Level-3 high-performance design and build thread

[Adrian A]

The test-bond of the two polyester/fiberglass tube sections is baking nicely on my dashboard now as a post-cure step. I faced my car into the sun, and the piece is too hot to hold, maybe 180F or so. To test it, I'm planning to use a 2x4 and my workbench, with a bathroom scale on one end of the 2x4, the tube bonding test on the other end, and a C-clamp that's about 90% of the way to the test article. That way the actual test force will be 9x the bathroom scale measurement. The bond line is about 3/4" wide, and the diameter is 2", so that's 4.7 square inches of bond area, all in shear. I think I'll stop at about 1000-1500 lbs or whatever makes me start being nervous about the 2x4 or workbench. I'll be surprised if it breaks before then, but that's what the test is for.

[AlphaHybrids]

You really need a hydraulic jack and simple pressure force gauge. Our school shop had one where the it was a tube with and ID of 1.125 and OD of 3". It had two 1.125" pistons in it with o-rings. In the middle we had a tap for a pressure gauge (dial type). When we wanted to do a quick and dirty test we would use a hydraulic jack to compress whatever we needed with the force gauge inline.

Edward

[Adrian A]

You really need a hydraulic jack and simple pressure force gauge.
Edward

That would be handy.

Instead, since I didn't have a deep enough C-clamp for the axial test I have in mind, I did a bending test. There was a big enough gap between the tube that the tube overlap wouldn't have been enough to keep the tubes together without the glue. I calculated about 1400 inch-pounds of torque trying to separate the tubes, but all that happened was that the tubes got significantly deformed. So I moved on to just trying to crush the tubes together with a clamp without any instrumentation. Nothing budged there either, so I moved onto a somewhat less-instrumented method:



Again, nothing budged, even after some really severe whacks. The glue joint (Aeropoxy with colloidal silica as a gap-filler) is plenty strong enough to prevent the tubes from coming apart for any sort of landing whack I can imagine. I may tempt fate and call this the "indestructo-rocket."

[dixontj93060]

Alright--my kinda testing!

[troj]

I love scientific, brute-force testing!

Adrian, I think you've proven it'll work!

-Kevin

[Adrian A]

This is encouraging enough that I'm contemplating putting together an L version in time for Oktoberfest on the 8th. A CTI L1115 sims to about 34k in RASAero. I have a Beeline GPS that I could use for recording GPS Tripoli record data. Lacking a good APRS receiver, I would want to try to fit in a Telemetrum and a Raven into the av-bay. I'll check that out later tonight.

My chute material is on its way, and I have some G10 sheet stock for fin core material, along with a lot of leftover carbon uni and Aeropoxy, so I just need a 3" body tube. G10 will do I think, since this would only go to Mach 2.2.

I may still want to reinforce the nose tube with an axial layer or two of uni carbon, though, just to be sure.

[Tominator 2]

Great thread Adrian, really looking forward to seeing the whole build.
I was wondering if the L version you are talking about is a whole seperate rocket? Just testing your new ideas?

[Adrian A]

Great thread Adrian, really looking forward to seeing the whole build.
I was wondering if the L version you are talking about is a whole seperate rocket? Just testing your new ideas?

Thanks.

The internal components, including the av-bay and chute holder, would be the same. I may make the av-bay extra-long to hold the longer electronics and then cut it down if/when I get done with a new Featherweight GPS tracking altimeter. For this build I would use my existing FG shockwave nosecone, standard fiberglass tubing, and make some fiberglass-core fins. For the M shot, I would use only contronics high-temperature epoxy, and I will probably roll my own custom carbon fiber tubes, fiberglass nosecone and carbon fiber fin stock.

[AlphaHybrids]

Adrian, last night I sewed a test toroidal parachute - it only has 2 seams. The main thing is it will only work in smaller (<30") diameters. I still have to attach lines but so far it looks like it will work nicely. I'll bring it to O'Fest. Also, I've got *lots* of very nice autoclave cured carbon fiber from .040" thick to 1/2" thick. I'll bring some samples if you want to look over them.

Edward

[Adrian A]

Adrian, last night I sewed a test toroidal parachute - it only has 2 seams. The main thing is it will only work in smaller (<30") diameters. I still have to attach lines but so far it looks like it will work nicely. I'll bring it to O'Fest. Also, I've got *lots* of very nice autoclave cured carbon fiber from .040" thick to 1/2" thick. I'll bring some samples if you want to look over them.

Edward

Wow, that's cool. Would the test chute be appropriate for my L shot that I'm planning to fly at Oktoberfest? It should have a descent weight of around 6-7 lbs. If you'd like me to try it out then, it would be good if I could have it this weekend for deployment tests. I probably have some goodies you might be interested in in exchange. Thanks.

[Adrian A]

Last night I worked out how I'm planning to build the av-bay. There is a big central 3/8" bolt going through the middle, and I need to arrange the electronics around that. The Big Red Bee has a GPS patch antenna that is mounted on top of the GPS receiver module with a stack-up that is too tall for this application. So I removed the shrink-wrap that is holding the antenna on, and I'll mount it off to the side. There is plenty of micro-coax cable length available for that. The Telemetrum would be mounted similarly on another section of the circle. Both of them have mounting holes at the top and bottom at about the same level. So my plan is to make a central mounting structure that includes a fiberglass tube as a bolt spacer to take the 3/8" bolt loads, and glue a plywood donut at the top end and a partial-donut on the bottom end to make a barbell shape. The barbell will be belt sanded down to out to provide flat recessed mounting surfaces for the electronics, and the electronics will be screwed directly onto it. I'll make some kind of mounting board along one side to mount the Raven and the batteries.

[AlphaHybrids]

I won't have the chute done and tested by the weekend - I'll definitely have it by Oktoberfest though. Why a 3/8" diameter bolt?

Edward

[cjl]

I'd guess because that's the thread size on a Pro75 forward closure.

[Adrian A]

I won't have the chute done and tested by the weekend - I'll definitely have it by Oktoberfest though. Why a 3/8" diameter bolt?

Edward

O.k. I'll continue with plans to sew my hemi chute then, and I'll make the chute holder large enough to accommodate it. Then at O-fest we can check out the toroidal chute for application in the M shot, where I will have the opportunity to shorten the av-bay and chute holder. Maybe fly it at O'fest if there's time for a ground deployment test, etc.

I'd guess because that's the thread size on a Pro75 forward closure.

Correct. I think it will be easier to find a socket wrench extension than a hex key extension, so I'm planning on using a regular bolt instead of a socket cap screw.

[Adrian A]

My chute fabric arrived tonight, so I got busy cutting and sewing. $10 in materials and about 3 hours later, I have the canopy done. I'll sew on some riser attachments tomorrow, I think.

I decided to document the chute build in the recovery section for easier reference. Here's a teaser:



That's a 65" hemispherical canopy in my hand.

[AlphaHybrids]

My 60" toroidal is just slightly (maybe 1") longer than that, sans lines.

Edward

[Adrian A]

My 60" toroidal is just slightly (maybe 1") longer than that, sans lines.

Edward

That would beat this one then, for drag vs. volume. Here's the build thread for the chute:

http://www.rocketryforum.com/showthr...841#post239841

[Adrian A]

The airframe tube arrived today, so I made some decent progress tonight:

I finalized the fin design and cut them out from some carbon stock with my tile saw:



I was debating about whether to sweep the trailing edge past vertical. I haven't done that on any of my recent rockets because they were all long enough that you get more bang for your buck, stability-wise, with the trailing edge swept forward. But this is a relatively short, squat rocket and I decided to go for the better stability despite the extra fragility. If I crack a fin on landing with the way I'm planning to reinforce the fins, that's good information to know for my L3 version.

This was the first time that I built a 2-plate fin jig like I have seen other people do. I had some wimpy rigid foam that was easy to make precise cuts into, so I decided to use that. Since it's not very strong, I decided to assemble the fins with the rocket upright and use a second marble tile to ensure that the reference edges of both plates are in a plane. For those who haven't worked with a 2-plate jig before, or who wonder how it works, the key is to make both plates have identical cutouts for the fins and tube, and at least one reference edge. Then you put the reference edge on a flat surface and spread out the plates, and that guarantees that the fins are at the right location and angle from the body tube, and that they don't have any more twist (roll) than does the flat surface that you put the reference edge on. Here I'm using marble floor tiles from Home Depot as my flat surface. These things are great for a variety of tasks, because they're rigid, polished flat and they only cost about two bucks apiece. They're great for laying up flat fin stock, checking perpendicularity, etc. Here I'm using the back one to make sure all the fin trailing tips in the same plane as the motor, and the one on the side is my reference surface to make sure that the fins aren't twisted.

With the fins in the jig, I tacked them in place with CA, and verified that they look good before I make epoxy fillets (tomorrow):



This is one of my favorite parts of rocket building, when you can see the rocket start to take shape.

[patelldp]

Looking good! I love the fin design.

I enjoy your builds because they are always very clean and aggressive in nature. You're careful in your design and you build for the application...something I wish I was more capable of from project to project.

[dixontj93060]

Adrian,

Have you simulated that fin shape? It seems like clipped delta or delta fins would give you higher performance.

-Tim

[Adrian A]

Looking good! I love the fin design.

I enjoy your builds because they are always very clean and aggressive in nature. You're careful in your design and you build for the application...something I wish I was more capable of from project to project.

Thanks. For sure, this is the cleanest state that this rocket will ever be in.

Adrian,

Have you simulated that fin shape? It seems like clipped delta or delta fins would give you higher performance.

-Tim

I have simulated it. Small changes in fin area make small changes in total altitude. The shape of the fin doesn't seem to affect the RASAero results much, though I think there is some benefit to keeping the leading edge angle less than the Mach angle. Above Mach 2 this becomes somewhat impractical, since the angle for Mach 2 is 60 degrees, which is about what this one has. In theory, another thing that should affect the drag is sudden changes in cross-sectional area. I try to avoid having perpendicular trailing edges for that reason, so if I used a clipped delta shape with a forward-swept trailing edge, the center of pressure would have moved up considerably.

It's interesting to play with the Barrowman equation results in Rocksim, and adjust the sweep length back and forth with the trailing edge fixed to the back of the rocket. For skinnier rockets, a clipped delta moves the Cp back the best, but for shorter, squatter rockets you can do better by moving sweeping the fins back past the back of the tube. Here I was able to get more stability margin by sweeping them back more, and I think the only real disadvantage for this rocket is fragility on landing. I'll take my shot at making them nice and strong with a lot of uni fiber carbon in fin reinforcing layups, and we'll see if that's enough to prevent damage.

Fillets are on now. I had some trouble with a fin breaking off when I was masking it earlier this morning, but it was pretty easy to fix with the jig. I used about 50 grams of Aeropoxy/colloidal silica mix for the fillets. and I put it in a heated cardboard box to speed up the cure. When I took it out, I found that one of the fins had cocked sideways from being set that way in the box. I spent some time with a heat gun, tape, and curse words to get the fin straightened out. It's curing on my dashboard now. More pictures later.

[dixontj93060]

For skinnier rockets, a clipped delta moves the Cp back the best, but for shorter, squatter rockets you can do better by moving sweeping the fins back past the back of the tube.

This may be the difference. My minimum diameter, high altitude designs have a longer profile.

[Adrian A]

Fillets are done and shaped. Next is designing the fin reinforcement layup and cutting the pieces....




This is just for fun, missing the nose section of the tube. When I'm done the motor will stick about 6" past the end of the aft tube and the nosecone will go from there.

[Adrian A]

I laid up one side last night.

Here are the carbon uni pieces:



The layup came out pretty well. I used a 55 gallon drum liner garbage back for the vacuum bag, which went well once I supported the ends against getting sucked into the middle of the tube. When I do the rest of the layup, I think I'll try putting another bag in the inside of the tube that has ambient pressure. The first tip-to-tip layup added 28 grams. I think it will be enough to provide the strength I want, but it's not overkill. Overkill might have been better though. I'll have a better idea of the fin fragility after I get the reinforcing layup on both sides of one fin.

[StanO]

Adrian

Great thread...love the fin jig..will try that on my next rocket...I'm subscribed..looking forward to more.

Stan

[Adrian A]

Thanks. Today I laid up the other two tip-to-tip sides at the same time, with the first side on the bottom. That went pretty smoothly. For the vacuum bag, I put a trash bag through the inside of the tube and blew some air into it, then tied up its opening along with the regular exterior bag. That worked like a charm to keep the vacuum bag from trying to pull into the ends of the tube.

I did a little post-cure in the oven, and the fins came out nice and strong. I can (and did) stand on the fins with no ill effects. The fin tube assembly came out to 590 grams, so today's layup came out at exactly 28 grams per side to match the first side. The only thing I'm not totally happy about is that now 2 of the 3 fins have a slight warp to them. For my L3 version of this I know now to watch out for situations that might bend the fins during reinforcement steps.

Still to do this weekend is the av-bay, reinforcing the nose tube, and filling finishing the fin can. But also work and attending a Colorado Symphony concert, so I think I'm running a bit behind. Tonight I will try to get going with gluing av-bay parts that need it so they can cure overnight.

[Adrian A]

On Sunday I used some Aeropoxy+colloidal silica to fill in divots on the fin can. It looks pretty good now. Still a couple of rounds of finishing left for it to be perfect, but I could fly it now after a quick sand if I wanted to.

I finally got going on the av-bay:

[ClayD]

? did you permantly afix the telemetrum?
Well i am guessign thats what that is.

what is your total avbay weight.

(can i borrow your avbay...)

[Adrian A]

? did you permantly afix the telemetrum?
Well i am guessign thats what that is.

what is your total avbay weight.

(can i borrow your avbay...)

I didn't permanently attach it, but I did remove a couple of its connectors to get it to fit. I'm attaching the front (antenna) end to the plywood central piece, and at the back end I'll solder some nuts onto the mounting holes and have screws attach it to the small fiberglass piece you see going across the front. I may have 2 of the 3 power wires soldered to those nuts too, so that I can use the mounting screws for the electrical connections. I'll permanently glue down the batteries and the 2 magnetic switches, but the Raven, Telemetrum and BigRedBee GPS will be fully removable.

I did a test fit with the av-bay outer tube, motor tube, av-bay assembly, all electronics and batteries, mounting bolt, and motor forward closure and it was 604 grams. That's everything but the chute, pistons, and harness, plus the forward motor closure. I'll weigh the forward closure by itself later so I can get the add-on weight. The chute tube and av-bay tubes are both pretty heavy, but they're very strong. This thing is going to look like a reinforced cannon when it's done. I'll glue the av-bay tube onto the chute tube tonight, or maybe if I go home at lunch.

[Adrian A]

I was just reflecting last night that it was exactly a week since it occurred to me to build this rocket for Oktoberfest. Since then, I have nearly completed the fin can, I made the chute, tested the electronics, and designed and built the electronics mounting structure. Still left to do is to mount and wire the electronics, cut and glue the nosecone airframe tube, drill the harness attachment holes, make the chute piston, caps and tie the harness. Add nose weight to the nosecone and add the nosecone shock cord And ground test. 3 evenings, 4 if I have to. I think I can do it, but it will be close. I'm debating whether I want to put a wrap of uni carbon around the nosecone airframe tube.