7.5" - 6" Terrier Sandhawk

[vahpr]

Here's the tube wrapped in 2 layers of 7 oz and 1 3.25 oz tight weave layer. I used a curing oven built by Bill Schworer from Dave Triano plans to stow the tube at 120 overnight. It's not a true post cure (I asked the guys at Raka for this info, no response) but the results are good. The teflon covered end caps worked like a charm, popped right out, no epoxy on the tube interior and it looks like you could use the same teflon again.

 

[vahpr]

So some observations and questions;

• This took longer than I'd remembered - fully 2 hours to do 1 tube (after all preps were done).
• I attribute this mainly to the difficulty wetting out the glass as the resin got to a tacky stage pretty fast, despite precautions (started with warm (80) resin/hardener, mixed thoroughly and poured onto a plastic plate on a piece of foam insulation, garage was about 70).
• I'm thinking I'd like to use another product, something with lower viscosity that stays low for a while, suggestions? Not sure what TG I need, these aren't min dia, but it gets pretty hot in the open-frame booster sections.
• Issue 2, waiting on heat shrink tape. I'm wanting to use this on the rest of this project as I understand it confers strength benefits by compressing the fibers, minimizing voids/air pockets and optimizing resin/fiber ration much like vacuum bagging. Can anyone speak to tips for using this material?
• Weight of the finished tube is 670 grams more than the dry tube (1700 total), of which 340 was glass and 330 resin, so a pretty good ratio by hand. It'll be interesting to compare this to the heat shrink taped tube.

 

[vahpr]

Moving on, the 1st thing I did was research an alternate epoxy system and landed on ProSet. The extra-slow hardener allows oodles of working time. With fairly easy post-curing (appx 180 for 8 hrs) you get a hdt of 173 along with some improved strength measures. Data sheet here: https://www.prosetepoxy.com/PDF/LAM-125_LAM-237.pdf. This stuff is nice to work with, good low viscosity and very low odor. The only drag is expense, including the now required hazmat for epoxy hardeners it'll set you back over $200 for the gallon of resin and 1/3 gallon hardener. Fortunately this goes a long way.

 

[MarkH]

Hazmat? Is this the same as the fee for motors? I bought a quart kit of Aeropoxy laminating resin a few weeks ago and didn't have a hazmat fee.
None on Cotronics I purchased about 6 months ago either.

 

[vahpr]

I wanted to try a few different techniques for glassing the tubes so in addition to the basic hand layup with post-cure I got some heat shrink tape from Dave Triano. The stuff he carries is the non-release variety so I also ordered the release-coated type directly from the manufacturer (Dunstone - www.shrinktape.com).

Below is the non-release tape over a nylon peel-ply ready for the oven. The tape requires 150 degrees to shrink. In my mind this is somewhat of a problem. The ProSet guys say to allow their system to reach initial cure (at room temp) before applying heat. But if you did that I'm not sure how effective the tape would be since it's now in a somewhat hardened state. For this experiment I didn't wait but compromised by heating to 150 for an hour then dropping to 80 for 8 hrs.

 

[vahpr]

Apparently it's a new DOT thing - both CST and Aircraft Spruce said the same thing about this.

 

[vahpr]

I'm thinking maybe using heat shrink tape is a trial and error thing improved by practice. Here's the 1st tube after post cure. The banding is insufficient overlay and will require filling. I got better results on the 2nd try with 50% overlap but still had some banding.

 

[daveyfire]

I'm thinking maybe using heat shrink tape is a trial and error thing improved by practice. Here's the 1st tube after post cure. The banding is insufficient overlay and will require filling. I got better results on the 2nd try with 50% overlap but still had some banding.

We didn't use heat shrink so I kept my mouth shut before, but when we did PE tape wrapping on our carbon tubes at USC we always went for about 50% overlap and always got banding, mostly because we pulled the tape so friggin tight. Of course, we never had time before a launch to paint anything, so it ended up not mattering. But the spirally texture is just kind of... there. I think you could eliminate it with even more overlap or not shrinking the tape as much, but then you're trading off debulking/compression. For this application, either way is probably fine

 

[vahpr]

To address the early-heating required by the tape and because I wanted to try it, I set up a tube for vacuum bagging. With this method I could let the resin initial cure without heat.

End caps are wax-paper coated and have a removable allthread axle. Despite care to get the bag evenly over the tube, I was unable to prevent the ripples you see in the pic. What I didn't know was that every single one of them would transfer to the fiberglass. The end result was a bit of a mess and has required extra sanding/filling work to smooth out. My least favorite part.

I'm thinking this problem could be alleviated by using bagging film and tape. That way you could get the "bag" down evenly over the breather.

 

[vahpr]

Yes I think you're exactly right - for this it's not critical. That said however, I was hoping to hit upon something that worked well with minimal finishing fuss. Oh well....

 

[vahpr]

To avoid more potential hassle however, I want back to basics for the last tube and did a regular hand layup without augmentation. The tube came out nicely, though again, I learned you need to rotate it in the oven or cover it with peel ply to prevent the resin from flowing to the bottom vertical surface and ponding a bit. It's always something

 

[MarkH]

To address the early-heating required by the tape and because I wanted to try it, I set up a tube for vacuum bagging. With this method I could let the resin initial cure without heat.

End caps are wax-paper coated and have a removable allthread axle. Despite care to get the bag evenly over the tube, I was unable to prevent the ripples you see in the pic. What I didn't know was that every single one of them would transfer to the fiberglass. The end result was a bit of a mess and has required extra sanding/filling work to smooth out. My least favorite part.

I'm thinking this problem could be alleviated by using bagging film and tape. That way you could get the "bag" down evenly over the breather.

Interesting. I vacuum bagged a four inch tube yesterday with 1 layer of 6 oz CF and a sanding veil layer of 2 oz FG, with a lot more wrinkles in the bag than yours. The FG layer had wrinkles but none transferred to the CF. I'm thinking CF is less susceptible to bag wrinkles due to stiffness, but FG moves around a heck of a lot more when applying than CF anyway.

 

[vahpr]

While I was waiting on epoxy and tape I knocked out the interstage arrangement. Similar to the original, this time I'm using 3/8" steel vs 1/2" aluminum. I needed the smaller dia rods to keep some meat on the centering rings in the sustainer. They slide nicely in the Delrin tubes so I hope the stages will drag separate but if not I'll have a sep charge ready to go via RC.

 

[vahpr]

Could be Mark - also might be that I didn't use enough vacuum - I was concerned with crushing the tube so kept the vacuum at about 7.5 Hg. Even at that though the bag seemed pretty tight......

Interesting. I vacuum bagged a four inch tube yesterday with 1 layer of 6 oz CF and a sanding veil layer of 2 oz FG, with a lot more wrinkles in the bag than yours. The FG layer had wrinkles but none transferred to the CF. I'm thinking CF is less susceptible to bag wrinkles due to stiffness, but FG moves around a heck of a lot more when applying than CF anyway.

 

[daveyfire]

While I was waiting on epoxy and tape I knocked out the interstage arrangement. Similar to the original, this time I'm using 3/8" steel vs 1/2" aluminum. I needed the smaller dia rods to keep some meat on the centering rings in the sustainer. They slide nicely in the Delrin tubes so I hope the stages will drag separate but if not I'll have a sep charge ready to go via RC.

Nah I think you can get away with smaller rods than that

(too soon? :duck

 

[vahpr]

HAHAHAHAHAHHA!

Maybe 1/8" titanium, as long as you fly with 60mph gusts )

Nah I think you can get away with smaller rods than that

(too soon? :duck

 

[vahpr]

Working on extending the fin slots for the leading edge bevel. One at a time, get the fin depth about right, secure with a couple bolts, Dremel the basic shape, test fit, adjust with file, test fit, adjust, etc, etc, etc. Was kinda dreading this but it wasn't too bad once I got rolling. It'll get additional nuts and bolts and some exterior mounts, but at this point the assembly weighs in at 10 lbs 6 oz.

 

[vahpr]

Slammin' to at least get the Sandhawk ready to fly at URRF in a couple weeks......

The tee nuts (48) had to be cut on the inner side so the motor would clear. I'll leave more room next time.

I doubled up the couplers for some added strength and handy thickness for the interior tee nuts.

 

[vahpr]

Recessed switches in the coupler and completed altimeter bay, ready to bolt in. The next 2 are shots of the nose cone bay and board, then I decided they were too narrow so made another, wider pair.

 

[vahpr]

Needed a bit of nose weight for the 1st flight on an 11k ns 98. A replacement ARTS 900mhz GPS transmitter is ready to go. Hope I don't need it.

The tube is epoxied in with some filler using the aft plate to retain in place while the glue dries. Then I foamed it in steps. The last is messy as the foam comes up through the relief holes but it locks in the aft plate via the washer "anchors" to be pretty much un-removable.

 

[vahpr]

The Rocketry Warehouse nose cone looks the part but required much extra work with this Red Arrow tubing. The shoulder needed material removed (as did the interior of the tube) while the base was too small and needed Bondo to match the airframe exterior. Eventually I got it sorted out but next time I'll try to find a better match.

Checking fit and screw hole locations for the motor retainer plate. I love it when the motor occupies a large volume of the tube!

 

[vahpr]

My fin painting "jig" works pretty well.

Rockets Of The World says the main portion of at least one Sandhawk was red-orange. I mixed 60/40 red/orange but the result was more on the orange side. Should be highly visible at least.

 

[vahpr]

As built the external mounts look a little much, which I don't like. I think I will cut these back to just over the white which will make it cleaner and maybe a little more scale.

 

[dixontj93060]

As built the external mounts look a little much, which I don't like. I think I will cut these back to just over the white which will make it cleaner and maybe a little more scale.

Personally I think it looks fine. A question or two... Is that just aluminum angle stock? If so, how are you adjusting for the radius on the airframe (making the angle >90*)? Also, it looks like you are using t-nuts on the wood frame for lateral attachment, what size are they? Finally, to attach the fins, what are you using? Through pins? Screws and nuts? PEM nuts? Any close up pics of this area would be appreciated--thx.

 

[vahpr]

Humm, I was pretty sure I'd posted the conformal mounts, looking back I see I didn't. Gettin' old.... Anyway, it's cove cutting technique on the table saw. There's a cool online calculator which tells you what angle to use, I find that gets me in the ballpark. https://woodgears.ca/cove/index.html

Then you rip the coves 3/4" to fit the alum angle. I've used this previously on a couple other rockets, works well.

 

[vahpr]

Fins attach at 2 points. Inside the airframe it's bolts & nylon lock nuts through the vertical spars. Really this is so solid I doubt the external ones add much but they don't hurt. Outside, it's short bolts and low profile nylon lock nuts through the fins (not yet installed - finishing that up later today) and vertical bolts down into the tee nuts in the spars. Very solid. It better be, the 1st flight will be on an 11,000ns N4000

 

[daveyfire]

I really like how the bolts from the conformal mounts serve double duty to hold the airframe on. Super slick! Can't wait to see the whole Sandhawk assembled

 

[dixontj93060]

Thanks for the details!

 

[grouch]

Tour de force of sexiness right here folks. Nothing but pure sexiness. This is the perfect example of a true composite rocket!

 

[patelldp]

I love the term Flying Furniture. You could trademark that and market some kits or instructions!

Looking forward to seeing your projects at URRF. You always bring cool rockets and motors!