Estes Cosmic Interceptor

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Note about using kevlar as shock cord anchor. Make sure it's long enough to reach above the wadding/dog barf, lest ye melt your elastic in the stuffer tube :-(

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3) make sure you sand the fin surface then REALLY carefully clean and remove the balsa sawdust off the fin before using the label. I've found a little norwex microfobre cloth is PERFECT for this. Failing to do so means you lose much of the stickiness as it just sticks to the little fibres and can lift.
My method is, after brushing off as much sawdust as possible with a soft paintbrush, apply a piece of blue tape to the entire fin surface and lift it off. This pulls an impressive amount of additional dust out. Sometimes I'll do it more than once.

5) I've tried applying thin CA to the middle of the paper to overcome (4), but with the Avery labels I have, I've discovered the thin CA doesn't penetrate through the paper - there's something in the paper / adhesive layers that prevents it soaking through. It works at the edges, but not really well in the middle of the fin.

I was advised early on in my papering career that CA didn't work well with the label paper, and so I went right to using wood glue. After sanding the paper edges so the fibers are kind of blended into the wood, I apply a thin bead of wood glue along the paper edges, then sand smooth with 400 grit when dry.

I admit this seems inadequate compared to the CA soaking that others do, but (knock on wood) I haven't even had a hint of edge lifting on a single fin yet. That said, I cannot (yet) vouch for the long-term durability of this method. I'll be bummed if they start lifting some years down the road, but I'm prepared to take that risk. This might also be a different story for rockets that are gonna go closer to mach and be subject to more severe forces while flying.
 
Note about using kevlar as shock cord anchor. Make sure it's long enough to reach above the wadding/dog barf, lest ye melt your elastic in the stuffer tube :-(

Ouch. >.<

Plan is 2x body tube length of kevlar with double or triple fisherman's bend to the full length of original elastic.

My method is, after brushing off as much sawdust as possible with a soft paintbrush, apply a piece of blue tape to the entire fin surface and lift it off. This pulls an impressive amount of additional dust out. Sometimes I'll do it more than once.

I was advised early on in my papering career that CA didn't work well with the label paper, and so I went right to using wood glue. After sanding the paper edges so the fibers are kind of blended into the wood, I apply a thin bead of wood glue along the paper edges, then sand smooth with 400 grit when dry.

I admit this seems inadequate compared to the CA soaking that others do, but (knock on wood) I haven't even had a hint of edge lifting on a single fin yet. That said, I cannot (yet) vouch for the long-term durability of this method. I'll be bummed if they start lifting some years down the road, but I'm prepared to take that risk. This might also be a different story for rockets that are gonna go closer to mach and be subject to more severe forces while flying.

I have many fluffy pets, so I recognise the effectiveness of a sticky roller treatment! Thanks for the tips in keeping the edges down.

Current status is still shaping fins. I'm trying to do a little a day, at least one edge per day. I've also made an angled block that will help to keep the trailing edges consistent when I'm sanding.

UPS have a 2kg package for me that they failed to deliver today. I have no idea what I've ordered that's that heavy, but I'm hoping for rocket bits!
 
Shaped both vertical stabilizers and one of the wingtip plates. Quite pleased with the result.




Spoke with Malcolm from Rocketsandthings. My order ships tomorrow! There was an issue with the full 30+ inch lengths of tubes not being in stock, but as I only need about 10in of each it's no problem.
 
My first two rockets flew brilliantly this weekend, an Amazon and a Crossfire, and now I'm looking to challenge myself.

I've liked the look of a Cosmic Interceptor.

product_image


It was either that or a QCC explorer for my next kit, and this is the one my local vendor had at the field today! It can take 24mm D or E motors, with a stuffer ring for the shorter Ds, and I was recommended a pair of D12-3s for it. I'm told it can also fit Cesaroni Pro24s. So this is my next build.

Before I start, I have an option: it looks like a relatively easy mod to 29mm motors, with an adaptor back to 24mm. Trim the strakes, larger motor tube. The original 24mm motor tube can be fitted with some balsa strake extensions an extra motor clip, and retained by the original clip on the new 29mm tube. It should retain its lines at the rear quite nicely. Is this mad? I've got no way to check the stability with that extra mass moved backwards.

Does anyone know if there's an Open Rocket file of the Cosmic Interceptor somewhere?

Check out my Intereptor 29. I flew it on a G79 or thereabouts. It flew beautifully.

https://www.rocketryforum.com/showt...rceptor-29mm&highlight=tomsmith58+interceptor


Tom
 
Thanks for the link Tom! Really interesting mods.
There's potential for having access to some 3D printers in future, that nozzle looks really cool. I'm particularly intrigued by the baffle system. It's worth considering as I've got plenty of body tube length to work with and filling the volume with wadding is going to be a pain. Did you consider a parachute shelf to stop the parachute going too far inside?

Anyway, got a fair bit done this weekend.

Firstly I finished shaping the fins. I made a couple of mistakes, but nothing that can't be corrected. Time to start sticking things together.

Next, painted the intake grill glossy black. I'm not 100% satisfied with the finish but it's impossible to do better on such a small and delicate part. Small imperfections won't be noticeable when it's installed anyway.

Finally, painted all the body tube bits with thinned down filler. I figure this filling and sanding stage is going to be a lot easier before everything is assembled! I'm a little worried about adhesion to the filler, but I can always rough up the contract patches before applying the glue so that is a card to balsa joint rather than filler to balsa.

200ml thin cyanoacrylate glue turned up today. Still waiting on motor tubes and centering rings though.

I'm aware my work station is a mess. I've ordered a mini vacuum cleaner to help keep the dust under control!




 
I hear you on the dust sanding part. I shaped my Blackstar's fin structures with a trashcan between my legs.
 
Two years ago I plastered a room and sanded it flat. So much dust! My poor Dyson vacuum cleaner has screamed at me ever since! Must have killed a bearing somewhere.
 
I flew mine on a AT 24 mm F-74-7 single use and F-39 reloads It handled them no problem
 
Not been able to do much recently. I plastered the body tube excessively and sanding it off generated too much dust in my garage so I was waiting for a mini vacuum I ordered before continuing.

Anyway, the lack of sim data has been bothering me. Open rocket won't work, so it's back to first principles to find Cd. Luckily I have two data points of altitude and thrust!
Rocket Reviews

I also have some formulae!
Rocket Equations

So I'll try and do some back calculating for Cd later tonight.
 
I went through those equations with my L1 rocket, and they kind of undershoot my sims even after accounting for M_boost and M_coast. I had to remove fin area from A and drop my Cd much lower than is realistic given the finish on that rocket lol.
 
Not been able to do much recently. I plastered the body tube excessively and sanding it off generated too much dust in my garage so I was waiting for a mini vacuum I ordered before continuing.

I was going to mention it before, but now seems like a good time: there's no reason to completely bathe the body tubes in CWF like you did. Apply and squeegee just enough to fill the spirals and you'll have just as good a result with waaaaaaay less sanding. This process has been documented many times on this site and others. Here's a good reference. Nowadays I just apply the stuff with my index finger, quick and efficient.
 
Still learning! It's taken me all evening to clean up the dust. :-\

Preliminary calc based on E20 to 579ft and F35 to 911ft is a Cd of 0.88.
Based on an estimated motorless mass of 10.1 ounces and cross sectional area of 1.5x2"Dia (3040mm2). I can refine these figures a little.

Edit:

Got the tape measure out. A total of 690mm length of 3mm thick wing. 2070mm^2.
Body tubes 1/2 circle 2" Dia and 1/2 elipse 2" by 40mm. 2609mm^2.
Total 4680mm^2.

That's significantly over my first estimate and the Cd drops to 0.57 for that frontal area. That seems low as I was expecting it to be a draggy model. I guess the 0.75 first estimate these sites suggest really doesn't include fins.

On a 286H42 Mellow that might be 2300ft and 140m/s max speed. Sounds survivable!
 
Bits turned up!


Now I have the 29mm tube and measurements I can start wrapping some rings.

The centering rings are a bit large on the OD, but they can be turned down to the correct size. My father in law has a lathe so that's on the to do list as well.
 
Right. That's all that sanded off. Next up is turning down the centring rings.

I'm thinking of getting a small altimeter. JL Altimeter Two is available locally, or I might be able to get an Altimeter Three by ordering from the states. I particularly like the Altimeter Three's smartphone connectivity. It also looks like it records the entire flight, unlike the Two. Worth the extra expense/hassle for the Three? What do you guys reckon?
 
Right. That's all that sanded off. Next up is turning down the centring rings.

I'm thinking of getting a small altimeter. JL Altimeter Two is available locally, or I might be able to get an Altimeter Three by ordering from the states. I particularly like the Altimeter Three's smartphone connectivity. It also looks like it records the entire flight, unlike the Two. Worth the extra expense/hassle for the Three? What do you guys reckon?

Worth every penny...
 
Right. That's all that sanded off. Next up is turning down the centring rings.

I'm thinking of getting a small altimeter. JL Altimeter Two is available locally, or I might be able to get an Altimeter Three by ordering from the states. I particularly like the Altimeter Three's smartphone connectivity. It also looks like it records the entire flight, unlike the Two. Worth the extra expense/hassle for the Three? What do you guys reckon?

Agreed. You want the three. I hear there's a four coming soon tho.
 
All right! On basis of two recommendations I've placed an order for the three. I also threw in a JL chute release, because why not? I'm sure it'll be useful at some point. A Four would be very useful for smaller rockets, certainly. I'm keeping a close eye for when it comes out!

This evening I spent clearing a space on the dining table. I'm going to need a nice big flat area for epoxying the fin pieces together.
 
Got a lot done the past couple of days!

Trimmed the engine strakes to fit a 29mm tube.
Wrapped a custom 24mm to 29mm centering ring with a roll of gum paper.
Wrapped a 29mm motor clip retainer with same.
Epoxied each of the two halves of the tie fighter fins together.
Papered the tie fighter fins. Sealed with CA.
Epoxied the boss onto each fin and filleted with epoxy.
 
Papered some more fins. Epoxied the filler pieces to the vertical strakes. They're a little sub-flush, so I'll need to level them out a bit. Small amount of tidying up required.

 
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