Fall 2023 batch of 5

[bjphoenix]

Recently I've been doing builds in batches. Maybe when I get geared up to build and have ideas in mind I have multiple ideas. I have 5 builds in mind, I haven't ordered parts for the last 2 so maybe consider this a batch of 3. This isn't a real build thread, most of the work of the first 2 is already done. I'll cover some bits that I managed to photograph.

Rocket #1: an upscale Astron Sprint. This rocket has interested me but never to the point of building one until recently. Last spring I built one in BT-55 size to share the elliptical nose cone from my Goblin. I had previously bought an Estes BT-60 nose cone pack and it contained an elliptical nose cone and tail transition. I didn't know what it was for, I didn't know the Sprint XL even existed, then it dawned on me that I could use those parts to build a BT-60 Sprint. I already had tubes and balsa, centering rings leftover from the Goblin because I built the Goblin with 18mm motor mount, and I had a pack of 2.75" motor hooks. I scaled up the fin shape to BT-60 size and got busy. It has 24mm x 2.75" motor mount. The fins are 3/32" balsa papered with copy paper. Here is what it looks like ready for primer.


Rocket #2: a Centuri Lil Hustler somewhat clone. I noticed that Apogee sells a nose cone/transition package and looking at the Centuri catalog I decided that BT-55 and BT-60 would be close enough in size. I came up with fin shapes using some photos and Autocad. This one has 24mm x 2.75" motor mount. The fins are one big piece with the little front strakes added on, then papered with thin cardstock for additional strength. I just got the fins on last night so fin fillets are next then it will be ready for primer.

 

[Hobie1dog]

good job on them.

 

[cwbullet]

Nice builds.

 

[Raptor 2]

What adhesive do you use when you papered the fins on these beauties? I always use mailing label sheets which are already sticky on the backside.

 

[mh9162013]

Good stuff!

How do you like that BT-55 to BT-60 transition + nose cone from Apogee? I've been thinking about getting it. Also,how does the nose cone that comes with the transition compare to the Estes Patriot nose cone? They look the same to me, but I'm not sure if they're nearly identicial or just similar.

 

[bjphoenix]

What adhesive do you use when you papered the fins on these beauties? I always use mailing label sheets which are already sticky on the backside.

I use Titebond II. I have a couple of pieces of smooth plywood and a sheet of flexible plastic similar to what some people use as a mat for chopping vegetables. I put a layer of glue on one side of the fin, spread it around, then use my finger to wipe off almost all of it. I work quickly when doing this. I put the paper on and go over it with an old plastic card to push it down and squeeze out any excess glue. then quickly put it between the plastic and boards and put the clamp on. I leave it for around 30 minutes then do the other side and leave it overnight. I work fast so the paper doesn't absorb moisture from the glue and start wrinkling. That's the reason I do one side at a time, I can get it clamped quicker that way.

I just finished papering the fins for build #3. I cut the fins oversize and I cut the paper even bigger than that. I stack the fins and align them the best I can then pin them together with a couple of small sewing pins, with the original paper pattern on top. Then I use a disk sander to sand everything down to the edge of the pattern. I did that this morning. I use a sanding block to round the edges of the fin except for the root edge then I paint watered down Elmers wood filler on the edges where balsa is exposed. Tomorrow I'll sand the edges then the fins will be ready to be glued down and filleted. The fin shapes give a little clue as to what build #3 will be.

 

[86mustang408w]

Nice man!!

 

[Raptor 2]

I use Titebond II. I have a couple of pieces of smooth plywood and a sheet of flexible plastic similar to what some people use as a mat for chopping vegetables. I put a layer of glue on one side of the fin, spread it around, then use my finger to wipe off almost all of it. I work quickly when doing this. I put the paper on and go over it with an old plastic card to push it down and squeeze out any excess glue. then quickly put it between the plastic and boards and put the clamp on. I leave it for around 30 minutes then do the other side and leave it overnight. I work fast so the paper doesn't absorb moisture from the glue and start wrinkling. That's the reason I do one side at a time, I can get it clamped quicker that way.

I just finished papering the fins for build #3. I cut the fins oversize and I cut the paper even bigger than that. I stack the fins and align them the best I can then pin them together with a couple of small sewing pins, with the original paper pattern on top. Then I use a disk sander to sand everything down to the edge of the pattern. I did that this morning. I use a sanding block to round the edges of the fin except for the root edge then I paint watered down Elmers wood filler on the edges where balsa is exposed. Tomorrow I'll sand the edges then the fins will be ready to be glued down and filleted. The fin shapes give a little clue as to what build #3 will be.
View attachment 609026

Wow that is a labor intensive process. I’m leery of using these glues due to the wrinkling and warping possibilities. Also as you stated you have to work fast. I cut my fins to their final size and sand the leading edge to a sharp or rounded edge as needed. I draw out a butterfly layout to match the fin on mailing label paper. I cut this out and crease the paper down the center line. I lay the leading edge of the fin in the crease and fold both sides down their respective sides. This way the leading edge is wrapped in the paper also. Lastly I coat the paper with CA glue and give it a light sanding. Done. The self adhesive labels stick well and are coated in CA. They haven’t peeled off any of my builds so far.

 

[bjphoenix]

Good stuff!

How do you like that BT-55 to BT-60 transition + nose cone from Apogee? I've been thinking about getting it. Also,how does the nose cone that comes with the transition compare to the Estes Patriot nose cone? They look the same to me, but I'm not sure if they're nearly identicial or just similar.

Sorry I'm just getting around to answering. The Apogee parts seem to be well made. They have more substantial lugs for attachment of recovery gear than Estes parts. The mold seam might be a little better but still requires work to smooth it. The shoulders are much longer than Estes parts and include lines where you could cut off parts that you don't need. For instance in the Lil Hustler the top part is essentially a payload section so I could cut off the top part of the transition and the bottom part of the nose cone.

As for comparison with the Estes Patriot Missile- I happen to have one of those, the lower one in the photo. The Apogee cone is essentially the same ogive shape but it has a little bit more point so that makes it a tiny bit longer. In the photo the Apogee parts have not been painted, the Patriot Missile nose cone is painted gloss white, probably Rustoleum.

 

[bjphoenix]

I've made more progress on build #3. I showed the fins in post #6, nobody has taken a guess as to what it was going to be. Now you can see it although it may or may not be obvious what it is or what it was inspired by. (Hint- the Estes Blue Sapphire.)

When I first saw an image of the Blue Sapphire it wasn't clear if it had 3 fins or 6 fins. I decided that I would build my own interpretation using 6 fins even though building and prepping fins my way is a lot of work. And now it is ready for fillets. I'm going to put big fillets on it because with this fin design the fins will need all the help they can get. I happened to have the long pointed nose cone from very long ago, I don't remember where I got it, but the nose cone is BT-55 size so I upscaled the entire design to BT-55. The body tube is a full 18" long piece of Apogee BT-55. The correct scale length for the Blue Sapphire would be more like 17", I think I'll just leave mine an inch longer. I'm not going to call it a Blue Sapphire, maybe I'll call it a Black Sapphire.

 

[mh9162013]

Sorry I'm just getting around to answering. The Apogee parts seem to be well made. They have more substantial lugs for attachment of recovery gear than Estes parts. The mold seam might be a little better but still requires work to smooth it. The shoulders are much longer than Estes parts and include lines where you could cut off parts that you don't need. For instance in the Lil Hustler the top part is essentially a payload section so I could cut off the top part of the transition and the bottom part of the nose cone.

As for comparison with the Estes Patriot Missile- I happen to have one of those, the lower one in the photo. The Apogee cone is essentially the same ogive shape but it has a little bit more point so that makes it a tiny bit longer. In the photo the Apogee parts have not been painted, the Patriot Missile nose cone is painted gloss white, probably Rustoleum.
View attachment 609469

Thank you for that detailed comparison; much appreciated!

 

[bjphoenix]

This is not a real build thread since I started it after the first 2 builds were mostly complete, but I can include some photos taken during the build.

These days I typically paper all of my fins. I cut them oversize and cut the paper skins oversize, then stack them along with the paper pattern and pin them together with sewing pins. I have an old disk sander that I can use to sand them down to the pattern and all of the fins come out the same dimensions.



Using my fin jig to glue the fins on. This jig is copied from a design posted by someone else, easy to build, easy to use and very accurate.

 

[bjphoenix]

Here are motor mounts for the first 2 builds, both 24mm x 2.75". I put a sleeve around the tube to double up the tube thickness where the motor hook might pull against it. Then I put 2 more layers over the motor hook to hold it on.


Here are fins cut out and papered for builds #2 and #3.

 

[bad_idea]

Looking forward to seeing some of these at Gunter next Saturday, or so I hope!

 

[bjphoenix]

Looking forward to seeing some of these at Gunter next Saturday, or so I hope!

I have to be out of town that weekend so no launch for me. But that will give me time to paint before the November launch. And I'm hoping to have builds 4 and 5 also done by then.

 

[bad_idea]

Well have a safe trip, and I look forward to seeing them in November.

I'm hoping to have a few recent builds and rebuild painted by November.

 

[cwbullet]

I have never used cardstock to paper - did you clamp them?

 

[bjphoenix]

I have never used cardstock to paper - did you clamp them?

Cardstock to balsa?
I clamped the fin between 2 pieces of plywood for around 12 hours.

 

[cwbullet]

Cardstock to balsa?
I clamped the fin between 2 pieces of plywood for around 12 hours.

Thanks. I will try it.

 

[bjphoenix]

Thanks. I will try it.

I have 2 pieces of smooth plywood and a sheet of flexible plastic similar to what my wife bought to use as a mat for cutting vegetables. Titebond II doesn't stick to the plastic. I tried waxed paper but Titebond would stick to it a little bit. I did find that other materials could work for instance I cut some pieces from a cardboard milk carton, waxed the surface, and Titebond wouldn't stick to it.

 

[BABAR]

I have 2 pieces of smooth plywood and a sheet of flexible plastic similar to what my wife bought to use as a mat for cutting vegetables. Titebond II doesn't stick to the plastic. I tried waxed paper but Titebond would stick to it a little bit. I did find that other materials could work for instance I cut some pieces from a cardboard milk carton, waxed the surface, and Titebond wouldn't stick to it.

Parchment paper has worked for me.

 

[bjphoenix]

I've been working on Titebond II fin fillets. The fin jig holds the airframe horizontal and is a good aid for fin fillets too.

 

[bjphoenix]

Yesterday I was starting on motor mounts for builds #4 and #5. Except for the tubes everything in the motor mounts will be scratch built. I made an improvised compass to draw circles and used some heavy cereal-box type cardboard. The holes in the compass are for BT-50, BT-70 and BT-80 size, with a simple push pin for the pivot. I used to have an actual drafting set from college with a couple of fancy compasses in it but gave that to a draftsperson when I was doing mostly CAD. I've thought about finding an old one on ebay but I think for this use the piece of cardboard works well enough.

I cut a lot of rings and I will laminate 2 pieces together for each finished ring which will give me 3 rings to use on the double 24mm mount. Today I'll cut some thrust blocks from an old 24mm motor and make some engine hooks from old windshield wiper blades.

The rings shown will be for a dual 24mm mount in build #5 which will be BT-80. Build #4 will be a single 24mm in BT-70.

 

[bjphoenix]

More work on motor mount parts today. I cut some thrust blocks- 3/4" pieces off the front end of a used D12 casing. I also made some engine hooks from pieces salvaged from windshield wiper blades. The are sized to work with E12 length motors with additional length so the front end will hook in front of the thrust block.
For anybody interested- the engine block weighs 0.12 ounce each and the long engine hook weighs 0.05 ounce each.

 

[lakeroadster]

More work on motor mount parts today. I cut some thrust blocks- 3/4" pieces off the front end of a used D12 casing. I also made some engine hooks from pieces salvaged from windshield wiper blades. The are sized to work with E12 length motors with additional length so the front end will hook in front of the thrust block.
For anybody interested- the engine block weighs 0.12 ounce each and the long engine hook weighs 0.05 ounce each.
View attachment 612242

Tip: You can peel away about half the thickness on the motor blocks, just take some needle nose pliers and take it off the i.d.

 

[bjphoenix]

I've been working on the motor mount for build #5. The center bulkhead will be glued first, the other 2 bulkheads will be removable during construction to allow access to internal fillets. The fins will extend to the motor mount tubes and be glued and filleted there before the aft bulkhead is glued in place. With the front bulkhead removable I can add more fillet to the center bulkhead. Actually with fins extending to the motor mount and all of the fillets there and at the outside tube the bulkheads don't need much strength. Staring at the photo right before I posted it I realized that I narrowly missed disaster- I put the engine hooks just outboard enough to miss where the fins come into the engine mount tubes. I worked out the tube and fin geometry in autocad but didn't include the engine hooks.

I also started working on fins today. I cut out balsa fins and cardstock skins, tonight I'll start the laminating process. 4 fins will take awhile but I won't receive the nose cone and main airframe until the end of next week.

 

[Raptor 2]

With four fins will two of them extend into the crevasse between the two motor tubes?

 

[bjphoenix]

With four fins will two of them extend into the crevasse between the two motor tubes?

That could work but in my case I've planned for the fin pattern to be rotated 45 degrees so each fin hits one of the motor tubes. I wondered how they would intersect the tubes although this is one of those problems that if you think about it a little bit you finally realize that you can solve it without math or CAD. I could have extended fins into the crevasse so 2 fins would have long fin tabs and 2 would have short fin tabs. The way I'm doing it all 4 fins have the same size tab. I've already cut out the fins so I can't change now.

 

[Raptor 2]

Rotating the fins 45 degrees would have the fin intersecting the motor tubes at an angle and not perpendicular to the motor tube surface.

 

[bjphoenix]

Rotating the fins 45 degrees would have the fin intersecting the motor tubes at an angle and not perpendicular to the motor tube surface.

You are correct. This is what I had worked out in CAD including my solution for the forces that might not resolve very well. I'm still thinking about rotating the pattern 45 degrees.
Either way my plan is to put the motor mount assembly in with the middle bulkhead glued in place and the rear bulkhead just slipped in, stick the fins through the slots and glue the base of the tab to the motor tube. Then I can pull the rear bulkhead out and make better internal fillets.