Mid Power: Building the Quest Big Dog (Part 7)

Click here for Part 1

 The Big Dog kit comes with a launch lug for a 3/16 inch diameter launch rod, but I scavenged that for my previous Estes Cosmic Explorer build in which I adapted that rocket to hold an E-sized motor (24mm instead of 18mm). But I wasn't worried about not having the right launch lug for the Big Dog, because I decided a while ago that, for this rocket, I would use launch rail buttons.

Most rocket kits, even high power kits, come with a traditional launch lug. Larger high power kits can have a huge launch lug, and require a really thick, long launch rod. But a lot of high power rocketeers have abandoned the lug-and-rod system in favor of launch rails - long metal extrusions with a t-shaped slot running its length.

A launch rail from Apogee Components

A launch "button" is a small piece of plastic material shaped like a little spool. The thin middle part fits into the slot on the rail. With two (or more, for bigger rockets) buttons attached to the rocket, you slide the whole thing onto the rail, and that keeps the rocket pointed straight up at launch.

Rail button sliding into a launch rail. From CDI Model Rocketry

Launch rails are sturdier than rods, and less likely to "whip" back and forth due to wind and the weight of a rocket and the force of its taking off. And people say that launch buttons produce less aerodynamic drag than lugs. I don't know if that's been confirmed scientifically, but a small button is less obtrusive than a huge lug. So it may reduce drag, and in any case, it looks better.

Some rail buttons are even airfoil-shaped.

Airfoil-shaped rail buttons from GiantLeapRocketry.com

The standard rail size for high power rockets is called 1010. The 1010 rail is 1 inch wide. Some really heavy rockets use a rail size called 1515 - 1.5 inch wide.

But, like a lot of things in rocketry, the t-slot rail was never intended for use on rockets. It's an industrial product you can use to make all kinds of stuff - furniture, kiosks, machining equipment... Whatever. It's like an industrial Erector Set. Rocketeers adopted the rail and came up with the rail button. So, there are other sizes of t-slot extrusion. They come in metric as well as English sizes.

For a while, the 1010 and 1515 rails were the only option if you wanted to use buttons. Hypothetically, you could put a 1010 rail button on any rocket, but for smaller model rockets, they're a bit too large to be practical. A small launch lug looks better, and produces less drag.

However, there is a company which now sells smaller sized rail buttons for use with lighter rockets, and teeny-tiny ones for use with small low power model rockets. Rail-buttons.com sells a mini button, which fits the metric sized t-slot rail, and even a micro button. With the micro button, you can make a launch rail system using one of a couple of smaller t-slot rails now available. The Makerbeam and the OpenBeam, both of which are used to make smaller, lightweight industrial stuff (a lot of people use them to make frames for 3D printers), can now be used to launch rockets.

A 1010 button would work fine on the Big Dog. But I don't currently have a 1010 rail, and a button of that size is larger than I need. In my opinion, as long as it works, smaller is better.

Mini button on the lower left; 1010 button on the upper right

I do have a metric rail and some mini buttons. I used those when I built my Estes Partizon (as was recommended by Randy of rail-buttons.com).

But even those looked a little larger than necessary for this rocket. The Big Dog is pretty light, so I have decided to go with the really tiny micro buttons, and launch the rocket from my Makerbeam rail, which is 1500mm long - about five feet.

The micro button - even smaller than I'd imagined

The first step is to drill holes for the buttons to screw into. I'd marked my rail button line back in Part 2 of this build series, and it was time to decide where exactly to place the buttons on that line. While the kit comes with one launch lug, you always need a minimum of two buttons. The kit instructions say to place rear end of the lug 10 inches from the bottom of the body tube, so that's where I put my forward button. But where to place the other one?

Well, as long as you have two buttons, you can hypothetically place them pretty close together. With a rocket kit with, say, a 3-inch lug, you could place the buttons 3 inches apart, exactly where the ends of the lug would go. But, I don't have a drill press, just a hand drill. What if I get the buttons slightly out of line with one another? If the buttons were close together, that would mean that the rocket would be pointed at an angle to the launch rod, rather than straight up. The further apart the buttons, the less extreme that angle would be.

Off-center rail buttons are less of a problem when they're far apart.

Many rocketeers like to place one button far aft, and one about the center of gravity. Or the center of pressure. Or wherever - there's a lot of discussion. I placed my aft button about 2 1/4 inch from the back - enough so that I wouldn't interfere with the centering rings. I chose the spot where the rail button line crossed an inner seam - just to have a nice mark to use.

I wish I could tell you what size drill bit I used, but I threw the packaging away. It might be 1/16 of an inch, but I think it's a little smaller. In any case, it's smaller than the diameter of the screw.

I drilled the holes for both buttons, then wicked a little thin CA (cyanoacrylate - hobby super glue) into the hole, and wiped away the excess.

The CA makes the hole harder, so you'll be able to thread the button screw in once it's dry. It will also allow you to sand off the burrs that come up from the body tube from the drill. I threaded the screws into the holes and then removed them. As it happens, I got the holes lined up pretty well, so I don't think there will be any issue with aligning the rocket on the launch rail.

I'll leave the buttons off until the very end of building the rocket, after it's painted. I could add them now, but leaving them off saves me from having to mask the buttons off while painting - and potentially leaving a bald spot in the paint job from masking tape.

Next up, I'll put on the fins and do some nice fin fillets - with epoxy, instead of my usual wood glue. This will add strength and give them a nice shape.

Click here for Part 8

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Mid Power: Building the Quest Big Dog (Part 6)

Click here for Part 1

Often, when I taper or airfoil a fin, I use some thin cyanoacrylate, or CA - craft superglue, basically - to reinforce the trailing edge. When you sand balsa to a thin point, it gets much weaker. A tip can break off when the rocket lands - or even when you're transporting it to the flying field, if it bumps up against something.

CA wicks into the wood fibers, making them harder. But these fins are so strong, I decided not to bother. Actually, it would have been a good idea regardless. CA not only hardens the wood, it seals it against moisture. I'll come to that in a minute.

Using Chris Michielssen's ratio of 2.5 parts Carpenter's Wood Filler (CWF) to 1 part water, I painted CWF onto all four fins of the Big Dog.

The Big Dog fins are on the right. On the left are the fins for an
Estes Cosmic Explorer I'm building with an E-sized motor mount.

CWF contains moisture, and moisture can cause wood fins to warp. The cells of the wood soak up water and swell, and if the cells on one side of a fin swell up, the fin curls to the other side. If you evenly and quickly paint both sides with CWF, many builders say that you shouldn't get any warping. While this makes sense, I still get warp on my fins some of the time with CWF.

Of course, to avoid warping, you want to allow air to get to the whole fin so that it can dry evenly. Some people stick a pin or wire into the root edge of the fin, fill the fin with CWF, and then stick the pin into some foam to keep the fin from touching anything while it dries. When I tried this, I shoved the pins through the face of my fins, and it generally didn't go well.

Usually, I press my fins under a book after filling them. Many people sandwich them between sheets of wax paper when they do this. I prefer parchment paper, because it wicks some of the moisture away from the CWF, allowing them to dry a little faster. But as it does, it causes the paper to form ripples, and the ripples cause the CWF to bunch into ridges, which, when dried, require more sanding. They can also leave low spots in the CWF that leave little imperfections when sanding them off, and it usually take me about three coats to get the fins where I want them. Fewer than that, and I can still see wood grain when I paint the rocket. Regardless of what paper you use, pressing fins makes the drying time take a lot longer - which, in turn, makes build time take longer.

So, I came up with a compromise.

The surface of CWF starts to dry pretty quickly. After filling the fins, as you can see in the picture above, I laid them on a cooling rack. I got a couple of these at Bed, Bath & Beyond for about six bucks, and I now use one for cooking and one for rockets.

After a few minutes, I flipped the fins over, just to assure that both sides got an equal amount of airflow to allow drying. If, after close examination, I saw any signs of warping, then under a book they would go.

The Cosmic Explorer fins dried just fine with no warping. About half the Big Dog fins were OK, except for two - and it was the tapered trailing edge that had begun to warp. They had to go under the Riverside Shakespeare.

The Big Dog fins are so large, both Shakespeare and Chaucer were required.

Here's where I thought it might have been a good idea to wick some thin CA into those trailing edges - not so much to keep them from breaking upon landing, as these fins are really tough. More because if I'd used CA on them, the trailing edges would have been waterproof. I could have let the fins air dry completely, and started sanding an hour or two later.

But, because I'd let them start drying before pressing them, the CWF didn't bunch up from the parchment paper. They dried more quickly than they would have with waxed paper, and because they'd got a decent start for about ten minutes in the air, they dried more quickly than if I'd put them under a book immediately.

When you sand the CWF down, it always feels so smooth, and each time I do it, I think this time, it's a breeze! But when I wipe off the dust, I always see little pits, divots and imperfections in the surface.

These pictures are in extreme closeup, so the details here are slightly exaggerated:

But I have had those pits show up in paint jobs before. This is a detail a lot of people who look at my rockets might not notice, but I can see it. More sanding is necessary, but I can almost never totally get rid of these with one coat. It's probable that a good coat of filler primer (not now, of course - later, after the fins are on and you start the painting process), followed by some good detail sanding and perhaps another coat of primer, would take care of these. But for good measure, I sanded as much as I could out of these fins. But usually if I do this and stick with only one coat, the fins look and feel very smooth. It's only after I begin painting that I realize that I've sanded some of the filler completely off, exposing the wood grain.

When I first started using CWF, this baffled me. I thought the CWF was supposed to fill in all of the wood grain. It's really more for scratches, holes and gouges. And I thought, I thought using this stuff was supposed to be easy!

And it is easy. But to get a really nice-looking rocket, it requires some patience and some care.

One of my as-yet unstated goals is the Perfect Build. Now, there's no such thing as a perfect rocket. But on every build, I've done something - sometimes something small, some times repairable, and often not - that I would consider a mistake. Something I didn't mean to do - either through a moment of carelessness, or impatience, or through trying something new I didn't know how to use yet. That last one is a good thing. Most stuff has a learning curve on it. And most of my "mistakes" are things only I would notice, unless I point them out. But some of them are obvious. Let's take a close look at the Cosmic Explorer:

Torn decals, with chunks missing

Instead of using decals for the stripes, I painted them on - and made some critical errors.

Compared to some craft mistakes, tiny little pits in the fins are minor, and won't be noticeable to anybody else. And I want to make this clear to other rocket n00bs - your rockets won't stay perfect. They will get dinged up in flight and landing. Wear and tear happens. But I like my rockets to look as good as possible, even if it's only for the maiden flight. When I take them out to the field, I like to be able to say, "Look, guys! I built this!" Besides, rockets spend a minute or two in the air at a launch. They spend a lot more time on a shelf at home, and I like to show them off.

As it turned out, Chad and my other friends liked the paint problems on the Cosmic Explorer. They said it made the rocket look "weathered." It sure did...

OK, enough digression. Back to the Big Dog.

Once I got the fins sanded to where I liked them, I decided it would be best to do a second coat of CWF. I nearly didn't, but I knew if I did not, I'd be disappointed with the results. The Big Dog was a little more expensive than a lot of Estes models, so I'm taking a lot of care with this rocket.

The good thing about a second coat of CWF is that you can thin it a little more with water than you'd do the first coat. You're really just trying to cover the parts that you sanded completely off, and fill any imperfections you missed the first time. So there's less to sand off the second time, and it's just easier.

Again, I had to turn to Shakespeare and Chaucer for help. When I was done, I had smaller ridges to sand off:

And using 400-grit sandpaper, I got the fins nice and smooth.

The fins are filled. The longest part of the build is finished.

Next time, I'll introduce any rocket n00bs reading this blog to the concept of rail buttons - tiny ones, for this rocket, but something commonly used in higher power rocketry - and we'll get those fins on the rocket.

Click here for Part 7

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The Estes Scion - Spare Parts Elimination Vehicle?

When I first read about the existence of the new Estes Scion on Chris Michielssen's blog, he hypothesized that this might be an S.P.E.V. - a model rocketry term meaning Spare Parts Elimination Vehicle. The rocket has a 3-inch diameter tube, and the nose cone and fins look just like the Estes Leviathan's - though the Leviathan has four fins, and they are flipped around from what you see above so they are swept back.

Estes Leviathan

My Scion just arrived today, and there here are a few interesting things about it.

First of all, there's no card - no art work depicting the finished rocket, no Estes logo - nothing. Just a bag of parts.

Because of this, you can see inside. What you find are two 3-inch diameter tubes, of the same length as the upper section of the Leviathan. The Scion, like all of the larger Estes kits, has through-the-wall (or TTW) fins - meaning that the fins have tabs which go through slots in the body tube to anchor them more securely , but neither of the tubes are slotted to accept the fins. Some rocket kits from some companies require you to cut your own slots, but Estes doesn't really do this.

The dead giveaway, though, is the package of fins. The Scion design has three fins, but the kit contains four. Furthermore, the wood grain runs parallel to what would be the trailing edge of the fins on the Scion. Normally, you find the wood grain running parallel to the leading edge. This is the standard practice, and with balsa fins, it's important, because it's stronger. With these plywood fins, it probably won't matter. But it seems pretty obvious that, rather than being based on Leviathan fins, these are simply Leviathan parts repackaged.

This isn't necessarily a bad thing - a lot of rockets have similar appearances. Mixing and matching parts gives each rocket its character.

But...

I have read that Estes is getting out of the Pro Series II mid power rocket builder kit game. If this is true, it's a sad thing. I love the look of the Leviathan and the Ventris rocket, and if I happen to mess up the build, or to destroy my rockets in a crash, I like knowing that I can always get a replacement.

Estes Ventris

So, it looks like we have an SPEV on our hands.

Don't get me wrong - I love the look of the Scion, being a cool twist on the Leviathan design. But I feel a little odd about it, knowing it's basically a bag of Leviathan parts - especially if that means the Leviathan is going away.

Note: Estes used to have a rocket called the S.P.E.V., and this might be where the term comes from. It was not a kit you could buy; rather, they would send it to you if you ordered a certain amount. It's a rare rocket, and it's interesting-looking. I have no idea what kits the parts come from, but it looks a bit like a NASA mockup. I doubt they still send it out, but people do clone it from time to time.

From rocketreviews.com

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Great Launch Day!

Saturday, I went launching rockets with Chad, David and Jeff. Chad is only in town for about a week every month and a half, and the weather doesn't always cooperate. This week, it was beautiful, despite the weather report saying it was going to be rainy and windy all week.

Chad was in town, and really wanted to launch some rockets. I've had a few losses lately, and it was supposed to be a little windy. The field where we launch is pretty big, but a little wind (and the presence of a pond) can make it feel small.

But it had been a while, and I love launching rockets when Chad's around, and it's more fun for other, non-rocket friends I invite. Seeing two or more nerds geeking out over rockets is kind of a comedy show, but when I'm the only rocket guy there, the civilians get bored. Chad and Jeff both love model rockets, and David loves watching them when those guys are in town. These are funny guys.

So the four of us and Ted, a retired vet who used to produce theater for the Army in Berlin during the cold war (I heard some great stories this weekend), went out to the park to light some candles.

Chad left me a box of rockets when he moved to upstate New York - mostly ready-to-fly models. So I started with a little orange and white rocket I'd never seen, the Estes Scrappy, a kind of ugly little thing which flies on mini motors. Most of Chad's parachutes were a mess and had to be cut off. Re-doing parachute shroud lines is a real pain, which is why I like to use snap swivels to attach chutes to the rocket in the first place - it's easier to untangle the lines. But this rocket only had a tiny, 6-inch parachute. I've seen enough plastic models come down with no deployment that I decided to cut the chute off altogether.

I've always been a little skeptical whether a streamer really slows a rocket's descent that much, but after seeing the Scrappy descend with no recovery system (other than "tumble"), I can say I'm a believer. It landed in the grass about 50 feet from the pad with no damage.

Next I flew the Estes Shuttle Express. This is an easy-to-assemble model I got for my birthday, and it carries two gliders which deploy at apogee. I was surprised how cool it looked going up. Those gliders made it look kind of hulky, which was fun.

The "gliders" don't so much "glide" as "dive straight into the ground." But the chute opened beautifully, and David went to recover the rocket.

This picture turned out looking really dramatic. David Sheehan - bravely recovering the astronauts...

Next I sent up another of Chad's RTF rockets, the Estes Hi Jinks.

Up to now, I'd been launching rockets on Estes C6-5 motors, and this one was no exception.

Liftoff was great.

The rocket flew straight and high. But then, it disappeared over these woods...

It's not too densely forested, and I thought perhaps I'll be able to recover the rocket. But more likely, it had landed in a tree.

Now I decided it was time to launch one of my built kits. I selected the Estes Crossfire ISX. I said "This might be the last flight of the Crossfire."

It's a pretty high-flying model. I launched it...

And then I remembered I had packed a B6-4 motor in it, to be on the safe side.

The guys and I often joke about "hubris" when we're launching rockets, but I suffer from it. Even though I know it's sometimes better to put a less powerful motor in a rocket, I like to see them go high, and I like a longer burn on the motor. But the flight was great - and I didn't lose the rocket.

That sealed it - from this point on, I'd stick with B motors, with one exception.

Next in line was the Estes Der Red Max. This was my first build, and I love this rocket. It's what got me into rocketry in the first place. It flies really straight, and I didn't want to lose it, so I swapped out the C6 motor for a B6.

Chad decided to tape his phone to a long pole to see if he could get some video from below the rocket as it lifted off. Chad's full of brilliant ideas.

But actually, it turned out not bad...

Jeff's phone also got great pictures.

The rocket didn't go as high, but I got it back. Sometimes you have to sacrifice a little altitude so you don't lose the rocket you spent hours, days or weeks working on. Take it from me, the feeling of loss outweighs the thrill of the initial flight.

Next up was the Cosmic Explorer - another favorite.

The ascent on a B6 was great - no roll!

For rocket n00bs, roll is that spinning motion a rocket gets around its vertical axis. You see it a lot in rocket-mounted camera POV videos, and sometimes it can make them hard to watch. Most rockets do it, but trying to build a rocket so it doesn't is the goal. The Cosmic Explorer flies straight, with no roll.

While the ascent was great, the recovery was... well, I'll just let you watch.

Stuck in the mud, about an inch and a half.

But when I pulled it out - no damage!

Whew! That was a close call!

Finally, we launched the Big Bertha, this time going back to a C6 motor.

The Bertha is what's called overstable. This means, in short, that it's really prone to arcing into the wind - for newbies, a phenomenon known as weathercocking. I have never had a straight flight with the Bertha, and I was sure it was going to end up in the dog park. Remarkably, though, it flew nice and straight, and it also landed short of the pond.

It's in the upper left-hand corner of the sky.

Once again, Chad got out his PVC camera boom, and I kind of got some good video out of it. I decided to make it dramatic...

The guys had to go back to the BPP, so they packed up and left. I went in search of that Estes Hi Jinks rocket.

The wooded area was very marshy, and I sank a couple inches into the earth quite a few times. The trees were sparse, but close enough together that I was sure I'd see it up in a tree. I looked up and down, and didn't find it in a tree or on the ground. I searched for 45 minutes to an hour. I even found a swamp, and a sign about wetlands. I didn't even know Bloomington had wetlands!

I got into some thicker forested area, and circled the school to the left in the above pictures - nothing. Eventually, I realized I'd gone farther back in the woods than the rocket could have possibly gone, and was about to turn back, when I decided to head further down the wide trail. And this happened...

For a day of launching mostly smaller rockets, it was a great launch day, and I wish more people could have joined us. And in the end, we didn't lose a single rocket.

In other news, the Trident 1A and Sounder I scratch built rockets are finished, and I'll have pictures to follow. The Quest Big Dog and Cosmic Explorer with an E-motor upgrade are also coming along, nearly ready to paint. The Big Dog series will continue in a day or two, and the Cosmic Explorer build series will start when I'm done with that.

And I need to finalize my rocketry camp plans and build the Donor's Rockets. A lot to keep me busy.

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