Here is my question. When building a rocket from scratch, how do you build a motor mount to except the reusable motor tubes. For the Estes engines it is a cake walk. But I have never used any other engines. Please advise. Thaks in advance. nukemmcssret

For 18mm and 24mm motors, build it just like normal, but cut or file the forward tip of the motor hook (the little piece which is bent in to block the front of the motor) back a little bit so that it is clear of the hole in the thrust ring. The ejection charge cap of reloadable motors (and single-use composites as well) extend forward beyond the front of the casing.

For 24mm, consider omitting the thrust and motor hook altogether so that you can use a wide variety of reloadables including Pro24 from CTI, many of which are longer than the standard D or E motor casings. When flying with a black powder motor (or an older composite), make a thrust ring by wrapping 1/4" masking around the aft end of the motor until you build it to about the outside diameter of the motor mount tube. This will keep the motor from flying up through the rocket, serving essentially the same purpose as a thrust ring glued into the motor tube. Retain the motor in place by wrapping some wider masking tape around both the tape thrust ring and the end of the motor tube.


Bill

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Thanks I will try that. I am tired of using Estes motors. I hear that other motors of the same grade have more thrust.

I would "second" Bill's advice in the second paragraph.

Your first APCP motor will be a rush!

If you need dimensional data, let us know and we can help.

Greg

You can build with the kit parts, and launch with composite motors, but you're going to wish you made some modifications pretty quickly.

You will want to dump the thin-walled motor mount tube that comes with the Estes kit. Composite motors burn hotter, longer, and will roast that thin-walled tube twice as fast as Estes blackpowder motors. You will want to order some heavy-wall tubing (and keep a supply on hand for future projects) such as BT50H for 24mm MMTs. The inside diam is the same but the thicker walls mean the outside diam is larger.

This in turn means that you will need to modify the centering rings, or order new ones. You can usually trim the inner edge off the CRs without much trouble, but until you do this a few times you might not be "happy" with it or confident in your results. You may want to get some CRs that are laser-cut to fit the heavy MMT precisely. Before you glue the CRs in place, there is more in the notes below.

For high-thrust motors, fins generally reach all the way through the airframe tube and down to the MMT. A portion of the root joint (like, maybe half?) has a "tab" that sticks down through the airframe tube. The airframe tube has a matching slot cut at each fin root; you can do this yourself pretty neatly with a straightedge and a freehand Xacto (lots of people have done it this way).

At assembly time you will fit all the parts together, tack them in place with a couple drops of CA (to get fin alignment right), and usually slide the forward CR (without glue) back until it is seated against the front edges of the fin root tabs. This makes several closed-off compartments around the MMT, and you will apply epoxy to all these joints all around the insides (I like to slightly thin the epoxy so it soaks into the tight joints a bit better). I use disposable thin paint brushes to work the epoxy into place. Note that you don't have to "fill" the compartments with epoxy (that would add too much weight) but the joints themselves do need to be well covered.

When you get the inside joints covered, then you slip the aft CR down the MMT into position against the rear edges of the fin tabs.

You use epoxy for this assembly because it *cures* by itself (it doesn't require air circulation in order to *dry*). If you try to assemble the fin roots/CRs/MMT with white or yellow glue, you're going to have a gooey wet mess that takes months to dry.

Lots of people seem to think they need to replace the cardboard CRs with hell-for-stout wooden ones. You do NOT need to do this if the fin root tabs are properly fitted and glued. Motor thrust loads are far more efficiently carried as shear loads through the tabs than as bending loads through the CRs. The only functions that the CRs need to perform are to (1) keep the MMT centered during assembly and (2) serve as a gas seal to direct the ejection gasses out the front. The cardboard CRs that came with your kits will work just fine.

And that's how you build a low-power kit to ACCEPT mid-power motors.