I can't figure out how to build this

[neil_w]

Or perhaps I should say, I can't figure out a sensible and straightforward way. Been working on finalizing the design for this rocket (thanks to @Bill S for decal advice):


The build and paint sequence is vexing me. The ring, in particular, seems like a nightmare, given that it goes through two tubes and a fin. And normally I would think of pre-painting the ring (tough to get a rattle-can into all the nooks and crannies after assembly) but in this case I don't see how I could glue it on after-the-fact. Getting the pods attached to the body on the two separate pylons would be challenging but I could make it work. That ring though.

Cutting the ring into pieces maybe would solve one problem while introducing others. I am pretty reluctant to do that but may end up with no other choice. Could be either two pieces (top and bottom) or three (top left, top right, bottom). If I want to keep the ring whole, or at least keep the top piece in tact, then I'll need a precisely slotted fin which I haven't tried to do by hand before. This rocket could call for some laser cutting, dunno.

Anyway: taking ideas for a sensible approach to this. I'd rather not modify the design just to make it easier to build, although there are worse things in life. But I'm not going to start a build until I have a plan that I believe in.

(also open to decal and/or paint scheme ideas, I'm still trying to nail that down as well).

 

[lakeroadster]

Cool design.

Maybe focus on the structural components and build / glue them first. Slot the orange tubes and install them last using a clear adhesive that won't eat the paint. Which would no doubt require some R&D ahead of time to pick a glue, and paint, that are compatible.

Think that might work?

 

[kuririn]

Instead of cutting full length slots on the fin and pod tubes how about cutting half slots in the ring and fin/tubes so that they nest into each other? That way you won't have to cut the ringtail.

 

[neil_w]

Maybe focus on the structural components and build / glue them first. Slot the orange tubes and install them last using a clear adhesive that won't eat the paint. Which would no doubt require some R&D ahead of time to pick a glue, and paint, that are compatible.

Think that might work?

Dunno, maybe? One tricky bit is that the ring is inset from the ends of the orange tubes, so slotting them from the end would leave some excess exposed slots at the end that would need to be dealt with.

Also, and I only just thought of this, those tubes are BT5, which is horribly flimsy and loses its integrity when it is cut. I gotta think about that. Perhaps I could glue couplers into the ends of the tubes before slotting.

Instead of cutting full length slots on the fin and pod tubes how about cutting half slots in the ring and fin/tubes so that they nest into each other? That way you won't have to cut the ringtail.

That would require extremely precise slotting. 5 slots on the ring, two slots on each orange tube, and one on the fin. I don't think I would be confident of being able to do it with the necessary precision.

 

[lakeroadster]

Dunno, maybe? One tricky bit is that the ring is inset from the ends of the orange tubes, so slotting them from the end would leave some excess exposed slots at the end that would need to be dealt with.

Also, and I only just thought of this, those tubes are BT5, which is horribly flimsy and loses its integrity when it is cut. I gotta think about that. Perhaps I could glue couplers into the ends of the tubes before slotting.

Maybe a circumferential joint at the aft end of the orange tube, and as you said, use a coupler. You might even be able to make the joint look more "real" with some rivets on either side?

Or maybe you could get somebody to 3D print the pods...

 

[asm109]

cut fin in half. Inner fin glues to inside of ring. Outer fin has notch. Glues to outside of ring and ends of inside fin.

Extra credit if you put a 13 mm motor mount in the pods and use A10-PT motors.

 

[BigMacDaddy]

Agree about the half slots.

For the main large fins -- it is difficult to see from the picture but are they discontinuous? Would it be possible to make them from one large piece of plywood or balsa and put them all the way through the pods in the front? A single continuous piece of wood could make that mount quite a bit stronger.

I would also consider making slotted centering rings that reinforce the fin / wing mounts. Could do one for a front tab on the side wings (could be the cap of a stuffer tube) and then two more in the rear that could support the motor mount as well as top Fin and side wings. I first did something like this on the A-10 but have done it on the R1 and some other models now as well.

If I was 3D printing this I would do some type of detail to close off the main tube in the rear and integrate a retainer cap of some type.

One other thought on the pods -- maybe close them off in the rear with a cap / boat tail of some type. This would let you slot the tubes for your ring tail and then slide a cap onto the rear of the pod to strengthen the tube and maybe the fin mount. I did little slotted cap on the rear of the P-38 that is like that. I don't lie slotting tubes all the way to the end since it is difficult to get them back into shape but maybe the cap could even go on the outside of the tube.

 

[neil_w]

For the main large fins -- it is difficult to see from the picture but are they discontinuous? Would it be possible to make them from one large piece of plywood or balsa and put them all the way through the pods in the front? A single continuous piece of wood could make that mount quite a bit stronger.

Here's a bottom view, with ring removed to show the structure more clearly I hope:

I'm not sure how those could be one-pieced, to be honest.

I would also consider making slotted centering rings that reinforce the fin / wing mounts. Could do one for a front tab on the side wings (could be the cap of a stuffer tube) and then two more in the rear that could support the motor mount as well as top Fin and side wings. I first did something like this on the A-10 but have done it on the R1 and some other models now as well.

Could do it, not sure it's really necessary on an LPR bird like this, but maybe. I guess it would make good sense for the pod supports to be TTW... at that point I'm not sure the extra strength from the rings would be necessary, but it certainly couldn't hurt.

One other thought on the pods -- maybe close them off in the rear with a cap / boat tail of some type. This would let you slot the tubes for your ring tail and then slide a cap onto the rear of the pod to strengthen the tube and maybe the fin mount. I did little slotted cap on the rear of the P-38 that is like that. I don't lie slotting tubes all the way to the end since it is

Capping the pods behind the ring with some sort of 3d-printed nozzle is a tempting idea. I'd have to change the pod support and the wings, though, because right now they both go all the way to the back of the tubes.... Has me thinking of the way it is handled on the SR71:


I could probably do something like that.

cut fin in half. Inner fin glues to inside of ring. Outer fin has notch. Glues to outside of ring and ends of inside fin.

Yeah, I was thinking about that... Lots of the finish-assembly-after-inserting-ring ideas will force me to do at least some of the painting after completing assembly. That worries me. I still don't quite understand how folks paint rockets with "interior" painted surfaces (like the inside of the ring). It would be much easier on larger rockets, but at this size it's a BT80 ring, which makes it pretty tight inside.

 

[BigMacDaddy]

I'm not sure how those could be one-pieced, to be honest.

With the CNC I cut much more complex fins than I used to. How big are these? Could they fit on 8"x12" plywood?

The rear part could definitely be separate since it could be seamed inside a 3D printed slotted tail. However, I think it would make the front part really strong if you could run a piece of plywood directly through the pod tube. Just a rough mark-up.

 

[Bruiser]

I'm thinking two pieces for the ring, an upper and lower separated at the "horizontal" fins. The pods would be slotted for the fin to go in to, aka ttw ring. The vertical fin would be two pieces and the top piece would be glued after the ring. The joint in the vertical would not be just a straight cut for the two piece either, it would be cut in like a tab like orientation ___l--------------l____

Just my 2 cents.
-Bob

 

[neil_w]

Plywood would be awfully heavy for an LPR rocket like this, and threading the pieces through slots in the pod tubes would seem like quite an adventure. I'm not convinced that strength is going to be a problem, although single-piece construction like that would ensure proper alignment....

 

[neil_w]

I'm thinking two pieces for the ring, an upper and lower separated at the "horizontal" fins. The pods would be slotted for the fin to go in to, aka ttw ring.

The nice thing about this approach is that it eliminates all problems slotting the BT5s from the rear. It would require precise assembly... maybe not too bad, dunno.

 

[BigMacDaddy]

Plywood would be awfully heavy for an LPR rocket like this, and threading the pieces through slots in the pod tubes would seem like quite an adventure. I'm not convinced that strength is going to be a problem, although single-piece construction like that would ensure proper alignment....

I am strange I guess since I just do everything with plywood these days... it is difficult to cut by hand but if you are using a CNC it works great. It is also cheaper than balsa, does not require papering or wood filling, etc... The weight is rarely a problem -- you have plenty of fins / drag here.

I like to make things extra sturdy since it is not any extra trouble to do so. For example, it is easier for me to mount fins with tabs into slotted 3D printed parts since there is no question mark about alignment or anything else. I don't like to surface mount fins since getting them straight is a stressor.

 

[BABAR]

by George I think I've got it.

First, Put the Rudder and Wings on, but initially cut the rudder with more forward length (so you can cut a slot in it that doesn't go all the way to the front, you can always cut the forward piece off AFTER you put ring in place), and cut the wings as ONE piece (including both the inside struts and the OUTSIDE parts) full length (you can cut out the inside "cut-outs" later, but you will only glue and fillet the forward and aft sections. Yup, the outside pods are gonna go over both the ring AND the wing.

If you feel REALLY confident you can pre-slot the rudder and wings BEFORE you glue them on the body, or you can hold the ring up to it after attachment and cut slots after attachment.

Okay, wings (full length, maybe even a little long, both inside and outside sections, and don't do the cut-out section yet) and rudder on, slots cut, put Ring in place and glue and fillet it. You can now cut the extra forward edge of the rudder off (the piece that was holding it together so slot wouldn't break it.

While that is going on, make the equivalents of long BT-5 couplers the length of your outboard pods. Basically take a BT-5, cut a longitudiinal lengthwise slot, and use masking tape or other rough surface tape to hold the edges together so it just slides inside an intact BT-5.

Stiffen these up a bit with thin CA on the outside.

Now cut each of these in half, lengthwise, and the cut an additional (edit again) WING fin width edge off each side.

Measure the inside width of each of these 1/2s (or slightly less than 1/2s), and cut a piece of 1/8" balsa that will just fit INSIDE it. We're getting pretty small, you may need to bevel or round the sides a bit. do NOT glue this to the coupler pieces (yet.) We're gonna call these "cheaters"

Figure out where the pods are gonna go, draw a center line down the wings for where you want 'em.

Glue the cheaters in place, centered on the lines, with cutouts where the ring is. May want to initially make the wing LONGER than planned near the tail, you can cut it off later. We will deal with the ring later.

Cut the couplers transverse, so you have a dorsal and ventral piece both forward and aft of the ring.

Place the coupler halves over the cheaters, both dorsal and ventral sides of the wings. Glue in place, but do NOT fillet.

Okay, now you have guidance and support for your pods forward and aft of the ring, still want to support the pods OVER the ring.

Cut 1/8" balsa cheaters the length of the ring, using the already present cheaters you should have a pretty good idea where to put the so the run between the forward and aft couplers, on the ring. You may need to sand a curve into the outer edge.

Slot the BT-5s to fit over the wings AND the ring. Yeah, their gonna be flimsy initally, but they are gonna have rock solid support and guidance.

Slide the BT-5s over the coupler/cheater/wing assemblies. I'd use white glue for this, it's paper to paper and will give you more working time. You may need some tape or other method to hold the long flimsy sections DOWN so they adhere tightly to the couplers.

Add your nose and if desired tail cones (cut off any extra tailward wing with the couplers if you initially went long.

NOW, cut out the "cut-outs" between the mid portion of the wings and the body tube. Leave a bit on the OUTSIDE edge (near the pods), so you can sand this down even with the pods' internal (meaning the edge of the pods nearest the main tube, not INSIDE the pods) edges.

Paint, schmaint.

Fill all the divits and do all the super prep work you are famous for, and lay down your base color. You'll need to fill the divots in the ends of the BT-5s that extend beyond the ring.

For all the orange stuff, use this:

https://www.horizonhobby.com/product/trim-monokote-international-orange/TOPQ4102.html
Looks pretty close to your current color. You may have a hard time matching the nose and tail cone colors, but maybe just use a contrasting color instead of trying to match it.

You can also use trim monokote on the INSIDE of the ring if you don't like the base color. You can also use self stick paper to finish the rings inside and out to hide the spirals.

Of course I am biased, but I think that individually each step here (with the exception of slotting the BT-5s, yeah, that's gonna be a challenge) is pretty easy. And even for the slotting, the fact that you have an underlying BASE (the couplers in front and behind the ring, and the cheaters of the ring itself) should make it pretty easy to attach. You can fill any gaps with CWF, and you're gonna cover the whole enchilada of the pods with Trim Monokote anyway.

It should make alignment spot on.

The combination of two 1/8" cheaters, the coupler tubing, and a white glue lengthwise connection with the BT-5 is gonna provide a lot of support to that wing, and the cheaters along the ring will also provide additional support for the structure.

Using Trim Monokote saves you all the masking, and the edges should be razor sharp.

Okay, I'm off the soap box.

 

[BABAR]

Probably lots of online places to get the trim monokote, but a 36"x5" sheet runs $9.32 (probably plus tax) delivered by Walmart.

https://www.walmart.com/ip/Top-Flite-Trim-MonoKote-International-Orange-TOPQ4102/37831891
interesting, the Horizon Hobby store says "discontinued", but the Walmart site says available, but selling out fast. No, I don't work on commission.

 

[BABAR]

Okay, back on the soap box. I think you can probably safely pre-slot the rudder and the wings. About the only critical thing (and this should be pretty easy) is that the wing slots need to be exactly equidistant from the body tube, which should be pretty easy. Heck, just stick one right on top of the other and cut both slots at the same time.

But what if I off a mm or 2 (or 4!)? NOT critical. The ring is going on in one piece, and that piece is a little bit flexible (okay, it may not be PERFECTLY round if you are off a few mm, but it's gonna be pretty close.) So the ring as a single piece will flex slightly to accommodate the slots being off laterally or vertically a bit. In fact, since it looks like you are intentionally eccentrically placing it a bit high relative to the body tube (doesn't look like it is centered on the main body tube), it your wing slots are off by more than YOU can tolerate you can widen them to fit (whichever way you widen them, the ring SHOULD be in direct contact with either the inside or the outside of the slots, and you can use the cheaters to fill in the difference. Structurally my biggest concer is those big cut-outs in the middle of the wings. In this case, once it's all put together, the ring in combination with that big dorsal fin should actually provide some good structural support. maybe not @lakeroadster 's "hell for stout", but pretty darn good. If you wanted more, you could cut three pieces of ring to fit just INSIDE the ring to make the ring even stronger.

 

[K'Tesh]

I'd cut the two smaller tubes ahead of the ring fin, then using a slotted tube coupler, I'd install it into the forward part of the tube, then glue in my ring fin, and add the slotted rear section to close it up.

Perhaps to hide the joint, use something like manilla cardstock, or a 3x5 card, to make some kind of detail (such as a simulated removable panel) that either goes over the joint, or sits just ahead (or behind) the joint to minimize its appearance.

 

[Antares JS]

I would just assemble it unpainted, spray the whole thing with gray primer, and paint the orange with Testor's and a brush.

 

[KenECoyote]

A bunch of great ideas here!

You, my friend, have a "take and give" situation here.

• Slot stuff and the parts end up weaker and more likely to break at the slot without fillets.
• Cut or slot the ring and it likely won't be as round and it's noticeable when rings aren't round.
• Use couplers and it becomes heavier in the rear and the joint is very hard to hide well.
• If you want something other than a simple paint scheme, you're screwed lol

So decide which one or ones are most important to you and take it from there.

Is it OK that the ring fin isn't perfectly round? Then the simplest may be to have it as three separate pieces. I'd use two layered cut pieces for each section formed inside of a fg ring and that should hold the curve nicely.

Is it OK to have the stuff slotted? Then options were noted above.

Compromise? Then try a long strip cut from a cardstock and feed it through slots and glued at the overlap.

Either way, good luck with this challenging build!

 

[neil_w]

I seem to have a lot to respond to here.

In the meantime, though, one clarification: my paint sequence questions have nothing to do with the decals. The orange stripes are no problem, I have at least 3 different ways to do that and all will be fine. What I'm fretting over is which parts have to be pre-painted, and how to integrate those in later. @hcmbanjo showed a lot of pre-painting strategy in his Estes Odyssey build. I feel like something along those lines will be necessary here, maybe not quite so extreme as that one though. In my experience, trying to get into nooks and crannies with a rattle can is very difficult; far too easy to either (a) not get full coverage, or (b) get huge runs. I have done a bit of pre-painting in the past and am never really comfortable with it, but it seems like there is no choice here... once the ring is installed there is no way I'm getting an even paint coat into all the interior areas of the tail end. I'll deal with it, but I do need to plan it out properly.

One thing I have definitely decided: I will reinforce the BT5 tubes wherever I slot them. I might even double-layer the whole tubes, since they're structural and it would make me feel better. Maybe not necessary but probably not harmful as long as I account for the weight.

 

[lakeroadster]

Is this a 24mm powered rocket?

 

[neil_w]

Is this a 24mm powered rocket?

Yes, definitely.

 

[lakeroadster]

Yes, definitely.

Awesome, no need to spare the couplers then. I'm amazed each time I select a 24mm motor in Open Rocket at the wide range of impulse available in the 24mm size.

Are you thinking balsa or basswood for the flat fins... and what's your material for the ring fin?

"Enquiring minds want to know."

 

[neil_w]

Awesome, no need to spare the couplers then. I'm amazed each time I select a 24mm motor in Open Rocket at the wide range of impulse available in the 24mm size.

Agreed. Plus you can adapt down and get the C and D Q- jets.

Are you thinking balsa or basswood for the flat fins...

Yes.

and what's your material for the ring fin?

BT80

 

[Back_at_it]

Nothing constructive to add to the conversation, but my god is that an awesome design......!!!!!

I really hope you figure this one out as I'd love to see a build thread on it.

 

[neil_w]

Thanks. It will definitely be built and threaded as soon as I figure it out.

 

[neil_w]

Before I begin: Regardless of whether I choose to follow any particular suggestion, I appreciate all the input. It has given me plenty to think about and will definitely result in my taking a better approach, regardless of which I choose.

While that is going on, make the equivalents of long BT-5 couplers the length of your outboard pods. Basically take a BT-5, cut a longitudiinal lengthwise slot, and use masking tape or other rough surface tape to hold the edges together so it just slides inside an intact BT-5.

I think I might do that no matter what. BT5 is so flimsy, I'll feel better if it's reinforced, given its structural role in this rocket.

Stiffen these up a bit with thin CA on the outside.

Now cut each of these in half, lengthwise, and the cut an additional (edit again) WING fin width edge off each side.

In parallel, I also had the idea to do halfsies on the pod tubes, except with some sort of 3D-printed parts that will nest together nicely, with precise slots and such. This would allow me to use single-piece wings like @BigMacDaddy is advocating, since they can have weird internal connectivity that won't be constrained by needing to slide into slots. I'm leaning against this approach, not because it won't work, but more because I don't want to rely on a 3D print to solve so many of my problems at once. What makes the build fun for me is doing the hard stuff, within reason. I am totally open to using 3D-printed parts in targeted areas to enable the final model to be and/or look better, though.

I think I am disinclined to completely slice the BT5 in half and then try to glue it back together. It might work it feels to me like it would too difficult to get it perfectly clean in the end.

I confess I kind of lost my grasp of what the rest of @BABAR 's post was proposing. I'd need pictures to understand better.

 

[Greg Furtman]

I seem to have a lot to respond to here.

In the meantime, though, one clarification: my paint sequence questions have nothing to do with the decals. The orange stripes are no problem, I have at least 3 different ways to do that and all will be fine. What I'm fretting over is which parts have to be pre-painted, and how to integrate those in later. @hcmbanjo showed a lot of pre-painting strategy in his Estes Odyssey build. I feel like something along those lines will be necessary here, maybe not quite so extreme as that one though. In my experience, trying to get into nooks and crannies with a rattle can is very difficult; far too easy to either (a) not get full coverage, or (b) get huge runs. I have done a bit of pre-painting in the past and am never really comfortable with it, but it seems like there is no choice here... once the ring is installed there is no way I'm getting an even paint coat into all the interior areas of the tail end. I'll deal with it, but I do need to plan it out properly.

One thing I have definitely decided: I will reinforce the BT5 tubes wherever I slot them. I might even double-layer the whole tubes, since they're structural and it would make me feel better. Maybe not necessary but probably not harmful as long as I account for the weight.

@neil_w I built an Odyssey during the height of the COVID pandemic and used an air brush & used Creatix paints. Lots of masking during the paint job but it turned out pretty decent. The Odyssey is definitely the most difficult rocket I've ever built.

 

[neil_w]

Did you do any pre-painting?

Certainly an airbrush give you a lot more control to get into tight places, compared to rattlecans which give you none...

 

[Greg Furtman]

Did you do any pre-painting?

Certainly an airbrush give you a lot more control to get into tight places, compared to rattlecans which give you none...

I've been using Zinsser B-I-N Flat White Shellac-Based Primer and a a HF cheap, small spray gun for priming. The spray gun actually works quite well as long as you have the air pressure right & the primer thinned properly. Because the Zinsser is shellac -based it dries quite quickly so I can put multiple light coats on in just a few hours.

https://www.harborfreight.com/adjustable-detail-spray-gun-92126.html