AT 18/20 Reload Liner Won't Fit?

So I recently purchased an AT 18/20 case and a couple D13 reloads to use at the CMASS launch on 9/26. I held off assembling the motor until I was at the field and ran into a bit of trouble. It seems that the diameter of the first reload I tried to build was just a bit too big. After inserting the delay spacer, delay grain and propellant grain into the liner, I noticed that the liner was a very tight fit in the case. This is the very first time I have used an RMS system motor before, so I wasn't certain this was typical. I expected it to be snug. I figured it was just hung up on the front edge of the liner, so I took it out and shaved the very front edge with a hobby knife to make about a 30-45 degree angle on that edge (delay grain side) and reinserted the liner 'assembly'. It still seemed tight, so probably pretty foolishly, I flipped it over and pressed it against the table to get it the rest of the way in. It slid in about 3/4 of the way and jammed to a stop. Nothing I could do would get the liner any further in or out, it was totally stuck. The propellant and delay slid out just fine though. Eventually I had to mangle the liner with a pair of pliers to twist/delaminate the thing enough to remove it.

I then checked the other reload to see if the other liner was the same. The second liner slid in OK (pretty snug still, but it never jammed). I went ahead and reloaded the propellent and delay in that one and it launched just fine. Man those little 18/20s are loud! Anyway, I assume that 'snug' is OK, but is it normal? Or are the liners normally an easy slide-in insertion? I don't think the instructions said anything about the liner needing grease or other lubricant.

Also, what do I do about my other reload now? I have everything except the liner, but obviously can't fly without it. It this something that I should call Aerotech about, or the vendor I bought the reload from? Any thoughts on how to get a replacement liner?

You can order a new liner from Aerotech, as they sell replacement parts. Your best bet may be to contact them and ask for help.

Because of environmental changes (temperature and humidity) the paper liner swells and loses tolerances. It's fairly common practice with Aerotech liners to peel away the outside layer of paper to get it to fit in the case. I've tried sanding the liner, but that takes quite a bit of time and has given me mixed results.

Greg

GregGleason said:

You can order a new liner from Aerotech, as they sell replacement parts. Your best bet may be to contact them and ask for help.

Because of environmental changes (temperature and humidity) the paper liner swells and loses tolerances. It's fairly common practice with Aerotech liners to peel away the outside layer of paper to get it to fit in the case. I've tried sanding the liner, but that takes quite a bit of time and has given me mixed results.

Greg

Click to expand...

Yes - it is OK to peel a layer of the cardboard liner to get it to fit. While unsettling when you're inexperienced with RMS, don't worry - there aren't any adverse effects to doing this.

If you attend a club launch, consult with an experienced flyer for guidance.

--Lance.

llickteig1 said:

Yes - it is OK to peel a layer of the cardboard liner to get it to fit.

Click to expand...

OK, that's really good to know, and something that I hadn't noticed when reading through all the other 'how to' threads for AT RMS's. Exactly what 'fit' should I be going for when I do this though? Just enough to get it in (pretty snug/tight) or should it be an easy (not loose) slip fit?

MCriscione said:

...Exactly what 'fit' should I be going for when I do this though? Just enough to get it in (pretty snug/tight) or should it be an easy (not loose) slip fit?

Click to expand...

You want it not to be loose (doesn't want to drop out when on end), or so tight that it is difficult to move. Anything that is "in between" is fine.

Greg

And a little bit of your lube on the the outside of the liner before you put it in the casing will help tremendously with cleanup.

kj

It is very common to have to sand the crap out of Aerotech liners, especially the black ones. I have taken many to my belt sander. Peeling the cardboard ones is so much easier. Just wait until you have to peel the casting tube from a grain to get it to fit. Yep, done that more times than I can count. Just gotta love the "hands on" approach.

I've got a quick update for you all. I called Aerotech's customer service about the damaged liner and was referred to their warranty department. I quickly received a response in which I was told "Don't feel bad, quite few liners get mangled every year." So I felt a bit better about making this mistake. They offered the same advice about peeling or sanding down liners and propellant grains and offered to send me out a couple replacement liners. Even though I'm the one that mangled them. Amazing. Anyway, the liners came in the mail a few days ago.

Needless to say, although I'm a new customer, I'm very happy with AT's customer service and plan to continue to use their products. I'm particularly happy that I don't have a useless reload laying around. For those who don't know, you can actually purchase these liners directly from AT's experimental motor website (https://www.rocketmotorparts.com/) but at 35 cents per liner and a minimum $9 shipping fee, I'm really glad they offered me a couple replacements. (I'm not anywhere near ready to fool around with 'experimental' anything and couldn't justify the shipping for just a liner)

Glad you had a positive experience with AT. Anytime I have had issues, they have been helpful to me.

My first composite motor was an AT RMS 18/20. I had some guys at a club launch who were experienced with reloads helping me out, since I didn't really know what I was doing at first. But when it finally lit, wow, what a rush!

The two most important things to remember with RMS reloads is: 1) Do not get grease on the delay element, and 2) do not forget the red BP cap (ejection charge) at the top of the forward closure.

Greg

You can make a tape well for BP if you loose the cap.

Karl and crew at Aerotech are good folks indeed.