Are motor retainers for use on FG and cardboard MMTs exchangeable?

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Bat-mite

Bat-mite

Rocketeer in MD
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I recently bought a Slimline motor retainer from GLR. When I went to install it on my FG MMT, it won't fit. Using a digital caliper, I discovered that the difference between the interior of the retainer and the exterior of the MMT is 3 mm. That's a lot! If I sand down my MMT by 3 mm, I don't think it will be structurally sound.

All of GLR's pictures on their site show their Slimlines going on cardboard tubes. So, did I buy the wrong retainer? If so, should I buy an Aeropack? Do I need to specify FG or cardboard?

Thanks....
 
Even the Aero Pack retainers come in different inner diameter sizes.
 
Last edited:
I notice on Aeropack's site that they have a "blank", "L", and "P" for each size MMT. What do those signify?
 
Bat-mite said:
I notice on Aeropack's site that they have a "blank", "L", and "P" for each size MMT. What do those signify?
Click to expand...

They make it confusing, but one fits LOC Brand MMT Tubes, and that's all I know. I got my Aero Pack Retainer from Apogee, and I think they had the sizing Chart on their Site for the different diameters.
 
They would sell more product if they made their sizing specifications more transparent, like just listing the Diameters, so that you could simply Mic' your Tube and order accordingly.
It actually kinda' Pi$$es me off that they don't.
 
Boy, this is confusing. I went to Apogee's site and saw the two outside diameters: 2.265 and 2.278. I have to assume I need the larger one, since the Slimline is too small. But the larger one says it fits GLR phenolic. I am lost.

Hmm, since Rocketry Warehouse only sells the "P" retainers, and I have to assume that they sell retainers that fit their tubes, then I'm guessing I need the "P".
 
The "L" stands for Loc/Precision and the "P" stands for Public Missiles Ltd. These were the two big kit companies of yore.

Generally, the "L" size is for cardboard tubes and the "P" size for phenolic so if your fiberglass tubes match the dimensions of phenolic, use those. There are no standards for tube wall thickness, so little consistency in O.D.
 
So, if I need to sand my tube down until the retainer fits, will that weaken it to the point where it is unsafe?
 
^^-- it will weaken it, but which is stronger, 'glass or paper? Is your choice of material to come down hard and fast on concrete?

I thought the ones for fiberglass were for thinner material -- maybe you need one for cardboard.
 
Bat-mite said:
So, if I need to sand my tube down until the retainer fits, will that weaken it to the point where it is unsafe?
Click to expand...
The way I see it, you're only sanding down the part of the tube that will have an aluminum retainer on it. So, while the tube might be weakened, you'll basically have a metal sleeve over that part of the tube, right? Maybe you can leave the last 1/4" unsanded, and then tap it down the last bit.
 
nute said:
The way I see it, you're only sanding down the part of the tube that will have an aluminum retainer on it. So, while the tube might be weakened, you'll basically have a metal sleeve over that part of the tube, right? Maybe you can leave the last 1/4" unsanded, and then tap it down the last bit.
Click to expand...

That's kind of what I was thinking.
 
Bat-mite said:
I recently bought a Slimline motor retainer from GLR. When I went to install it on my FG MMT, it won't fit. Using a digital caliper, I discovered that the difference between the interior of the retainer and the exterior of the MMT is 3 mm. That's a lot! If I sand down my MMT by 3 mm, I don't think it will be structurally sound.

All of GLR's pictures on their site show their Slimlines going on cardboard tubes. So, did I buy the wrong retainer? If so, should I buy an Aeropack? Do I need to specify FG or cardboard?

Thanks....
Click to expand...

The best thing to do is contact the people from Aeropac, I've done this on a few occasions and they helped me figure out which retainer that I needed and how to install the retainer if it were to big or to small. Yes the size chart is confusing and needs updating, it's why I call them to make sure I get the right retainer.:2:
 
TopRamen said:
They would sell more product if they made their sizing specifications more transparent, like just listing the Diameters, so that you could simply Mic' your Tube and order accordingly.
It actually kinda' Pi$$es me off that they don't.
Click to expand...

15628862912_981e0f48b2_b.jpg
 

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