5 at a time

[bjphoenix]

I had a lot of different ideas that came together at one time so I ordered a couple of packs of tubes, gathered up the other spare parts and started all at the same time. I'll update this thread as things progress. These are all LPR, 4 with BT55 tubes and 18mm mounts and one with BT60 tubes and 24mm D mount. One is a kit, the other 4 are scratch built.

Two of these are 4FNC, one is 3FNC, the other 2 are 3FNC but with split fins. That's a total of 23 fins. These days I always paper my balsa fins so here is a stack of 19 of them after papering.


And here are the 5 motor mounts in progress.


I've installed a couple of motor mounts and I'm working on a tail cone for one model. Here you see the kit with some glue fillets drying, and the tube for the second model and mockups of the tail cone. I put a small ring of BT material inside of the rear of the tube for the front of the tail cone to glue to. The model with fins on it should be recognizable as an Estes Goblin. The model with the tail cone will be a clone of the Estes Sprint upscaled to BT55.

 

[bjphoenix]

I'm starting to attach fins. I've made these paper templates in the past for one time use. The last time I made them I decided to make them such that I could save and reuse them so here are templates for BT55 and BT60 with markings for 3 fins and 4 fins.


And using my new fin jig to put the first fin on the 3rd model. It might be recognizable but this is a clone of the original Centuri Javelin upscaled to BT55. I had a separate thread talking about simple LPR fin jigs.

 

[Hobie1dog]

I love building things in multiples.

 

[cls]

Nifty fin jig! Good idea.

 

[Cape Byron]

I love building things in multiples.

Me too.

 

[mh9162013]

There's something therapeutic about building things with your hands, but in an assembly-line manner.

 

[bjphoenix]

Nifty fin jig! Good idea.

It is simple to build if you have a table saw, but I can't take credit for it. Someone referred me to this:
https://www.rocketryforum.com/threads/homemade-fin-alignment-guide.9694/#post-80188

 

[bad_idea]

These days I always paper my balsa fins so here is a stack of 19 of them after papering.
View attachment 551937

Do you bevel them as-is and just sand the paper away, or do you trim them back before beveling?

 

[bjphoenix]

Do you bevel them as-is and just sand the paper away, or do you trim them back before beveling?

1. The next step is to hit the edges with a sanding block to remove the excess paper, it doesn't take much sanding for this. So this trims the paper back.
2a. If these fins are from a kit they are probably laser cut and all match. I do more sanding of the edges perpendicular to the fin surface to get off excess glue.
2b. If I marked and cut them out myself then they will be oversize and a bit irregular. I stack them aligned the best I can and pin them together with some sewing pins, then sand all of the edges until they are all flush so that all of the fins match. I might do this with a sanding block but with a stack of fins for 5 models I drug out my benchtop disk sander.
3. Then I use a sanding block to round the edges except the root edge. I paint on some thinned Elmers wood filler on all of the rounded edges. If there are any big irregularities on the papered surfaces I'll brush on some thinned filler over those. I used to bevel/airfoil my fins but I discovered that sharp edges on the fins didn't stand up to abuse from handling, storing, carrying out to the launch field, hard landings, etc. so I figured that rounded edges were more durable.
4. Now they're ready to be glued on and I put on a couple of layers of Titebond fillets.
5. I'll spray on a coat of primer and sand. This gets rid of the fuzzies and seals the surfaces that would soak up too much paint. Depending on how this looks I might do another layer of primer.

 

[bjphoenix]

I've been busy with other stuff this week so not much build progress, but the Javelin and Goblin are pretty much in one piece now. I need to build up the fin fillets a little more then start with primer and paint.

 

[bjphoenix]

I've spent some time working on the tail cone of the Sprint. First I wanted to see if I could derive the equations for laying out the pattern on a piece of cardstock and I did that. Then I cut a couple of samples out of postcard advertisements we get in the mail. From the images and sims I've found for the Sprint if I scale up to BT55 size then the back end of the cone is 1" diameter. I'm building this with an 18mm motor mount so I wrapped cardstock around the back end of the motor tube to get it to about 1" diameter. Then I cut a tail cone from cardstock and did a test fit. I need to make a small adjustment at the front end of the cone, glue it together with a backer piece at the seam, then I think I'm going to double up with another piece of cardstock on the inside to make the cone stronger. I think I've only made paper transitions like this twice and both were a very long time ago- once for the original Estes Arcas kit and once for the Estes Camroc carrier. The fins are ready and waiting to be glued on when I get the tail cone complete. I didn't build this model with a tail hook because I didn't want to be cutting a notch in the tail cone. I'll use friction fit on these motors.

 

[Sandy H.]

I've spent some time working on the tail cone of the Sprint. First I wanted to see if I could derive the equations for laying out the pattern on a piece of cardstock and I did that. Then I cut a couple of samples out of postcard advertisements we get in the mail. From the images and sims I've found for the Sprint if I scale up to BT55 size then the back end of the cone is 1" diameter. I'm building this with an 18mm motor mount so I wrapped cardstock around the back end of the motor tube to get it to about 1" diameter. Then I cut a tail cone from cardstock and did a test fit. I need to make a small adjustment at the front end of the cone, glue it together with a backer piece at the seam, then I think I'm going to double up with another piece of cardstock on the inside to make the cone stronger. I think I've only made paper transitions like this twice and both were a very long time ago- once for the original Estes Arcas kit and once for the Estes Camroc carrier. The fins are ready and waiting to be glued on when I get the tail cone complete. I didn't build this model with a tail hook because I didn't want to be cutting a notch in the tail cone. I'll use friction fit on these motors.View attachment 552796
View attachment 552797

Check out the Apogee article on the 'Super Shroud' (or similar name). Since you're into the math, I think you'll like the article and also wheels will start turning in your head. I did a variation on what was presented, but can't find it right this minute. Either way, once you start thinking multiple shroud wraps and consider thickness, things turn out pretty darn well if you do the math, IMO.

What you've done so far looks great!

Sandy.

 

[bjphoenix]

Check out the Apogee article on the 'Super Shroud' (or similar name). Since you're into the math, I think you'll like the article and also wheels will start turning in your head. I did a variation on what was presented, but can't find it right this minute. Either way, once you start thinking multiple shroud wraps and consider thickness, things turn out pretty darn well if you do the math, IMO.

(For anybody interested check out Apogee newsletters #136 and #349.)

My problem is I don't have a good compass for layout. (Make a mental note to add this to the thread on tools.) I made an impromptu compass by taking a thin piece of scrap wood and drilling a few 1/16" diameter holes the right distances apart. I was thinking I would get the outer shroud just like I want it, then cut a similar piece, roll the first shroud and glue it, then insert the inner piece and make marks on it to show how much to cut it down. I'll think about that some more over the next few days.

 

[bjphoenix]

Yesterday and today I worked more on the tail cone for the Sprint. Just like I remembered- these cardstock transitions are a lot more trouble then they are worth, but the boat tail is an important design element of this model so I had to go on with it.

I cut out the cardstock, taped it, did a test fit and all was well. The back end was a little tight but I didn't pay attention to that. Then I glued the tab on the back and took off the tape. There was some pucker on the outside of the seam, the 2 edges didn't fold down tightly against the tab. I figured I would have to do some sanding and wood filler. I cut another piece of card stock and trimmed it to become a liner then glued it inside. After all that dried awhile I decided to hold my breath and glue it on. I put glue inside the upper end of the cone and on the 2 making surfaces of the main airframe, the slid the cone on. First it was hard to slide on because the back end was a bit too small and I got to re-learn an old lesson. The front end had softened because it sat for a few seconds with the Titebond inside and it mushed/wrinkled as it was going on. The lesson is that you can't monkey with cardstock after the glue has had a chance to soak in a little bit. I immediately pulled that cone off and wiped glue off of the airframe surfaces.
By now I've had experience cutting the pieces so I quickly cut out another new cone and put it together. My first steps were to make a couple of sample cones from postcard mailers so when I glued the tab I put the cone inside of one of these samples to act as a form to hold down the outside surfaces tight to the tab. Then when I put the reinforcing layer in the inside I used the sample cones on the outside to maintain it round while it dried. Test fitting again it was still tight at the bottom so I peeled off a layer of cardstock wrap from end of motor tube and sanded it down a little bit more so it would slide on easily. I didn't put any glue inside the cone, just on the airframe, and slid on the cone as quickly as I could.

In the photo you can see the 2 sample cones and the ruined cone. There is a small gap between airframe and cone, I can fill that with wood filler and sand it smooth.

 

[bad_idea]

Lot of work, but you should be proud: end result looks great! Look forward to seeing it at a launch soon.

 

[bjphoenix]

I've been to the point of repetitive putting fins on and multiple layers of Titebond fillets so really not that much to photograph.

Here is the fin jig in action on the last of the 5, a BT-60 size model inspired by the Wildman Darkstar. The combined length of both fins did not fit on the jig so I had to modify the jig in a couple of places by sawing off some pieces. All 3 fins are now on and they are as straight and parallel as I can tell by eyeball.



I don't have much workspace so I've got rockets laying around various places letting the fillets dry. Here is the Sprint (3rd of 5) and another one that hasn't been photographed yet (4th of 5). It is a BT-55 size model inspired by the Madcow Frenzy.



In a couple of days all 5 of these could be ready to launch (without paint). I have to put launch lugs on all of them, I may have to make a few launch lugs if I don't have enough in my stash. I have to add shock cords to all of them which is a bit tedious. And I have to extend the main tubes of the Frenzy and Darkstar, they both need more than 18" long airframes.

 

[bjphoenix]

I'm through with the fin fillets. On most rockets I'll put on 2 thick layers of TitebondII. On the Javelin and Sprint since their fins stuck out more than normal I put on 3 layers. I added the launch lugs and put 2 layers of fillet on them. I added the tube extensions to the Frenzy and Darkstar. I was ready to start the painting process with a couple of primer coats and had a problem with my spray primer.

In the first photo left to right are the upscaled Centuri Javelin and Estes Sprint, both BT-55, and the mostly stock Goblin. In the second photo left to right are the Wildman Darkstar (BT-60) and the Madcow Frenzy (BT-55).

 

[James Owen]

View attachment 555223
View attachment 555225

These all look gorgeous! Especially the darkstar and frenzy!

 

[FredA]

I did the "Fleet Build" once --- someday I'll post a thread about it.....

 

[bjphoenix]

After dealing with paint setbacks I put in the work to paint the Javelin. This copies the paint scheme from the 1972 Centuri catalog.

 

[bjphoenix]

I know people all over the internet have been holding their breath waiting for this thread to be finished...

I finally got the paint work finished and took some photos.

Here is the Wildman Darkstar (bt-60 downscale) and Madcow Frenzy (bt-55 downscale)



Here are the other 3- Centuri Javelin (bt-55 upscale), Estes Goblin, and Estes Sprint (bt-55 upscale). The Sprint has the wrong nose cone, I only have the one from the Goblin that matches the Sprint styling but I can switch the nose cones back and forth when I get ready to launch.