(Very Slow) Demon 5 Build Thread

[jmasterj]

Third fin is on, completing step 10 from the first post. Again no picture because it looks the same as attaching the first fin.

I also completed step 9, though, cutting the short (1.375") slots in the coupler to fit over and lock into the fin tabs. This will allow the coupler to extend deeper into the tailcone for additional overlap.

It turned out to be much easier than I expected: I clamped the coupler down, clamped a vacuum inside it, and slowly cut them with a Dremel plus 3 stacked cutoff wheels. Thanks to @Pem Tech for the tip from 13 years ago!



I will check the fit tomorrow after the third fin cures. I did forget to mark which slot on the coupler went with which fin slot, so that will probably take some trial and error (and sanding).

Next big steps are internal and external fin fillets, though I'm just now thinking external ones maybe should wait until I attach the fin can to the airframe. Any opinions there?

 

[Pem Tech]

Third fin is on, completing step 10 from the first post. Again no picture because it looks the same as attaching the first fin.

I also completed step 9, though, cutting the short (1.375") slots in the coupler to fit over and lock into the fin tabs. This will allow the coupler to extend deeper into the tailcone for additional overlap.

It turned out to be much easier than I expected: I clamped the coupler down, clamped a vacuum inside it, and slowly cut them with a Dremel plus 3 stacked cutoff wheels. Thanks to @Pem Tech for the tip from 13 years ago!

View attachment 553533

I will check the fit tomorrow after the third fin cures. I did forget to mark which slot on the coupler went with which fin slot, so that will probably take some trial and error (and sanding).

Next big steps are internal and external fin fillets, though I'm just now thinking external ones maybe should wait until I attach the fin can to the airframe. Any opinions there?

Glad we could help.

 

[jmasterj]

Nuts. Just tested the coupler fit over the fins - it might be too good. Can't get it out now. I tried pulling, obviously. Tried putting the motor tube on the ground and pushing the coupler down from the sides. No movement. Any ideas on how to get this out?

 

[John_461]

Drill two holes in the coupler big enough to route a kevlar line through (won't affect the coupler strength). Tie the line into a loop and place a bottle jack on the motor tube and cinch the loop tight against the jack head. A few pumps on the jack will have it loose.

Or, throw the whole thing in the fridge for a couple of hours. Then pull it out and while everything is still cold, gently warm up the outer tail cone with a hair dryer. It may loosen up enough to separate them.

 

[Theory]

I see you are in MD. If you are anywhere close to me (around Fredrick) some time in the 20 degree outdoors should help.

 

[jmasterj]

I see you are in MD. If you are anywhere close to me (around Fredrick) some time in the 20 degree outdoors should help.

Weirdly enough it's 50 degrees out today and is supposed to stay that way for a few days.

 

[Theory]

Weirdly enough it's 50 degrees out today and is supposed to stay that way for a few days.

yes, thats KRAZY! was 3 a few days ago

...what i get for being in the home office since 6:00

 

[jmasterj]

Forgot to ask my dad to borrow a bottle jack. It won't fit in my fridge or freezer and it's not cold enough outside. I should see him on Monday and ask for it then.

 

[jmasterj]

Thanks to @John_461's suggestion, the coupler was easily removed with the correct equipment.



I then proceeded to internal fillets. Normally these are pretty simple: damn the front end with some tape, pour the epoxy down the inside wall of the airframe, and do some tilting to level things out. Remember I said that the fin slots were a little too wide? Forgetting about that gap just bit me in the ass. I spent as much time trying to clean things up after pouring epoxy as I did everything else involved in this step. The tailcone and fins recessed from the edge I was pouring didn't make anything easier.



I did get one pair of internal fillets poured (I think you can just make the right one out in the picture), though, and I'll be prepared to seal the gap along the side of the other two fins. Slow and steady gets my rocket built.

 

[jmasterj]

I definitely used too much epoxy for the first set of fillets. (Overthinking things now) I can't decide whether it would be better to use the matching amount on the other sets or a lesser, more appropriate amount.

Either way, the first thing I need to do is securely tape the gap on the fin slot so nothing leaks out again. I probably won't get to this till next week; I'm taking my sons to the MDRA launch on Sunday and need to prep the rockets we're bringing.

 

[Theory]

don't worry about trying to "match" epoxy amounts from side to side. the rocket wont care

 

[StreuB1]

Agreed, the rockets mass is FAR greater than any differential mass in epoxy. Meaning, it will have zero affect.

Get on with the build!

 

[jmasterj]

Agreed, the rockets mass is FAR greater than any differential mass in epoxy. Meaning, it will have zero affect.

Get on with the build!

I said it would be slow!

 

[StreuB1]

Slow is still progress!! As long as you are moving on it, then thats what counts!

 

[gamewood]

Did you have a RockSim or open rocket file? What was the original motor mount tube length?

 

[jmasterj]

Did you have a RockSim or open rocket file? What was the original motor mount tube length?

There's a more stock one attached earlier in this thread.

 

[StreuB1]

Did you have a RockSim or open rocket file? What was the original motor mount tube length?

Posted a reply with the file in your thread.

 

[jmasterj]

Finally got a second set of internal fillets done. I'm glad this rocket only has 3 fins!

I learned my lessons from last time and managed to avoid making a mess. I also used two pumps of epoxy instead of three; that ended up being the perfect amount.

 

[Hobie1dog]

this is going to be one serious Rocket.

 

[jmasterj]

Almost 5 months later... Last set of internal fillets!



Next steps should happen a little quicker. They don't involve the same kind of potential mess. Coupler fitting and placement is next, followed by the centering ring to seal up the tail section.

 

[jmasterj]

I probably should have prioritized some paint work today, but I hate painting. So I got a little more work done on the Demon!

Coupler was sanded to a good fit (with a couple of mallet insertion + bottle jack removal cycles) and then epoxied in. Added a centering ring to seal up the boat tail and ensure the coupler was centered over the motor mount.



(additional, temporary upper centering ring not pictured)

 

[jmasterj]

No pics of this part, but I laser cut the plywood parts of the recovery anchor bulkhead I'm going to use. Cut the coupler pieces yesterday. Dug out all the recovery parts except the main parachute and started thinking about how I want to lay out the av-bay and what I want to make myself vs what to buy commercially.

Tonight I washed the main airframe and then measured and drilled rail button holes. Didn't quite get to the backing nut epoxy tonight; maybe tomorrow. Meant to drill the vent holes but forgot, of course.

 

[jmasterj]

Got the epoxy on the backing nuts on Saturday morning. One more airframe test fit, then I can epoxy the fore centering ring on. I haven't decided whether to attach the airframe to the fin can before or after the recovery anchor (that also needs to be finished) goes in.

 

[jmasterj]

Did my first work on this rocket (or any!) since moving!

After spending 30 minutes finding some alcohol, I put up my little folding table, and gathered the rest of my supplies. Then I surface prepped everything I was going to work on tonight. Two parts of this rocket: the centering ring sealing up the fin can, and the recovery anchor.

Nothing complicated about the centering ring:


(Pic was taken upside down since there's some epoxy behind the ring for a fillet.)

I need to create a diagram for the sandwiched recovery anchor I made, but it's 2 layers of 1/4" ply, 1 layer of 1/8" FG that is missing the top layer because of bad water jet cutting, and another layer of 1/4" ply. There's a 3/8" stainless u-bolt through that sandwich, then 2 coupler rings on the top (smaller cut to fit inside the regular size) and 1 on the bottom.

I decided to go with this anchor so that I can start this rocket out on long 38mm Js at a local site with that upper limit. I don't trust a closure-mounted recovery anchor in a 38-75 adapter, so here we are.

 

[jmasterj]

Epoxied the airframe onto the fin can for the second bit of progress this month!



Looks more like a rocket now, lol. I put a vent hole in the airframe and CA'd the loose fibers as well. Recovery anchor installation is next, and then I get to move onto the electronics bay and recovery setup.

 

[jmasterj]

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.

Do you by any chance have pictures of your main harness setup for HED? The drogue setup is the same as regular DD, so I'm set there, but with the main anchor point buried in the nose cone and the need to pull it out of that nose cone I'm have trouble picturing that setup.

I found one of your posts that answers another question I was thinking through. For symmetry I'm thinking 3x #2s booster/av-bay and 3x #4s av-bay/nose cone. Have you compared the amount of 3F vs 4F in any of your rockets? I have two different charge well sizes, with the first going up to around 3g and the second going to 6g. I assumed the 3g would be enough for the main event, since the nose cone will be so full, and it sounds like that's reasonable.

In my Demon 150 (6.25" thick wall FG) I use 3x#2 at the booster to AVBay/NC (apogee) and 3x#4 for the NC (main)

For my Demon 5 (5" std wall FG) I use 3x#2's and then 4x#2's in the same orientation as above, both are HED.

I agree with Tom (above), "Either blow it out or blow it up." Within reason, of course. Purely for reference, I use 3.6g (3F) and 2.2g (3F) in the Demon 5 (drogue/main respectively), and 4.5g (3F) and 2.0g (3F) on the Demon 150. Yes, the Demon 150 takes LESS powder than the Demon 5 to blow the cone at main.

Gathering your kevlar harness into single wrap taped bundles of 5 z-folds, 6" long, on 20" centers, does a really good job as a progressive shock arrestor for both the apogee deployment as well as the main deployment. Helps harness those forces on larger rockets that require larger shear forces.

 

[jmasterj]

Last night I found the recovery package I'd put together and put it in a more memorable place. OBD 7/16" kevlar, big quick links and swivels that I know I sized before to match the kevlar strength (but I don't remember the numbers since it's not in front of me now).

I also gathered what I think are all the parts I need to build my av-bay. Brought them to work so I can put it together over the next couple weeks in our well-lit makerspace rather than my dim basement. I'll get some pictures of that when I get in there.

 

[jmasterj]

Drilled all the av-bay lid holes. Alignment between threaded rod/eyebolt holes and charge well holes is pretty mediocre, but it's ultimately irrelevant. I forgot to bring the threaded rod over to the shop, so cutting that will come later.



Av-bay progress will be at work and as slow as this whole thread. Fin can/airframe seam fill and fin fillets are next on the main rocket. Switch band mounting and switch/vent holes are also coming up. Also slow, but am making progress.

 

[jmasterj]

Attached hardware to the av-bay lids overt he last couple months.

Attached my electronics to the sled today! Just have to wire things up and this part will be done. I have to get back to the actual airframe and do fillets and attach the recovery anchor. With no Red Glare for 2024, I have to hope I can make it to the Higgs launch in Feb/March or get permission to take my sons to LDRS to fly this thing.

 

[kjhambrick]

That's a BIG beautiful AV-Bay. @jmasterj !

Thanks for the picture !

-- kjh