LOC Comet - Custom project for LDRS 37

That's a great looking rocket, even naked. Good call on the longer nose cone. Perfect '50's future tech look.

Me likey.


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I love the classic sci-fi and mid-century rockets! These just reek of everything that attracted me to rocketry, space travel, etc. as a kid. This kit looks amazing too! Hope LOC decides to start offering it. PIX!!!!

We may have to give Jay a written warning. I can't believe he didn't talk you up to the 54mmt. As Steve said, you can ALWAYS adapt down! Good luck with the build!

LOC said:

We may have to give Jay a written warning. I can't believe he didn't talk you up to the 54mmt. As Steve said, you can ALWAYS adapt down! Good luck with the build!

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I’d hate to see a black mark on Jay’s Permanent Record! That kind of thing can follow a person their whole life! He’s still young enough to turn things around, so maybe let him off with a gentle scolding.

I think I am going to upgrade to the 54mm mount. The kit is a bit heavier than I thought it would be, and there will be added construction weight if I glass the fins, and if the kit ends up needing nose weight. I’m going to go through everything and see if there is anything else I need, and then I’ll contact Jay about the motor mount.

ThirstyBarbarian said:

I’d hate to see a black mark on Jay’s Permanent Record! That kind of thing can follow a person their whole life! He’s still young enough to turn things around, so maybe let him off with a gentle scolding.

I think I am going to upgrade to the 54mm mount. The kit is a bit heavier than I thought it would be, and there will be added construction weight if I glass the fins, and if the kit ends up needing nose weight. I’m going to go through everything and see if there is anything else I need, and then I’ll contact Jay about the motor mount.

Click to expand...

Well, hell, you might as well go for the 75 mm MMT…
[emoji4]

Steve Shannon said:

Well, hell, you might as well go for the 75 mm MMT…
[emoji4]

Click to expand...

Steve Shannon said:

Well, hell, you might as well go for the 75 mm MMT…
[emoji4]

Click to expand...

JAYatLOC said:

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I’m usually easy to up-sell, but there ARE limits!

You might be able to go the way Wildman does the Demon 98, and recess the Aeropack retainer body inside the tailcone opening to keep the motor protrusion shorter. That way only the cap is below the tailcone.

jd2cylman said:

You might be able to go the way Wildman does the Demon 98, and recess the Aeropack retainer body inside the tailcone opening to keep the motor protrusion shorter. That way only the cap is below the tailcone.

Click to expand...

It looks like the aft centering ring provided sits a little bit more than 1/4” inside the end of the tail cone. So the retainer will be slightly recessed, but I don’t think it will be entirely inside the tail cone.

ThirstyBarbarian said:

I’m usually easy to up-sell, but there ARE limits!

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Good for you. It looks great and it makes me want to do something like it.


Steve Shannon

Jay and I have been emailing about the 54mm mount, talking over what rings need to be recut, and I think we have an improvement in the works.

One of the things I wasn't sure I liked about the original parts was that there was really no way to make internal fillets. There was a small ring that was designed as the aft ring, and it fit inside the tail cone near the bottom. It was too wide to be inserted from the aft end, so it needed to go in from the forward opening. And there was also a ring that goes into the tail cone and fits up tight against the inside of the cone's shoulder. That one you put in the from the forward end too by squeezing the opposite sides of the opening bit so you can slide the ring in sideways. Then you turn it perpendicular to the tube and pull it tight up against the narrow part of the shoulder. You can't do that with the motor mount tube in place. In other words, you need to install the two rings first, then the MMT, and then the fin tabs, so there 's no way to fillet the fin tabs to the MMT.

Another issue is that the fin tabs do not contact any internal centering rings, particularly the aft ring. So with this setup, the thrust of the motor has to be transferred to the airframe though the strength of the glue joints, which I always think is a tiny bit risky. I prefer a system where the thrust of the motor gets transferred to the airframe through interlocking parts that push directly against each other, instead of through joints that would slide past each other if the glue failed.

So, when we get the new motor mount tube and rings, we are going to set it up as a thrust plate in the aft end. That will allow me to dry fit the thrust plate to support the motor mount tube and keep it centered while gluing the forward end into the forward rings. Then I can remove the thrust plate to do internal fillets. And then glue the thrust plate back into place at the end. The thrust plate will also make it so thrust is transferred directly to the airframe, not relying on the strength of glued joints --- the motor thrust ring pushes directly against the retainer, which pushes directly against the aft thrust plate, which pushes directly against the tail cone, etc.

The tradeoff is that the retainer will no longer be recessed into the tail cone. That would have been nice aesthetically, but this is a better design from the point of view of constructing the rocket, and making it strong.

Here are some pics I mocked up of the thrust plate using the extra rings that Jay made while experimenting with the aft end rings. He sent them to me as extras, and they turned out to make a great thrust ring setup. Now I just need them in 54mm!

Here are two rings like the ones that will form the thrust plate. I will probably glue the two together stacked this way.




The smaller ring fits just inside the ID of the tail cone. By dry fitting that in place while gluing the forward end of the MMT, I can keep the tube centered. Then I can pul it out and access the inside of the tail cone for internal fillets.




The larger ring matches the OD of the tail cone at the cut. After I glue it in place, I'll be able to shape it to seamlessly match the tail cone. the retainer will fit over the motor mount tube, and will be able to sit right up against the thrust plate to transfer thrust directly to the plate --- no stress on the MMT or anything that is glued to the MMT.



In other news, I was talking to a friend recently, and it turns out he has a well-equipped workshop with a few different routers, and he is happy to put a nice rounded edge or bevel on my fins. Sweet!

EXCELLENT! My work here is done. Muahahahaha!!!!

Actually, you could make the thrust ring so that it fits the OD of the permanent portion of the retainer and butt it against the forward centering ring. That way the cap would be butted up to the thrust ring.

ChrisAttebery said:

EXCELLENT! My work here is done. Muahahahaha!!!!

Actually, you could make the thrust ring so that it fits the OD of the permanent portion of the retainer and butt it against the forward centering ring. That way the cap would be butted up to the thrust ring.

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Yes, you and my many enablers have done your work well! The 54mm is almost a necessity at this point, because the rocket is going to weigh a decent amount more than I expected. And the 54mm motors look pretty cool!

Jay said he could send me some 38mm to 54mm rings, and with the motor tube and rings I already have, I can make a 38mm motor adapter.

I'm not sure I completely understood what you were saying about the thrust plate. Are you saying make the ID of the thrust plate ring a little wider to match the OD of the retainer part that gets glued to the MMT? The permanent part of the retainer would be partly recessed into the thrust ring?

The new motor mount and centering rings are on their way today.

This build is going to require a few techniques and materials I’ve never used before, so I have s few questions:

Fiberglassing fins: I’m worried about the points of the long, thin fins getting crunched on landing (or even in handling, or with the rocket standing vertical on a hard surface). I think I should probably fiberglass the fins, or at least the tips, but I’ve never done it before. Can anyone point me to a good thread or outside resource to step me through the process in detail? What laminating epoxy should I use? What kind of fiberglass? What tools and safety equipment do I need? What’s the technique? Who are the good vendors? Etc...

Injecting internal fillets: It looks like the only way to do internal fillets is going to be through the aft opening, which is not going to be very big. Every other rocket I’ve built, I had an inch or more wide opening and not very far to reach inside, so I’ve used the “glue on a stick” method. This time the opening might be 1/4” wide, and I need to reach 8” inside the tail cone to get to the forward tab. What kind of tools do you use for that? What kinds of epoxy or other glues work well for that? Any threads, outside references, tips, vendors, etc?

Large external fillets: I think this rocket is calling for external fillets with a large radius. I haven’t generally built up large fillets on my rockets in the past, and usually I’m dealing with paper and wood, so I use the heavy molding and trim glue. This time I’m bonding to plastic nose cone, and possibly a fiberglassed fin. What product should I use for that? Any tools, tips or techniques? Threads, vendors, etc?

If you’ve got info to help me out on any of these, please let me know. thanks!

For glassing fins, here’s a pretty good video:
https://youtu.be/duoTBM8QRS0

Also, be sure you look at John Coker’s website.

Another video (the one I learned from more that 14 years ago) is one Dave Triano used to sell on his site.
I really like Aeropoxy laminating epoxy but any laminating resin will work. You want very low viscosity. I like 5.7 oz. fabric. It wets out well and is heavy enough to add strength.
Mix the epoxy in a shallow container and don’t worry about getting fancy with vacuum bagging or the like.
Also, don’t sand the glass smooth or try to fill the weave with epoxy. Wait till it cures and fill the weave with lightweight body filler. A gallon of filler is about an eighth the cost of a gallon of epoxy.
Practice on wood scraps first.

Steve Shannon said:

For glassing fins, here’s a pretty good video:
https://youtu.be/duoTBM8QRS0

Also, be sure you look at John Coker’s website.

Another video (the one I learned from more that 14 years ago) is one Dave Triano used to sell on his site.
I really like Aeropoxy laminating epoxy but any laminating resin will work. You want very low viscosity. I like 5.7 oz. fabric. It wets out well and is heavy enough to add strength.
Mix the epoxy in a shallow container and don’t worry about getting fancy with vacuum bagging or the like.
Also, don’t sand the glass smooth or try to fill the weave with epoxy. Wait till it cures and fill the weave with lightweight body filler. A gallon of filler is about an eighth the cost of a gallon of epoxy.
Practice on wood scraps first.

Click to expand...

Thanks for the info, Steve.

I checked out the video in the link. It looks like laying on the laminating epoxy and the cloth is not that difficult. I do have a few questions. It looked like he was working with fins that have flat edges, no bevels or curved edges. I’m planning to have a curved edge put on the fins by a friend who has a router. And it’s mainly the edges I want protected, especially the pointy tip at the bottom. What would be the best way to have the fiberglass protect the edge and leave a relatively tidy edge that is not going to need a ton of work to restore the nice radius put on by the router. The video didn’t show how to trim the excess and clean up the edges.

I checked out Coker’s site, and there’s a lot of great info and techniques described there! Very useful. I didn’t see a section on laminating fins, but there was some good info about handling the fiberglass cloth. Do you know if he has any fin laminating techniques, maybe within a longer video on a separate topic?

Where do you like to buy your cloth and laminating epoxy? Thanks!

Not to hijack the thread, but I do have related questions. My level 1 rocket, a Madcow Cowabunga was built without the benefit of internal fillets on the motor mount. In fairness, it was early on in my return to the hobby and there was no mention of them in the instructions from MadCow.

So I sealed up the bottom centering ring with epoxy nice and tight. Since then, I've become increasingly worried that the fins might come off during a hard landing. Our field has some big rocks on it, including one boulder that I managed to hit.

Is there any practical way to apply internal fillets on the rocket now that it's constructed? I thought about drilling holes in the centering ring and trying to fill that cavity with expanding foam, but another thread cautioned against using "Great Stuff" in an enclosed space. Some rocketeers recommended using a two-part expanding foam instead. But i'm not sure how much strength that would add.

Maybe I should just scrap the rocket, and build another? Hate to do away with it though. Sure wish I'd known to do internal fillets in the first place. Any hope for this patient rocket doctors?

lowga said:

Not to hijack the thread, but I do have related questions. My level 1 rocket, a Madcow Cowabunga was built without the benefit of internal fillets on the motor mount. In fairness, it was early on in my return to the hobby and there was no mention of them in the instructions from MadCow.

So I sealed up the bottom centering ring with epoxy nice and tight. Since then, I've become increasingly worried that the fins might come off during a hard landing. Our field has some big rocks on it, including one boulder that I managed to hit.

Is there any practical way to apply internal fillets on the rocket now that it's constructed? I thought about drilling holes in the centering ring and trying to fill that cavity with expanding foam, but another thread cautioned against using "Great Stuff" in an enclosed space. Some rocketeers recommended using a two-part expanding foam instead. But i'm not sure how much strength that would add.

Maybe I should just scrap the rocket, and build another? Hate to do away with it though. Sure wish I'd known to do internal fillets in the first place. Any hope for this patient rocket doctors?

Click to expand...

Personally, I would not worry about it until it breaks, which it might never do. If it ain’t broke (yet), don’t fix it (yet).

You did put some glue on the fin tabs before inserting them, so they are glued to the motor tube, right? Internal fillets to the motor tube are just for added strength. But if the rocket is holding together for now, then it’s probably more trouble to fix the issue before the fact than to just fix it later if it breaks. If a fin pops off, then you’ll have access to the cavity to fillet the other fins. Fixing rockets is part of the hobby. And making mistakes and doing it better next time is too. I’d just fly it as is.

I have considered using foam on this project, but I think I’ll be able to do the internal fillets instead. The amount of foam to fill the tailcone would be a lot on my rocket. If you do decide to use foam on your rocket, use the 2 part kind and plan for how to deal with the overflow.

Another option would be to drill holes in the aft centering ring and inject epoxy with a syringe. Hopefully we get some good advice on that technique, because that’s what I think I’ll need — a syringe with at least an 8” reach.

Good luck to you!

Now back to our our regularly scheduled thread already in progress...

ThirstyBarbarian said:

Thanks for the info, Steve.

I checked out the video in the link. It looks like laying on the laminating epoxy and the cloth is not that difficult. I do have a few questions. It looked like he was working with fins that have flat edges, no bevels or curved edges. I’m planning to have a curved edge put on the fins by a friend who has a router. And it’s mainly the edges I want protected, especially the pointy tip at the bottom. What would be the best way to have the fiberglass protect the edge and leave a relatively tidy edge that is not going to need a ton of work to restore the nice radius put on by the router. The video didn’t show how to trim the excess and clean up the edges.

I checked out Coker’s site, and there’s a lot of great info and techniques described there! Very useful. I didn’t see a section on laminating fins, but there was some good info about handling the fiberglass cloth. Do you know if he has any fin laminating techniques, maybe within a longer video on a separate topic?

Where do you like to buy your cloth and laminating epoxy? Thanks!

Click to expand...

Sorry - I left you hanging.
I have bought most of my laminating supplies from Aircraft Spruce. Here’s a link that will take you right to their composite supplies page:
https://www.aircraftspruce.com/menus/cm/index.html
The nice thing about that 5.7 oz cloth is that it drapes really well to follow curves, rounded edges, and beveled edges. You may have to snip a little wedge shaped piece out of the cloth on the sharper corners. A little sharp scissors helps with the nips and tucks. Keep in mind it doesn’t have to be perfect; just fix it with the body filler afterwards.
As far as the sharpest tip at the bottom you may want to glue a piece of hardwood or plastic there or build up multiple layers of fabric. Those points are always going to be a concentration of stress and there’s not much that I know of to do about that. Maybe put the sharp tips on hinges so they’re “pre-broken”. 🤨
I’ll look to see what else might be on John Coker’s site. His site and the Triano video were my go to resources when I did my first glassing. I devoured everything I could, but that has been a long time ago. Nowadays I would mix in a healthy serving of TFish38 from YouTube.
Here’s a video by Mr. Coker on laminating fins. https://www.jcrocket.com/nike-custom-fin.shtml

These are done using vacuum bagging using a Foodsaver. You might check your local Goodwill to see if they have Foodsavers cheap. Everyone bought them for a while so there may be some.
Don’t hesitate to stray outside of our hobby. The videos on laminating surfboards, snowboards, and skateboards all are applicable and there are many of them on YouTube.
Your favorite online rocket shop may also have different weights of cloth and laminating epoxy.
Also, Burt Rutan has a course on composites for aircraft that Aircraft Spruce sells as well as a practice kit which contains different kinds of materials. I always wanted to get both, but never got around to it.

Yes, that's what I was trying to say. Then you can butt the cap right up against the thrust plate.

ThirstyBarbarian said:

I'm not sure I completely understood what you were saying about the thrust plate. Are you saying make the ID of the thrust plate ring a little wider to match the OD of the retainer part that gets glued to the MMT? The permanent part of the retainer would be partly recessed into the thrust ring?

Click to expand...

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Steve Shannon said:

Sorry - I left you hanging.
I have bought most of my laminating supplies from Aircraft Spruce. Here’s a link that will take you right to their composite supplies page:
https://www.aircraftspruce.com/menus/cm/index.html
The nice thing about that 5.7 oz cloth is that it drapes really well to follow curves, rounded edges, and beveled edges. You may have to snip a little wedge shaped piece out of the cloth on the sharper corners. A little sharp scissors helps with the nips and tucks. Keep in mind it doesn’t have to be perfect; just fix it with the body filler afterwards.
As far as the sharpest tip at the bottom you may want to glue a piece of hardwood or plastic there or build up multiple layers of fabric. Those points are always going to be a concentration of stress and there’s not much that I know of to do about that. Maybe put the sharp tips on hinges so they’re “pre-broken”. 廊
I’ll look to see what else might be on John Coker’s site. His site and the Triano video were my go to resources when I did my first glassing. I devoured everything I could, but that has been a long time ago. Nowadays I would mix in a healthy serving of TFish38 from YouTube.
Here’s a video by Mr. Coker on laminating fins. https://www.jcrocket.com/nike-custom-fin.shtml

These are done using vacuum bagging using a Foodsaver. You might check your local Goodwill to see if they have Foodsavers cheap. Everyone bought them for a while so there may be some.
Don’t hesitate to stray outside of our hobby. The videos on laminating surfboards, snowboards, and skateboards all are applicable and there are many of them on YouTube.
Your favorite online rocket shop may also have different weights of cloth and laminating epoxy.
Also, Burt Rutan has a course on composites for aircraft that Aircraft Spruce sells as well as a practice kit which contains different kinds of materials. I always wanted to get both, but never got around to it.

Click to expand...

Thanks for the info, Steve. That John Coker video looks pretty good. I got partway through and got interrupted, but it looks like it will cover what I need.

Ill check out Aircraft Spruce too for the laminating epoxy and the glass cloth.

Do you have any favorite products for the actual structural adhesive? I’ll need to glue the fins to the paper motor tube and also bond them to the plastic tailcone. I build Mostly cardboard and wood rockets, so I seldom use any epoxy in my builds other than JB weld for motor retainers, so any advice on that would be appreciated.

And I’m also looking for a product for filleting the fins to the tailcone. I think this style of rocket calls for fat fillets with a big radius for cosmetic reasons.

The 54mm motor mount tube and rings arrived, so once I purchase the retainer, laminating epoxy, glass, structural epoxy, and filleting product, I can get started!

ChrisAttebery said:

Yes, that's what I was trying to say. Then you can butt the cap right up against the thrust plate.






Sent from my iPhone using Rocketry Forum

Click to expand...

Got it, Chris. That sounds like a nice, clean look. But the rings already arrived this weekend, so I may just go with it as is.

This looks to be a great fun project, really different for a change.
Might I mention if using a silver finish...Rustoleum indoor/outdoor metallic silver.
They only make a handful of colors in this metallic & it's recoat anytime, with a nice glossy finish.
It will not tarnish from handling/sun/time like so many others do.

Good luck!

ThirstyBarbarian said:

Thanks for the info, Steve. That John Coker video looks pretty good. I got partway through and got interrupted, but it looks like it will cover what I need.

Ill check out Aircraft Spruce too for the laminating epoxy and the glass cloth.

Do you have any favorite products for the actual structural adhesive? I’ll need to glue the fins to the paper motor tube and also bond them to the plastic tailcone. I build Mostly cardboard and wood rockets, so I seldom use any epoxy in my builds other than JB weld for motor retainers, so any advice on that would be appreciated.

And I’m also looking for a product for filleting the fins to the tailcone. I think this style of rocket calls for fat fillets with a big radius for cosmetic reasons.

The 54mm motor mount tube and rings arrived, so once I purchase the retainer, laminating epoxy, glass, structural epoxy, and filleting product, I can get started!

Click to expand...

I tend to use Aeropoxy laminating epoxy for everything. I add silica or chopped FG or carbon fibers for strength. Silica thickens it perfectly for a finished appearance.
I paint the material with unthickened Aeropoxy first to get good coverage or penetration.
For your adhesive application you could easily use Titebond.

ThirstyBarbarian said:

Thanks for the info, Steve. That John Coker video looks pretty good. I got partway through and got interrupted, but it looks like it will cover what I need.

Ill check out Aircraft Spruce too for the laminating epoxy and the glass cloth.

Do you have any favorite products for the actual structural adhesive? I’ll need to glue the fins to the paper motor tube and also bond them to the plastic tailcone. I build Mostly cardboard and wood rockets, so I seldom use any epoxy in my builds other than JB weld for motor retainers, so any advice on that would be appreciated.

And I’m also looking for a product for filleting the fins to the tailcone. I think this style of rocket calls for fat fillets with a big radius for cosmetic reasons.

The 54mm motor mount tube and rings arrived, so once I purchase the retainer, laminating epoxy, glass, structural epoxy, and filleting product, I can get started!

Click to expand...

There's a bunch of different laminating epoxies out there. I like System 3 Silvertip, but any of them will do the job. Wood flour (aka fine sawdust) is a good structural filler, as is milled fibers. For sanding fillers, I like microballoons mixed in to a peanut butter consistency. I typically pull the first run at the fillet with something structural, sand it mostly smooth, then come back with microballoons or a sanding filler. That lets you get a solid fillet with a nice finish without a huge amount of work. For the fin edges, you might buy some narrow fiberglass tape and just do the edge with it. You'll need some darts, but the tape is somewhat flexible as well. If it was my rocket, I'd probably do one layer of tape over the edge, one layer of tip to tip that covers the edge of the tape on each side of the fin, then another layer of the edge tape.

For the laminating and filleting jobs, you might look at some of the boatbuilding videos. This one ([video=youtube;eWxeNLIoric]https://www.youtube.com/watch?v=eWxeNLIoric[/video]) is pretty good, with filleting starting at 20:30 and a whole lotta fiberglassing around 28:30. The guy in the video could have saved a lot of cleanup by masking his fillets better, though.

blackjack2564 said:

This looks to be a great fun project, really different for a change.
Might I mention if using a silver finish...Rustoleum indoor/outdoor metallic silver.
They only make a handful of colors in this metallic & it's recoat anytime, with a nice glossy finish.
It will not tarnish from handling/sun/time like so many others do.

Good luck!

Click to expand...

Thanks, Jim. I do like that paint. I used the silver on my Pod Rocket (pics in the earlier part of the thread). And I used the red, black and blue for some of the details. It’s actually really easy paint to work with, which is not usually the case with metallic rattle-can paint.

Steve Shannon said:

I tend to use Aeropoxy laminating epoxy for everything. I add silica or chopped FG or carbon fibers for strength. Silica thickens it perfectly for a finished appearance.
I paint the material with unthickened Aeropoxy first to get good coverage or penetration.
For your adhesive application you could easily use Titebond.

Click to expand...

That sounds great. If I could use the same product for almost everything, that would be perfect.

boatgeek said:

There's a bunch of different laminating epoxies out there. I like System 3 Silvertip, but any of them will do the job. Wood flour (aka fine sawdust) is a good structural filler, as is milled fibers. For sanding fillers, I like microballoons mixed in to a peanut butter consistency. I typically pull the first run at the fillet with something structural, sand it mostly smooth, then come back with microballoons or a sanding filler. That lets you get a solid fillet with a nice finish without a huge amount of work. For the fin edges, you might buy some narrow fiberglass tape and just do the edge with it. You'll need some darts, but the tape is somewhat flexible as well. If it was my rocket, I'd probably do one layer of tape over the edge, one layer of tip to tip that covers the edge of the tape on each side of the fin, then another layer of the edge tape.

For the laminating and filleting jobs, you might look at some of the boatbuilding videos. This one ([video=youtube;eWxeNLIoric]https://www.youtube.com/watch?v=eWxeNLIoric[/video]) is pretty good, with filleting starting at 20:30 and a whole lotta fiberglassing around 28:30. The guy in the video could have saved a lot of cleanup by masking his fillets better, though.

Click to expand...

Thanks for the info info and the video. I’ll take a look. I like the idea of taping the fin edges. The edges are my main concern so that sounds like a great idea.

Wow, it's been a long time since I started this thread. An update: I built this ticket and flew it on its test flight about 2 weeks ago at LDRS 37 in Helm, CA. I think it turned out pretty nice, and it flew great!

I didn't have time for a build thread while building, because, like everything I do, it was a big rush at the end to finish! But I did take pics and I'm going to do a build thread based on the pics and my memory.

The first thing I did was to get some help adding a rounded bullnose to the fins and also cut off the excess fin tab so that they would fit properly with the 54mm motor tube (I had upgraded from 38mm, so each tab needed about 8mm cut off. I don't have proper tools for this kind of work, but I have a friend who does.

He used his table saw to cut most of the excess tab off (left it a hair long). And then he used another tool that I don't recall the name of to shave off the rest with successive pases. Got it to fit perfectly with good contact to the MMT, and a very tiny gap in places between the fin root and the curved profile of the boat tail.

Then he used a router to put a nice curved edge on the outer edges of the fin. Saved me an eternity of sanding!