FlisKits Tres - A Challenging Build Part 3

Click here to go to the beginning of the build.

Once I had the motor mount installed in the FlisKits Tres, it looked pretty good and felt nice and solid. But there were small gaps between the motor tubes and the main BT-60 body tube. I suspect this may be the case for most, if not all, builders of this kit.

Those will need to be filled in. Now, it's not just that I don't like the way this looks. Remember that there is only one "centering ring" in this rocket, and it's at the very base, flush with the end of the body tube. So there's not a second ring at the top of the mount to make a nice, airtight seal.

When the ejection charges on the rocket motors go off, they need to pressurize the inside of the body tube in order to blow the nose cone off - and eject the parachute. If you have large gaps like the ones in the photo above, all the ejection charge gasses may just leak out the back. This would lead to a failure to deploy the parachute. The rocket would then come in ballistic, meaning it would nose dive fast and hard into the ground. This would most likely destroy the rocket - and is potentially dangerous, should it hit something or someone.

So, we'll need to fix that. To do this, we'll use glue and make a nice fillet around each of the engine tubes where they meet the body tube.

Even if your rocket has no gaps here, it's not a bad idea to put fillets around the motor tubes. It will hide any jagged edges you've got left, and will make the whole rocket look neater.

To make the fillets, I used the same thing I use for most of my fin fillets - Titebond No-Run, No-Drip molding and trim wood glue. Ever since hearing about this stuff from Chris Michielssen's Model Rocket Building blog, I've used it to make fillets. Swapping out the wide Titebond nozzle for an Elmer's fine point nozzle is a tip I picked up from Chris.

Because it's less prone to sagging and shrinking, and because it starts to dry quickly, this stuff is ideal for filleting these gaps.

I started by running a bead of glue from near the top of the motor tube to the end of the body tube.

You don't need such a thick bead, by the way. Most of this is coming off. When my bottle gets lower, sometimes I squeeze out a bead of glue, and there are gaps in it. So I went a little heavy here to make sure I had one, unbroken line of glue.

If you try to smooth the whole fillet in one swipe, you'll end up with a mess. By the time you get to the end, you'll have so much excess glue built up on your finger that it will end up overflowing the sides of your finger. It's better to do a few swipes and clean off your fingertip with a damp sponge or cloth.

So I started about a third of the way up from the back end, and swept the excess off toward the end of the tube.

I went another third of the way up, and again swiped to the bottom.

Finally, I flipped the rocket over, and attempted to smooth the last bit over the top end of the motor tube. My hope here was that with a few fillet layers, I could actually smooth that joint over, so it would look like the motor tube was simply a part of the body tube, like the branch of a tree, rather than having a sharp ridge where the tube was obviously poking through.

You may prefer to keep a sharp separation. It's an aesthetic choice.

As you can see, there was a bit of excess. That's easily cleaned up by going over it with a clean finger.

Allow the first fillets to dry, then do the other sides, allowing each to dry.

Don't worry if the glue shrinks slightly after the first fillet, leaving a little gap. Do another couple of layers and the fillets should not only close off any air leaks in the tube, but also look nicely rounded. This will show in the paint job.

Next up, the fins. That's my favorite part of a build - it's when the rocket really starts to look like something!

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Nothing Flies Like a Flis - The Model Rocket Show - Episode 2 - FlisKits

Claude Maina's Streaming UFFO lifts off. Photo courtesy Jim Flis.

Episode 2 of The Model Rocket Show podcast is up, and I'm pleased how it turned out.

This show was meant to come out a year and a half ago, on The Rocketry Show, but one thing and another happened, and... well, I think we finally have a good episode.

Curtis Heisey's upscale FlisKits Deuces Wild

We're talking about FlisKits, and in the first half of the show we revisit the final FlisKits Anniversary Launch from September of 2018. Then we spend time talking to Ray DiPaola, one of the current owners of FlisKits.

Jim Flis, the company's founder, has already told me he liked the show, which was my hope. I love seeing Jim at launches. He's a great guy, and I know he was probably looking forward to hearing what we recorded so long ago.

Jim Flis holding a Saturn V prototype. Photo courtesy Curtis Heisey

The show is on most podcast apps or on the show's website (with some show notes and photos), if you prefer to listen on the web (click here to go to the website and show notes).

Give it a listen. I hope you'll enjoy it.

Part 2 of my FlisKits Tres build is coming soon.

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FlisKits Tres - A Challenging Build

To get better at building more challenging rockets, you have to build more challenging rockets. Often, rocketeers will hold on to a model for years, thinking "I'm not up to that skill level yet," or "I need to do this one justice!"

It's understandable. Some models - scale kits, particularly - hold a special place in rocketeers' hearts. And their wallets. And they can tend to be difficult to build perfectly.

Some rocketeers look at the "skill level" on an Estes kit and think Level 3? Level 5?? Expert??? No way!

I used to try for perfection, and since I always make some mistake, there are rockets I waited ages to build, and some I figured I'd never be able to tackle. But it helps to realize that, while some advanced rockets truly are harder, there's no ajudicating body on "skill level." Even if you build an advanced rocket beyond what you've done in the past, it's unlikely you'll end up with something that's not flyable. And if you take your time, it will probably turn out better than you thought it would.

In any case, if you want to have nice looking, harder to build rockets, you have to be willing to build beyond your skill level and just try it. Challenge yourselves, newbie rocketeers, I say!

Maybe don't start with something rare, out of production, or really expensive. But other than that, just give it a shot. Instead of perfection, I now aim for pretty good - as good as I can get it - but I don't beat myself up over mistakes. And I usually have pretty good results.

* * *

Anyway... FlisKits!

The next episode of The Model Rocket Show, dropping early this Saturday, is all about FlisKits, a small indie model rocket company from New England. The episode has been a year and a half in the making. I know, this is only the second episode of the podcast, so how could it have taken over a year to make this episode???

Well, it's a long story. Just listen to the show.

I decided recently, since we're all stuck at home and I'm finally putting this show together, I should actually build that FlisKits Tres I bought directly from Jim Flis over four years ago.

The Tres is a large, 3-motor cluster model with canted motor tubes. If you look at the image at the top of this post, you'll see that means the motors stick out the sides a little. This makes for a wide jet of flame and smoke, and it's a fun rocket to watch fly.

But that motor mount is the main thing that's the challenge in this rocket. I thought I'd do a build on the subject.

I have no picture of just the parts laid out on the table, but the rocket is made up of one 18 inch BT-60 tube and one 18-inch BT-55 tube, balsa nose cone and transition, and balsa sheet - that means no precut fins!

Since this is a cluster rocket, there are three 18mm motor tubes (that's A/B/C sized engine tubes for you fellow Rocket N00bs).

Here they are:

Each tube has a mark 3/4 inch from the bottom. Going through that is a straight line all the way up the tube. Use a small piece of aluminum angle for that, if you have it, or just use a door jamb as you would with fin lines on any model rocket.

Engine block rings (also known as "thrust rings") are glued inside the tops, flush with the ends. So far, so easy. These are your motor tubes. No engine hooks will be necessary for this rocket.

There is a sheet of card stock in this kit you'll use for a number of parts of construction. To assemble the motor mount, there is a small shroud you must cut out from this card stock. You'll also use the custom centering ring, which is more of a round card stock plate with three little divots cut out.

You cut the shroud out with a hobby knife and straightedge. Instructions tell you to "lightly score" all the fold lines on the shroud with a hobby knife.

Be very careful not to cut the shroud at this point! I happened to have a very dull knife blade handy, so that worked. But all you are doing is making sharp fold lines in the card stock, not actually trying to cut it. If you don't have a dull blade, or are worried about using too heavy a hand with the knife, you could use a small dowel you've sharpened to a point in your pencil sharpener, or even a thumbnail.

Apply a very small amount of glue to the glue tab and glue the shroud together.

EDIT: When I first posted this, I should have mentioned that it's a good idea to test fit the custom centering ring into the bottom of the BT-60 body tube. It should just fit inside the tube, like a standard centering ring. If it's slightly too large, you can sand it before proceeding to build the motor mount.

I didn't check, and when I went to install the motor mount, the centering ring butted up against the body tube - it was almost the same diameter as the tube itself. Not a problem if this happens to you - you can still sand that ring. It's just harder, with all the engine tubes glued on. But I did it rather quickly, using an emery board. Most mistakes are fixable.

Once the glue has dried, you can put a thin bead of glue onto the bottom edges of the shroud, carefully line the corners up to the divots in the custom centering ring, and then glue the shroud to the ring.

This might seem pretty flimsy at this point, but believe me, this will work! Once the glue has dried, you can put a thin fillet around the base of the shroud where it contacts the centering ring, for added strength.

I don't have pictures of every step in the next part of building the motor mount, so I'll try and describe it as best I can.

Run a bead of glue down one corner of the shroud, and on the edge of the same cutout in the centering ring. You want a thin layer of glue here, I think. You don't want a large glob of glue.

At this point, I'd recommend waiting 60 seconds before gluing the motor tube on. If you apply the tube immediately, and have a lot of glue, you're going to have to hold the tube in place for a long time. You might involuntarily move the tube out of alignment. You might drop it and get glue everywhere.

So, wait 60 seconds. The thin layer of glue will start to get tacky. Then you can lay the motor tube in place. Line up the 3/4 inch mark on the tube with the centering ring, and use the mark up the tube as a gluing guide for the shroud.

Hold it in place until it sticks, then set it safely aside for it to dry a bit, before proceeding with the other two tubes.

For good measure, I applied fillets between the motor tubes and the shroud and centering ring, everywhere they came into contact. The whole construction seemed pretty solid and really neat when it was complete.

That's the canted motor mount for the FlisKits Tres. As you can see, it's not that hard if you work carefully.

Wait... Installing the motor mount - that's the hard part.

But it's also not too hard. We'll hit that next time.

Click here for Part 2.

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