Estes 24mm in an MPR

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Well-Known Member
Jan 18, 2009
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I think I understand how Aerotech type motors are retained (a flange at the base of the motor that provides both retention and thrust ring functions). So after you build a rocket to take Aerotech SU or RMS (with no thrust ring and flange-holder of some sort), how do you use an Estes-type engine in that rocket? I've heard people say friction fit, but I prefer something a little more positive. I am really at a disadvantage here because there are no vendors locally for anything other than Estes engines, so I can't just look at it and figure it out. Sorry if this is an obvious question.
Hey prowlerguy!

I'm not sure I completely understand your question but let me take a whack at an answer. RMS motors have rear thrust rings and we normally install forward thrust rings to help retain Estes motors during thrust. Then you have some type of motor retention to prevent both types from being kicked out the back from the ejection charge. A SU Aertotech motor is built very similarly to an Estes - no thrust ring.

I build some Estes "D" engine kits as normal and the AT 24mm RMS motor fits just fine. The standard engine hook will keep the AT RMS casing from kicking out the back. The AT SU motor fits just like and Estes 24mm engine.

I could post a couple of pictures of the AT RMS cases if that would help.
Take a BT-50 ( or better yet, LOC 24 MMT tube) and slice off 1/4". Slide this on your motor and attach with your favorite modo-tough adhevise. This works as a thrust ring. You can also make one out of 1/4" masking tape, which is easier, but you don't seem to be fond of, even though it'll work for O Motors . If you don't have a hook, wrap the engine in masking tape for a friction fit. If you don't want to do that, you'll need to rig up some sort of Kaplow Klip or PML style retainer. The Sunward kits use a funky screw in hook. See the reviews on EMRR for details...

Okay, I think you're off on the Aerotech retention thing. The flange on the bottom of the RMS casing will serve as a thrust ring only. Positive retention is still needed. With Aerotech kits, they provide a motor hook - same idea as Estes, just bigger. When loaded, it will look and function the same as an estes set up. Aerotech kits also have thrust rings. The flange is only needed when flying a kit that does not have a motor hook or thrust ring.

Basically, to fly an Estes motor in an Aerotech kit, it all comes down to adaptors...24/29mm adaptor to fit the width, and spacers to set the motor against the bottom of the hook so it works just like the Estes setup. Make sense?
Thanks. For some reason I thought the 24mm RMS was longer than an Estes 24mm, thus you could not install a forward thrust ring in a rocket you intended to use a 24mm RMS in. I am glad to hear I was mistaken. I said the thrust ring performed two functions because most of the retention devices I have seen pictured (with the exception of the wire method) clamp down on the flange. At least, that what it looks like in the pictures.

Let me make sure I have this right. If I have built 18mm and 24mm rockets with standard engine blocks/hooks, I can fly 18mm and 24mm Aerotech RMS and SU engines without modification of the rocket, right?
Originally posted by prowlerguy
Let me make sure I have this right. If I have built 18mm and 24mm rockets with standard engine blocks/hooks, I can fly 18mm and 24mm Aerotech RMS and SU engines without modification of the rocket, right?
That has been my experience with one exception -- The RMS case is actually longer than a standard Estes motor, but it is smaller in diameter at the end with the ejection charge. That smaller end will fit through a standard paper engine block but on one model the part of the engine hook that goes throught the BT needed to be filed down a bit because it stuck out further than the engine block. It was easy to fix. I will try to post a picture so you can see what I am describing.
When building a 24mm mount that may be used for AT motors, I always clip off part of the upper end of the engine hook to be certain the AT motor will slide in. Better to do it before assembly than try to file it down while it is inside the rocket.