Fatty Finn - Fanga’s L3 design and build

[MClark]

White base is always good. Nose a second color, no masking, then vinyl letters and accent.
simple and good

 

[Jeremy Sim]

Awesome work mate, looking forward to your updates

 

[fanga]

White base is always good. Nose a second color, no masking, then vinyl letters and accent.
simple and good

Got the lettering ready to go. The name Fatty Finn is an Aussie cartoon strip. I got someone to create me a vector of the original font. I am contemplating whether to get it made as a decal or try and paint it on. I might go with the latter if I have enough time.

 

[fanga]

Awesome work mate, looking forward to your updates

Awesome. Thanks mate. i forgot to mention to ya that I was no longer on FB but you found me here now anyways .

Hows your project coming along?

 

[Jeremy Sim]

Awesome. Thanks mate. i forgot to mention to ya that I was no longer on FB but you found me here now anyways .

Hows your project coming along?

I will be starting on it over the XMAS break

 

[fanga]

Some more updates. Yesterday I completed the nose cone prep. I needed to replace the bolt in the tip with an eye bolt to anchor the shock cord to. I also epoxied the nose cone joiner in place. Similar approach, Surface prep with 120 grit paper, applied small bead of epoxy and inserted coupler into cone. Note i did mask up the areas I didn't wont epoxy going on this time, which was handy as I did end up with a little drizzle and some fingers on the tape.





I also epoxied a coupler into the booster extension section ready. Same prep and application.

 

[fanga]

OK Did a test run of my external fillets. I made a couple of joins using some cardboard and a peice of pine to speed things up. The external fillets will have a 15mm radius so I fashioned a forming device by rounding the end of a plastic putty knife to a 30mm diameter, using a bottle cap as the template. I measured 15mm from the corner on both sides of the join and then ran some blue tape along the edges to form the fillet area.



I added some more wide tape over the blue tape. this may not have been required but gave me more confidence while adding the epoxy. Using the forming tool, I then placed a bead of epoxy up the join. Once enough epoxy was present, I ran the tool down the join, forming the radius of the fillet. I could not get a clean run of the fillet because of the corrugation in the cardboard but got it pretty close.



I can see some air bubbles had formed. This is probably because I rushed to get it placed into the 45^ angle as it looked like the shape was deforming before the epoxy could set. When I do the external fillets, I plan on doing one side at a time with both edges being completed will be at a 45^ angle already. I will also be extra careful to make sure air bubbles are removed.

I also forgot to remove the tape before the fillet was completley set. Fortunatley when i removed the tape it formed a perfect break in the hardened epoxy. I will make sure to remove the tape prior to full setting on the external fillets.




Also the ends of the fillet area will be taped as well to stop overruns on the real ones.

 

[fanga]

Lots of progress made over the weekend. Here is the construction process. First I cut the fins from 4 x G10 4.8mm fibreglass sheets that were aligned at the bottom of the root tab and clamped to hold together. The sides where then cut and sanded flat on a bench top belt sander to make all the fins even. Once done, the airfoils where shaped on sander.

As per design

 

[fanga]

The motor mount was then placed inside the booster by epoxying the centering rings to the tube. All contact points were prepped as normal with 120git sandpaper and wiped clean with acetone. I measured the top centering location and drew a line as an indicator of where to epoxy. I pushed the MM assembly into the booster and beyond the final location. I then applied epoxy to the body tube where the middle centering ring will be placed. I then pushed the assembly slightly the final adhesion spot and and applied epoxy to where the top centering ring will adhere. I then moved the assembly into its final spot, having epoxy applied to both areas.



Once dried, I applied a fillet to the top centering ring

 

[fanga]

To attach the fins to the booster, I built an alignment jig from 2 sheets of plywood and spacers. The plywood had part of the radius of the body tube cut out and a slot cut out for the fin at 90^. This maintained the fin at the correct location whilst the fin joints cured.

To attach, I prepped the surfaces as per normal, ran a small bead of epoxy on the root edge of the fin then inserted into the rocket. I then used the alignment jig to ensure the fin was at 90^ to the body tube. I then heat cured the join in the hotbox for 30 mins as per approach.

 

[fanga]

Whilst waiting for the fin attacements to cure, I began prep of the bulkheads and aft centering ring.

The charge wells were prepared. I drilled a hole into the end caps and mounted the caps to the bulkhead using M4 bolts and a locking nut arrangement. I then cut a 20mm length of pipe to fit into the charge wells and extend to hold the max charge size. I also surfaced prepped the location for the Wago electrical connectors to be epoxied to the bulkhead. Botht he charge well tubes and Wago connectors were then epoxied in. Once cured, I tested the charge well for the charge size of 5g of black powder. There was pleanty of space to pack with dog barf and tape over.




The Aft centering ring has 3 threaded inserts epoxied where the thrust plate will be attached to with countersink screws.

 

[fanga]

Next up was the internal fillets. I prepped the areas for epoxy as per normal and also masked off the areas where i didnt want to get epoxy. This part is always messy and yep I ended up with a bit more in the tubes then I hoped for.

 

[fanga]

Moving onto the external fillets. I did the surface prep as per normal for each fillet then masked off the area for the fillet. I added extra tape to protect the surrounding areas. Using the same tool I formed in the fillet tests, I then poured and shaped the external fillets, doing 2 fillets at a time on each side. Once formed, the filleted were heat cured for 30 mins and allowed to cool for another 30.



The back of some fillets did not form correctly but these were fixed up later with the Dremel.

 

[fanga]

Whilst waiting for each of the fillets to dry, I started ont he eBay sled. First I marked out the area of the sled on some 7mm plywood. I then positioned the parts to make sure everything was going to fit. I then cut out the sled and sanded down each edge on the belt sander.

Once this was done, I drew the center line of the threaded rod the sled will attach to and marked the holes for the cable ties. I also placed all the parts back ont he board and marked the mounting holes. I then drilled all the holes and gave the sled a slight sanding to remove any sharp edges.

Then all parts were attached to the sled by cable ties or by stand offs bolted to the sled.

I then wired up each device as per the wiring diagrams in the design and loomed the wiring with cable ties to tidy up and help provide some structure.

I attached the threaded rods to the bulk heads with nylon threaded bolts on one end and attached the sled to the rods using cable ties.

I then finished the wiring by cutting and inserting each of the charge wires to the appropriate Wago connector.

 

[fanga]

The Aft centering ring was then attached to the booster. the surface area was prepped, a small bead of epoxy was placed at the adhesion point and the centering ring was placed in position. I then masked off all the external areas so not to get epoxy on them and then applied a small fillet of epoxy to the booster body and motor mount joins.



At this point I also prepped and applied epoxy to the area that was damaged during transport of the tubes. This is the spot on the top right of the second pic.

 

[rocketgeek101]

Very nice build so far!

 

[fanga]

Very nice build so far!

Thank you very muchly. I am enjoying the build.

 

[troj]

I'd like to hear exactly what you want to see in the original proposal . I assume an OR drawing, all the materials you want to use throughout the rocket, and why you chose this model?

Note: I'm neither a TAP nor an L3CC, but I've been through the process as well as having watched others go through it.

What someone will want to see can depend on a variety of factors - one of them being how well they know you and how much they've witnessed your flights. Someone who doesn't know you may want to see some documentation on previous flights you've made, to gauge your skills and experience.

Before buying a single component, it's typically best to have the design reviewed and agreed to. Otherwise, as the discussion progresses, you may end up having to make changes, which means additional purchases.

For someone remote, I'd expect to provide more "physical" documentation. For someone local, you can go more of the "conversation" route.

Regardless, I'd expect to have to provide a design and evidence that the rocket will be stable on ascent and recover safely. In addition, show the certifying individuals that you're ready to go after a Level 3.

-Kevin

 

[Jeremy Sim]

great build so far Brad, when will you be doing the flight?

 

[fanga]

great build so far Brad, when will you be doing the flight?

Thanks mate. I am looking to fly at Mullaley on 29th Sept. Just a few weeks away.

 

[OzHybrid]

Whilst waiting for each of the fillets to dry, I started ont he eBay sled. First I marked out the area of the sled on some 7mm plywood. I then positioned the parts to make sure everything was going to fit. I then cut out the sled and sanded down each edge on the belt sander.

Once this was done, I drew the center line of the threaded rod the sled will attach to and marked the holes for the cable ties. I also placed all the parts back ont he board and marked the mounting holes. I then drilled all the holes and gave the sled a slight sanding to remove any sharp edges.

Then all parts were attached to the sled by cable ties or by stand offs bolted to the sled.

I then wired up each device as per the wiring diagrams in the design and loomed the wiring with cable ties to tidy up and help provide some structure.

I attached the threaded rods to the bulk heads with nylon threaded bolts on one end and attached the sled to the rods using cable ties.

I then finished the wiring by cutting and inserting each of the charge wires to the appropriate Wago connector.

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If you cable tie lithium ion packs too tightly, you can cause them to short internally. That becomes really bad when the flight G force adds enough additional pressure to take that critical. You want the packs restrained, but not crushed. The smallest looks crushed.

 

[fanga]

If you cable tie lithium ion packs too tightly, you can cause them to short internally. That becomes really bad when the flight G force adds enough additional pressure to take that critical. You want the packs restrained, but not crushed. The smallest looks crushed.

Thanks Norm. I think I did that on the previous rocket. I had a closer look and I think its just in the casing. Or maybe not as I went to test the electronics yesterday and that batter is screwed. I've got a replacement for it.

 

[fanga]

Alrighty time for Layups. Each tip-to-tip section gets 3 sheets of fibreglass, the sebcind cut at 45^ to the weave to increase the strength. The first covers about 1/3rd of each fin and the layers then move out. I then placed a layer of peel ply on top to soak up excess epoxy.

I created some templates for the fibreglass sheets out of paper. You can see in the photos how each layer goes. Then its lots of sanding and acetone for surface prep. I then cut a set of fibreglass sheets ready to go.

I then prep the epoxy. I am using West Systems 105 resin with 207 hardener. I am using the measuring pumps so no need to weigh. Starting with layer 1, I pre-preg the sheet and also the surfaces. I then put layer one in place. I repeat the pre-preg for remaining layers and place them on the body. Then I lay the peel ply on top to help soak up the excess epoxy.

I then placed the booster into the hot box for heat curing. 30 mins at ~50^c followed by 30 mins cool down.

I then repeated this process for the other 3 surfaces.

 

[fanga]

Also finished off the wiring of the switches and clear coated the switch band.

With the switches, I am using Schurter Selector Switches. Now I can hear people going to be pointing otu to me that they may not be the best but i have been using them in 2 other rockets for the last year. My Taps are OK with this choice so I will go ahead and use them.

Given they are voltage selector switches, they are not designed with a lot of duty cycles in mind. I am about to replace the ones on one of my other rockets as its seen about 6 flights and probably about 30 cycles each.

I soldered the switch ends and used JST power plugs to allow the switches to be disconnected from the main wiring. The wiring is loomed with cable ties to reduce tangles and to add strength. The JST connectors will be taped together with electrical tape to reduce the likelihood of vibrating loose.

I created a drill template around the switch band to mease the switch holes and the static ports. These were then drilled and sanded down to remove rough edges. I then surface prepped the switch band for painting. I gave the surface a sanding and a wipe with Acetone. I then use a spray can of clear coat to paint the switch band. I then repeated for a second coat.

Once the clear coat was dry, I mounted the switches with the locking nut on the back and applied hot glue to stop movement.

 

[fanga]

With the final finish, I decided I will go clear coat. It just looks awesome, even with warts n all.

 

[fanga]

Now all the layups are dry, I removed the peel ply, used a knife to cut the excess glass away and sanded each surface until smooth. There are a few blemishes but I think I can live with this and I don't think they will cause weaknesses in the layups. Might be time to learn how to Vacuum Bag.

 

[loopy]

Very nice!

 

[Jeremy Sim]

Hey Brad, tip to tip glass really necessary? what's purpose? I would have assumed that the internal and external filets would have been enough?

 

[fanga]

Hey Brad, tip to tip glass really necessary? what's purpose? I would have assumed that the internal and external filets would have been enough?

I was border line not doing T2T and then was convinced to include them due to the cuts in the booster body for the fin slots. This introduces weakness in the body tube. With that in mind and the fact I don't mind adding the extra mass (Lo and Slo goal) I included T2T.

I think the fillets should have been enough but this just game me some extra insurance for the cost of a bit of mass.

 

[fanga]

Got the electronics completed today, along with a new battery for the Featherweight. After testing all the connections, I placed hot glue over each of the terminal blocks to help secure the connection in place. I also taped up the JST connectors so they don;t come undone during flight.




I will do final testing of the electronics with a vacuum test