy was to leather stage. Removed peel ply and was mostly pleased with the results, some spots are a little resin starved and a few air bubbles, but not bad for my first time. A bit of filler and a few hours of sanding should make it usable if not pretty.

manixFan · Jul 20, 2019

One thing to keep in mind with carbon fiber is you don't want to sand into the fibers themselves, mostly to preserve strength. It's common to cover carbon fiber with a lightweight fiberglass 'sanding veil' that is mostly sacrificial for sanding and finishing. In your case I don't think you'll have to worry about strength since you have a LOC tube under the CF. Make sure you scuff up the area where you are going to bond the fins to get a good mechanical bond, even if you are doing tip-to-tip.

Good choice on the 5:1 VK nosecone. I'm using that for a 29mm build and the extra length makes is a lot easier to fit a tracker inside of it. Yours looks very robust.

Tony

dwightr · Jul 23, 2019

I rough cut my tubes to length, then chucked them in a lathe and made a skim cut on the OD. Just cutting excess epoxy and touching the carbon fiber in a few high spots. That eliminates a lot of sanding. I sprayed on a light coat of sandable primer, then sanded it off. That makes it easy to see the spots that need filling. I filled the low spots with spot putty, let it dry, chucked up again and sanded it smooth. Cut the ends to final length with a band saw and sanded to square everything up. l didn't get a picture of the sanding but I'm posting a picture of my sanding jig squaring a piece of BlueTube.

I've made a disc that I can screw on one end of a bench grinder and then stick on a piece of adhesive backed sandpaper. I built a little table to hold workpiece level and clamped on a piece of 3/4 plywood to hold things square. It has a hole drilled in the back side for a vacumn cleaner hose to keep the dust under control. I built this setup while I was building an AcroSport II. There are hundreds of little plywood gussets in the wing that have to be sanded before gluing.

Finished view of carbon over paper tube. It finished to about 1.730" OD and 8.52 grams/inch.

dwightr · Jul 28, 2019

Working on the MD38 again today.
I started by wicking some thin CA on the ends of the tubes to strengthen them.

Then I fabricated a laundry shelf and recovery attachment point. It's a 3/16" plywood bulkhead with a 1/2" hole in the center. I fabricated a U ring from a piece of 1/8" SS TIG rod. I drilled holes in the bulkhead, slid the Uring thru, slid a nut over each end, wrapped every thing in a wet rag and TIG welded the nuts to the rod. A 8-32 ubolt would have been a lot easier but I didn't have one handy so I had to adapt and overcome.
I slid the bulkhead in the tube and secured it with JB weld then I glued a 1/2" long piece of BlueTube coupler in above the bulkhead to reinforce the joint. The Uring will be too far down in the tube to use a Quick Link but I should be able to loop a piece of Kevlar around it.

dwightr · Jul 28, 2019

I started working on the fins. I cut them out of a sheet of .062" G10 Fiberglass with a bandsaw with a fine tooth blade. Squared everything up on a table sander.

I tacked them on with thin CA and allowed them to dry for a few minutes.

Then I roughed everything up with 120 grit sandpaper, cleaned with acetone, and layed down small fillets with JB Weld. After a few minutes I smoothed with my gloved finger dipped in Alcohol. I wasn't too concerned with cosmetics since everything is going to be covered with Carbon Fiber tip to tip.

dwightr · Jul 28, 2019

I've cut out carbon fiber cloth for the tip to tip. This is a fairly low performance rocket so I'm only using two layers instead of the more traditional three layers. First layer goes about half way up, second layer covers everything and will be trimmed when epoxy is at leather stage.

Scuffed the fins with 120 grit, measured and made some pencil marks as a reference for the first layer.

Mixed up 12 grams of 30 minute epoxy thinned with about 2% denatured alcohol. Brushed on a thin layer, placed the first piece of cloth and wet out.

Put the top piece of cloth in place and wet out with epoxy.

Put on a piece of peel ply and wet out.

I'm not set up for vacumn bagging so I used a Ziploc bag filled with lead shot to hold everything in place.

After about 40 minutes I peeled off the peel ply and trimmed the Carbon Fiber cloth to near final size. There is one small air bubble near the trailing edge that will have to be dealt with. I'm not completely satisfied with the results but I guess it's okay for first attempt. Now I've just got three more sides to go. Then some sanding and filling, sanding and filling, and more sanding and filling.

dwightr · Aug 3, 2019

Filled and sanded fins, applied first coat of primer, sanded, little bit of spot putty, more sanding and another coat of primer.

Sanded a couple of spots down to the CF to attach rail guides.
Small sanding drum on a Dremel tool made short work of it.

Glued on conformal rail guides with JB Weld.
I hope they're a bit less noticeable after painting, they really look obnoxious right now.

dwightr · Aug 5, 2019

Avionics sled with RRC2+ altimeter
Space is really tight in a 38MM coupler, I had to bow the #8 allthread rods to make room.
I may try building a sled from G10 and just have the sled extend thru the bulkheads with a hole for the quicklinks.
I'm open to suggestions.

dwightr · Aug 7, 2019

I decided that I really didn't like the sled that I had built so I started over.
I cut out a piece of .062" G10 to rough size, glued on doublers where the quick links will attach and let it dry.

While the JB Weld was drying I slotted my bulkheads so the sled could pass thru. I squared up the corners of the holes with a file for a good fit.

After the epoxy was dry I trimmed the sled to final shape and size and glued it to one bulkhead with a generous fillet of JB Weld.
Once it's dry I'll drill for the switch and altimeter and glue on a block to fasten the other bulkhead to with a screw.

dwightr · Aug 11, 2019

Mounted the switch and RRC2+ altimeter on the top side of the sled.

Mounted a 1S 500 mAH LiPo on the back. Epoxied a small block of aluminum to the sled.
Drilled and tapped 6-32 for a screw to hold the bulkhead on.
I'll use a little epoxy to fill one of the holes in each bulkhead and use the other hole for charge wiring.
I plan on using glove fingers for charges and a little dab of modeling clay or RTV to seal around the wires.
I think this is a lot better looking sled than my first attempt.

I'm still trying to decide on a paint scheme for the rocket.
Any suggestions?

dwightr · Aug 13, 2019

I decided that since this rocket is my first attempt at carbon fiber, first minimum diameter and first Mach+ I decided maybe a "experimental rocket" paint theme would be appropriate. Fins and nose cone are orange like some target drones and avionics bay has a Mercury Redstone inspired roll pattern. Every thing is just Rustoleum rattle can paint. Like all of my paint jobs it looks good at 30', upclose it's functional but not really beautiful. I have a lot of respect for people that have the patience to paint well and the courage to take a beautiful paint job out and fly it. A few scuffs and scratches will just add character to this bird.

38MD Carbon Sleeved Paper Build

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