Holey Fins & Tranny's Batman!

I like em, and I'm still making em. Yup, Tranny's....aka transitions. While largely used in low power more often, I still love the way they add an aesthetic look to rockets. I've read where, some folks don't care for them at all. BLASPHEMY! There may be a number of reasons for that line. One of which might suggest, they can't make em right. Or have no real designing skills. Whatever the reason, this thread is devoted to those that love building with them and designing hollow fins. I started my first hollow fin build back around 1985, or so, and it was this little unnamed model. The paint job is a dead giveaway for lack of finishing skills back then. A few years ago I upscaled it and Kathy Miller gave it the name ORCHIDO. (Or-kee-doh) You'll also notice, most of my models have tranny's too. You got some too? Let's see.

Nice birds Mr Byrum.

Thanks Scotty. Here's a look at my second effort in my hollow fin fleet. I actually have an upscale drawing of it I've been sitting on for a couple of years. Both of these birds are really good flyers. This one measures 2' tall.

Nice work!

Gary Byrum said:

Thanks Scotty. Here's a look at my second effort in my hollow fin fleet. I actually have an upscale drawing of it I've been sitting on for a couple of years. Both of these birds are really good flyers. This one measures 2' tall.

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Great job on the curved edges of the fins. I don't think I have a bird that would fit in this thread.???????????

I love that second one, simple but very interesting. The fins are attached to a transition (which I really like); is that a paper cone? If so, how did you handle that structurally?

Here's mine, recently completed. We've got yer transitions and holey fins right here:


I chickened out of doing paper transitions for this one, and had Sandman turn me a couple of custom pieces out of balsa.

WOW!! What a paint job! That is beautiful work.

Maxter said:

WOW!! What a paint job! That is beautiful work.

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Thanks. It's a testimony to how many times you can screw up and still salvage some good results if you don't panic and just keep solving the problems as they arise.

neil_w said:

I love that second one, simple but very interesting. The fins are attached to a transition (which I really like); is that a paper cone? If so, how did you handle that structurally?

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Sharp work you've done on your model. Definitely qualifies as a "holey fin".

The transitions on the one you asked about, "Lil Sister", are indeed paper and the diagram below shows how I did it. It may look like it's built wrong or flimsy, but when you look at the big picture, the connections inside the BT55 are designed to support each other. It would have been easy to build with CR overkill to accomplish this, but you can see clearly, it didn't have to be. The CR's just had to be mounted correctly and as accurate as possible. As far as connecting the fins to the shroud, this is a practice that is usually frowned upon because the shrouds are usually weaker than a BT and don't have as much strength. I've flown this rocket many times and nary a problem with it. The biggest headache was painting the BT 20. I'm pretty sure it had to be done with a brush instead of spraying.

I didn't even realize that the top and bottom were different BT sizes. Now I like it even better.

I guess just gluing the fins to the paper cone might be OK (especially for 18mm motors); somehow that hadn't even occurred to me. What weight cardstock do you use?

You mention painting... I would have thought there was more than enough space in those fins to enable decent spraying. In the Diamond Cutter I did not trust that I had enough room, and pre-painted the transition before attaching the fins. I had an advantage there that those fins were not actually attaching to the transition, so pre-painting was practical.

Oh, and I should say I'm having a hard time figuring out your paint colors from those pics.

neil_w said:

What weight cardstock do you use?

Oh, and I should say I'm having a hard time figuring out your paint colors from those pics.

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Lil Sister is Fluorescent Pink and Black. 110# card stock

Nice! I gotta get out of my color rut, I always gravitate towards black, white and primaries.

I also just noticed the excellent launch lug placement there...

neil_w said:

I also just noticed the excellent launch lug placement there...

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In most cases, I use 2 lugs. That one would have accompanied another one mounted on the side of the fin. I have no idea why I didn't do that. That one little lug really isn't safe enough. That other rocket beside it in the pic got two and for a good reason. My rule of thumb is, if only one lug is used, make it longer. With 2 lugs, you can use smaller lengths.

I love this thread. Gonna have to get into doing this again. I do have a few fins I cut out for 1/4 inch ply that I then used a scroll saw and cut a hole into and then I carved the back edge of the hole like a toy whistle.
I was going to a whistle effect while flying fast. Never finished it. It was going to be about the same size as a LOC 4.

I finally got the Skyjacker built, now for a good day to hit it with the primer. Here's the fin assemblies and the motor tubes.



Almost ready for assembly. Parked next to a couple other builds.



And the final nekkid pic. It's right at 44" tall.

Those fins are just beautiful.

Great looking rockets!
Never tried making those fins......maybe my next project

neil_w said:

Those fins are just beautiful.

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Thanks a bunch Neil. You'll really be shocked to see where and when those fins originated. Back in the late 60's / early 70's I used to draw vertical lines on a sheet of notebook paper and went crazy with a pencil, drawing random sketches of fin shapes. I filled 3-4 pages of these so I could go back and see if there was one worthy of using in a build. Granted, some of these are "dog ugly", but there's 1 in 10 that had some hope. See if you can find these fins. OH btw, I realized you had some links in post #9 that I overlooked, so I took a look and saw that there was a lot more going on with your Diamond Cutter than met the eye. Impressive!

Gary Byrum said:

I like em, and I'm still making em. Yup, Tranny's....aka transitions. ... You got some too? Let's see.

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My first experience with the transition was with one of my first rockets back in the day, the Centuri Excalibur from the Big Shot launch set. While not scratch-built original designs, these cardstock mini-engine min-dia downscale clones are my homage to that classic transition rocket from yesteryear. These were all the variations of the paint schemes I could find from past catalogs on-line. The printable templates for these are in the cardstock forum here. I used PayloadBay.com to generate the transition outlines. I have all the SEMROC parts for an original size Excalibur from eRockets and am toying with the idea of making it a gap stager. Since the BR-78 transition is solid balsa, I would have to drill it out to accept a 13mm or 18mm engine mount, not sure if anyone makes a hollow plastic transition that size. Or, I will just make my own cardstock transition for that project.



Nice to see that Estes has several cool transition rockets in their current lineup, including the Centuri among others.

With transitions in the spotlight, I wanted to showcase one in particular that was a bit of a challenge. This rocket was my spinoff of the Estes Trident using three gas chambers. The gas chambers are BT-5's mounted around a BT-50 center tube and all of that, housed by a 50/70 transition. Gas exchange ports are inside the transition. The forward airframe is a BT-50 to a BT-55 and the ports are in the BT-50. The tough part was knowing I had to mount the 50/70 tranny first, custom cut the chamber holes in it, align and mount the chambers one at a time to the exhaust holes. Yeah, it was a PIA. But a fun one.



I call it the Argus Transport. Flies true and works like a charm.

This is a great thread. I wish I had more rockets to contribute. One day I will necro this thread and post something new.

Gary Byrum said:

You'll really be shocked to see where and when those fins originated. Back in the late 60's / early 70's I used to draw vertical lines on a sheet of notebook paper and went crazy with a pencil, drawing random sketches of fin shapes.

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It's awesome that you still have them. I used to make lots of drawings for possible design-of-the-month entries, although I never actually made one (and they weren't great designs as I recall). But I don't have any of that old stuff anymore, sure wish I did. If I had OR back in the day.... yeesh.

(fourth down on the left, by the way, and my oh my they look exactly like the ones you built up there).

GlenP said:

While not scratch-built original designs, these cardstock mini-engine min-dia downscale clones are my homage to that classic transition rocket from yesteryear. These were all the variations of the paint schemes I could find from past catalogs on-line. The printable templates for these are in the cardstock forum here.

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Lovely. I can't decide if I want to try doing some cardstock models, but I probably should if for no other reason than to get a lot of good practice making transitions....

Gary Byrum said:

With transitions in the spotlight, I wanted to showcase one in particular that was a bit of a challenge. This rocket was my spinoff of the Estes Trident using three gas chambers. I call it the Argus Transport. Flies true and works like a charm.

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Best one yet, I love all the little details in it, particularly the three BT5's disappearing into the aft transition. And really nice paintjob!

I simply cannot ever get tired of looking pictures of the great work that other folks do.

Here's a goofy design (but kind of neat, maybe) inspired by this thread. This is one of two ideas that woke me up at 4:30 this morning when I desperately wanted to sleep (the other went into my tube-y thread). Only way to get it out of my head it to record it.

I call this "The Blob".

There ya go! Already got the creative juices flowing. Sorry about the loss of sleep. I deal with that constantly.

That fin resembles one in my immediate stockpile of CAD renderings that I keep in my drawing page. The hole in mine is moved a bit more forward though. If you like this one, use it. My gift. It's not to any kind of scale, but I can scale it or any other fin for that matter. I'd be interested in seeing what your skills lend using it. If you like it of course.

Ha ha, your fin is too clean for that rocket. Needs to be more blobby. Actually, I was trying for the rear fins to approximately track the shape of the, uh, little ones.

There is not a lot of room in that design to squeeze a parachute.

Anyway, I've got another scratch build to keep me busy for a while, so I'll let this one percolate, and tweak a I go. I already know the proportions are a bit off, that needs adjusting. I probably won't be able to decide if I *really* like it until I test out paint schemes.

But it would give me something to add to this thread, anyway.

Kinda looks a bit like a fish with all the fins, doesn't it?

Sorry. I wasn't suggesting that you replace your fins. It's just another fin design for you to play with. Sometimes all it takes is the right fin pattern to inspire the entire concept. Have some fun.

Oh, got it. No problem either way. I do like that fin, maybe for other designs.

BTW, I'm still blown away by the Argus Transport, that one really is a beauty.

neil_w said:

BTW, I'm still blown away by the Argus Transport, that one really is a beauty.

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Thank you. LW assisted me in the design. You should see how it started out..:rofl: One of my bigger issues with it was using so many colors. The more you use, the harder it is to distribute a balance.

I was just browsing your tube-y thread and saw that is was more of a design thread rather than the usual build thread most people post. That was cool. I agree with you that your final choice in the list of concepts should be a done deal. That is really worth being built. Nice going. On another note, painting these kinds of birds has it's own set of issues and one that helps me out, is painting certain parts before they get assembled. I've done this and had to mask off the areas where glue joints go with minimal touch ups to follow. You just have to remember, that not everything needs to be spray painted. Hell, I've made my own paint swabs just to get inside smaller areas where a brush wouldn't suffice, nor a spray can could go. I hope you do a build thread on the Biohazard.

Gary Byrum said:

Thank you. LW assisted me in the design.

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...which reminds me to go ping his Apparition thread, starved for updates over there.

I was just browsing your tube-y thread and saw that is was more of a design thread rather than the usual build thread most people post. That was cool.

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That is a really fun thread for me. I tend to have a hard time choosing which forum to post things, since there's so much overlap. I suppose design threads like that should probably be here, while build threads... well, they could go either way. But the LPR and Scratch Built forums seem to have different user populations, doesn't seem to be a way to hit everyone who might find it interesting. Oh well. Next design thread I'll do here, we'll see how it goes.

I agree with you that your final choice in the list of concepts should be a done deal. That is really worth being built. Nice going. On another note, painting these kinds of birds has it's own set of issues and one that helps me out, is painting certain parts before they get assembled. I've done this and had to mask off the areas where glue joints go with minimal touch ups to follow.

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Yes indeed. I'll only go forward with a design when I'm confident I can come up with a doable build/paint sequence. In that case I definitely foresee some pieces being painted pre-assembly, and the ring will go on after everything else is complete. I shall definitely do a build thread once I get through the preliminaries. Should be fun.

These two should do.