Tag: launch
High power rocket construction: part 4 (rail buttons)
One issue that is becoming increasingly obvious to me is that I don’t have a proper workbench, or workshop, or anything remotely suitable for the gluing, cutting, and other madcap activities required for rocket construction or assembly. I’m just using a dining room table. Sometimes the line blurs between utensils and tools, and I end up spearing food with a screwdriver.
The point is, if I’m going to keep building rockets – especially bigger and more complex ones – I’ll need to find a better work space.
But anyway: RAIL BUTTONS.
This is one of the more straightforward parts of the rocket build. Smaller rockets (low and mid power) generally have “launch lugs,” which are like straws. Paper straws, not plastic – we’re not barbarians here in Seattle.
The idea is simply that you set up a launch pad with a launch rod – just a long, thin metal rod – and the lug slides right over it. It keeps the rocket upright while launching.
But high power rockets are bigger and heavier and require a different solution. They typically use rail buttons, instead, which is just a variation on the same concept. The buttons are like guideposts that slide along a stronger, larger rail that, again, keeps the rocket straight during launch.
The installation of these is pretty simple. They’re just metal screws with a plastic rail guide or button, and they can be attached to the exterior of the rocket body as pictured here. They need to be a certain distance apart, and one should be as close to the rear of the rocket as possible, but the exact measurements depend on the size of the rocket you’re building.
Rail buttons can be attached several different ways. What I did here was drill a smaller hole through the rocket body into the side of the wooden centering ring, and then drill the screw into that hole, so it connects directly and securely to the centering ring. This is true for both rail buttons. To help ensure they’re secured in place, I also added a drop of epoxy into the holes I drilled prior to inserting the screw.
Another technique would be to use a small bolt with a nut on the inside of the rocket body to secure it (and again, use epoxy on the nut to keep it in place). I had already put together the rocket body and motor mount by the time I attached these rail buttons, so there was no easy way for me to do anything on the inside. I probably should have attached the rail buttons earlier in this process, but this works fine too. I’m confident these rail buttons will hold.
[fast forward to both breaking off and me sobbing uncontrollably]
High power rocket construction: part 3 (rocket body)
The motor mount is built, and the fins are attached. (Note: sometimes this part of the rocket is also called a “fin can.”) What next, you ask?
Well, next, the motor mount or fin can goes inside the rocket body, and it’s glued in place. Because the fins go “through the wall” and are already solidly attached directly to the motor mount inside, this method requires cutting the rocket tube slightly in order to slide it over the fins. The cut tube can always be sealed up again later with wood glue.
If you look closely at this first image, you can see where the rocket body tube was cut for each fin to slide past it. Fits like a glove!
As a side note, this end of the rocket is the “aft” end. Aft means rear. I confess that I did not initially know this. You may already be more acquainted with nautical terminology than I am.
You can’t see them here, but remember the motor mount tube has three wooden centering rings. Just before each centering ring slides inside the rocket body, flush against the body tube wall, you can add some wood glue to seal it. You can also add lots of additional glue to the final centering ring at the aft end, but that can easily be done anytime after this.
Finally, while the fins are already attached on the inside to the motor mount tube, they should also be glued again on the exterior to ensure an extremely secure bond.
You know what they say about a rocket that loses a fin.
Actually, I don’t know what they say, but without getting too deep into aerodynamics here, if your rocket loses a fin it will definitely be unstable during flight and will crash. And then you will feel bad.
A real WAC launch: video highlight reel
High power rocket construction: part 2 (e-bay)
This post is largely meaningless because I’m not actually including any electronics into this rocket, at least for its first flight. I should probably have titled it “How to build an electronics bay without any electronics.”
Meh.
So first, what the hell is an e-bay?
An electronics bay (or “e-bay” for short) is where you attach any electronics that you want to fly in your rocket. It’s also sometimes called an avionics bay.
What kinds of electronics would you want to fly? Well, there are a lot, and it can get pretty interesting. A few examples of things are:
- Altimeter. Measures the maximum height of the rocket (i.e. its apogee).
- Explosive charge. If you put black powder on the outside of the e-bay and wire it up with some electronics on the inside, you can manually detonate the charge and cause the rocket body to separate on descent, for another parachute. This is called dual deployment, as you’re deploying two parachutes.
- Camera. A GoPro camera can be installed on the outside of the rocket body, wired to electronics stored inside the e-bay.
The e-bay is actually pretty easy to assemble. It’s just a few pieces of wood, and some metal screws, washers, and nuts. You start by gluing together the wooden “sled,” and then sliding two very long metal screws through the slots, along one side. Each end has a circular piece of wood with an eyebolt (which can hook to other things like shock cords and parachutes) and it all stays together with some washers and nuts.
Now, if I actually had any electronics in this thing, it’d be more interesting. But I built it anyway for two very important reasons:
- It’s necessary to act as a coupler and keep the rocket body together so it can fly in one piece. Without this, there’s nothing to connect the top and bottom halves of the rocket.
- I plan to add electronics to this rocket for future flights.
So there you have it. Not your granddad’s e-bay.
Catastrophic failure: video
Catastrophic failure
Last weekend, I attended a launch event hosted by my local rocket club. It was a great experience, and I enjoyed watching others launch a ton of rockets, large and small. A launch report that the club sent out afterwards said that there were 111 total flights, ranging from motors sized 1/2 A up through G. (It was a low and mid power launch, so nothing higher than that.)
Something else made the day particularly memorable: my rocket self-destructed.
But first, a little background.
A rocket launch can go wrong in a lot of different ways. A LOT. One of the most common issues is a failure of the recovery system – for example, the parachute fails to deploy properly, and the rocket comes crashing down. But a rocket can be constructed perfectly and the launch can still end in disaster if the motor or engine malfunctions. Motors are designed by people with advanced degrees in chemistry and engineering, and constructed with expensive equipment in large facilities (with hefty insurance policies), but they’re effectively just small explosive devices and things can understandably go wrong at times. When a motor fails, it’s termed a “catastrophic failure,” commonly referred to in the rocket-launching business as a “cato.”
This launch day had an unusually large number of catos, including during one of my own launches.
I flew the “Mean Machine” twice, and the first time everything went well. It launched smoothly, flew high, the parachute deployed, and it drifted back to the ground. I recovered it and prepped it for a repeat performance.
But on the second launch, the motor suffered a catastrophic failure. It seems that the propellant inside the motor somehow exploded out of the casing, which meant a small fireball shot upwards through the rocket, superheating the body tube and blowing off the nose cone prematurely (and shearing off the parachute’s shock cord, severing it from the rest of the rocket). The body tube, which is normally very hard and difficult to bend, crumpled from the extreme heat. It then quickly cooled, and is now frozen and unbendable in its current sad and broken state.
I’m reassured that this “cato” was solely due to a defective motor and not my shoddy construction of the rocket, and I’m further encouraged by the fact that something similar happened to several other people on the range that day. (Not that I’m happy it happened to anyone else, but at least we could commiserate.)
And to be honest, it’s not really a big deal – the fins are totally fine. With a little work, I can cut away the damaged part and re-join the two halves of the tube into a single straight rocket again. It’s a good learning experience, and it makes for a great video clip, too, which I’ll post shortly.
Local rocket club launch
This weekend, our local Seattle area rocket club (Washington Aerospace Club, or WAC) held a small launch event at 60 Acres Field, a park that’s roughly a 30 min drive from where we live. We decided to stop by and check it out, and I brought along the Mean Machine and some E motors. This was the first time I’d been to a club launch and it was a great experience – it was well organized and coordinated, with a carefully set up range area and a range safety officer (RSO) in charge.
I didn’t know quite what to expect but they’d already set up all the launch pads and equipment, which made things really easy. Several dozen people attended, including families and young children, some to launch and others just to spectate. There were some really impressive rockets out there. Other groups were on the field too, aside from our club members – several groups of students were there for the Team America Rocketry Challenge, or TARC, so rockets were constantly in the air.
I was able to launch the Mean Machine with an E motor twice – the first launch and recovery was a textbook success, while the second was… more interesting. More on that in my next post. But I also plan to upload some video clips from the event!
Improbable Ventures 