Saturday, August 1, 2015

Horrible Error

I've started building my first rocket in months. I decided to take one of the smaller rockets off the build pile - the Estes Reflector.

It's a small, BT-50 (24mm) based rocket with a short payload section. I'm building it with the intention of adding a camera to the payload, following the instructions on this Instructables build, because it's a pretty cool project, and I have yet to successfully launch a camera payload (Janus II had a weird flight and vanished without a trace, and the camera wasn't working anyway. I may post video soon.).

An Estes Reflector with internal, horizontally-
oriented camera, from

Despite having become much more confident in my building skills, sometimes mistakes happen.

Well, first of all, I airfoiled the fins, and one or two came out a little uneven. Not badly, and I hadn't done it in a few months, but the problem was due mainly to rushing the job.

Then, a couple of the fins warped when I brushed on CWF to fill in the wood grain. I pressed them under a heavy book (my trusty Riverside Shakespeare, an invaluable rocket building tool), but there was still a nasty warp on one of the fins. I dunked the bad fins in water, and am re-pressing them. We'll see how that turns out.

The real problem is the motor hook.

Like most Estes low power kits, it comes with a standard motor hook with a little recurved bit on the end as a thumb grip.

Some rocketeers religiously remove the thumb grip and smooth off the remaining bit with a file. I actually like the thumb grip - it makes it easier to install the motor. But in some cases, it gets in the way.

A lot of rockets with backward-swept fins will sit nicely on a shelf with no need for a stand or support. Many rockets have fins that don't sweep backwards, so in order to display them on a shelf in a convenient, upright manner, you need to make (or buy, but don't ever buy) a stand of some sort.

The Reflector has swept back fins, but they don't go too far back. On a standard Estes motor hook, the thumb grip is longer than the fins, meaning you cannot simply rest the rocket on its fins. On an old-fashioned, simple motor hook, which is basically just a strip of metal with a bend at the front and a bend at the end, you'd have plenty of space at the bottom - no need for a stand.

Here's a picture from Chris Michielssen's blog with a before and after pic of a modified Estes hook:

The top hook has been modified, and looks more like an old-fashioned
motor hook. This is the kind of hook you get when you order parts online
from vendors such as Jonrocket.
First, I tried cutting the thumb grip off with a pair of wire cutters.

I've had these probably since I was 12. I've used them for trimming guitar strings for 29 years. They didn't work... Didn't even make a dent.

Looking around my Rocket Room...

My Rocket Room in Boston - a couple weeks ago, in progress
...I found a pair of PVC pipe cutters.

This evil parrot-looking thing cuts through 1 inch PVC pipe with little effort.

I figured these would have more power. But instead of cutting the hook, it bent it - backwards. Now there was no more hook to the hook. It wouldn't hold the motor in - but of course, the thumb grip was still attached. AND I dented the end of the airframe, slightly...

I reached for a pair of needle nosed pliers to try to re-bend the hook into shape. What I ended up with looked like this:

It will hold the motor in, and the hook is now definitely short enough to not extend beyond the aft end of the fins, but it looks pretty janky. And the thumb grip now sticks out beyond the diameter of the airframe. This could catch on a two-piece Estes launch rod. Chad had that happen with a bent motor hook on his Estes Crossfire ISX once, and the rod went flying with the rocket! It was terrifying.

Fortunately, I do not use the two-piece rods, and, because of the payload section, the launch lug for this rocket is actually on a stand-off, so it's not likely that the rod will come into contact with the hook.

I could have tossed this whole thing out. I do have plenty of spare parts. It would have been easy for me to cut a 10-inch piece of BT-50 body tube, and make a whole new lower section of this rocket from scratch. But I wanted to go forward, not backward, and as you can see above, I went ahead and started gluing on the fins.

This kind of laziness is not like me - not in rocketry, anyway. I'm usually very meticulous with my rockets (if only I could be that diligent in other areas of life). But it's been so long since I built a rocket, I wanted to move quickly.

If I had it do do over again, I'd have saved the Estes motor hook for another rocket, swapped out a plain hook from Jonrocket, and have saved myself the trouble of all this. Live and learn!

I'm sure I can still make this rocket look pretty good, and when I'm done, the flaw won't be noticeable. Perhaps I'll even find a better cutter to take care of that hook later.

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  1. Hi Daniel,
    Cutting off a finger tab is usually easier before it is glued to the mount. I cut them off right after I open the kit bag. I have cut them off afterwards though.
    Try to score the cut location with the wire cutter, don't try to cut all the way through. Just squeeze and make a visible cut line mark.
    Use two small pliers. Position one to the left of the score (Model side) to hold the hook still.
    The second pliers goes on the other side of the score mark. The second pliers bends the unwanted hook end up and down at the score mark. The first pliers hold still and doesn't move.
    3 or 4 up and down bends should part it.
    Use the first pliers again to hold it still and fill off the sharp corners if you can.
    Good luck!

    1. Hi, Chris.

      I'm pretty sure I need a new pair of wire cutters for this application. The ones I have didn't even make a dent!