LOC RNWS - Removeable Nosecone Weight System
My goal with this “technique” build was to familiarize myself with the LOC Removable Nosecone Weight System so I could use it in some upcoming LOC builds I had on the pile.
I can say that the system works well and it is worth the effort, but, if you have a way to fabricate your own plywood parts, it would be pretty easy to replicate the system using any standard nosecone. I use a Shapeoko 3 CNC router to fabricate my parts, so if I need to build out future versions of this system, I feel confident in doing it myself. The system is pretty simple and the only thing you would need to buy extra from a rocket kit is a bit of hardware, your own plywood and some tubes that are appropriate for your build.
I am building out the 7.6” version of the RNWS kit, which consists of a 7.6″ nosecone, a “main” tube they refer to as an MMT in the instructions (“main mounting tube”?), a number of “cartridge” tubes (they sent me 5 total in the kit I bought – not sure if that is standard (On their website, it only shows 1 cartridge tube and one spacer tube), some bulkheads, and some hardware.
Couple things you should be aware of if you build out an RNWS. The instructions and pictures on the website are for the 5.5″ version. This is significant, because one difference is that the “spacer” tubes on the 5.5″ version are a different length than the “cartridge” tubes, whereas in the 7.6″ incher version, all the tubes are the same length. That threw me for a loop because in the instructions it talks about the short spacer tube, which I couldn’t find. It took me a bit to figure out what they were talking about. To confuse matters a bit more, the instructions alternate calling the “spacer” tube and the “cartridge” tubes “couplers”. They are couplers, for sure, but I admit when I figured out what they meant by “spacer” and “cartridge” and then the next instructions say “insert the couplers in the main tube”, I was lost for a minute before I realized what they were talking about.
Anyway, parts photos for what I got are below. The nosecone you get with the RNWS is exactly the same as the one you get in their other 7.6″ kits, they just sliced the end off. So, you could just slice the end off the one you get in your rocket kit and use that.
RNWS nosecone on left, Bruiser NC on right:
My next change to the kit was to replace the tee nuts
Frankly, it appears to me that what LOC has is a lot of generic parts laying around and they just grab the bits you need for each kit. What happens is that you get the same tee nuts for 1/4″ plywood as you do for 1/8″ plywood. The thickness of the various plywood pieces is all over the place.
So, for both the RNWS rings, the tee nut barrel extends 1-2mm past the other side of the wood. To me, this is a bit lazy. Either use thicker wood for those parts or tee nuts that fit. Most experienced builders will be able to get around this issue, but if you were uninitiated in the use of tee nuts and follow the directions, which are basically “put the ring on a hard surface and smash the tee nut in with a hammer”, you will definitely either break your hard surface or break your tee nut and make it unusable.
As a test (knowing I would not be using this tee nut and knowing this is not the way I would normally install a tee nut), I put the ring on the concrete floor of my garage and smashed a tee nut in with a hammer. As expected, the edged of the tee nut broke off and a screw would definitely not thread into the nut anymore (I tried). Bad picture, but here are the results:
The other issue I had with their tee nuts is that they used ones that have teeth that are also longer than the thickness of the wood, so they tend to break through the other side and it is difficult to get the nut in evenly. Heck, the teeth are longer than the barrel!
So, I replaced them with higher quality tee nuts that have the exact barrel length of the wood thickness and teeth that go about half way through the wood. In the picture below, the LOC tee nut is on the left and the ones I used are on the right. In the picture it looks like the LOC one is the same thickness as the wood and the other ones are short, but that is due to my poor picture taking, not reality.
With the properly sized tee nut, it is easy to use a vice to get a clean, even insertion of the tee nut and ensure you get a good result.
To build out the main tube, you insert two of the cartridge tubes in the main tube (or, a spacer tube and cartridge tube if you are making the 5.5″ version), and make them flush at one end. That will become the end that faces the aft end of the nosecone. On the other end of the main tube, the cartridge tubes should come to about an inch away from the end. Put the “MMT Bulkhead” in that end (it should have a couple holes to allow the air to pass through when you put in a cartridge later) and epoxy it in place.
Next, I epoxied the backs of the tee nuts and used some tape to keep the epoxy out of the threads. In the photo below, there is also some rings from an MMAS system I was building out at the same time.
The next part in the directions can be a bit confusing. It talks about tilting the nosecone, pouring epoxy in so it doesn’t get on the tee nuts, etc.
This isn’t that difficult. The main tube will touch the nosecone up near the tip. They are talking about getting some epoxy on the inside wall of the nosecone up there to stabilize the main tube. This isn’t going to be structural in the sense that this epoxy isn’t going to really hold the RNWS in (the large main “shoulder ring” will do that), this is just to keep the main tube stabilized and straight.
To illustrate, I took a picture of the main tube in the NC before I inserted the shoulder ring.
Make sure you remove the cartridge tubes from the main tube before proceeding. You could inadvertently epoxy them into the main tube.
I roughed up the inside of the nosecone thoroughly with 60 grit. It is some tough plastic. It was difficult to make a mark, even with 60 grit.
Then I inserted the shoulder ring (with the tee nut backs facing toward the tip of the nosecone – you want to pull on the tee nut when you tighten a screw in it) and snapped in place.
I poured a bit of epoxy behind the shoulder ring and rotated the tube to make a fillet behind the ring. I let that cure, then put a healthy fillet on the aft side of the shoulder ring as well.
Then I poured some epoxy straight down through the hole in the shoulder ring into the tip of the nosecone and rotated the nosecone to coat the inside wall where the main tube would hit. You don’t need a huge amount here, if you use too much epoxy, it will drip down inside the main tube and that could make it hard/impossible to insert the cartridges later.
With the main tube in place, I screwed the large retainer ring on to hold it in place then turned the whole nosecone right-side up and let it sit overnight to cure.
When I went to build the weight cartridges, the parts (or lack thereof) they sent me seemed a bit wonky.
They send enough parts to make one complete cartridge. There are some extra tubes, though, but no bulkheads or hardware.
Hardware is easy – it is just an eyebolt and some washers and hex nuts. I didn’t like their bent eye-bolt anyway, so I replaced it with a forged one. I realized that, if you want to be able to fly the nosecone without weight, you need at least one empty cartridge, so they should send you at least two complete sets.
I CNCed enough extra bulkheads to make 3 cartridges.
Procedure is pretty simple – epoxy a solid bulkhead at one end of the cartridge and leave yourself enough space to fillet it really well. I left myself about an 1/8″ and just poured some epoxy over the end of the bulkhead as a “fillet”.
I then mixed up a pound of BBs and epoxy and poured the slurry into the cartridge. Once it was cured, the instructions say to fill the rest of the empty portion of the cartridge with newspaper. I chose to foam it. I mixed up about 25ml of the PML two-part expanding foam with 3 drops of water. Turned out to be the perfect volume. While the foam was still a little soft, I inserted the top bulkhead with the eye-bolt in it and the end of the eye-bolt was secured in the foam.
I poured another epoxy dam on top of the bulkhead to secure the whole thing in place.
Then, just label them as you go.
I am not sure if LOC has a solution for this (There is nothing in the instructions about this I could find), but when you try to insert one of the weight cartridges in the main tube, there is nowhere for the air in the tube to go since you epoxied the main tube to the end of the nosecone. I solved this with two small 1/16″ vent holes right near the tip of the nosecone. After that, the cartridges slid in and out with no issues.
And that’s it – system complete. When you want to use it, determine the weight you need, attach your shock cord to the eye bolt, insert the cartridge in the main tube with the spacer on top of that and secure it place with the large bulkhead and ¼”-20 screws.