Minimum Diameter 3" design/build

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Conway Stevens

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Going to be building a 3 inch rocket for altitiude. In the planning stages right now. Looking at the Wildman Blackhawk 75xl as the base for the platform. May be other ways to skin this one but here are my ideas. I would do Rocket it as is and do t2t carbon fiber on the fins and build it to fly...... OR... I wont use the fins on this body tube (use them on something later) and utilize a aluminum fin can that mounts directly to the motor case and then slide the body tube down, cleance the fins of the fin can so the body tube slide down under the leading tip/base edge of the fins. The motor and the lower body tube would give me over 60 inches of clearnce for long motors (think long burn long case research motors as well as comercial flights) the rocket would have motor retainer done in the rocket above the motor similar to the aeropack min diameter retainer but fastened with set screws and thread into the forward closure of the motor. This would be the tie in point for the lower drouge harness with stainless one piece eye bolt. it would also be the retainer for the motor, the lower bodytube. the fincan also would retain the motor as it is the thrust ring point. will have dual altimeters of different brands on board. Choices with what I own will be RRc3, Raven 4, Proton. redundant charges with things set to ofset so charges wont go off at the same time. On board will also be a nose code av bay for GPS tracking from either Featherlight or Eggfinder. But this is my starting point. currently in the design stages ive managed to utilize the Aerotech M985 for altitudes well into the 35k ranges. This rocket also has the ability to be changed from standard duel deploy to HED dual deploy. It allows me to change the lengths of the rocket by changing out the booster body length with different tubes, as well as HED. This allows for a somewhat modular assembly to be able to fit any 75/76mm motor combo and change the weight, length or deployment capacity adding video flights or just purely altitude flights.

Always open to suggestions and ideas. not one of us knows everything.
 
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Conway Stevens

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Ok I've actually decided to expand this thread on to several different minimum diameter projects I'm doing. One Is the Wildman Mach2. Another is a 75mm min diameter custom built unit utilizing a aluminum Max Q fin can from Binder Design. Another will be 54mm mach min diameter Mach 1 kit and a 75mm min diameter Mach one kit. Unfortunately around just before Christmas I got horribly ill with covid, that turned nasty to covid and bacterial pneumonia. Then a blood clot that caused a pulmonary embolism. Was in the hospital for some time but now I'm home and have all these great projects here. Unfortunately I have some hopeful short term neurological issues from covid that making working on rockets difficult. I will be out of work for the next 6 weeks trying to recover from it all and would like to work on these to pass the time on something I enjoy. looking forward to sharing these. .
 

Conway Stevens

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Finally got the fin can From Mike Fisher at Binder Design. worth the wait and the cost. 75mm sub minimum diameter can. Mounts directly to the motor case. Done in polished aluminum then anodized purple.
 

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Conway Stevens

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Started doing some of my hands drawn up ideas along with rocksim 10 and open rocket designs.
Want this rocket to be fairly modular. Be able to change lengths, standard dual deployment zippereless or head end deployment. Handle any length or power motor 75mm can deliver. But specifically for altitude and long burn motors.

Rocket in dual deployment mode will be its heaviest and longest. With motor case no propellant. Completed should weigh around 10lbs. And 19 to 20 on the pad ready to fly with the AT m685. Currently weighing all the pieces except for the added piece of airframe. And the final modifications. It weighs 5lbs. I do need to modify he fins and grind just enough for the body tube to tightly slide under the fin tips of the fin can and but up against the fin can body.
 

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Conway Stevens

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Im trying to decide if I want to modify the fins of the can by shaving a small amount off each one so the body tube would slide down and but up against the fin can body. Or.... cut slots in the body tube that would allow the fins to go into them and again allow the body tube to slide down and but up against the fin can. I'm leaning towards slots in the air frame. It shouldn't make any physical or structural differences as the fins will fit tight and slide in place. It's then secured tightly with an internal retainer that uses set screws to hold the retainer to the body tube. Then will bolt into the forward closure of the motor. The recovery harness will attach to the retainer. With an stainless steel eye nut/bolt. This should hold all the lower section tightly together, Retain the motor, fin can and lower body tube.
 
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rfjustin

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Im trying to decide if I want to modify the fins of the can bu shaving a small amount off each one so the body tube would slide down and but up against the fin can body. Or.... cut slots in the body tube that would allow the fins to go into them and again allow the body tube to slide down and but up against the fin can. I'm leaning towards slots in the air frame. It shouldn't make any physical or structural differences as the fins will fit tight and slide in place. It's then secured tightly with an internal retainer that uses set screws to hold the retainer to the body tube. Then will bolt into the forward closure of the motor. The recovery harness will attach to the retainer. With an stainless steel eye nut/bolt. This should hold all the lower section tightly together, Retain the motor, fin can and lower body tube.
I like the idea of small slots in the body tube... it then basically "indexes" with the fin can.
 

Conway Stevens

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I like the idea of small slots in the body tube... it then basically "indexes" with the fin can.
Was the direction I was leaning. If I decide on a different project I can utilize the fins again and just use a different body portion of the fin can to fit other things.

I notice alot if your minimum diameter stuff uses 4 fins. I assume this helps control spin of the rocket a little better? How much loss in altitude vs 3 fins fo you feel there is? Thought about doing fin can 4 fin.
 

rfjustin

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Was the direction I was leaning. If I decide on a different project I can utilize the fins again and just use a different body portion of the fin can to fit other things.

I notice alot if your minimum diameter stuff uses 4 fins. I assume this helps control spin of the rocket a little better? How much loss in altitude vs 3 fins fo you feel there is? Thought about doing fin can 4 fin.
 

Conway Stevens

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Makes sense. Committed to a 3 fun design at this point will just have to let it fly and sew how it does. Will double check the empty propellant stability. initial Sims in the shortest and lightest configuration with head end deployment should be close to 30k on m685

Thank you as always for the input Justin. Always appreciated.
 

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Conway,

I'm glad you're doing better health wise! Sounds like a great project and I'll be following your progress.

Fred
 

Conway Stevens

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Conway,

I'm glad you're doing better health wise! Sounds like a great project and I'll be following your progress.

Fred
Thank you Fred. Still gonna be another 6 weeks of recovery. Dealing with blood clots in my lungs, suffered some pretty heavy lung damage. Let alone the ongoing fun neurological stuff. But definitely better than I was. Glad the hobby is here for me to put my hands on and give me something to feel good doing. Appreciate my friend!!
 
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Conway Stevens

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Finally got some more pieces for this project. The motor case i mocked it up with for now is the Loki 76/6000 case. I just got my AT 75/7680 hardware
There is a pretty decent size difference. As well as a weight difference in favor of the AT motor. My intended motor will be the M685. Long burn 7562 ns motor. Burn time almost 12 seconds. Initial thrust 341 lbs. Im starting this particular project with FWFG airframe. There is the potential i may build a carbon fiber airframe to see if i can futher lighten the weight.
 

Conway Stevens

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Here is some shots of the motor hardware Loki 76/6000 vs 75/7680 AT. Including weights. Weight of just case, and each motor hardware set complete minus propellant weights.
 

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Conway Stevens

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So for more NS in the AT hardware there is also substantial weight savings. This allows me to run as large of a 75mm M motor thats a non research load. Not sure if there is weight savings vs the 75/7680 case and a CTI 6 grain. CTI has only one long burn M motor and it fits the 6 grain case. M840. It has 9 seconds burn time. With initial thrust of 459lbs. So harder off the pad but not nearly as long burning. At this point everything including Sims have the AT M685 as the best choice. I have not made my sims 100% spot on. Still more design. Weight and data input to do. But at thid point a rough guesstimate would be around 30k.
 

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Will be measuring, weighing, and dialing in my components as a majority of them are here. With basically a pile of parts not yet trimmed down minus the electronics, main chute, ejection charges and ematchs, plus minor hardware comes in right under 10lbs. So 12lbs with everything minus propellant isnt out of the question with FWFG air frame. I suspect i should be able to dial that down some more. Plus.... being an aluminum fin can it should handle any boost you put it under.
 

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Measured a 5 ft section of FWFG airframe for weight. It weighed in at 42.3 oz. Thats 0.705 oz per linear inch of airframe. Measured a 5ft section of carbon fiber airframe. it weighed in at 29.09 oz. Thats 0.485 oz per linear inch of airframe.

Total difference between the two is 13.21 oz less for the carbon fiber in weight. I havent figured out what the total length the airframe is yet. But if i need to switch to CF airframe not an issue. The end goal is below 14 lbs total minus propellant.
 

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Got a chance for a little work on the project.

Wss able to cut some tubes. Booster tube cut to 29 inches. Upper body tube cut to 28. The booster tube where its at gives me tye ability to run 38" long motor cases. If i need to go longer a different tube is easy to set up. The upper single piece tube will house all the recovery and av bay. The booster is set up as zippereless. The upper coupler is also the motor retention. Need to square up a couple ends. Managed to measure and dremel cut the slots for the fins so the booster tube will slide down and mate up with the fin can.
 

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Conway Stevens

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Worked on the nosecone as well. Set up the tracking bay. Wanted the nose cone bay to be serviceable. As well as the nosecone tip. This is a high temp wildman nosecone. The av bay is from Mac performance.

Nose bay components. Nose cone and coupler.
 

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Conway Stevens

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Used #8-32 set screws x 3 around the nose cone abd coupler. Tapped the holes as well installed pem nuts into the coupler. Now the bay can be removed as a unit. Things serviced. As well as be shared across other 3 inch platforms.
 

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Conway Stevens

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The bay weight is almost nothing. Its actually extremely lightweight. Haa a 54mm sized tube.
 

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Tractionengines

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We use Avdel's rivet nuts all the time at work. Never tought to use it in a rocket till I just saw your photo. ... thanks.
 

Conway Stevens

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We use Avdel's rivet nuts all the time at work. Never tought to use it in a rocket till I just saw your photo. ... thanks.

Ive used them for probably the last 20 plus years. I get the low profile ones. They tend to install flush. Or with a little filing... use them to screw rail buttons in, mount Av bays and parts. Or to keep whatever im looking to together. Strong, light, reusable.
 
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