Saturday, November 30, 2019

The Thrifty Rocketeer


This month, I succeeded in re-starting this blog through my #NaRoBloMo effort. I didn't seem to make an impact on social media. I think I'm the only person who used that joking hashtag.

But one reader did join me. Kirk G, a longtime listener and supporter of The Rocketry Show podcast, as well as reader of this blog, has started his own rocketry blog, The Thrifty Rocketeer.

It's always good to see more rocketry blogs out there. We always love seeing other people's builds and techniques.

CLICK HERE to check out Kirk's new model rocketry blog!

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Thursday, November 28, 2019

Estes Nike-X - Part 1


Once I got the Semroc Bandit all glued together, the next kit I semi-randomly pulled from the build pile was the Estes Nike-X, another nice BT-55 kit.

I like BT-55 rockets. It might be my favorite low power tube size. I'm not sure why. A BT-55 tube (1.325 inches in diameter) feels nice and sturdy, and it's versatile. Some BT-55 kits look like little rockets, and others are surprisingly big.

All I know is that a lot of Estes kits which grab my eye happen to be made of BT-55 tubes.

The Nike-X is loosely based on the Nike Zeus missile.

Several missiles in the Nike family, with the Nike Zeus closest to the camera

Here are the parts to the Nike-X kit.


You can see from the decal sheet that the black parts of the rocket are all decals. That means painting will be easy - the whole rocket will be done in gloss white. Sometimes, it's nice to have a simple paint job.

Just below the sheet of balsa fins, you see the motor tube. This is longer than a lot of motor tubes you get for 18mm A/B/C motors. A beginner might wonder why the long engine tube?

That's because this rocket has what's called a stuffer tube. The motor mount is longer, with the forward centering ring farther up in the body.


With the centering ring closing off the body tube much closer to the nose cone, the volume of the inside of the rocket is smaller. This is to aid in ejecting the nose cone.

With a large volume rocket, sometimes a small ejection charge can have trouble pressurizing the entire inside of the body tube enough to successfully eject the parachute. By using a stuffer tube, you make the inside of the rocket effectively smaller, meaning there's less space for the ejection charge to have to pressurize.

Truly, though, for a rocket of this size, I don't think that's really necessary. I have plenty of BT-55 rockets the same length as the Nike-X, and some larger rockets, none of which use a stuffer tube, and I've never had an issue with recovery.

The Big Bertha is an interesting example.


It uses a BT-60 body tube, and so is larger in diameter than the Nike-X. Some Big Bertha kits come with a stuffer tube, and some come with a standard 2.75 inch long engine tube. Mine has a short tube - no stuffer. And I've never had a problem with the nose cone ejecting.

But using a stuffer tube here isn't going to hurt anything, so I guess it's better safe than sorry.

The fin sheet was warped slightly.


Warped fins can drive you crazy, but they can be fixed. CLICK HERE for my post on different methods of fixing warped fins.

When I examined the fins more closely, it looked like the balsa sheet had warped in the bag. While the sheet had a bend in it on one side, the fins looked like they might actually still be flat.


In the above photo, you can see the underside of the sheet. The sheet curves away but the fins stick out.

Once I cut the fins loose and stacked them on the table, they looked like they were fine.


I wouldn't need to break out the glass cleaner this time around.

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Friday, November 22, 2019

Brodak Is Back


A few months ago, I learned from Bill Cooke's Rocketeer's Corner blog that my favorite sanding sealer, by Brodak, was out of stock.

I learned about Brodak from Bill's blog, and I love using it to seal the wood grain on balsa fins.

Everyone has a favorite method of hiding wood grain on balsa fins to make them nice and smooth for painting. The top three favorites include sanding sealer (which goes back to the early days), Elmer's Carpenter's Wood Filler, and papering fins. I did a detailed study here on The Rocket N00b blog a while back, focusing on how much weight each method added. CLICK HERE to read that post.

While I use each of these methods occasionally, by far my favorite is sanding sealer. Not only does it add the least weight, I find it the least frustrating.

This is just a personal taste thing. There is no "best" method.

A popular brand of sanding sealer in the past was Aerogloss, but it went out of production a few years ago. There are other brands of sanding sealer out there, but Brodak is my favorite to work with of the ones I've tried.

Brodak was out of stock for a while, and I worried it was simply not coming back, so I emailed the company to ask when it might be returning.

Patti from Brodak replied:

Hi Daniel,

We are waiting on the metal cans to come in. This should be back in stock within the next 2 weeks.

Sorry for the delay.

This was in early September. It must have taken longer than anticipated for the cans to be resupplied, because I kept checking the website, and long past a two-week period, the sealer was still out of stock.

But it's finally back, so I ordered more.

Sanding sealer, particularly this one, is more expensive than other methods of hiding wood grain. It puts out fumes, and should therefore only be used in a well-ventilated area. And, unless you can find a local supplier of it, you'll have to order directly from Brodak.com and pay shipping. But I like the stuff, so I consider it worth the price tag.

Also, I like the quality of it. Every time I opened a new jar of Aerogloss, if I didn't use the whole thing up in a few days to a week's time, it would crystalize and become useless.

I've used an opened can of Brodak on multiple projects for nearly a year, and only at the end did it start to thicken up. A dash of lacquer thinner made it useable one last time.

Brodak comes in 4 ounce or 16 ounce cans. The 16 ounce is a far better deal.

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Monday, November 18, 2019

Sounding Rockets; Cutting-Edge Science, 15 Minutes at a Time


At 2pm today, NASA live-streamed an hourlong program on sounding rockets - research rockets which carry scientific payloads on short, suborbital trajectories.

Here is the video:


If the player does not work for you on this blog, CLICK HERE to go directly to the video on YouTube.

I like sounding rockets, because of all launch vehicles, they're the ones which most closely resemble what we do in hobby rocketry. They're usually fin stabilized, they usually use solid propellants, and rather than go into orbit, they go up and come back down.

Sounding rockets look much like sport models, and doing a scale model of one is often much simpler than doing an accurate scale model of, say, a Saturn V or Mercury Redstone or Falcon Heavy, or Atlas Something.

In fact, one of the earliest model rocket kits, the Aerobee Hi, was a scale model of a sounding rocket which looked so much like a sport model, that when you see a scale model of it, you'd be forgiven for thinking it was just another model rocket.

The Aerobee Hi sounding rocket

I've been wanting to see more on YouTube about sounding rockets from NASA, but until today, I didn't find a lot that was terribly informative. Now that I have time to sit down and enjoy it, I'm hopeful it will have some interesting stuff in it.

Enjoy!

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Sunday, November 17, 2019

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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Monday, November 11, 2019

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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Tuesday, November 5, 2019

Technical Difficulties

I was trying to illustrate the next post on the N00b T00b last night, with a screenshot from OpenRocket, on the MacBook Air I use for The Rocketry Show podcast.

But the 3D image of designs in OpenRocket on this MacBook all display as really tiny.


This is as large as I can make the image.

Looking at it in preview, I guess in this case it's not terrible, but I wanted a larger image, and after an hour of messing with it, I got fed up and went to bed.

I might see if I can dig out the really old, slow, clunky laptop I used when I started The Rocket N00b blog, because at least I can load photos from my camera onto it, even if it's old junk.

We shall return to #NaRoBloMo shortly...

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