The Semroc Bandit - Part 2

The ducted ejection motor mount system for the Semroc Bandit can be seen above. This is apparently a re-creation of the original Estes baffle system in the 1971 Bandit. The parts fit together well, and it's pretty neat - although it does add significant weight. If you went with a simple motor mount and just used recovery wadding as per usual, you'd probably get the Bandit to fly a lot higher.

But part of the pleasure of flying the Bandit is watching the whole flight. It's a pretty bird.

The end of the motor tube is plugged with a balsa bulkhead or nose block. Into that bulkhead, you attach one of the supplied screw eyes to anchor the shock cord.

The shock cord which comes with the kit is a thin piece of sewing elastic. I decided against using it here for a couple reasons.

First, it's a little short for my taste. While I do use sewing elastic in my low power model rockets - a lot - I like to make my shock cords very long (more on this in a future post).

Second, despite the ejection baffle, I worry that the elastic will wear out over time after repeated ejections. Not from the heat, but from the chemistry. The caustic vapors from black powder charges have a negative effect on the latex in the elastic, making it brittle and prone to snapping. If I mounted an elastic shock cord that far down into the rocket, when it broke, I wouldn't be able to replace it.

I prefer to attach my elastic cords to something less prone to wearing out - Kevlar kite string.

While Kevlar will burn through after so many charges if it's right by the ejection site, with the baffle system, it will probably be just fine here.

I replaced the elastic cord with a Kevlar string, which I attached to the bulkhead on one end. On the other, I tied a loop. The Kevlar cord is just long enough that you can see it at the end of the body tube.

This will allow me to attach an elastic cord, which I can cut off and replace when it becomes brittle.

With the elastic attaching to the Kevlar inside the body tube, the shock cord is less likely to damage the tube should the parachute come out while the rocket is moving at high velocity. If the Kevlar extended beyond the end of the tube, there's a chance that the cord could cut into the end of the tube, possibly causing a jagged tear down the side of the rocket, known as a zipper.

I sanded the fins into airfoil shapes, which I often do. I like the finished look it gives to a model rocket.

While these aren't perfect, they turned out better than this picture implies. Sometimes a closeup can distort things in a photo. They look pretty even in real life, and once on the rocket, you won't be able to see the imperfections without close examination. I could have taken a second crack at them and probably gotten better airfoils, since I have a spare set of fins (see Part 1), but I decided I was happy enough with these.

I sealed the balsa nose cone and even the fins with thin CA - cyanoacrylate or Super Glue - and sanded them smooth. On the fins, I left the bottom 1/4 inch unsealed. If you get CA on the root edge, wood glue won't bond to it as well, and a fin could easily pop off.

I used the Guillotine Fin Jig to glue the fins on. I made a couple layers of glue fin fillets and then treated the root edges of the fins with CA, then sanded again.

The whole kit looks pretty nice.

You'll notice that I did not fill in the spiral grooves on the main body tube, but I did on the white upper payload tube. That's because the lower tube didn't really have grooves as such. The spirals were more of a tight overlap, so there was nothing to fill in. My hope here is that a good few coats of filler primer will hide those overlaps.

You can fill in spiral grooves with heavy coats of filler primer, too, but I prefer carpenter's wood filler. Filling grooves in with primer alone takes a lot more primer, which is more expensive than wood filler. I like hiding the grooves, and I like getting more than one rocket out of a can of primer, so I usually use the wood filler method. You don't have to fill spirals if you don't want to, but I like doing it, and I have a pretty hassle-free (i.e. not much sanding involved) method.

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The Semroc Bandit - Part 1

I've realized I made a mistake with #NaRoBloMo. That is, I promised to follow up the first N00b T00b post with another N00b T00b post, addressing specific topics. Then, I kept feeling obligated to write that before writing anything else, making this blog feel like work. This is part of my hobby - and supposed to be fun. So, I'm going to jump around as I see fit.

Semroc is one of those model rocket companies which nearly disappeared a few years ago, when its previous owner, Carl McLawhorn, unexpectedly passed away. Eventually, Randy Boadway of eRockets.biz purchased the company, and continues to produce its high quality model rocket kits and parts.

Despite the fact that eRockets is a sponsor of The Rocketry Show podcast, and that I've had several Semroc models waiting on my build pile for a long time, I'd never actually built one. My Estes back stock was just so out of control.

But I hadn't built a kit in a while. After finishing the N00b T00b, which was just a quickie scratch build to get me back into it, I decided it was time to grab something off the pile of kits and start. But what?

I haven't counted my pile. It's... well, it's enormous. If I tried to count it, I'd probably miss something, as I have kits stored here and there. So, what to build next seemed like a huge decision.

I decided to build something non-Estes to start with. I had some FlisKits, some AeroTech, a Squirrel Works Arapahoe E (which looks like a really great kit), plus a number of Rocketarium scale sounding rocket kits, plus some stuff from Quest. And maybe more, I'm not sure.

I thought this was all of my smaller non-Estes pile. I realized later it wasn't even close.

I made a small pile of what I thought were all of my non-Estes low and mid power model rockets (I decided not to start with high power). I realized later there were a few missing from the pile.

Nonetheless, after some thought, I decided it was high time I built a Semroc, since it was one of the first non-Estes companies I had heard of, but I'd never actually started a model. And I chose the Bandit - a "Retro Repro" model - a pretty close recreation of a classic, out-of-production kit (in this case, a 1971 Estes model). It was a nice, classic (I know I have used that word too frequently already, but it's what it is), great-looking model. Having seen a few online and one really nicely built one at a club launch, I felt I needed to have one.

One thing which impressed me about the Bandit was the quality of the parts. The tubes are all very nice, and the balsa nose cone and nose block fit very well. The other thing about the balsa nose cone I liked was how closely the base of it matched the outside diameter of the body tube.

A lot of long-time model rocketeers seem to prefer working with balsa nose cones, rather than plastic, if what I've seen in various online forums is true. Since I've only been practicing rocketry for about five years, I actually haven't worked with that many balsa nose cones. Estes has switched over to plastic, and the few kits they produced with balsa cones either are out or production, or soon will be.

The thing I've encountered when working with balsa cones - again, in my limited experience - is that the base of the nose cones often seem to have a wider diameter than the body tube, so that the cone overhangs the tube by a significant step.

A balsa nose cone which overhangs the tube a bit. It's not so easy to see on camera with the black paint.

A balsa cone with a significant overhang. I turned this one upside down into the light so you could see it better.

I always assumed that maybe it was harder to get balsa to a specific diameter on a larger scale of manufacture without taking off too much material, and so they'd err on the side of slightly too large. Something like that - it was a guess.

Anyway, I encounter that far less frequently with plastic nose cones, and I really don't like that step. If I were to sand the base of the cone down to match the size of the tube, I'd change its shape. So I don't want to bother with that.

When I made my hand-turned balsa cone for my scratch-built Big Bertha, I tried - and succeeded - to get the diameters to match pretty closely. But that was me spending a lot of time and effort on just one cone. Maybe they couldn't do that with a large batch, I figured.

But the Semroc nose cone is such a nice fit.

The Bandit comes with a ducted ejection charge system. Basically, the motor mount is an ejection baffle. Rather than allowing the ejection charge to blow straight up through the tube, the hot gasses pass through a series of holes in two tubes. The flame shoots straight up and hits a balsa bulkhead, but the air passes through the baffle system before pressurizing the rocket and ejecting the parachute. This means you should not need recovery wadding (though the instructions do recommend a sheet or two, just to be on the safe side).

The holes are all laser cut and quite neat.

The one issue with the parts was that the fin sheet was kind of beat up, and one fin had snapped in two along the grain.

This was unfortunate, but not reason enough to my mind to complain.

I can't remember if I bought the Bandit directly from eRockets.biz, or from JonRocket.com. In either case, if I had sent an email to complain, I'm sure would have done something to make it right. But both are - quite literally - "mom and pop" type operations, small family businesses. If there had been something badly wrong with the rocket (say, it had been crushed or something), I'd have sent an email. But in this case, it's not like there was any negligence or bad handling, and I didn't feel like making anybody jump through hoops for me for a bit of balsa.

The kit was otherwise in fine shape. This is one of those things that happens, and it's an easy fix. First, the fin split cleanly along the grain, and could easily be glued together. The bond would be strong and invisible.

Another option would be to trace a fin onto some balsa or basswood fin stock and make a replacement.

I often make an extra whole set of fins, so I can sand them to a particular shape if I want to. Say, I want to sand an airfoil. It's nice to have a set of spares, so if you make a mistake, you have extras. Frequently, they all turn out pretty good, so I'll build a second rocket - a copy of the kit. Then I have two.

I glued the broken fin back together, and after stack sanding the set, I traced them onto both some 3/32 inch thick hard balsa stock, as well as onto some basswood. I liked how the balsa came out better, so I used that. After stack sanding, I had two identical sets of balsa fins to play with.

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Two Days Till NARCON 2017

Inside the Udvar-Hazy Center, image from the National Air and Space Museum website.

NARCON 2017, the National Association of Rocketry's annual conference, is sold out. They increased the available reservations to double the previous record, meaning that this year's conference will be the most-attended in history. Despite the increased capacity, NARCON sold out a couple of weeks ago!

This year's conference will be in Herndon, VA, near Washington, D.C., and will include a tour of the Udvar-Hazy Center of the Smithsonian Insitution's National Air and Space Museum. Included in the museum's collection is the Space Shuttle Discovery, seen in the amazing room full of stuff in the photo above.

In advance of the conference, we talked to museum curator Dr. Jennifer Levasseur on The Rocketry Show podcast, who gave us a virtual tour of the Udvar-Hazy Center and told us a lot about how they do things at the Air and Space Museum.

Dr. Jennifer Levasseur, curator at the National Air and Space Museum

I am simply busting with excitement to go to this year's conference. It's going to be packed with fascinating presentations on model rocketry, high power rocketry, TARC, and professional rocketry and spaceflight.

Jim Barrowman will be there!

Jim Barrowman, around 1966

In 1966, Jim and Judith Barrowman presented a paper at NARAM 8, as part of the Research and Development competition, in which they demonstrated a mathematical method of determining the aerodynamic center of pressure on a rocket. This changed everything. Model rocketeers were no longer left to guess whether their designs would be stable, or to use the less-than-ideal "paper cutout" method (more on this method when we return to my series on model rocket stability).

Lee Piester of Centuri Engineering Company will give the keynote speech after the banquet. Centuri was a model rocket company you hear a lot about from long-time rocketeers. They eventually became part of Estes Industries, and sometimes you can still see their design influence today in certain Estes kits.

Trip Barber, who did some important work on model rocket staging back in his college days at MIT, and who was an early NAR president, will give presentations on TARC - Team America Rocketry Challenge, a program he was instrumental in building.

Current NAR president John Hochheimer, as well as the most recent former president Ted Cochran, will both be in attendance.

Tim Van Milligan of Apogee Components will be a presenter. Tom Ha and Adam Martin will discuss rocketry in Australia. A number of representatives from NASA will be on hand giving lectures on the sounding rocket program, the Orion program, satellite launching, the James Webb space telescope, and more, and a representative of the Federal Aviation Administration will discuss the process of obtaining FAA waivers for high power rocket launches. There will be so much information packed into just a couple of days!

Also, plenty of vendors will be there. AeroTech, of course, will make an announcement - or perhaps several. Matt Steele of North Coast Rocketry, a mid power rocket company, said he'll have "some news," which sounds pretty exciting.

Show sponsor North Coast Rocketry's SA-14 Archer. They sent this as part of their sponsorship - it was on my wish list!

I'm pretty sure John Beans of Jolly Logic will be on hand, as will Randy Boadway of eRockets and Semroc. Since Tim Van Milligan will be there presenting, I'm sure that Apogee Components will also be there as a vendor.

What I'm most looking forward to is the chance to get together with a bunch of fellow rocket obsessives and talk rockets all day. This is what I've been wanting for over two years!

CG and I plan on talking to as many people as we can for the podcast (and I'll give some updates here as well). What I want to know is - what do you want to know? Ever have a question for James Barrowman? Always wanted to know something about some of your favorite old Centuri rockets? What about a question for the NAR president?

I can't promise I'll ask every person every question. Just looking at the schedule, there's so much going on, I won't possibly get to all of it. I'm going to have to plan my day carefully. I'll probably cover the more n00b stuff - model rocketry, etc. - while CG will probably focus more on the HPR stuff. But who knows who I'll bump into and what fascinating conversations we might have? A chance encounter could become an entire show or blog post.

But I would like to know what you would like to know, so that if I get the chance to ask, I can. If there's something you'd love to ask someone at NARCON, email me at iamtherocketn00b@gmail.com, or email the show at mailbag@therocketryshow.com.

I cannot wait!

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