L3 build - Wildman Ultimate Darkstar

I'll add more pics and organization as I go.

Here's a link to the basic information file. https://docs.google.com/document/d/1T7NLmEyboIeUgveng9yrV8AqFyct7YarYccKQoEnlNs/edit?usp=sharing


But this happened and I thought you guys might have more ideas...

I put the initial epoxy on the centering rings. I was testing the fit and discovered that I managed to get the aft ring on about 1/4 inch too far aft. This will cause some issues with the injected filets, so I stopped there.

I could cut a new CR in half to install it in the proper location.

I could CA some stops in to keep the epoxy where it belongs. Even creative masking tape might work.

I'm leaning towards just cutting a plywood CR to keep the epoxy in place. Is there a problem with that I'm not seeing? Or even foam, cardboard, etc..

Adding some pics to keep things going.

Dry fits are looking good, other than the slight misaligned rear CR. I also discovered the tubing is too thick for the plastic rivets I have onhand. I'm looking into alternatives if anyone has some they know work well with this thicker Wildman tubing. Looks like the tube is about 1/8" thick.

Are you saying one of the centering rings is not against the fin so when you inject the epoxy it will run out of the intended area?

I wouldn't recommenced using plastic rivets on this air frame. I used the 8-32 pem nuts and screws for the av bay/payload on my Ultimate Wildman build. Very easy and clean installation.

https://www.mcmaster.com/#pem-style-nuts/=17d4qo7

markkoelsch said:

Are you saying one of the centering rings is not against the fin so when you inject the epoxy it will run out of the intended area?

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Yes. Totally my fault, but I don't see any reason why just having something there to block the epoxy from flowing out of the filet area won't get the job done. I will be doing filets to the airframe as well, between that and the MMT I don't think the fins are going anywhere. I'll be prepping the fiberglass based on the sticky about bonding composites to help ensure a good bond. I still need to mark the fin locations on the MMT so I can sand those areas better.

PokerJones said:

I wouldn't recommenced using plastic rivets on this air frame. I used the 8-32 pem nuts and screws for the av bay/payload on my Ultimate Wildman build. Very easy and clean installation.

https://www.mcmaster.com/#pem-style-nuts/=17d4qo7

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Interesting. I had considered well nuts, but not PEM nuts. I have a pack of 3mm and matching stainless screws from some other projects. Looks like #8 is about 4mm...

PokerJones said:

I wouldn't recommenced using plastic rivets on this air frame. I used the 8-32 pem nuts and screws for the av bay/payload on my Ultimate Wildman build. Very easy and clean installation.

https://www.mcmaster.com/#pem-style-nuts/=17d4qo7

Click to expand...

I second the suggestion of #8-32 PEM nuts and button head cap screws. #6 or 3mm would work as well.

PokerJones said:

I wouldn't recommenced using plastic rivets on this air frame. I used the 8-32 pem nuts and screws for the av bay/payload on my Ultimate Wildman build. Very easy and clean installation.

https://www.mcmaster.com/#pem-style-nuts/=17d4qo7

Click to expand...

How did you install the PEM nuts?

I used these on my F200. To use, epoxy over the nut, hold it to the hole, apply Vaseline to the screw, insert and tighten the screw, allow epoxy to dry, extract the screw. The Vaseline allows the screw to come back out, and also forms a threaded covering of hardened epoxy over the back of the nut.

I use adhesive nuts. They're specifically designed to do what we want; glue them into place.

https://www.mcmaster.com/#98007a110/=17d7ssr

They have a nice backing with holes to allow adhesive to cover a wide area and form epoxy rivets.

mccordmw said:

I use adhesive nuts. They're specifically designed to do what we want; glue them into place.

https://www.mcmaster.com/#98007a110/=17d7ssr

They have a nice backing with holes to allow adhesive to cover a wide area and form epoxy rivets.

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Wow! Smart!

mccordmw said:

I use adhesive nuts. They're specifically designed to do what we want; glue them into place.

https://www.mcmaster.com/#98007a110/=17d7ssr

They have a nice backing with holes to allow adhesive to cover a wide area and form epoxy rivets.

Click to expand...

I really like those adhesive nuts, have to order some to try out. Thanks for the link.

Wow. Nice.

They're easy to tack into place with a drop or two of CA. Then go over the mesh with epoxy to lock it in. No need to go over the nut.

I'm using some of the adhesive nuts for the thrust plate mount. They seem to be easy to use. The only annoying thing about them for this use is 3 waits for epoxy to cure. Not a big deal. And the local Lowes stocks them.

ttabbal said:

Yes. Totally my fault, but I don't see any reason why just having something there to block the epoxy from flowing out of the filet area won't get the job done. I will be doing filets to the airframe as well, between that and the MMT I don't think the fins are going anywhere. I'll be prepping the fiberglass based on the sticky about bonding composites to help ensure a good bond. I still need to mark the fin locations on the MMT so I can sand those areas better.

Click to expand...

Could you inject something to dam it so to speak? Even a little two part urethane foam- once set you could inject your epoxy.

markkoelsch said:

Could you inject something to dam it so to speak? Even a little two part urethane foam- once set you could inject your epoxy.

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That could work. I just tried cutting a foam CR with the same idea. It seems like it might work. Use a little CA to hold it in place, inject epoxy. I'm going to think about it, no big rush to complete the build.

ttabbal said:

That could work. I just tried cutting a foam CR with the same idea. It seems like it might work. Use a little CA to hold it in place, inject epoxy. I'm going to think about it, no big rush to complete the build.

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Excellent. Many times with my Formula 200 I had to stop, take a breather, think things through, and sometimes go in a different direction.

I did a bunch of dry fitting and experiments. The difference is smaller than I expected. Some will manage to drip past, but I don't think it's enough to get too worried about. And I can build it up with a couple small injections.

I'm going to sand it in the glue areas more thoroughly as mentioned in the bonding composites thread. Then clean with acetone before mixing the epoxy.

Some pics of the dry fit and the adhesive nuts for the thrust plate. I need a couple more clamps to hold a piece of angle iron to a pair of fins to make sure they are aligned nicely. The guides get it 90% or so, but I want them to be closer.

Here's a pic of the angle holding the fins aligned. Internal filets are complete. Is it worth adding internal filets between the fins and body tube?

ttabbal said:

Here's a pic of the angle holding the fins aligned. Internal filets are complete. Is it worth adding internal filets between the fins and body tube?

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No.
It had it's place and time, before all fiberglass tubing became standard.
With proper thickened external fillets, installed correctly... no need.
I've flown my UW on N-10,000 & N-5800. I would stick an O-3400 in it , if I had the money without a second thought. Same for U DarkStar.

Waste of time and unnecessary weight now.

+1 to CJ. Just added weight at this point assuming your current set of internal fillets and coming externals are done reasonably well.

Thanks for the info. I suspected that was the reason it wasn't in the instructions, but it's nice to have confirmation. No point in adding weight if there is no strength benefit for it.

Inspecting the internals with a flashlight looking through the MMT, they look good. So I'll move on to the externals next.

For holding the payload bay to the AV-bay, has anyone used well nuts? It seems like a decent option, particularly as I have one hole about the right size drilled when testing the rivets.

Just to be the other voice, I add internal fillets at the airframe. It doesn't add that much weight, and it gives me a warm fuzzy, especially on a big, heavy rocket. Is it necessary? Probably not. Is it a waste? I don't think so.

Bat-mite said:

Just to be the other voice, I add internal fillets at the airframe. It doesn't add that much weight, and it gives me a warm fuzzy, especially on a big, heavy rocket. Is it necessary? Probably not. Is it a waste? I don't think so.

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Oh so that's why your Formula 200 seemed to weigh 14 tons when I was carrying it back from the field in LDRS

blackbrandt said:

Oh so that's why your Formula 200 seemed to weigh 14 tons when I was carrying it back from the field in LDRS

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Lead filets FTW!!

blackbrandt said:

Oh so that's why your Formula 200 seemed to weigh 14 tons when I was carrying it back from the field in LDRS

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Do you even lift, bro? :lol: j/k

On a more serious note, do internal filets on the underside of the tube even make much difference? You already have the tube there keeping the fins from wobbling. All the strength needed is where the fin root touches the motor mount.

Plus, the external filets should be sufficient. Seems to just add weight with onyl a fraction of the added strength. :shrug:

mccordmw said:

On a more serious note, do internal filets on the underside of the tube even make much difference? You already have the tube there keeping the fins from wobbling. All the strength needed is where the fin root touches the motor mount.

Plus, the external filets should be sufficient. Seems to just add weight with onyl a fraction of the added strength. :shrug:

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I think that dead horse was beat down good last year when there was an entire engineering thread on it. IIRC, the weaker the tube and the weaker the fin, the more an internal fillet on the underside of the tube contributed to overall stiffness. The more robust the tube and fin, the less so. I don't overly remember anyone quantifying it, but I think the consensus was anything that's being sold as MP or HP that's more stout/stiffer than the Estes PSII kits probably doesn't benefit any from internal tube to fin fillets when cost/time/weight are figured in.

Cool. I don't want to derail the build thread, so I'll hunt that filet thread down myself. Thanks!