fyrfytr310's Level 3 - Polecat 10" Nike Smoke

OH NO!!!

Upon removal of the fin can, it became apparent that I didn't press down on the fin hard enough, or something, leaving a significant gap between the root and MMT on one fin.



Could I just fill it in with epoxy and no one would be the wiser? Yes. But why would I set aside prudent construction technique and risk the flight and everyone's safety. Sigh. I marked the fin position on the CRs and set off to cut the fin free. Fortunately there was enough gap that a Dremel cutoff wheel snuck in quite easily.





The remnant JB on the MMT was easily removed with a sharp knife and a Dremel grinding wheel cleaned up the fin nicely.

Round 2:

I mixed up a new batch of JB and reset the fin. Gap again! Upon closer inspection, I found a small obstruction on the forward side of the aft CR. Dremel to the rescue again and we are once again drying.



If I had not set out in the course of making the whole fin can removable for construction, I would have never seen this flaw and we could have had a seriously failed flight...

I too like building my fin cans removable. I did one that was all held together with hardware. I plan to do my L3 the same way when I get around to it.

First set of internal fillets. This is West 105/205 with milled fiber. I plan to finish the internal fillets and take this assembly to my prefect for inspection this week if we can get schedules to work out. We will discuss additional reinforcement at that time (fiberglass, overall epoxy layer etc).

Fillets between the CRs and fins are drying. I used JB for this exercise.

Assembling the avionics sled.


(very focused lol)



Tomorrow I will modify the av-bay lids to accept the larger and additional u-bolts.

I don't plan on epoxying the av-bay into the upper airframe per the instructions. I will use at least (4) 1/4-20 screws and nuts to secure this in place so I can totally disassemble if I need to.

Av-bay lid assembled and drying for the night.

Filling the existing u-bolt holes on the av-bay lids with JB.



A little pressure to keep things smooth.



I am looking into the av-bag assembly now. Like I said before, the instructions call for permanent installation with 4" of coupler into the upper airframe including the upper lid. I don't like the idea of permanent install because of the difficulty it will cause during ejection charge loading.

Originally, I was thinking about using (4) 1/4-20 bolts to secure to the upper but now, given only 4" to work with, I am thinking about moving forward with epoxying the coupler, without the upper lid. This would allow me to build the charges outside the rocket, then slide the upper lid into place. The all-thread hardware would be permanently secured to the upper lid. I am not concerned with wear over time on the ID of the airframe because this rocket will very likely be a one-and-done bird (certainly low flight count anyway). The obvious challenge will be getting the coupler epoxied in without epoxy buildup leading to lid interference. Any thoughts on this? I'll run it past my TAP tomorrow as well.

Av-bay lid and nose bulk plate hardware coming together:





Al hardware secured with JB.

Securing the top side of the av-bay all-thread nuts.



I have also began looking at the calculated volume of the nose cone for foam application. I am treating it as a standard cone, ignoring the aft end variance near the shoulder. I am coming up with ~.8 ft^3. As a result I should be using slightly less than half of the mixture purchased to get it done.

Keep in mind, that the foam will create a lot of heat. So it is best to do it in small quantities and even put the cone in bucket with water.

thomas said:

Keep in mind, that the foam will create a lot of heat. So it is best to do it in small quantities and even put the cone in bucket with water.

Click to expand...

I plan to use the garbage can full of water method.

I have installed the 1/4-20 screws to secure the av-bay. There is an awful lot of clearance between the bay and the ID of the airframe. I might be stuck with gluing if I don't get reliable results during the ground testing.

Not sure how much/what for you are foaming the cone. If you are filling quite a bit of the cone, might I suggest a little something I do, dealing with large volumes. It will save weight & quite a bit of foam:

Use packing peanuts either full size or cut in half to "fill" in the foam. Think rock/gravel added to concrete. Lighter than foam, but mixed in adds strength & takes up volume.

I do a pure foam fill in the tip.....then add peanuts ...pour foam around them, add peanuts, pour foam, etc. continue till I reach level needed. Last couple inches pure foam again to cut level if need be. This also cut down on heat generated by quite a lot.

This makes the cone rock solid for taking hard landing hits, with out adding all the weight just pure foam adds. In large volumes foam gets heavy fast, just pick up the containers it comes in..LOL

blackjack2564 said:

Not sure how much/what for you are foaming the cone. If you are filling quite a bit of the cone, might I suggest a little something I do, dealing with large volumes. It will save weight & quite a bit of foam:

Use packing peanuts either full size or cut in half to "fill" in the foam. Think rock/gravel added to concrete. Lighter than foam, but mixed in adds strength & takes up volume.

I do a pure foam fill in the tip.....then add peanuts ...pour foam around them, add peanuts, pour foam, etc. continue till I reach level needed. Last couple inches pure foam again to cut level if need be. This also cut down on heat generated by quite a lot.

This makes the cone rock solid for taking hard landing hits, with out adding all the weight just pure foam adds. In large volumes foam gets heavy fast, just pick up the containers it comes in..LOL

Click to expand...

This is a great idea!! Once again, thanks Jim!

blackjack2564 said:

Not sure how much/what for you are foaming the cone. If you are filling quite a bit of the cone, might I suggest a little something I do, dealing with large volumes. It will save weight & quite a bit of foam:

Use packing peanuts either full size or cut in half to "fill" in the foam. Think rock/gravel added to concrete. Lighter than foam, but mixed in adds strength & takes up volume.

I do a pure foam fill in the tip.....then add peanuts ...pour foam around them, add peanuts, pour foam, etc. continue till I reach level needed. Last couple inches pure foam again to cut level if need be. This also cut down on heat generated by quite a lot.

This makes the cone rock solid for taking hard landing hits, with out adding all the weight just pure foam adds. In large volumes foam gets heavy fast, just pick up the containers it comes in..LOL

Click to expand...

I like this one!

fyrfytr310 said:

I plan to use the garbage can full of water method.

I have installed the 1/4-20 screws to secure the av-bay. There is an awful lot of clearance between the bay and the ID of the airframe. I might be stuck with gluing if I don't get reliable results during the ground testing.

Click to expand...

2 questions about the Av-Bay screws:

Are you going to epoxy those nuts into place? I would consider getting some weld nuts and doing just that. Less chance of it ripping through the coupler (which is phenolic?)

Did you reinforce the hole with a thin set CA glue? I also recommend this as it will harden up the material around the hole and make it more durable over repeating insertion and removal.

NateLowrie said:

2 questions about the Av-Bay screws:

Are you going to epoxy those nuts into place? I would consider getting some weld nuts and doing just that. Less chance of it ripping through the coupler (which is phenolic?)

Did you reinforce the hole with a thin set CA glue? I also recommend this as it will harden up the material around the hole and make it more durable over repeating insertion and removal.

Click to expand...

Provided I don't end up gluing the av-bay (cardboard) permanently, yes, I will be epoxying weld nuts. The nuts shown were just temporary.

The holes will be hardened with CA as is typical for my cardboard builds. I am toying with the idea of glassing the inside of the av-bay but I haven't convinced myself to take that step.

Thanks for the input!

Honestly, the retainer installation was the most nerve racking part so far. There isn't a lot of room for error for an imprecise fellow such as myself and on a 4 fin bird you don't have many opportunities for do-overs on an installed aft CR.

Thankfully I was successful on my first go. I spent a lot of time making sure I got the first two inserts lined up just right before I went all the way around the assembly.







Moment of truth shot below:


Success!


Thanks to Gary for letting me use his hardware for alignment!

Looks good so far. I keep thinking about doing a Polecat kit, probably not this big...

Rear support ring installed. I am using just a simple 5 minute epoxy here. I am finishing the edges with the same epoxy between the clamps and will finish the rest once the clamps are removed.







From here I will push the fin can rearward and begin epoxying from top to bottom.

I hate those retainers for the simple fact that I couldn't get hardly any of those hex screws to line up. Seriously made me mad haha. I ended up JB welding the whole damn thing in in the end... Kudos to you for getting it right the first time!

Have you discussed the motor recession with your TAP.
Altough it seems not deep enough for Krusnik Effekt, the heat might be a problem for the airframe.

thomas said:

Have you discussed the motor recession with your TAP.
Altough it seems not deep enough for Krusnik Effekt, the heat might be a problem for the airframe.

Click to expand...

The recession is by design of the manufacturer. That said, in the image above, the can is a lot farther forward than it will be when complete. The can will be pulled rearward to butt up against the support ring making the recession ~4". Then the support ring is going to be lined with a thin metal heat shield (again, by manufacturer design).

Can pushed into position against the support ring and forward side of forward CR epoxied with thickened West. Of course I had a mishap in application and you get to see the sloppy results:

Epoxy injected between the forward 2 CRs to create a bond between the rear of the forward most CR and the airframe. The airframe was rotated several times initially and again every 15 minutes for an hour to help ensure even distribution.

Fin slots taped and epoxy injected to bond the forward of the middle CR to the airframe.

Pictures won't upload right now for some reason...

Prepping for internal fillets between find and airframe.

Painters tape was used to seal the gap left by the overly wide slots and the fins.



1/2" holes were drilled between each fin for both epoxy injection and, once fillets are complete, foam injection.

Jeez. Aft end is going to be a tank. What kind of metal are you going to use for the heat shield? I'd be so tempted to use 18 gauge steel...

Tonimus said:

Jeez. Aft end is going to be a tank. What kind of metal are you going to use for the heat shield? I'd be so tempted to use 18 gauge steel...

Click to expand...

Yeah, you're not kidding. After discussion with my TAPs we all felt the weight penalty was worth the strength gained with such large fins. I won't lie, I am a little scared to see what kind of counter weight I am going to need... That said, low and slow is fine by me for a cert flight.

The metal provided by the manufacturer is a little thicker than common housing flashing (I haven't broken out the mic yet).

I totally agree about the strength. Come down sideways on a fin, and that's a hell of a load. That's part of the reason I'd go with 18, or even 16 gauge steel for the inside. Between that and the two layers of cardboard, should hold up even if it lands funny. Not sure what adhesive to use though. Maybe PC Auto Bond. What do you plan on using?

Can foamed this afternoon:



And the mess: