21-inch by 19-foot "Unfinished Business"

[CarVac]

I have personally vacuum bagged up to 3-layer layups on cylindrical mandrels, and it is fairly difficult. My best work involved spending a few minutes massaging the wrinkles out through the bag prior to the epoxy gelling up, not the most time-efficient of efforts.

I suspect that the percentage circumference change for 3 layers of cloth on 38mm is going to be similar to that of a large diameter layup with foam core, but I cannot say for certain, since I've never used Spheretex before. I have used flow-cloth in 2-D layups (https://www.acpsales.com/Aero-Mat.html), however, and strong vacuum does cause a noticeable amount (15%) of crush, but Spheretex might be different.

 

[Feckless Counsel]

TRF,

Made the trip to my local concrete supply store and purchased a 12-foot length of 20-inch Sonotube. What I learned is:

1. Sonotube is shipped "nested." There is a true 20-inch ID piece shipped inside a slightly larger off-dimension tube. Therefore Sonotube couplers exist. They are, however, loose fit.

2. Inside and outside pieces are differentiated by an underlined SW mark as shown in the picture. Mine has no underline and is, therefore, true dimension ID.

3. Wall thickness is 0.25-inch. The tube material is a bit soft especially on the ends where handling has fatigued the piece.

4. Inside tube is a silicone release coating. Poison to bonding. Be prepared to scrub, peel or wash if you're considering a Sonotube airframe.

5. Outside surface to Sonotube is ROUGH with the spiral wrappings. Significant work is required to make it smooth, especially on large tubes.

6. Call ahead to be sure your supplier can cut tubes. Otherwise you'll have a VERY awkward load for transport.

7. My dealer had 36-in diameter x 12-foot tube in stock. Wall thickness is 0.40-inch and weight is approximately 160 pounds. Dare to dream?

8. Published data have Sonotube at 5.5 pounds per-foot. My 12-foot piece weighs 50 pounds or 4.2 pounds per-foot. Not bad and, I assume, is because I have the true dimension inside piece.

9. I'm very tempted to glass that tube as an airframe and move forward. If I did the final weight might be 56-pounds.

10. I'm considering a 2-core-2 layup using Sonotube as a mandrel. Calculations show such an airframe would weigh 45-pounds equivalent length with superior strength. Overall, however, the rocket may weigh the same because an "extra" coupler is required to join 3 pieces 48-inch sections.

Comments anyone?

Feckless

 

[dixontj93060]

Many use reinforced Sonotube as an airframe material (which I believe you are suggesting although you also mention mandrel, but maybe that is for the coupler) so you should be fine.

On #4, I'm a bit surprised, although I can see why the inside would be coated for concrete forms, but the standard stuff I get at Home Depot had a raw inside and a coating in the outside.

 

[SMR]

4. Inside tube is a silicone release coating. Poison to bonding. Be prepared to scrub, peel or wash if you're considering a Sonotube airframe.

Comments anyone?

Sounds like you're off to a good start. I have found that the silicone coated interior layer peels off quite easily, like the glassine layer on conventional body tubing. Start on one end and slowly peel it off in a big spiral.

I have glassed some smaller tubes, two wraps of 1 1/2 circumference each, making 3 total. I did not bag them, but did use peel ply. There was some slight wrinkling, but not too bad. 12" sonotubes come in three nesting diameters, and the smaller one fit quite nicely as a slip-fit coupler and a nose cone shoulder in the middle size. I made the centering rings before glassing the tubes, as they aren't perfectly round unless given some internal guidance. The centering rings also made good spacers for the rotisserie I used in the process. (The setup you used to make the tubes for the A.M. was awesome!)

12' tubes will fit in a 10' trailer with a vee nose.

 

[Feckless Counsel]

Tim,

I bought the tube as mandrel material for an all composite airframe but, having weighed the tube, am tempted you just glass it and go. Have to balance that convenience against my low weight objectives. An additional 11 pounds is about 8% the goal.

Feckless

 

[JStitz]

Feckless, I was wondering about this as you will have a lot of finishing work doing the Peel and Ply with the Sono-Tube mandrel.
These tubes even when they are in stock have dings and end damage. It can be trimmed and you are there.
Some people peel and sand the inside out and tons of flyers have just screwed their centering rings to the air frame.

John from JAX

 

[Feckless Counsel]

JSitz,

Thanks for your message and good to hear from you again.

Yes, the tube is rough on the outside: dents, scrapes and spiral grooves. Fairing those will add weight and require labor. So, perhaps to your point, I'd be reluctant to use Sonotube as a disposable one-shot mandrel. John Coker, however, teaches a collapsible mandrel made from paper tube: https://www.jcrocket.com/waccorporal.shtml. Then some investment at fairing may pay.

Also, check out how the big-boys do it: https://www.youtube.com/watch?v=8Q5YCCXjr6w

Admittedly I'm a bit weight conscious and I do enjoy the concept of composite construction. So I'm leaning that way tonight.

Feckless

 

[dixontj93060]

Also, check out how the big-boys do it: https://www.youtube.com/watch?v=8Q5YCCXjr6w

Wow! Now you can build your full scale Saturn V!!!

 

[JStitz]

Feckless, John has a great idea there and answered my question about the ridge left inside the tube...seems the tape strip kept the resin in.
Split mandrels might just catch on!
Maybe I didn't read his method close enough, but did he fill the spirals on this tubing? I don't think the peel ply will cover that ..maybe without vacuum.

 

[Feckless Counsel]

JSitz,

From what I understand Mr. Coker ordered a custom, externally smooth and thick walled tube manufactured by Yazoo Mills, Pennsylvania. So, perhaps, he was spared the surface preparation.

Feckless Counsel

 

[JStitz]

The samples in the add still had spirals, but maybe he had them wind them without seams? We have all seen where the glassine tubes were over wound and that was just as bad as spiral grooves!

 

[Feckless Counsel]

TRF,

So I'm settled on an all composite airframe. I recognize the expediency of simply laminating Sonotube. But that's another project because:

1. Consistent with the original goal, I'm after the ultimate in lightweight.
2. No local dealers carry outside dimension Sonotube in 20-inch.

The question now is how to do it. So may I describe my thinking for your criticism?

1. Prepare mandrel bulkheads and shaft as in project Anima Mundi post #5:https://www.rocketryforum.com/showthread.php?28235-Anima-Mundi.
2. Measure tube for OD differences. Larger end is for airframe, smaller is for coupler.
3. Cut tube in half (already cut in truth).
4. Prepare surface of coupler end for release: surface dress, polish and liquid PTFE.
5. Wrap coupler end with 2 layer 7628, then 2mm Spheretex core and then 2 layer 7628. Vacuum bag process.
6. Pull coupler. If mandrel survives make another as back-up.
7. Prepare surface, but do not polish or release coat, the airframe side.
8. Dress airframe side with 3 layer 7628, then 2mm Spheretex core and then 3 layer 7628. Vacuum bag process. Those stick to and become part of the airframe mandrel. Note additional thickness by layers.
9. Split airframe mandrel as in Mr. Coker's method of release. Surface dress, polish and liquid PTFE.
10. Layup airframe with 2 layer 7628, then 2mm Spheretex core and then 3 layer 7628. Vacuum bag process. Repeat 4 times yielding one back-up piece. Release coat between each application.
11. Trim components and sand to fit and finish.
12. Whiskey and a cigar.

The thing to note is, by top dressing the airframe mandrel in step 8, couplers should just fit into the airframe.

Feckless Counsel

 

[Feckless Counsel]

TRF,

Another issue is locking the free ends of a split mandrel. There I'm concerned my mandrel is more flexible and sloppy than Mr. Coker's.

I'm considering a sliding dovetail that runs along the parting line. Tail would be divided and attached to either side of the mandrel's parting line. The socket would be driven and pulled as necessary to close and open the mandrel.

Make sense? Observations, criticism or experience?

Feckless Counsel

 

[Feckless Counsel]

TRF,

I've finished some other business. Now back to this?

Please find recent photos of the next tube winding station. Features include:

Frame - Made from familiar 1010 extrusion. Outside dimensions are 74x38x36 inch. It's square, adjustable, reasonably stiff and collapsible for storage.

Mandrel - Made from 20 inch Sonotube internally reinforced by two MDF disks. All that is chucked onto a 1 inch hardened shaft supported by pillow bearings.

Reel - Made from 2 inch PVC tubing and 1 inch DOM steel tube. Reel supports fiberglass cloth as it feeds tube winding. Reel assembly is supported with quick release stanchion mounts by 80/20.

Tray - Made from pressboard. Affordably disposable and supports the frame's base against racking opposite corners

Comments on this construction:

1010 is not as stiff as it appears and the 80/20 load calculator is misleading to the novice. I selected 1010 for economy. Anyone considering a similar station might want to consider 1515 or 1530.

Anima Mundi used black iron pipe as a mandrel shaft. Although cheap I was unhappy with the flex and run-out (not straight). This time I spent $65 on 1 inch DOM tubing. It didn't fit the bearing race as actual OD is 0.050 oversize. I tried to expand the race using a brake hone and drill press. Waste of time. The races are just too hard. And, frankly, the run-out was not much better.

Bottom line, pay the $100 for an 84 inch super straight and hardened shaft. Properly stored it's a tool for life.

Feckless Indeed

 

[MasonH]

How did I manage to miss this build...glad I found it.

 

[JStitz]

Do you have 2 more 36" pieces to put right under the Pillow bearing? Take advantage of the vertical strength. I never cut longer than a 48" piece,but I can imagine the flex with that weight..and thats before the cloth and resin
It looks like you might have to notch the tray to do that.



John

 

[CarVac]

Do you have 2 more 36" pieces to put right under the Pillow bearing? Take advantage of the vertical strength. I never cut longer than a 48" piece,but I can imagine the flex with that weight..and thats before the cloth and resin
It looks like you might have to notch the tray to do that.



John

Or he could just bolt more 1010 right below the crosspiece to stiffen it.

 

[Feckless Counsel]

TRF,

One layer of 16 ounce tooling cloth is applied to the mandrel. That will stiffen the Sonotube, will reinforce circularity and will serve as a release surface foundation.

Notes on this application:

I used a chip brush to lay a "starter strip" of epoxy on tube. That helped to tack down and align the cloth's leading edge. From there I didn't bother with chip brushes. Just poured the epoxy and worked it with gloved hands and a squeegee. The method was messy but very fast.

Sonotube absorbs a lot of epoxy. Three square yards of 16 ounce cloth required 52 ounces of epoxy to achieve a lean, somewhat textured surface.

Feckless

 

[CarVac]

Would lighter cloth not have absorbed (slightly) less epoxy and left a smoother surface that needs less filling with release agents?

 

[Feckless Counsel]

CarVac,

Thank you for your reply. I wrestled with that decision. Bottom line? The heavy stuff was available for cheap in 63 inch width. I wanted something wider than the 50 inch cloth used for airframe.

An interesting effect is pictured below. Spiral grooves are "tented" by the heavy cloth. Tented spirals appear dry by contrast but, upon inspection, are reasonably saturated. Perhaps that is an advantage of heavy cloth on deep spiral tube? Or perhaps those areas will flake and crack under vacuum? We'll soon know.

Just applied a "crumb coat" of fairing compound. That is 32 ounces of epoxy mixed with 3 ounces of phenolic micro-balloons. Mixture had the consistency of pancake batter. Application time was 30 minutes. That is also pictured below.

Feckless

 

[THarrison]

Glad to see this thread is back to life

Looking forward to the build!

CarVac,

Thank you for your reply. I wrestled with that decision. Bottom line? The heavy stuff was available for cheap in 63 inch width. I wanted something wider than the 50 inch cloth used for airframe.

An interesting effect is pictured below. Spiral grooves are "tented" by the heavy cloth. Tented spirals appear dry by contrast but, upon inspection, are reasonably saturated. Perhaps that is an advantage of heavy cloth on deep spiral tube? Or perhaps those areas will flake and crack under vacuum? We'll soon know.

Just applied a "crumb coat" of fairing compound. That is 32 ounces of epoxy mixed with 3 ounces of phenolic micro-balloons. Mixture had the consistency of pancake batter. Application time was 30 minutes. That is also pictured below.

Feckless

 

[Feckless Counsel]

Todd,

Also good to know that you are still with The Forum.

Sanded the mandrel near fair using 60 grit paper on a palm sander. Dust was controlled using a shop vacuum. This process required about 40 minutes.

I'm ready to apply a final coat of fairing compound. Anyone care to contribute ideas for making that coat glass smooth without a lot of sanding?

Feckless

 

[CarVac]

Todd,

Also good to know that you are still with The Forum.

Sanded the mandrel near fair using 60 grit paper on a palm sander. Dust was controlled using a shop vacuum. This process required about 40 minutes.

I'm ready to apply a final coat of fairing compound. Anyone care to contribute ideas for making that coat glass smooth without a lot of sanding?

Feckless

...Glass smooth? It's easy to get glass smooth but it's difficult to get glass smooth without being lumpy or needing to sand.

 

[Neil]

Todd,

Also good to know that you are still with The Forum.

Sanded the mandrel near fair using 60 grit paper on a palm sander. Dust was controlled using a shop vacuum. This process required about 40 minutes.

I'm ready to apply a final coat of fairing compound. Anyone care to contribute ideas for making that coat glass smooth without a lot of sanding?

Feckless

Red Glare 14 or 15?

Neil

:flyingpig:

 

[Feckless Counsel]

Neil,

Nothing motivates without goals. I will say Red Glare 14 with an 80% probability of making schedule. Much of that comes down to the nosecone, an entirely new skill for me.

Either way, it will be Red Glare.

Feckless

 

[Feckless Counsel]

TRF,

Applied mandrel's top coat of fairing compound. That is 20 ounces of epoxy mixed with phenolic micro-beads to peanut butter consistency. Application required about 40 minutes using the pour and squeegee technique.

I had considered peel ply to level and smooth the surface. Reconsidered that and tried to level with a chip brush. That started to pull material from the surface forming holes and pocks. Repaired that with the squeegee and opened a beer.

I'm with CarVac. Sometimes there are no shortcuts. I'll wet sand it to 1000 grit in stages using the rotisserie method.

Feckless

 

[Neil]

Neil,

Nothing motivates without goals. I will say Red Glare 14 with an 80% probability of making schedule. Much of that comes down to the nosecone, an entirely new skill for me.

Either way, it will be Red Glare.

Feckless

Take your time, build it right....one time. Remember, rocketry is as much about the journey as it is the flight.

If you need a sanity check, give me a call........that's something you won't see to often, me being the sane one.......:wink:

Neil

:flyingpig:

 

[CarVac]

I'm with CarVac. Sometimes there are no shortcuts.

I discovered this by spending hours and hours sanding Disappearing Act's fins to a polished finish. I applied Aeropoxy over it at one point to fill in the peel-ply texture, but it all had to come off (except the pinhole fill) because while shiny, it was lumpy.

And Disappearing Act's fins have one... 500th of the area you're dealing with?

 

[troj]

Sonotube absorbs a lot of epoxy. Three square yards of 16 ounce cloth required 52 ounces of epoxy to achieve a lean, somewhat textured surface.

Would lighter cloth not have absorbed (slightly) less epoxy and left a smoother surface that needs less filling with release agents?

Replying to an old message, I realize....

We've discovered the same thing -- Sonotube is a sponge for epoxy. It'll suck it out of the cloth, if you don't apply liberal amounts.

The method we found, to prevent this, is to put epoxy on the tube, then allow it to cure to the sticky stage. Then, while the tube is still sticky, come back and put on the cloth, and enough resin to wet out the cloth. It bonds well, and keeps the tube from sucking up so much epoxy.

-Kevin

 

[soxfan121]

Nice build so far glad you haven't thought of giving up, especially this early with the tube giving you trouble, remember like a few others have said, often there are no shortcuts, you just have to suck it up and power through whatever task you need to complete. good luck, keeping an eye on this build.