Build Thread: 24mm USS Andromeda (F Powered Upscale)

[stormbringergrey]

Continued from Plans: https://www.rocketryforum.com/threa...-sized-for-mid-power-ork.179851/#post-2432026

Unresolved issues from plans:
- Unsure about the added engine core detail and stator fins. On the plus side they reinforce the inside of the ram jets (the tube fins) hopefully keeping them round if the rocket lands directly on a ram jet, on the negative side they add drag with significant leverage to detach either the ram jet itself or possibly the entire pylon. One consideration for reinforcements: two BT-60/80 centering rings (the same as the exposed radiator rings), quartered and mounted on the end of pylon to form an exposed engine cradle mount, better for the tube fin but lots of aerodynamic stress on the pylon.
- Considering "normalizing" the scale measurements to get rid of all the extra decimals, related: want to commit the measurements to either imperial or metric

Day 0, Plans & Parts:

 

[stormbringergrey]

Fin fabrication pictures deleted...

The scaling of the sail fin and antenna array has bugged me from the start. The Estes instructions aren't drawn to scale and no measure of the fin root is given. I found a picture of the Semroc fin sheets and a build picture that provides a functional side view. I traced the fin pattern and use the side view to scale up. Bottom line... I am going to update the design file and recut the fins. The root change isn't drastic (+10mm) but it's enough to redo and the antenna array in my original was significantly oversized and not positioned properly on the sail fin.

 

[stormbringergrey]

Day 2: Fin Fabrication & Dry Fit, Take 2.

All wood fins recut with improved scaling. 3/32 basswood. On the fence about papering the wood, it feels plenty strong enough for larger F's and G's but I'm intrigued by a possibly improved finish (never papered before)

Last two pictures show a dry fit of how the sail fin tab interlocks with the inner centering rings, in the final build the aft edge of the reactor tube (the outer tube) will be flush with the aft edge of the sail fin and the tab will extend through a slot. The ram jet pylons have two teeth that extend between the radiator rings.

While not apparent at this stage, I decided to let the engine retaining ring be exposed rather than be flush with the reactor tube. It will be much easier to access and when painted I think it will be a nice detail (the original ends rather abruptly.)

 

[stormbringergrey]

Day 3: Fin Papering (not shown)

Day 4: Aft Main Tube and Reactor Tube Final Assembly, Sail Fin Attachment

Motor mount/main body tube assembly was conventional. Applying glue to the inside of the reactor tube to capture the inner centering rings proved much more difficult than expected; had to thread the reactor tube over the middle ring, then brush glue from each end at the anticipated contact point. Reactor tube froze in place earlier than expected, about 2mm forward of desired position. (I adjusted the fin slots to match, just going to live with it). The third, forward centering ring was relatively easy once the other two had set, just an ring of glue on both tube and pushed it in.

Reactor Tube assembly with radiator rings. Note: cut-out in radiator rings for launch lug passage.

Ram Jet Pylon fit check

Sail Fin fit check

Note: The Sail Fin appears left of the centerline, this is just a perspective issue, the alignment is good.
\
Tin can jig:

 

[Hobie1dog]

genius to use cans to hold the fins

 

[Bill S]

I take it you used wood glue for the motor mount, not epoxy? I am more and more preferring to use 30-min epoxy (I don't have any 15-min epoxy) so that I have time to move the mount exactly where I want it, and I don't get the dreaded shrink rings where the glue puckers in the body tube. I hate those.

The drawback is that using epoxy delays construction somewhat, but it forces me to learn patience.

 

[stormbringergrey]

I take it you used wood glue for the motor mount, not epoxy?

Yes, and it's killing me. I'm an epoxy guy myself, I use it for everything except plastic on plastic. I have 5 minute for quick work (95% of builds) and 30 minute when alignment is an issue.

I don't know why, but since this was first serious rocket build in 20 years ( I've done more recent RC planes) and my first MPR (I've done HPR and LPR back in the day) I researched glue choices and all the cool kids seemed to be using Elmer's Carpenter's glue.

To be honest, I've been satisfied with Elmer's set time for wood on coated surfaces (and I like that its sandable, water clean-up) but for the uncoated interiors of the BTs the set feels almost instantaneous on contact. Glad I learned now... I'm going to continue with the Elmer's for external surface mounts but this project requires 3 tube couplers and 2 more centering rings for the crew/recovery module... no question I'm using 30 min epoxy for those.

 

[Bill S]

Yes, Carpenters glue will seize up fast on centering rings, and pretty much instantly on couplers (unless you go super overkill on the quantity, essentially "lubing" the tube while you move it into position, then clean up the excess. But that is challenging on the interior of longer tubes.

 

[neil_w]

Day 2: Fin Fabrication & Dry Fit, Take 2.

View attachment 582616

I’m all for the challenge of hand-cutting fins, but I’m trying to imagine how those could have been done in the days before die-cutting. Did the original Andromeda come with cut-your-own fins, or was die-cutting around by then?

(Sorry for the digression)

 

[neil_w]

To be honest, I've been satisfied with Elmer's set time for wood on coated surfaces (and I like that its sandable, water clean-up) but for the uncoated interiors of the BTs the set feels almost instantaneous on contact. Glad I learned now... I'm going to continue with the Elmer's for external surface mounts but this project requires 3 tube couplers and 2 more centering rings for the crew/recovery module... no question I'm using 30 min epoxy for those.

White glue (eg Elmer’s Glue-All) is also much slower to grab than wood glue, and works fine for couplers and motor mounts and such.

Wood glues (especially TBII, which is my glue of choice for most stuff) are ideal when their strength and grabbiness are assets, which is to say everything except most instances where you need to slide a component into position. It’s possible to make it work (more glue=better lubrication) but usually not worth the risk when there are alternatives.

 

[stormbringergrey]

Did the original Andromeda come with cut-your-own fins, or was die-cutting around by then?

If I recall, even in the 70s most kits from major manufacturers (rockets and planes) were die cut (but not laser cut).

The Andromeda had a 2 part die-cut balsa sail fin and no scale templates which was problematic for this project.

I can see the imperfections in my hand cut and I considered getting a laser cutter but I'm also a realist about working models... this rocket will be flown, it will get beat up... if it looks good a safe distance from the pad, I'm satisfied.

 

[stormbringergrey]

Day 5: Recovery design revisited (no construction).

Been busy and no construction work has been completed (hoping to work on it tonight), however, I blew up an Estes FaceBook group with a question about shock absorption and I happened to mention a 48" chute for a 1.0-1.5 pound rocket. Even if you build strong, the Andromeda is ridiculously fragile design.

OR says 48" = 9 fps descent rate and PML says a 9 fps descent rate = a drop from 1' (ouch), however, the consensus on FB is that at 9 fps the rocket will float into the next county. I considered a spill hole to increase the descent rate and prevent a pendulum swing into the ground which could be just as bad, however, in the end, while the 48" thin chute will fit into a BT-60 as advertised, it requires about 9" which doesn't leave room for anything else.

I have ordered a 36" chute which OR says will result in 14-15 fps and a 24" chute which the sim says should be 20ish fps. I also downgraded the shockcord from 1500 pound test braided Kevlar to 300 pound test braided Kevlar for space and weight.

 

[Tobor]

My fix for using Titebond 2 & 3 on cardboard rockets...
I use a wet a paper towel to wipe the surfaces to be bonded and then apply the Titebond. (I prefer to wet the towel with filtered or distilled water). You will still need to assemble the parts fairly quickly but it does work. Just be sure not to over saturate the cardboard with the towel, especially Estes, as that will certainly weaken the parts until they dry.

 

[stormbringergrey]

Day 6: Mounting Ram Jet to Pylon - Scratch Tests

I've been trying to build as strong as possible while maintaining the look of the Andromeda which is anything but strong. One area of concern is the connection between the Ram Jets (BT-60 tube fins) and the Pylon fins (3/32 basswood). All of the main body fin connections are TtW braced by centering rings and well reinforced, on the stock Andromeda the Ram Jets are flush mounted to the ends of the pylon fins. My concern is that these fins mount 5.5" from the center line and will be more subject to flutter and aerodynamic stress than components that mount on the main body tube, flush mounting on a 3/32" fin edge doesn't sound like a great idea so I played with some reinforcement ideas...

Sample flush mount...

My first thought was to build a brace by gluing two triangular 3/32 balsa strips into a trapezoid shape...

Using a miss-cut engine pylon fin as a test, I glued two trapezoid braces to the top and bottom of the pylon tip, then glued sandpaper to a damaged BT-60 to carveout a matching circular mounting surface...

Plenty of mounting surface area but I don't love the look, too blocky...

Rounded the edges, better, still don't love it...

Going back to an earlier idea, I'm going to use the same BT-60/80 centering rings I used as the exposed Radiator Rings on the main body. I just need one cut into four 1/4 arcs. I'll use a pair of these arcs on each Pylon to create an engine cradle as shown in the mock-up below. It kills me to pay shipping on just a centering ring but I think the look complements the design better than the alternative.

 

[stormbringergrey]

Day 7: To Glass or Not To Glass, Fiberglass Sleeves? - No Construction

The June and July launches have been canceled which gives me 2 months to build before the next launch. I have a lot of travel between then and now (almost 50%) but still that's a lot of time. I have never used fiberglass but I watched a video using sleeves and it looks simple enough and if you believe their ads, the heat shrink tubing gives a finished surface with no sanding. Since the aft section is already built I would only be able to glass the main tube (BT-50T) from the reactor tube up, about 5.5 feet. I could reinforce the aft section internally with coupling tubes but would need to leave clearance for the largest possible motor. Given the range of "shrink" it looks like it might be possible to glass the main tube, transition, and crew tube (recovery bay) with one piece. The cost of the sleeves ($20) isn't that bad, adding 1qt resin ($60) however makes this an expensive upgrade. If I can get a smaller quantity of resin this could be a possibility.

https://sollercompositesllc.com/

 

[tsmith1315]

If you're using a single layer, you don't need laminating resin. Any epoxy with a reasonable working time and thin enough to wet the fibers is fine.

Keep in mind Mach 1 sells nice BT50 Fiberglass tube for $9 per foot, I wouldn't approach that price with a hand layup or sleeve over paper.

https://www.mach1rocketry.com/product-page/fiberglass-airframe-tubes

 

[stormbringergrey]

Thanks for the tip. If I go glass that is definitely the way to go, I'm all about making the build easier and faster. I'm going to run some sim's tonight and see where I am with the weight before deciding to order.

 

[stormbringergrey]

Day 8: Ram Jets & Pylons

It has been a while with work travel and other obligations but this build is still very much alive. It's going to be a busy summer but I hope to be in flying condition, even if unpainted, for our next launch on August 5th.

During the hiatus I looked into fiberglass options for the main BT-50 tube; Mach 1 isn't responding to emails (not just me) and other sources don't offer anything smaller than 29mm... Ultimately I decided to go with a double-walled main body tube using full length coupler tubes from Balsa Machining Services, even with a dry fit the combined tubes feel extremely strong.

Following the experiments to strengthen the Ram Jet mounts on day 6, I have decided to create an exterior engine cradle fashioned from a heavy-duty BT-80/60 centering ring (the same ring type used for the radiator ring detail).

Engine cradles attached to engine pylons.

It is entirely possible that a ram jet edge could be the first point of impact on landing. With this in mind, I am double-walling the ram jet BT-60's in the same fashion as the (not yet fabricated) main body tube.

Ram jet components fabricated, exterior BT-60's and coupler reinforcements.

Given my earlier, near disaster of wood glue catching too early, I used 5 minute epoxy to glue the couplers inside the BT-60's. The couplers slid inside smoothly without any resistance (I will be using epoxy on the main body tube as well, although probably 30 minute). The ram jets were then mounted to the engine pylons using conventional wood glue.

 

[Bill S]

Good idea on using epoxy instead of wood glue for the couplers.

 

[stormbringergrey]

Day 8.5 & 9: Engine Pylon & Antenna Array mounting - also disaster and acceptance.

Late on day 8 I mounted the engine pylon assemblies to the main body, no issues. The friction from the TtW mounts and plenty of surface contact with the radiator rings held the assemblies tightly and perfectly aligned even with just a dry fit.

The antenna array probes were cut from bamboo skewers, smaller diameter and stronger than the standard wood dowels from Hobby Lobby (and I had them laying around). I mounted the probes to the antenna wing tips and left overnight under a weight to press everything flat.

On day 9 I mounted the antenna wing to the main assembly. Lots of angles that needed to be square with no support so I broke out the deluxe tin can jig.

After drying and filets, the business end is structurally complete (gap filling remains). I also trimmed the ram jet cradles to end parallel to the wing which I believe improved the look

And while taking pictures I noticed a disaster. The port side of the antenna wing and probe are fine but the starboard side probe is canted inward by at least 5 degrees and it's pretty clear the fin template shifted while being traced. Given the complex attachments of the other fins I checked and rechecked fit every step of the way; I guess I treated the antenna array as largely cosmetic and wasn't as diligent. I could cut the wing off with minimal damage to the sail fin but I'm inclined to leave it until it breaks. IMHO, it's only visible when sighted directly down the centerline from the top.

 

[stormbringergrey]

Day 10: Crew Compartment (recovery bay)

After the complexities of the fin can, the forward end of the Andromeda is refreshingly simple.

Note the doubled centering rings. The forward rings are doubled to give the shockcord screw eye more to bite into, the aft centering rings are doubled to provide a sandable base at the transition seam.


The BT60 Crew Compartment attached, a double wall sleeve for zipper protection about to slide in.


Detail of the doubled wall. The 1" margin allows clearance for the nose cone shoulder.

 

[Bill S]

That seems like a good idea, the doubled up tubing.

 

[stormbringergrey]

Day 11: Transition, Mid-section Assembly, Forward Connection

Transition (reducer) BT-60/recovery bay to BT-50TW/main body. I couldn't find specs for scale so I eyeballed the transition length. My original transition (in background) was too gradual, I shorted the transition length by 2 cm to make it more pronounced. The card stock still needs to be saturated with low viscosity CA for strength (didn't have any handy), the seam needs to be filled, and everything will then need to be sanded.

The mid-section is two BT-50TW's x 17" with two full length couplers running through the entire length and extending 13" out the front and 4" out the rear. The forward section will insert into the recovery bay and end flush with the recovery bay bulkhead, the aft end will insert into the fin can leaving 10" clearance to accommodate the 9" Cesaroni 6 grain hardware (ie: a G65 motor). When assembled, the entire length of the rocket will be double-walled either by coupler or centered tubes the exception of a 4" section of BT-50TW forward of the reactor tube. More on why this weak spot exists and a fix on a later day. Note the rocket was deliberately assembled in three sections to isolate the impact of any catastrophic assembly mistakes and to make each section easier to work with.

The mid-section has been glued to the recovery bay, the fin can is just a dry fit. I am going to complete the wood-filler work on the fin can before final assembly of the airframe, again, to keep handling easier. The 15' Kevlar shockcord is mounted in the recovery bay but no chute yet. Still need to fabricate the iconic conduits including the forward launch lug.

 

[stormbringergrey]

Day 12 & 13: Conduit pylons, forward launch lug, conduits - ready for launch trials

Note the notch in the conduit pylon. The conduit is a 3/16" dowel (accurate scale up of the 1/8" stock Andromeda), the pylon is 3/32" fin material. The overhang of the conduit would conflict with the launch rod beyond the notch. The notch allows continuation of the conduit topline without conflicting with the launch rod.

Careful measurements to insure alignment of the forward launch lug. The offset of the aft launch lug must be recreated on the conduit pylon. The excess lug was later trimmed flush with trailing edge of pylon.


Hero shots similar to earlier pictures except this time everything is glued in place along with the conduits. A bit of wood filling remains, and of course painting, but my F/G Andromeda is ready for launch trials.

 

[John_461]

Have you flown this yet? If so how did it go?

 

[BABAR]

Have you flown this yet? If so how did it go?

Tough call…. ?? Paint it and get the beauty shots before the flight (this looks like it may land delicately), so you have them in case of a non-nominal flight. Or make it earn its paint?

 

[stormbringergrey]

Tough call…. ?? Paint it and get the beauty shots before the flight (this looks like it may land delicately), so you have them in case of a non-nominal flight. Or make it earn its paint?

Not yet. No launch was scheduled for August & September due to the South Florida heat. Next launch window is October 7. I very much would have flown it unpainted if the opportunity presented itself. Unfortunately, time is the enemy of progress but I do have the first coat of primer applied (flat black) and I solved and built a solution to reinforce the main body tube when not using a 9" G motor casing.

Two surprises with the primer. I've read all sorts of cautionary tales about using Rust-Oleum rattle cans but I thought, bah! I've been using rattle cans on other projects and never experienced a problem... sure enough the 2X primer formed a sand grain like texture on my papered fins and pilled a little worse on the uncoated launch lugs. The texture on the fins is kind of cool, a lot like the textured flat black finish on some newer Jeeps, but, it's not completely even and wasn't the look I was going for. I have an electric orbital palm sander, should be easy to sand down those giant fins and the launch lugs are small. Fortunately, the finish on the coated tubes is fine other than needing a second coat and the balsa nose cone sealed with CA needs just a little sanding.

The second surprise with the primer is that I love the flat black look. The published paint scheme calls for flat black (one of the reasons I went with this primer) but every built sample I've ever seen, including mine from the '70s went with gloss. I'm sticking with the flat, my only remaining concerns are how to deal with glossy decals (if/when I buy them, Wildman sells custom sizes) and how to keep the finish from showing fingerprints.

The reinforcement solution popped into my head a few weeks ago and is ridiculously simple. The main, 24mm body tube is double-walled along it's entire length except in the motor mount area which was built to accommodate anything from a 3" F to a 9" G. For the shorter F motors I simply built a removable stuffer with something of an internal heavy-duty centering ring to provide a lip for removal with a hook.

Pictures coming.

 

[BABAR]

.

The second surprise with the primer is that I love the flat black look. The published paint scheme calls for flat black (one of the reasons I went with this primer) but every built sample I've ever seen, including mine from the '70s went with gloss. I'm sticking with the flat, my only remaining concerns are how to deal with glossy decals (if/when I buy them, Wildman sells custom sizes) and how to keep the finish from showing fingerprints. Anyother question, if I like the primer look, do I really need a finish coat in the same color?
.

sorry about the paint issues, been dere, done dat.

probably @neil_w can correct me, but I believe decals work best on gloss or semigloss for APPLICATION, but after application you can put a MATTE clear coat OVER the decals.

lots of painting, and lots of opportunities for more orange peel.

only rule I’ve seen consistently is don’t rush. If you aren’t recoating within the short recoat window (I’ve seen 15 minute to an hour) let each coat dry for a few days if not a week if you can,

 

[stormbringergrey]

only rule I’ve seen consistently is don’t rush. If you aren’t recoating within the short recoat window (I’ve seen 15 minute to an hour) let each coat dry for a few days if not a week if you can,

Lol, 90 degree Miami days @ 90% humidity (along with a busy schedule, both work and my other money sucking hobby, boardgames) has made waiting easy. I'm at one week since the first coat, will go for the second on the next coolish evening.

 

[stormbringergrey]

Day: ??, who knows, this model has been sitting on my bench, untouched, for months, but, tomorrow is launch day.

2X Rustoleum flat black. It's a "looks good from the launch pad" quality of finish but I'm OK with that. Really loving the flat vs more common gloss finish.

If it survives I'll paint the accent colors and order custom fit decals.