Fiddling Around

My schedule is all over the place. Sometimes I work late at night; sometimes early, early in the morning. All this back and forth has left me with less time than I'd like for rocket building or blogging. I get maybe two good building days a week, and I work slowly.

Fortunately, I have OpenRocket - free rocket design and simulation software.

As any gamer or couch potato can tell you, even if you're really tired, you can still spend hours fiddling around on your computer.

So, when I don't have the time or energy to build rockets or write about them, I play around with different designs. It's a way of staying an active rocketeer when I'm too busy to be actually building.

Once you know the basic principles of stability and rocket construction, it isn't that hard to design a basic rocket - or at least to get one started. You might need to make revisions, weigh components and change a few things, but you can come up with some cool basic designs in short order. I've even built and flown rockets that took me 20 minutes to conceive, and I only had to make minimal revisions.

Here are some designs I've been working on.

The Circe Series

I started this the other night. I wanted something simple to replace my lost Estes Hi Flier - a small, lightweight, high-flying rocket. It performs so well because it's a minimum diameter rocket - meaning it is only as big around as it needs to be to hold the motor. It has no motor mount - the body tube is the motor mount!

Circe A - a small rocket which will hold a standard 18mm diameter (A-C) motor, and go quite high

Though I am trying to build bigger and bigger rockets (and currently building two of my Estes Pro Series II rockets), I just had the urge to design this little thing.

OpenRocket has a scale function, so you can take a rocket of a particular size and scale everything up or down by the same amount. So while Circe A (pictured above) will only take a C sized motor, Circe B looks exactly the same, but is larger and will take a D or C motor. When you scale things up in OpenRocket, sometimes you have to adjust components, because, for example, the mass of the nose cone might actually end up being much greater than the part you actually have on hand. Other than that, it's pretty simple.

I went up to a BT60 sized rocket with the Circe series before going to bed. BT60 is a 1.637 inch diameter tube, and is the same size as the Big Bertha. The cool thing about the BT60 is that it's just the right size to fit a cluster of 3 standard motors.

Circe C2 - looks much the same, but has a cluster of 3 motors. You'll notice the nose cone is slightly shorter - this is due
to the size of nose cones I have on hand, which are a of slightly different ratio than the BT20 nose cones I have.

If you're an advanced rocketeer and are good at making stuff from scratch, you can make your own parts. All of them - even the body tubes. And, of course, nose cones.

I'm not to that level yet. I don't have access to a wood lathe, and I haven't picked up the skill of designing and making a custom-shaped nose cone. Fortunately, there are a lot of good parts on the market.

So what I do, for now, is look at the parts that are available - either in my parts box, or online, and design around that.

Here's a lovely balsa wood nose cone I picked up from JonRocket months ago.

This shape is a spherically blunted tangent ogive, and the nose cone fits a BT70 tube, which is about 2.2 inches in diameter. This is getting toward the higher end of body tube size you'll find for low power model rockets, and into the mid power range. If you're new to model rockets, this thing will look huge to you - there are not many BT70 kits out there!

I have realized I need to get more of these, or get some other BT70 nose cones, because over the months, I've designed a number of rockets around this very nose cone.

One of the first was called Horus.

The Horus Series

People give rockets all kinds of zany names. A quick look at an Estes catalog gives you some idea - Sizzler, Prospector, HiJinks, etc. A rocket can have any kind of name. But I guess I'm more of a classical kind of guy. I like to name my rockets after Greek, Roman, or sometimes Egyptian gods or mythological characters, or after celestial bodies. Horus is the falcon-headed Egyptian god of the sun.

Seemed like an appropriate name for a rocket.

I wanted to design my own rocket which looked vaguely like the Sirius Rocketry Eradicator - a beautiful rocket which has been on my wish list since I first saw it - but would be simpler to design and construct for a n00b.

The Eradicator, from Sirius Rocketry, available here

(Eradicator - there's an interesting one. I love this rocket, but the name reminds me of this Kids In the Hall sketch)

No offense, Sirius Rocketry - you guys are awesome!

Anyway, I love the two differentiated diameters of the airframe on the Eradicator. I designed this one:

Not too bad, I thought. But in order to get a minimum of 1 caliber stability, I needed to have 5 fins, if they were to be swept forward. I was able to decrease the number of fins to four by adding fin vanes.

This increases the surface area of the fins, moving the center of pressure aftward, without making the fin span inordinately wide.

The Eradicator has a lot of great detail - it looks like a real launch vehicle. That level of design was a bit advanced for me. That's not to say you can't add additional detail to the build, but it's tricky to add it to the OpenRocket design.

FMLV

This is a simple recent design, but one I like and am building now. It's another BT70 design with a 24mm motor mount. Like the Circe rocket, it's got swept back fins, but as you'll notice, the tips are not parallel to the rocket.

I've seen a few designs like this recently, and I like the look of it. Actually, a lot of classic kits have fins like this, but I've only just recently thought of changing the shape of the fins in OpenRocket.

You can select a few basic fin shapes in OpenRocket. I almost always opt for "trapezoidal," and then simply change the dimensions of the root chord, tip chord (chord is the distance from the leading edge to the trailing edge) and height (the distance from the airframe to the tip of the fin).

That means that most of my designs look like this:

Imperius, formerly known as the "Donor's Rocket"

See how the tips of the fins are parallel to the rocket body tube? Nothing wrong with that, of course.

But part of what gives a rocket its character is the shape of the fins. I went with a few designs that had the fins swept forward, like the Horus series above, and the Copperhead (formerly known as "Keith's Rocket").

And I like these designs. But you learn by playing with the tools you have, so I decided to try a different shape. Still simple enough to cut with a ruler and hobby knife, but a little different from what I'd made before.

FMLV stands for First Massachusetts Launch Vehicle, because it's the first scratch design rocket I'm building here in Boston. I'm using a 24mm Estes "quick release" screw-on motor retainer so that I can use my newly-acquired AeroTech 24mm reloadable casing, or an Estes black powder D or E motor.

That gives me a lot of motor options.

It will also be the first rocket I build from scratch which will have through the wall or TTW fin construction. This means that the fins have tabs at the base which will go through slots in the airframe and attach directly to the motor tube. You fins this as pretty standard in mid power and high power kits, and even some Estes low power kits, like the Cosmic Explorer.

Attaching fins to the Cosmic Explorer. In this kit, the slots are already cut for you.

Of course, in a kit, the slots are cut for you. For the FMLV, I'll have to cut my own fin slots for the first time.

BT80 Rockets

Also included in my parts box is a BT80 sized parabolic nose cone.

You may have noticed that this nose cone has a similar profile to the Big Bertha nose cone, but while the Bertha uses a BT60 body tube - 1.637 inches in diameter, the BT80 is 2.6 inches in diameter. For a beginning model rocketeer, that's really big!

Regular readers of the blog may also recognize this nose cone as part of the ICU2 camera payload bay from Make: Rockets: Down-to-Earth Rocket Science by Mike Westerfield, which I used in the design of the Janus II two-stage rocket.

Since I had another one, I played around a little with a few designs.

A really large rocket, called Titus, after my girlfriend's nephew.

Meh... This kid needs to have a cooler looking rocket named after him.

Also played around with a large two-stage rocket.

Could be fun, especially with the two large 24mm diameter motors. But still a little inelegant. It was probably late at night when I did this one.

I might make a larger, not-quite-proportional version of the Copperhead rocket pictured above.

A larger Copperhead design with the BT80 nose cone, and a 29mm motor mount, for E, F or G motors

Of course, the Janus II with its payload bay was lost on first flight, so I may just rebuild that...

Finally, a design I nearly forgot about. This must have been months ago.

Arrowhead

I had this idea when building both Sounder I, a tiny minimum diameter rocket I lost on its first flight, and the Ceres B booster, again from Mike Westerfield's book.

I stacked one on top of the other with a balsa transition I had in the parts box.

 

It reminded me of some of these:

This looks like a two-stage sounding rocket, but it's really just one stage. Not that you couldn't do a two-stager here, but it would require some electronics I haven't worked with just yet.

I haven't discussed staging on the blog yet, but in brief, most model rockets with multiple stages rely on the first motor igniting the second. The first motor has no delay grain or ejection charge, or even clay cap.

From Apogee Components

The propellant is exposed at the forward end of the motor, so when it burns up, hot particles shoot forward into the nozzle of the second motor, igniting the second stage propellant.

An illustration of model rocket motor staging
from the Estes Model Rocketry Technical Manual

Many multi-stage rockets have the motors touching each other. This is known as contact staging. There can be a gap between them, in what is known as gap staging, but the gap can only be so wide - 12 inches is probably the maximum.

This rocket is longer than that, and the two parts are separated by a solid balsa transition, so there would be no way for the hot propellant particles to reach the top portion. You can make hollow paper transitions, but I'm not very good at that yet, and balsa transitions of all sizes are available online.

Again, for a beginning designer, working around available components is the easiest way to get started.

High power rocketeers do multi-stage rockets using altimeters, or sometimes timers, to electronically ignite upper stages in the air. This is known as an air start.

Still, even as a one-stager, I like it.

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(A) Little Time for Rockets

I'm in the final week of rehearsals for my final show at the Bloomington Playwrights Project, the theater which is also responsible for me discovering rocketry.

As a result, I've been rather too busy to blog much, so my final post in the mid power Quest Big Dog series will be out in a few more days - maybe a week.

But I'm going to launch on Wednesday - and this time, I'll be lucky enough to launch at a farm! One of my fellow cast members has a huge place, and he's having us over for some rocket time.

This is great news, because this will be the last time Chad will be in town before I move to Boston, so it will be our last launch together here in Bloomington.

So I'll be pulling out all the stops, and launching everything I've got - including the Big Dog, the recently-built Estes Cosmic Explorer with an E motor mount, and the Quest Quad Runner - which I've had ready to go since December, but haven't wanted to risk losing on its maiden flight.

Here are the never-flown additions to the fleet that I will finally be launching:

Estes Cosmic Explorer with a larger motor mount

Quest Big Dog

Sounder I - a small scratch built rocket which will go high and fast

The Ceres B booster, from Mike Westerfields book
Make: Rockets: Down-to-Earth Rocket Science

Trident 1A - a 3-motor cluster, my first ever design

The Quest Quad Runner - a 4-motor cluster

Janus II with a camera payload bay.
This also holds an altimeter.

Aside from these new additions, I'll launch the rest of the current fleet as well. Pictures and video to follow!

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Mid Power: Building the Quest Big Dog (Part 5) - Experiments in Papering Fins

Click here for Part 1

I'm going to digress from this series for a moment, because this is the point where I needed to make some decisions about how to proceed. In order to make that decision, I had to try a few things.

On most of my rockets, I make the fins smooth for painting by filling them with Elmer's Carpenter's Wood Filler, commonly abbreviated CWF.

This works, and it's pretty common among rocketeers looking to hide the wood grain that will show through the paint job. The common way to do this in the old days was to use sanding sealer, which would fill in the pores in the wood, and after several coats and several times sanding, you'd have a smooth, plastic-like finish.

Sanding sealer seems to have fallen out of fashion these days. I don't really know why - I've heard that it smells bad, but so many materials we work with in rocketry smell bad and irritate the eyes (I'm looking at you, cyanoacrylate!). Perhaps it's not as good as CWF, I don't know. I've never tried using it, though I'm considering doing so, just to see what it's like.

CWF works, but it takes time, produces a lot of dust (the sanding produces such a fine dust that it gets all over everything in the spare bathroom where I work), and often requires multiple coats; and, since it's water-based, CWF can warp fins if you're not careful.

A lot of rocketeers "paper" their fins. That is, they cover the fins with paper skins, carefully glued on and flattened out. It takes less time, and can make fins much stronger, as the paper reinforces the balsa fins. With paper skins, you're much more likely to have a fin break off  long before you risk snapping one in half.

People have their different methods of papering fins, but here's a basic method by Tim Van Milligan, of Apogee Components:

The quicker build time, less mess and added strength are very appealing to me. And papering fins is supposed to be easy. But I've had a bit of a time with it, so I decided to try it out on the practice fins I airfoiled in the last post.

Now, I've tried papering fins before, with mixed results. Some have turned out well; some have not. I've tried different methods, all of which seem pretty straightforward, using different adhesives, from wood glue to white glue to spray adhesive, and using two skins (one for each face of the fin) and one skin (which wraps around the leading edge of the fin).

I figured if I could get this papering thing down, I'd do that for the kit fins; if I couldn't, I'd stick with the CWF. I'm not willing to risk making a $45 dollar rocket look bad because I decided to try something new.

Well, I get a good result on about 1 out of 4 fins:

The six big fins are practice airfoils for the Big Dog. The bottom right three fins, from left to right, are from
my scratch builds: Sounder I, the Ceres B booster, and the Janus II two-stage rocket
with a camera payload. The upper left is just a scrap I tried papering.

The basic method is to apply some kind of glue to either the surface of the fin itself, or to the paper, wipe off all but a thin layer, then glue it to the fin. Do both sides, allow to dry, and then seal all the edges (except for the root edge) with thin CA (superglue). Once the CA is dried, you sand off any extra paper from the edges.

Some people use spray adhesive, and some people like to wrap one skin around over the leading edge of the fin. I liked this idea, because it means that you have once piece and don't risk showing a seam under the paint job, or having exposed wood grain on the edge. But the trouble with that is that the skin tends to pull away from the wood before its dry, leaving a bubble underneath.

I've tried spray adhesive, and my best fin seems to be with that method.

I was also able to get one skin wrapped around the leading edge. Unfortunately, other fins I attempted to do this way had a gap at the leading edge between the paper and the edge of the fin. And on at least one rocket I've built using the spray adhesive method has a bubble I only noticed when I started painting.

Hard to see, but if you press on the fin on the left, you can feel it give; there's a bubble
under the paper skin where it pulled away from the fin either during papering or afterwards.

OK, so the Trident A fins were done using a weaker spray adhesive than I used on this Big Dog fin. Perhaps spray adhesive would work just fine. But there's also the problem of the leading edge. Even on one fin that didn't have a gap between the edge of the fin and the paper, there was some wrinkling where I folded it over the edge.

Well, that's not going to look good! So I tried curling the paper first, or folding it. Folding it would probably have worked pretty well, if I had gotten the leading edge of the fin in there perfectly. But working with sticky materials is hard - you keep getting your fingers stuck, then the material moves, then you don't get the part placed the way you want to. I ended up with such a bad gap on that one, I ended up cutting it, sealing it down with CA, and treating it as if I had used two skins:

This one might turn out OK - I guess we'll see when I sand off the excess.

Working with white glue and wood glue turn out alright, provided the fin isn't too large.

But the Big Dog fins are quite large, and I kept dropping them while holding them by the edges. This means I get blobs of glue where I don't want them, such as on the paper itself.

And with glue, you have to work fast, so wrapping the fin around the leading edge doesn't seem to be an option for me, at least until I get better at this. Look at this horrible sight!

Ripples and tears, from the paper becoming saturated with the glue. I wasn't able to work fast enough with this fin, and this happened. When you paper fins with glue, it's a good idea to work quickly and then press the fins under a book to prevent them warping. Between sheets of waxed paper, of course - you don't want fins glued to your Shakespeare!

I had one fin turn out reasonably well with glue, except that the leading edge is prying away, despite being sealed down with some CA.

Even with a successfully papered fin, if you're fussy and want to hide all wood grain, you still need to deal with the tip edge, which shows the actual capillaries running through the wood.

This can probably be done with a minimum of CWF or some other sealer. And of course, you won't know how things really turned out until you put on primer and paint - and by then, what's done is done.

All of this is to say that with the Big Dog, I decided in the end to go with CWF. It may not be perfect, but I know I can get good results with it. I'll keep working on papering fins on my own scratch built rockets, until I get comfortable enough with it that I am willing to paper the fins of a kit I've paid money for. Papering fins is probably one of those things that simply take doing until you get less clumsy with it. Once I feel good enough about my ability to paper fins, I'll show you how I end up doing it here on the blog.

As for the three fins that came out reasonably well...

...well, they're not perfect, but they're plenty good enough to be put on a scratch build. It's an E-motor quad cluster which uses the Quest Big Dog fin planform, so until I can come up with a better name for it, I'll call it the Quad Dog.

It'll be a simple, big rocket that should have some awesome flights. And cheap to build!

I've now finished filling the fins, so in the next post, I'll show that part of the build, and attach the fins to the rocket. I'll also decide what size rail buttons I'm going to use. Stay tuned.

Click here for Part 6.

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5... 4... 3... 2...

I've nearly completed the three rockets I've been working on for a month and a half, just in time for tomorrow's Epic Rocket Launch. Just a bit of paint here, a few stickers there, and a couple knots tied, and we'll be All Systems Go.

Janus II with camera payload bay, Quest Quadrunner 4-motor cluster rocket,
and 3D Rocketry's Nautilus II, the first kit I ever purchased
which wasn't from Estes (which is where most of us start)

All that's needed now is a few details.

The Janus II - which is the big brother of my first ever designed-and-built (or "scratch built") rocket Janus I - will get a touch of black on the fin tips.

Looking at this rocket, with the gray body and fat payload section, it kind of reminds me of a shark - which gave me an idea for a new design I'm going to play with (but which in the end may be unstable and therefore unflyable) called the Hammerhead. Mostly I like names for rockets that don't try too hard to sound "badass," but I might make an exception in this case. Stay tuned.

Here are the two Janus models side by side for comparison.

Janus I and Janus II. Janus I uses standard 18mm (A-C) rocket motors,  while
Janus II is designed for 24mm motors - one D and one E. Both are two-stage rockets.

 
Even without a special payload section, you can see that Janus II is taller than Janus I - this is because since it's made to take larger (and heavier) motors, which sit in the aft end, the rocket needs to be either longer or weighted in the nose in order to be stable without using oversized fins. This has to do with the relationship between the center of gravity and center of pressure, and if you're new to rockets, we'll get to that in another post on the basics of rocket stability.

Also notice that Janus I has four fins on the booster and main body (sustainer) of the rocket, while Janus II has only 3. This reduces drag and increases altitude (and makes building faster - less sanding and fewer fin fillets to apply). My simulation estimates that Janus II will top 1700 feet.

But just to check, I also have an altimeter.

Altimeter Two, from Jolly Logic

This tiny little guy will tell me what the peak altitude reached is, and a number of other flight data points - such as top speed, maximum acceleration up to 23 Gs (!!), altitude at parachute ejection and the velocity at which it descends (with that parachute). It's can go up to 29,500 feet, so I think it'll do the trick.

Here's the camera seated in the Janus II payload bay:

Peekaboo!

So, this rocket will carry two payloads - the camera and the altimeter - it has enough room for both, plus an egg if I wanted to do that (though I'd like to spare my new altimeter the potential humiliation).

The Quadrunner is in pretty good shape, considering the ordeal I blogged about a few days ago. It's not perfect, but once the decals are on, the little flaws may not be noticeable.

The Quest Quadrunner -
tall, powerful, beautiful...

With four C6 motors, this should easily top 2000 feet, although I may add a bit of weight just to slow it down a bit. Four motors can lift a lot of weight. This rocket is not that heavy - and in a recent Youtube video I saw of a launch, the thing took off so fast the camera couldn't keep up. After a month and a half of work, I'd prefer to minimize the risk of my losing this rocket on its maiden voyage.

The Nautilus II by 3D Rocketry will get copper fins and perhaps nose cone, although I'm tempted to leave it this flat black color. It looks imposing like this.

But I got the copper paint, so I feel like I should go through with it. I hope I don't regret that decision! The rocket flies on a D motor, and should go pretty high.

We're also going to attempt to launch Chad's Aspire rocket from Apogee Components. This thing is supposed to top one mile in altitude. Last time we launched, I must have inserted the igniter wrong (it's a composite motor, not black powder, and I'm not used to those yet), because it flashed, and nothing happened. Such a disappointing end! I have four spare igniters for this rocket, so we'll try our best. We'll probably never see it again...

I was going to hold back on a few of my smaller rockets, but I realized, hey, this is the last launch of the year! I should go all out! So I'm launching everything I've got - everything I've built, that is. My pre-made, ready-to-fly models will probably stay at home, or I'll launch one first to check the wind direction and speed.

But here's nearly everything I built myself since I started doing this less than six months ago - the fleet for tomorrow's launch:

Back row: Janus II, Cosmic Explorer (Estes), Nautilus II (3D Rocketry), Aspire (Apogee Components), Magnum Sport
Loader (Quest Aerospace), Big Bertha (Estes), Quadrunner (Quest Aerospace). Middle row: High Flier (Estes),
Crossfire ISX (Estes), Der Red Max (Estes). Front row: Star Trooper (Estes), Mini Honest John (Estes)

Janus I is retired, due to damage, but everything else I've built is going into the sky tomorrow, and I hope to have pictures and video to share - including POV video from the nose of the Janus II!

The weather looks good, so we shouldn't have to scrub the launch like we did Saturday. Honestly, I was glad for a few more days to finish these three rockets, but now it's Go Time.

I've been putting together a video compilation for a few weeks of all my launches - or, at least, all the ones that came out OK, and after tomorrow, I'm going to put a Slo-Mo Supercut on my Youtube channel. Rocket porn, basically. Now that I'm building bigger rockets, I hope to get some good video. Small rockets are really impressive to watch in person - they go so high so fast! But on video, it's hard to convey the exciting nature of the launch. Bigger rockets look better on video.

If I stick with this (I plan on it), I think I'll try to make it an annual tradition of putting out a slo-mo launch supercut of the year on January 1. I've got some bigger rockets to build, so hopefully years to come will see some good video - and who knows, maybe a Level 1 high power rocket certification launch??