L3 Build Log - Wildman Interceptor A.A.D. 98

I see what you're doing there.

My set-up was a bit different. I used my nose cone as an av-bay for my tracker. The 9' Rocketman in its 18"x18" nomex burrito wrap (plus the harness) was jammed in pretty tight between the bulkheads of the nose cone and the coupler av bays. The rocket weighed 13.6 lbs with the Rocketman. It deployed well. I think the four shroud lines and slippery chute material helped. But brought the rocket down a little slower than I liked, it was heavy and the fit was problematic.

I ended up trading it out for a 70" Topflight. It shaved the weight by a full pound to 12.6 lbs and opened up some room in the payload bay. I also used a Widman Recon drogue chute. Both work well with multiple flights. The Rocketman is a good chute, I just decided it was a better fit in larger air frames.

As far as the tailcone and centering rings set-up, that's a lot to get lined up correctly. As an option you may want to consider and discuss with your TAP/L3CC:

Rocketpoxy's pretty thick. If you triple-butter the fins, it gets a lot of epoxy at the fin to MMT joint. (triple butter means you spread a bunch on the root edge, push it in the slot until it butts up against the MMT, remove it, spread some more on, push it back in, and then do it one more time.) If you mix black dye in, you can see the joint through the MMT. In fact, looking through from the inside of the MMT, you can see it sags a bit into an internal fillet.

Between epoxy at two joints per fin and the thrust plate property you get from the lip on the tailcone, that's a lot of area to transfer forces. It should be more than enough strength. This would allow some tolerance in the CR location, since you wouldn't be injecting runny epoxy that could leak through a possible gap. I like playing the odds, and I know that if I were to trying to line-up a tailcone and four centering rings with three fins, I'd blow it somewhere. And if I messed up the tailcone location, it might create an unfixable problem.

Just another trick for the toolbag if you want it.

Double and triple dipping. I like it. My epoxy is not usually thick enough to do this, but if i snag some aeropoxy in the future I'll definitely try this.

I have been doing the double dip method for sometime now using Rocket Poxy and it seems to work out very well. No fin has come loose yet.

My solidworks model is for the most part now complete. Seeing the rocket put together also helped me plan a bit better. I have 2-56 (x3) shear pins as a stand in for now and will review them again when everything is assembled (prior to drilling the holes of course). My solidworks drawing was mostly an experimental area. I'm a E.E. and embedded systems engineer so don't let your eyes bleed too much at my first attempt using solidworks.

View attachment interceptoraad98.PDF

3' Rocketman ProXP came in. It weighed about 110g and fit in the booster section like it didn't even exist. My only complaint is that I now have two black parachutes. I prefer the unicorn-diarrhea assortment of colors to help spot it in the sky.

Which reminded me that I need to look into my tracker/locator. I'm considering getting the standard RTX/GPS unit for my RRC3.

fatherchaos said:

3' Rocketman ProXP came in. It weighed about 110g and fit in the booster section like it didn't even exist. My only complaint is that I now have two black parachutes. I prefer the unicorn-diarrhea assortment of colors to help spot it in the sky.

Which reminded me that I need to look into my tracker/locator. I'm considering getting the standard RTX/GPS unit for my RRC3.

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Black is the best for visibility in the sky, from my experience.

patelldp said:

Black is the best for visibility in the sky, from my experience.

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Good to know. I hope that holds true for my eyes, either way I'm sure to find out soon.

fatherchaos said:

Double and triple dipping. I like it. My epoxy is not usually thick enough to do this, but if i snag some aeropoxy in the future I'll definitely try this.

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I've only ever used the triple butter method with Rocketpoxy.

If you decide to use Rocketpoxy: If you let a mixed batch sit over a short amount of time, it gets thicker. When I first mix a batch it’s runny. Starting about 10 minutes after done mixing, I check it every couple of minutes. Keeping in mind the ambient temp and the age of the epoxy will affect this: I find it’s usually good for the triple-buttering around 12-15 mins. It’s good for external fillets around 20 mins. Around 25 minutes it starts to feel more like clay.

So for the triple butter method, doesn't this introduce additional air into the fillet that is being damned up? I was comparing this approach to the sticky on bonding composites, and it appears that by removing the fin you pull air back into the bond area then push air back into the bonding damn when you place it back in. I think the internal fillet injections will be my best approach for now.

I'm also looking into setting up a vacuum chamber to degas the epoxy before I use it.

I am certain that my rocketpoxy tripple buttered fins are as good as any internal fillets that I've ever done. Dave McCann posted pictures of his exploded MAC rocket that had buttered only fin roots and they were as solid after the CATO as before.

I agree with you about the triple butter deal inducing air into the epoxy.

As for the degassing of epoxy I think that is not needed. Use a thinner laminating epoxy like Aeropoxy or West, mix it, leave it sit for a few minutes, suck into syringe, and inject. This will be adequate.

I think we have all agreeed now that a strong epoxy bond is a strong bond. And a bit of air doesn't really matter at the level of power we fly. I will try the butter method on another build to see how I like it.

Also, I really want to make a vacuum chamber. I'm designing a new altimeter to fit my particular needs but it won't be ready for my l3. Sometimes our hobbies are just thin excuses to make more gadgets .

fatherchaos said:

I think we have all agreeed now that a strong epoxy bond is a strong bond. And a bit of air doesn't really matter at the level of power we fly. I will try the butter method on another build to see how I like it.

Also, I really want to make a vacuum chamber. I'm designing a new altimeter to fit my particular needs but it won't be ready for my l3. Sometimes our hobbies are just thin excuses to make more gadgets .

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shhh... don't tell our wives!

Update for everyone: I've designed and printed my camera shroud. One more final print for wall thickness and layer height. Everything is parameterized so I can print for different body tubes and angles. My current version is with 2 degrees tilted off the body.

Just a point of curiosity- have you added the shroud to your simulation to see how it will effect your Cp and stability margins?

I haven't put it in the sim yet. I'll make a pass at it this weekend in open rocket.

I took a bit of a rocket break with a vacation to Alaska and Canada. Below is my recent progress.

The solidworks model is nearly complete, just pending my attachment of the camera shroud. Everything else has been accounted for (rail buttons, shear pins, electronics, etc.) Shroud lines are not shown as I have them conceptually wrapped up in the parachute sausages.



Forward centering rings were filed and rounded with a rat tail file to allow the kevlar Y harness to be attached to the MMT. The top of the MMT was also beveled to wear less on the kevlar straps.

The MMT and centering rings were slid into the body and the fins inserted to act as a guide to tack on the CRs with gorilla super glue. It was more of a gel than I remember but worked well. Once one CR was set as a reference the fins were taped to the MMT and the other CRs were tacked on. CRs were then glued on using west systems epoxy and collodial silica. I believe my final ratio was 1:1 for silica and epoxy. It had a mayo like consistency that worked well. Final result is that I have a small 0.15mm variance on the rearmost centering ring to the lip of the tailcone. I'm satisfied with that.

The Kevlar Y harness is now epoxied in place with a good glob of cat hairball, I mean epoxy with chopped carbon fiber.

Body tube prepped with 5/32 holes for fillet injection and holes for #10 screw for rail buttons. I also solved my rail button dilemma. I want to be able to swap 1515 & 1010 rail buttons. Turns out apogee rockets has 1010 buttons that use #10 screws and I can use a small spacer from mcmaster car to adapt to the 1515, https://www.mcmaster.com/#93441a175/=19gcqy6.

I'm using adhesive nuts for for the #10 screw backing https://www.mcmaster.com/#98007a024/=19gcri6. This rocket has a space of only about 1/3 inch between the MMT and body tube so this felt like a good space saving option.

Adhesive mount weld nuts are now in place. Binding areas were cleaned with 91% isopropyl alcohol then allowed to dry. Weld nuts were then tacked in place with super glue. A thickened mix of slow cure west systems epoxy + colloidal silica was added heavily around the nut. This was delivered via syringe & a length of tubing to act as an injection guide. A screw was threaded into the nut so that the nut could be lifted to make sure the epoxy flowed under the adhesive nut, then tightened to ensure the nut was firmly against the tube. The lower adhesive nut was clamped in place by tightening the screw in gently against the MMT, letting the screw act as a spreader to force the nut against the inside of the booster tube.

Next up, FINS!

Fin tacking using my fin jig. Root edge of fin covered with devcon 2 ton 30 min epoxy. Fin alignment confirmed using a printed fin guide.

I've wrapped up the injected fillets and external fillets. For the injected internal fillets I mixed up a batch of west systems epoxy with a pinch of chopped carbon fiber. My first batch I put in too much carbon fiber, about 2 pinches. This created a hard to use hairball that did not flow when injected. Initially I had injected 5ml per injection hole (10ml for each fin tab face). I had to follow up with another batch of just west systems without any fillers. I put in about 4ml per injection hole and was able to get it to flow slightly.

For the remaining holes I toned down the carbon fiber to 1 pinch and injected 5ml per hole. This worked out well and would settle slowly. To sum it up, each centering ring segment got about 10ml of carbon fiber & epoxy mixture. This gives about 30ml per centering ring face on the fin facing side. Each fin tab face got 10ml of the epoxy mixture, giving me a total of about 40ml of epoxy per fin.

For the external fillets I mixed up a batch of west systems epoxy and colloidal silica in a 1:1 mixture. About 23ml of epoxy and 23ml of loose colloidal silica. This gave a thick mayo consistency for the external fillets. The fillet areas were marked by rubbing a 1" diameter PVC pipe that I had coated with a sharpie, making a visible drag line. This was then taped off using frog tape along the line. Epoxy was poured and then smoothed with a clean 1" PVC pipe piece. The leading area of the fin to body was shaped to a point by hand and the tail end of the fin was rounded off.

A bubble was trapped in one external fillet so I had to release the bubble and excavated the area slightly. The epoxy had not yet fully cured so I made another batch of west systems without any filler and poured it carefully into the cavity. I took time to smooth the area again and with some patience was able to maintain a good finish as it set up.

If you look closely in the photo with the external fillet, you can see the dark area along the centering ring. This is a block of epoxy with CF. Not much of a fillet; more of a bucket fill.

A 5/32" static relief pressure port was added 4" from the top of the booster section, placing the hole about 1" below the ebay edge.

Remaining items:
Glue the nosecone coupler and fillet the inside ridge so chute won't snag.
Drill 3 2-56 shear pins in nose cone coupler
Drill and epoxy pem nuts and external washers to hold the payload tube to the ebay. Reminder that this is a head end deployment.
Drill and epoxy pem nuts for camera mount
Finish ebay electronic layout & drill bulkheads
Install & test electronics, including magnetic switch
4F charge size tests
shakedown flight at roctober 14th or 15th (aerotech K1103x)
TAP approval & L3 flight. I'm leaning towards the cesaroni M1830 or M2250 (assuming its in production, I've not bought any Ms before). Both put the rocket about 12.5k ft.

I got a few more things completed yesterday.... And a nice mishap that wasted about 2 hours last night.

So the good things:
Ebay bulkheads were drilled and test assembled. 5/16", 1" ID U-bolt is used on both ends for attachment ( https://www.mcmaster.com/#8896t68/=19r9kl8). 1/4-20 (2) threaded rods are used to bind the bulkheads of the ebay together. I spaced everything so that I could reuse the ebay sled from my madcow torrent just in case. Test fitting went together well.

Vent band was drilled with 3x 5/32 based on the port sizing guide from https://www.vernk.com/AltimeterPortSizing.htm.

3x 2-56 shear pin holes made in the payload tube and nose cone coupler. As before, I line up the parts and bind them with tape so they can't slide around. Then I drill the first hole and insert a nylon screw. Drill the second hole and insert a nylon screw, and then I drill the third hole and insert the last nylon screw.

Epoxy chamfer fill inside the nose cone to make a smooth transition between the nose cone and coupler. I did this to reduce the likelihood the parachute will snag on the edge of the coupler. West systems 105/206 was mixed with collodial silica till I got a nice creamy peanut butter consistency. The mixture was applied with a small dowel. The first pass was to glob it in place and fill the gap. On the second pass I angled the dowel across the edge of the coupler to the inside wall of the nose cone. This was then walked around the nose cone to smooth out the epoxy and capture any excess. A quick inspection showed that this was fairly smooth.

Pem nuts to hold the ebay and payload tube together were epoxied in. My first attempt at this failed. The pem nut requires a 1/4" hole to be drilled. The fins on the pem nut extend to give a diameter of 0.27", so when they are press fit there is some cutting and capture of the substrate. This did not go according to plan.

I attempted to press fit in the pem nut to the ebay hole with a clamp but it did not penetrate. So I got the bright idea to use one of the washers I will have on the outside and try to pull the pem nut in using one of the #8 screws. This worked fine at first, the screw went in nicely and once I had everything tightly together the pem washer deformed to fit the tube perfectly.

Then my socket head snapped, leaving a the screw socket hole completely filled. I got the bright idea to use a pair of pliers to twist the screw out by grabbing the exposed threads inside the ebay. This worked just enough to encourage me as I got about a quarter turn before I couldn't grip it anymore in the position it was in. So I pry at this for a while without any success. The more I couldn't turn it the more I was determined to grip it and turn it. A rather comical cycle of frustration.

After a while my brain decided to offer some advise, "Hey, use the dremel to cut a slot in the screw and just screw it out. That's what we usually do instead of grabbing the threads." So, finally remembering how I remove plugged socket screws I cut a slot and was able to twist the screw a bit with a screw driver. It came loose just enough to encourage me to keep trying to grip the pem nut with pliers and back the screw out. But the crushed threads did not have any interest in proceeding through the pem nut so I had to cut and peel back the pem washer for a bit. Then ever so carefully cut off this tiny 1/4" protrusion of a screw head without damaging the fiberglass tube. Another 20-30 minutes of surgery removing the screw head with the dremel and the screw just fell through.

With the pem nut removed I waited until this morning to epoxy it in. A nice sun exposed heat cure to help hold the West Systems epoxy in place.

I'll tag some images up later today.

Didn't get a chance to get my pictures up last night. But I'm excited about tonight.

Charge size testing!

My charges will be using the nitrile glove finger tip method. Pour required 4F into finger tip of nitrile glove (already cut off), insert ematch and zip tie together. The overall package should be snug without a lot of excess air with care taken not to pack or compress the 4F. I'll be aiming the rocket at a nice soft bush that I don't like.

Why don't you want to pack or compress the BP?

I've been taught to pack it loosely for something like this (loose charge). When I say pack, I mean compress it I to a tight conformal shape, such as a cylinder or ball. Past experience taught me it is safer to load and handle if I use the grains as poured.

I think there is an old thread here too about not compressing the 4f.

Hi all,

I have a big update inbound. In the meantime I have nearly all the weights dialed in, assuming my bathroom scale was accurate enough for me+rocket minus me only. All weights were measured on my lab scale to .1g accuracy. Unfortunately, the scale is limited to 2KG, so I'm only reasonably certain on the booster section (+/- 100 grams). Parachute, Kevlar harness, tail cone, etc are all spot on for weight.

The great news is that my rocket comes in about 11.6lbs/5.26kg. Dog barf will add a few grams, so I'm confident using these as my running numbers. My original over estimation in weight was due to including the motor casing and enclosures. I read that the motor weight includes that of a nominal case. I'll update the on the pad weight once I have a motor in hand.

My design file is attached for everyone to review. I'd appreciate any comments towards a sanity check.

Pending are my adjustments to the rail buttons and camera pod. I have not added the camera pod yet, as I'm trying to figure out exactly how to do that.

View attachment Wildman AAD 98 Interceptor.rkt

Updated sim file with motor selection, finish, camera pod stand in, rail buttons, and some just for fun texturing.

View attachment Wildman AAD 98 Interceptor.rkt

My "just before the paint" update. Ebay is now complete, pending additional review of how I mounted the 9V battery. On the sled is a Missleworks RRC3 and Featherweight Raven3. RRC3 is activated using the Featherweight magnetic switch and powered by a 9V battery. The switch terminals were jumpered since I control the power source. The raven3 is mounted using the power perch, so the same magnet activation is used. While not shown in the picture, I will be using the included 130maH battery.

The Ebay bulkheads have been drilled and the 5/16 U bolt with 1" internal spacing have been mounted. One 4 port touch safe terminal was mounted on each bulkhead allowing for primary and backup charges to be connected. The fly nut shown is just so I can easily assemble & disassemble. The final assembly uses a nylon locknut. The wire hole will be sealed using duct seal putty https://www.lowes.com/pd/Gardner-Bender-1-lb-Pug-Duct-Seal/4595233. The wires from the bulkhead are joined using XT60 connectors so the ebay sled can be disconnected from the bulkheads and swapped in full to other rockets. I have a 7" fiberglass sled prepped

The ebay has 3 pem nuts mounted inside and held with epoxy. These are joined by #8 screws to the pem washers visible on the payload bay. In this way the payload bay is secured with the ebay for head end deployment.

The rocket will use the air foil rail guides from apogee, re-threaded with a #10 screw. The #10 screw allowed me to use either 1010 or 1515 rail buttons.

I met with my TAP and got the nod to proceed. Now to get the rocket in final prep and have my paperwork in order. Looks like I'll be going up on an AT M1780NT in a CTI 75mm casing. Sims are placing apogee about 13K feet with 2m/s | 4.5mph winds. At 2 m/s wind I have just about 1.1 calibers of stability off the rail (8ft rail) and an off the rail velocity of 101ft/s | 31.8m/s. If I adjust the wind to 5 m/s | 11 mph, the off the rod stability caliber is about .85. So, the take away here is that if the wind is calm a minimum 8ft rail will do without any additional hassle. If there is a bit more wind (about 10mph) I'll need a 12ft rail and add about 200g of weight to the nose. One small jar of nutella chocolate peanut butter or two sticks of butter is about 200g.... Just so I have a reference.

For tracking I've placed an order of the Missileworks T3 (https://www.missileworks.com/t3/). It should be here Saturday.