Friday, September 19, 2014

I Designed My First Rocket - And So Can You

I just whipped up my own rocket design. You know, no big deal.

This is a major goal of getting into rocketry - designing and making your own rockets. "Scratchbuilt," they call it.

I found the idea really appealing, but kind of daunting. Where to start? What is it going to look like? What's it supposed to do? Won't my rockets look like any generic rocket (for fellow n00bs, a common term is "three fins and a nose cone," or 3NFC)?

Well, I just finished reading the book I mentioned in my last post, Make: Rockets: Down-to-Earth Rocket Science, by Mike Westerfield, which was really good.


There were a few things the author didn't talk about, which I wish had been in the book, and maybe I'll do a review of those things in another post.

But it was really helpful. Throughout the book, you use parts to make semi-scratchbuilt rockets. I say "semi-" because they are of the author's design, but the point is that they aren't from kits. Some are more complicated than others, and by the end of the book, you have some basic skills to start designing your own, and the final project is to do so.

This is where rocket simulator software comes in.

While it's possible to design a rocket on paper, it's complicated. It requires some drawing skill, but if you want to know anything about the rocket's stability or how it will perform, it also requires some advanced mathematical skills. The software walks you through the drawing phase, and does the calculations for you.

There are a number of rocket design and simulation programs, but two of the most popular are RockSim and OpenRocket.

RockSim is from Apogee Components, and is the most sophisticated, most popular, and probably most useful rocket simulator. It's also over $120 currently. But it can handle almost all rocket design problems, and I believe it even runs animated simulations. If you're really into rocketry, my understanding is it's worth the investment. They even offer a free 30-day trial of the software. I plan on getting it, but I'm not there yet.

OpenRocket is also very good - and it's free! The other day, I discovered that OpenRocket could read RockSim files, and my mind blew up! For one thing, there are libraries of Rocksim files for Estes rockets which you can download. That way, you'll know where the center of gravity and center of pressure are, and you can run simulated launches using different motors and under different weather conditions - even at different elevations above sea level. I thought that without Rocksim, I wouldn't be able to view these - I was wrong!

Estes Der Red Max Rocksim file - in OpenRocket

Here's the rocket I designed today. It's called the Trident 1A.

This is what the 3D "finished" view looks like
 
You can rotate the rocket in 3D view - here, I've installed 3 C6-5 motors
 As you can see, I was ambitious - I designed a three-engine cluster vehicle with exposed motor tubes. What's missing from this image is the engine mounting rings and bulkhead - I cannot figure out how to install these in OpenRocket. Even the author's cluster design was missing this part, so perhaps it's not possible. I also had to trick the software a bit to get that ring on the end. That's a body tube, and in order to get it there, I had to put another body tube length between the front tube and the end ring - but with a diameter and mass of 0. That's why you see that warning in the bottom right hand corner about "Discontinuity in rocket body diameter."

Look closely at the picture - from the simulation, you can see that the rocket should go nearly 750 feet into the air and hit a top velocity of 256 feet per second - that's 195 miles per hour.

Here's what the rocket looks like in design mode:


You start designing at the front of the rocket with the nose cone, and add components as you go back.

When you're done, the software can create a PDF of component parts. Which means you can take your design, print it out, trace parts such as fins onto balsa wood, and cut them to the right size. Essentially, you've created your own kit - that's what scratchbuilding is.

I haven't built this yet, and I have a lot of stuff on my to-build list, so it may be a while before I get to this. But I think this is not a bad design for a rocket n00b, eh? What do you think?

One thing I have to think a lot about before I build this, though... With those exposed tubes in red, the white body, and the black fins with a fin tab on front - I've created kind of a painting nightmare. I have no idea how I'm going to mask this thing so I don't get paint where I don't want it!

Any ideas, please comment below!

1 comment:

  1. I know this is nearly a 3 year old post... But for paining, I would finish all the parts including priming and sanding individually first. Basically in 3 parts:

    - body / nosecone.
    - 3 motor tube complete assembly (glued together and cured)
    - rear tube w/fins glued including fillets all ready to paint.

    Take note to place "masking tape" exactly where your engine centering rings/bulkheads will touch the inner upper and lower body tubes.

    If it is going to be a pressed fit (just gluing the 19mm tubes to the inside of the others), then just prime and paint as-is. Use sand paper to sand of the paint and primer when dry to press-fit. Then glue!

    The key would be to prime and paint each of the sections separately.

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