Once I got the Semroc Bandit all glued together, the next kit I semi-randomly pulled from the build pile was the Estes Nike-X, another nice BT-55 kit.
I like BT-55 rockets. It might be my favorite low power tube size. I'm not sure why. A BT-55 tube (1.325 inches in diameter) feels nice and sturdy, and it's versatile. Some BT-55 kits look like little rockets, and others are surprisingly big.
All I know is that a lot of Estes kits which grab my eye happen to be made of BT-55 tubes.
The Nike-X is loosely based on the Nike Zeus missile.
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| Several missiles in the Nike family, with the Nike Zeus closest to the camera |
Here are the parts to the Nike-X kit.
You can see from the decal sheet that the black parts of the rocket are all decals. That means painting will be easy - the whole rocket will be done in gloss white. Sometimes, it's nice to have a simple paint job.
Just below the sheet of balsa fins, you see the motor tube. This is longer than a lot of motor tubes you get for 18mm A/B/C motors. A beginner might wonder why the long engine tube?
That's because this rocket has what's called a stuffer tube. The motor mount is longer, with the forward centering ring farther up in the body.
With the centering ring closing off the body tube much closer to the nose cone, the volume of the inside of the rocket is smaller. This is to aid in ejecting the nose cone.
With a large volume rocket, sometimes a small ejection charge can have trouble pressurizing the entire inside of the body tube enough to successfully eject the parachute. By using a stuffer tube, you make the inside of the rocket effectively smaller, meaning there's less space for the ejection charge to have to pressurize.
Truly, though, for a rocket of this size, I don't think that's really necessary. I have plenty of BT-55 rockets the same length as the Nike-X, and some larger rockets, none of which use a stuffer tube, and I've never had an issue with recovery.
The Big Bertha is an interesting example.
It uses a BT-60 body tube, and so is larger in diameter than the Nike-X. Some Big Bertha kits come with a stuffer tube, and some come with a standard 2.75 inch long engine tube. Mine has a short tube - no stuffer. And I've never had a problem with the nose cone ejecting.
But using a stuffer tube here isn't going to hurt anything, so I guess it's better safe than sorry.
The fin sheet was warped slightly.
Warped fins can drive you crazy, but they can be fixed. CLICK HERE for my post on different methods of fixing warped fins.
When I examined the fins more closely, it looked like the balsa sheet had warped in the bag. While the sheet had a bend in it on one side, the fins looked like they might actually still be flat.
In the above photo, you can see the underside of the sheet. The sheet curves away but the fins stick out.
Once I cut the fins loose and stacked them on the table, they looked like they were fine.
I wouldn't need to break out the glass cleaner this time around.
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An interesting blog entry, Daniel. I had never thought about a stuffer tube, as my Big Bertha never have one either. And older one, inherited from a retiring rocketeer, apparently had problems, as I launched it once after replacing the parachute, and discovered the elastic shock cord had deteriorated, and, well... let's just say the launch did not go as hoped. I recovered it all, and have removed about a half inch off the top of the body tube, replaced the chute AND the shock cord. But I've never gone with kevlar string instead of the Estes shock cord and t-bag. I guess that's because I can never find the right gauge kevlar string nor afford a whole spool of it when/if I do. Can you recommend a source/size in one of your blog entries?
ReplyDeleteI have a few different gauges of Kevlar kite string I got from emmakites.com. It's a pretty good resource for affordable Kevlar thread, and it's braided rather than twisted, which means it's a little less stiff.
DeleteI'll do a post about how I anchor shock cords soon.
If you haven't already done so, you should check out Squirrel Works rockets. The majority of their kits use a BT-55 and many are nice looking rockets.
ReplyDeleteOh, I have a Squirrel Works on the build pile!
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