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.

Rail button close-up on rocket body
Rail button on rocket body

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.

Rail button placement on rocket - top view
Rail button placement

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.

Airframe: aft end and motor tube
Airframe: aft end

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.

Fins attached to rocket body
Fins attached to rocket body

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.

High power rocket construction: part 1 (motor mount)

I finally got my head out of my ass and started putting together this high power rocket. (My head is often firmly lodged in my ass, so extracting it is time-consuming and unusual.)

The basic parts are similar to those in smaller rockets. You build a motor mount (to hold the motor in place) by attaching three centering rings. These rings keep the motor mount tube centered – hence the name – within the larger body tube of the rocket. Then you attach the fins to the motor mount. All of these attachments should be made using a strong wood glue or epoxy.

Motor mount
Motor mount

Later in the process, the larger body tube will slide over the mount and will be flush against the edges of the fins, where they can be secured with glue again on the outside of the rocket. They’re held firmly in place, inside and out, which is important because of the high stresses that will be placed on them during launch.

Motor mount with fins attached
Motor mount with fins attached

Finally – you attach a steel eyebolt through one of the centering rings, using some washers and nuts and then a strong epoxy to hold it all in place. The purpose of this is so that you can attach it to a strong (and fireproof) cord inside the rocket body, where the other end of the cord is attached to the nose cone, along with a parachute inside for recovery. This allows the rocket’s nose cone to pop off just after the rocket hits apogee (its highest point in the air) and lets the parachute deploy, while ensuring that all the parts stay together on the way down.

Motor mount with fins, standing upright
The core of the rocket

As a side note, if you include an electronics bay (“e-bay”) in the rocket, which is optional, then you need two cords: one to attach the motor mount to the e-bay, and another to attach the other side of the e-bay to the nose cone, so again everything stays together. The e-bay also have steel eyebolts on both ends for attachment. Just FYI, I’m building and including an empty e-bay in this rocket; I’m not actually installing any electronics in it for the first launch. I want to keep things relatively simple for my level 1 certification flight and will start putting in some interesting electronics for the next launch after that.

If you’ve built and launched any rockets before, you’re probably rolling your eyes at how I’m oversimplifying much of this, and you also likely already identified several inaccurate statements I’ve made. On the other hand, if you’ve never done any of this before, I probably just confused you with a bunch of inadequate and lackluster descriptions.

In fact, I’m pretty sure I’ve failed to satisfy anyone at all with this post. But then, who cares?