L1 Build: Wildman Darkstar Jr

So I decided I wanted to do my L1 this year. After 20 years of just LPR, I bought an MPR last year and that was awesome. So naturally, why not go bigger and higher!!

I decided on the Wildman Darkstar Jr - quite frankly I just love the split fin look and thought fiberglass would be a different experience. Waited for the black Saturday sale to order and got all stocked up. It finally came a week ago, so I started the build this past week.

Nothing new here, but wanted to document my build to keep myself honest and because I know I'll have questions along the way.

First up was sanding/rinsing the parts.

I do have to say, the biggest negative I have with this kit was the amount of sanding I had to do to get the parts to fit. Especially the centering rings. Not sure if this is true with all Wildman kits, or just mine, but I probably spent close to 4 hours (~1 hr each!!) to get them to fit the MM tube and body tube. Needless to say, my arms were tired and I was not happy to have to waste so much time.

Parts sanded and cleaned - let the building begin!!:

First thing I did was to glue the aeropack retainer on to the bottom of the MM tube. Then glued on the bottom centering ring. These were done with JB weld:



Let that dry overnight and the next day I did the next centering ring. I used the bottom fins to set the distance and to help keep centering ring square. I also bought rocketpoxy to use with this build. So far its pretty good stuff. My only other epoxy experience is with the generic hobby shop stuff I've used for building rc planes.

Setting up ring:




Ring glued on. I also did a fillet around the top. It's pretty ugly, but I didn't really care too much as its inside.

Also used left over rocketpoxy to go ahead and glue the nosecone mount together. Also did an internal fillet - hideous, but was a pain to try to get the epoxy down in there. Especially because it had thickened quite a big and didn't run at this point:

Next up I did the coupler. Taped off the edges of the center and then applied it:

Next I did the 3rd centering ring. I goofed on this one and did the fillet on the wrong side!!!! So I wiped as much as I could off and moved it to the correct side. You can see the residual epoxy though here. I'll have to sand it off when its time to glue the MM into the body tube.

Oops!!



Next was top centering ring. I used a dremel to slot it for the kevlar:



Then did a similar thing as I did with the bottom fins. I used the fins to set the centering ring, glued it, and then glued the kevlar to the MM tube:

blueapplepaste said:

I do have to say, the biggest negative I have with this kit was the amount of sanding I had to do to get the parts to fit. Especially the centering rings. Not sure if this is true with all Wildman kits, or just mine, but I probably spent close to 4 hours (~1 hr each!!) to get them to fit the MM tube and body tube. Needless to say, my arms were tired and I was not happy to have to waste so much time.

Parts sanded and cleaned - let the building begin!!:

View attachment 160288

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This is common on WM, RW, and MC FG kits - centering rings and bulkheads to need adjustment.... I use my dremel tool and sanding round....you can do all the centering rings and sand down the MM to fit retainner in matter of minutes.

I always find fin slot too small too... I use the dremel with sanding disc... a few minutes later they are perfect.

Now here's where I've run into my first problem. The coupler isn't square with the body tubes. When I sanded it, I just briefly sanded the edges flush to remove residual pieces of fiberglass, so I don't think I made it so not square. And it wasn't so off that it was obvious until I did a dry fit of body tubes and glued coupler.

Here's a pic I drew (was hard to see in photograph). This is over exaggerated, but I think the point gets across. Is this OK? Between rivets and friction fit, will this matter? Should I try to correct it? If so, how?

robbdm said:

This is common on WM, RW, and MC FG kits - centering rings and bulkheads to need adjustment.... I use my dremel tool and sanding round....you can do all the centering rings and sand down the MM to fit retainner in matter of minutes.

I always find fin slot too small too... I use the dremel with sanding disc... a few minutes later they are perfect.

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Hi David - thanks for the info. I was worried about using a dremel and taking off too much too fast. Though I didn't even think of using a disc, was just thinking of a drum. Which disc do you use?

The bad fits is a thing of the past now from Wildman, all parts are now cut with a state-of-the-art high precision CNC router. I've had poorly fitting parts in the past, but without any extra work - mine were too loose.

blueapplepaste said:

Now here's where I've run into my first problem. The coupler isn't square with the body tubes. When I sanded it, I just briefly sanded the edges flush to remove residual pieces of fiberglass, so I don't think I made it so not square. And it wasn't so off that it was obvious until I did a dry fit of body tubes and glued coupler.

Here's a pic I drew (was hard to see in photograph). This is over exaggerated, but I think the point gets across. Is this OK? Between rivets and friction fit, will this matter? Should I try to correct it? If so, how?

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a metal flat file helps , also there where be a sweet spot where all 3 pcs will line up

michigander said:

a metal flat file helps , also there where be a sweet spot where all 3 pcs will line up

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Yup - I feel like an idiot now. Flipped the coupler and rotated it and voila! It fit! Still some teeny tiny gaps in the upper body tube, but nothing that concerns me like it did before. Thanks for the tip!! Exactly why I chose to document this build to save myself from my own stupidity!

blueapplepaste said:

Hi David - thanks for the info. I was worried about using a dremel and taking off too much too fast. Though I didn't even think of using a disc, was just thinking of a drum. Which disc do you use?

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I use 446 1/4" 240-grit Sanding Bands or I think of them as the brown ones.

I use the EZ412SA EZ Lock™ Sanding Discs, 120 grit for the slots

chadrog said:

The bad fits is a thing of the past now from Wildman, all parts are now cut with a state-of-the-art high precision CNC router. I've had poorly fitting parts in the past, but without any extra work - mine were too loose.

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I agree, couplers problems are thing of the past, but centering rings, fiberglass bulkheads, and fin slot still need adjustments... my 2013 BF/BS kits needed the ring and slot sanded..

robbdm said:

I agree, couplers problems are thing of the past, but centering rings, fiberglass bulkheads, and fin slot still need adjustments... my 2013 BF/BS kits needed the ring and slot sanded..

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Actually, tube fits is the one thing he has no controll over.

If any of you have a problem with a fit on the outside dimension of a centering ring please give me a call .
The outside dimension of the MMT I can not control but all of our rings should be dead on for the inside of the body tube.
On the slots during the Black Saturday sale I had a G10 manufacture problem and had to get material from several different suppliers so I ended up with several different thicknesses. example should be .125 ended up anywhere from.120-.139 which is within the G10 industry tolerances. We needed to make a choice weather to leave the slots tight or make them loose, we obviously made them tight.

Thanks for the reply Tim. Good to know about the various thicknesses. The slots are a little snug. But was able to sand those easily.

The big problem were the centering rings. Were too small for the MMT tube and too large for body tube. I got it all sanded. So all good now. Not a big deal. Will remember for future wildman builds though!


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Shaped the leading and trailing edges. Any reason I should do the sides of the fins, or is it OK as is?



Also ordered a MissileWorks RRC2+ altimeter. Been thinking a lot about planning/building the AV bay, probably over thinking it.

blueapplepaste said:

Shaped the leading and trailing edges. Any reason I should do the sides of the fins, or is it OK as is?

Also ordered a MissileWorks RRC2+ altimeter. Been thinking a lot about planning/building the AV bay, probably over thinking it.

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Should be fine just like that. That's how the bigger ones come! What did you bevel those with? They look very uniform.


Braden

UPscaler said:

Should be fine just like that. That's how the bigger ones come! What did you bevel those with? They look very uniform.


Braden

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Sounds good - this is how they'll stay then.

I used dremel sanding discs: https://www.dremel.com/en-us/Accessories/Pages/ProductDetail.aspx?pid=411

I used the screw that attaches them as a guide, similar to how bearing on a router bit works. I wanted to rig up a jig, but couldn't think of a (safe) way to do so with the tools I had. I taped the first one off, but realized that the radius of the disc was perfect for beveling the fins, so I didn't tape the rest and just free handed it. The discs wore out fast though. Probably used ~2.5 discs per side of an edge. So probably close to 25-30 discs total (there were a few left over from a brand new package). Was a pain, but I'm happy with how they turned out.

Looks pretty awesome. I am thinking up a jig to bevel my carbon fiber minimum diameter fins. If your fiberglass ate up those wheels, my cf probably would too. Great idea and nice execution though!



Braden

blueapplepaste said:

Shaped the leading and trailing edges. Any reason I should do the sides of the fins, or is it OK as is?

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If you are planning to paint the fins, taking the corners off the outside edges by rounding them a bit will help the paint stick and reduce wear off.

UPscaler said:

Looks pretty awesome. I am thinking up a jig to bevel my carbon fiber minimum diameter fins. If your fiberglass ate up those wheels, my cf probably would too. Great idea and nice execution though!

It didn't so much "eat" them up. It was more the dust was so fine it just clogged up the sanding wheel. But I imagine CF would be quite similar if you used the same discs I did.

The problem I was having trying to think of a jig was the material is so thin, which effectively meant the tool used in the jig would be extremely close to the rest of fin, giving you very little working room. Tried making a jig to manually sand it - but that was too much of a pain for me. Will probably do the same thing I did here next time. Only took ~ 30 minutes to do all 6 fins. Probably half of that was spend changing the discs out.

Braden

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WoShuGui said:

If you are planning to paint the fins, taking the corners off the outside edges by rounding them a bit will help the paint stick and reduce wear off.

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Hadn't thought of that. In the middle of gluing the fins on right now, but should be fairly easy to do the sides afterwards.

Fins are all glued and getting ready to do internal fillets. The rocketpoxy is pretty thick and am not sure about using it for injection.

Has anyone injected rocketpoxy? Instructions say you can thin with isopropanol, but from my rc planes most always felt it weakened the epoxy. Not sure with this stuff. Would thinning and injecting work?

Or lastly, would just generic epoxy from hobby shop be good enough? I don't want to drop some more coin on something like west systems or aeropoxy. Thanks for any suggestions.

If you want some cheap epoxy, get some from US composites. Goes great into a syringe, and is really thin. Try that. For example, a 16oz kit is $15.

blueapplepaste said:

Fins are all glued and getting ready to do internal fillets. The rocketpoxy is pretty thick and am not sure about using it for injection.

Has anyone injected rocketpoxy? Instructions say you can thin with isopropanol, but from my rc planes most always felt it weakened the epoxy. Not sure with this stuff. Would thinning and injecting work?

Or lastly, would just generic epoxy from hobby shop be good enough? I don't want to drop some more coin on something like west systems or aeropoxy. Thanks for any suggestions.

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I have used Rocketpoxy, but you need to work fast to do the injection within 5 minutes after mixing, while the Rocketpoxy is in it's less viscous phase. One set of fillets at a time can be done if you get everthing set up and laid out before mixing. If you are adding chopped carbon fiber, use even less than the recommended dime size as it will thicken Rocketpoxy even more. I load the syringe from top using a popsicle stick to pack it in. Use gloves, as it is a little messy. Have your IPA handy on a prewetted paper towel to wipe outside of syringe and keep gloves clean. To be honest, I suspect Rocketpoxy does not flow all the way up and down internal fillet like a thinner epoxy would. It's hard to tell with the black FG. That said, I still feel it is stronger than using thinned or lower grade epoxy.

Was hoping to use what I already have on hand. Have rocketpoxy and generic epoxy from LHS.

Gotcha. Thanks for the advice. I was more worried about it flowing the length of the fin. And as you said the black FG you can't tell. If a shorter fillet of rocketpoxy is better than a full fillet of the generic stuff then maybe I'll try it.

What about thinning with IPA?

I've thinned rocket poxy with denatured alcohol to make it more fluid, I've not noticed any loss of strength. What was left over hardened up as hard as any other I'd mixed.

Ok good to know. I'll give it a shot tonight and report back!

chadrog said:

I've thinned rocket poxy with denatured alcohol to make it more fluid, I've not noticed any loss of strength. What was left over hardened up as hard as any other I'd mixed.

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I wonder if the Rocketpoxy G5000 manufacturer Glenmark or anyone else has data on how thinning affects strength. West Systems, for example, says there is a loss of strength when their epoxy is thinned. https://www.westsystem.com/ss/thinning-west-system-epoxy/

Even if there was some loss in material strength, thinning could still be better in order to ensure more complete fillets.