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!
Id hate to see a black mark on Jays Permanent Record! That kind of thing can follow a person their whole life! Hes 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. Im going to go through everything and see if there is anything else I need, and then Ill contact Jay about the motor mount.
Well, hell, you might as well go for the 75 mm MMT
[emoji4]
Well, hell, you might as well go for the 75 mm MMT…
[emoji4]
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.
Im usually easy to up-sell, but there ARE limits!
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.
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.
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?
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. Im planning to have a curved edge put on the fins by a friend who has a router. And its 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 didnt show how to trim the excess and clean up the edges.
I checked out Cokers site, and theres a lot of great info and techniques described there! Very useful. I didnt 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!
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?
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.
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
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? Ill 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 Im 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!
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!
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!
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.
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.
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