(Very Slow) Demon 5 Build Thread

jmasterj

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I bought this rocket from Wildman early this year and picked it up at Red Glare. I did some additional thinking, bought some longer parts, and then left it for months. I decided to make it one of my goals for 2023 to get it built. I'd love to stick a 75mm K from my Black Friday order in it at Red Glare 2023, but that's probably too optimistic given my work and family commitments over the next 4 months.

To start, here are the parts that make up my back end:

demon_5_fin_can_parts.jpg


10" of 5" coupler tube (longer than the kit default, which I plan to use elsewhere)
5" slotted tailcone, forgot to measure the length (14"?)
24" of 3" motor mount (again longer than the default)
Fore CR that fits 5" airframe tube
Aft CR that fits 4" airframe tube
Giant Leap Slimline Retainer
Fins

I like to build my fin units sandwiched by centering rings on either end, with the motor retainer butting up against the aft CR. In my head, at least, this transfers thrust from the motor thrust ring to the retainer, to the CR, to the fins, to the airframe, without really relying on the strength of any glue joints. The trouble here is that the aft CR isn't the correct size to butt up against the rear fins while still contacting the tailcone. To deal with that, I'm going to laser cut a series of additional CRs from 1/4" (and one 1/8") ply to fill the 1.625" between the front size of the aft FG CR and the back of the fins. I'll sand them into a smoothish bevel so they fit nicely into the back end of the tailcone and bridge the aforementioned gap.

I want to extend the distance the coupler extends into the tailcone and the airframe, thus the extended 10" coupler. The sharpie marks show where I'm going to cut slots to allow the coupler to slide over (and bond tightly with) the fins and slide farther into the tailcone. I will use a CR tacked into the middle of the coupler when I install the motor mount into the tailcone to get alignment correct. The long motor mount extends just past the front of the coupler, allowing it to bookend the whole tail section. At on point I had considered attaching the airframe to this tail unit with a bunch of screws to allow for repairs, etc. but I think that's off the table (that was part of the inspiration for the longer coupler too, if I remember correctly). Question for readers: with what tools would you cut the slots in the coupler?

None of this touches at all on the front end of the rocket. My current plan is to reuse the sled and electronics from my 4" DD rocket, using the coupler and bulkheads from this kit and just requiring me to space the allthread the same. The terminals on my existing 4" av bay all have connectors between them and the electronics, which would allow me to just move the sled between av bays as necessary. I'll see when I get there if that plan survives contact with the build. Recovery attachment hasn't been determined yet. U-bolt on the fore CR will be inaccessible once the whole thing is built but is an option. My favorite option the last time I thought about this was a bulkhead installed up near the top of the airframe with a coupler piece to reinforce it, leaving just enough room for the one end of the av bay and the drogue part of the recovery package.

So my steps going forward:
1. Cut a bunch of ply CRs to fill the gap between the aft CR and the back end of the fins
2. Cut a CR to go (at least temporarily) in the coupler
3. Install the motor retainer and aft CRs onto the motor tube
4. Sand the ply CRs to shape so the assembly fits nicely in the tailcone
5. Tack the CR from #2 into the coupler
6. Prep the section of the motor tube that will be inaccessible for bonding the fins later
7. Install the motor mount into the tailcone, with the coupler/temporary CR slid in behind for alignment
8. Remove coupler
9. Cut short slots on coupler
10. Install fins
11. Do internal fin fillets
12. Do external fin fillets
13. Install coupler
14. Determine if recovery attachment needs to be included here and add it if so
15. Install fore CR(s)


I'm sure I've overlooked some things, so please point those out to me so I can fix them now. I'm also positive I've overthought this and am overbuilding it, but at this point I don't think you're going to talk me out of that part. ;)

Thanks for reading, and I appreciate encouragement to keep working on this as it drags out over the next several months.
 

StreuB1

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I am a big fan of the Demon. I have the 5" and the 6". The 5" is my best flying rocket I own from a performance perspective (its very slippery aerodynamically) and from a photography point of view (it doesn't rotate AT all on the way up).

Flew both at MWP several weeks ago. Demon 5 went mach 1.6 and the 6" went mach 1.4

You will absolutely love this rocket.

If you need anything regarding build, electronics, etc. Let me know.
 

jmasterj

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Demon 5 on the M1780NT to 13k
Demon 150 on the M4500ST to 11k

I'm going to start much smaller than that, lol. Level 3 is out of my financial reach unless I severely curtail my number of flights. I'll Probably start with one of the big 38mm Js, then Ks after that. This should be the rocket for the K1800ST I ordered from Wildman on Black Wednesday and the 2G C-Star L I ordered the Saturday after that.
 

jmasterj

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Progress has been made on steps 1 and 2! Progressive tail and coupler centering rings cut. Only wasted one loosey goosey one (not pictured).

PXL_20221208_214440674.jpg

Next step is a quick dry fit in the tailcone, glueing them together, and then onto the motor mount, followed by sanding to final shape. Not positive how I'm going to do that to keep them round, though.
 

jmasterj

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The spacer rings will need some sanding; my imprecise measurements (internal meaurements on a nose cone are tricky) made them slightly too large. I will consider cutting a more precise set. I should have had the tailcone with me and cut test pieces from acrylic first, but ah well. Sanding will do fine if I can do it without taking things too far out of round.
 
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StreuB1

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I'm going to start much smaller than that, lol. Level 3 is out of my financial reach unless I severely curtail my number of flights. I'll Probably start with one of the big 38mm Js, then Ks after that. This should be the rocket for the K1800ST I ordered from Wildman on Black Wednesday and the 2G C-Star L I ordered the Saturday after that.

Oh heck yeah dude! My Demon 5 is not terribly heavy, rather light actually, and it could fly on big high thrust J's or normal K's. K1100 or K1000 would be great in it as would the K1800ST. Its first flight for me was on an L1520T; I just said heck it and went full-send on it. My Demon 150 though, its maiden flight was on a K1999N and it flew to like 4k. So even it could fly on even smaller motors.

Like I said, you will love that rocket. It flies so so so well.
 

Theory

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@StreuB1, what does your Demon 5 weigh?

...and not surprised the 150 flew on a K1999, though I have also never heard the 1999 refereed too as "small" ; - )
 

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Either works. Can approximate the weight of recovery gear as the systems used in that kind of rocket are likely within 1/2 pound of each other
 

jmasterj

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No pictures, but I got my spacer ring stack glued together last night and sanded down to rough fit today. I just rolled it on the belt sander in the makerspace at work. I also cut a better-fitting coupler CR.

I will probably get the retainer and FG aft CR glued on this weekend so I fit the separator stack and fins next.
 

StreuB1

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Either works. Can approximate the weight of recovery gear as the systems used in that kind of rocket are likely within 1/2 pound of each other


Final weight and CG is exact.

Ignore the fin root tab at the trailing edge. No idea how to make a multi-depth root in OR and it doesn't affect it at all from a performance perspective.

My motor retainer is a 75mm flange mount Aeropack.

Any questions or if you want pics, please let me know. I heavily document my builds and if I don't have pics, the rocket is in the basement and I can get whatever info anyone might need.
 

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jmasterj

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Retainer and aft CR attached:

PXL_20221213_013410462.jpg

Will let cure, then proceed onto dry fitting the spacer ring stack into the tailcone with fins. I think I'm going to laser cut a fin guide out of acrylic (free in my work makerspace) for that as well.

Slow progress, as promised.
 

jmasterj

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Tailcones are one place where I definitely prefer the GLR slimline retainers to Aeropacks. They're definitely slower to take on and off, but they nestle nicely inside things. I'll get a picture of that dry fit next to show what I mean in this particular case.
 

Theory

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Tailcones are one place where I definitely prefer the GLR slimline retainers to Aeropacks. They're definitely slower to take on and off, but they nestle nicely inside things.

Agree 100%!!! Used one on my Laser Loc 313 and it’s perfect
 

jmasterj

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Spacer ring stack shortened a touch so the fins fit and glued onto the motor mount.

PXL_20221216_222246729.jpg

Next up is another dry fit with the fins and then gluing the mount into the tailcone.
 
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jmasterj

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Fin guides are cut from 3/16" acrylic scrap. They seem to fit nicely. Dry fitting the fins with the motor tube inserted doesn't get them flush with the tailcone afore the slot, so I have to figure out why that is and fix it.
 

jmasterj

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Did a little sanding on the fin that didn't quite sit flush and marked the fins, slots, and motor mount rotation.

PXL_20221221_204951408.jpg

Need to do the final clean and surface prep of the motor tube and inside the tailcone so I can glue the motor mount into the aft end of the tailcone.
 

jmasterj

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Did the surface prep, had just enough time to epoxy the aft centering ring and spacer stack into the aft end of the tailcone. Used West Systems GFlex (bought for fillets) because it mixes up really quickly and doesn't drip. Also put a thin (but uneven, whatever) layer of epoxy on the aft rim of the tailcone to avoid getting any stray fibers in my skin when using the retainer.

PXL_20221221_221053505.jpg

I know you can't see much in the picture, but there's really not much to see.
 

jmasterj

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First fin on! Double-dipped it, but I have access to do real internal fillets without resorting to injection.

PXL_20221222_222518247.jpg

Trimmed-down chopsticks force the fin to one side of the slightly-loose slots. I forgot the surface prep of the tailcone forward of the slot until after I had buttered the fin with epoxy the first time. Whoops! Managed to quickly clean/sand/clean, though, without making a mess.
 
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