AeroTech RMS 18/20 issue

I just sent this to [email protected]
hoping I could also get some input here.

Dear Sir or Ma'am
Let me first say that I have been building and launching model rockets for quite some time, but have just receintly entered the reloadable motor by purchasing an Aerotech RMS 18/20.
I purchased the RMS 18/20 casing from the local hobby shop, and purchased a package of D13-7W and D24-10T reloads directly from Aerotech.


Being new to reloads, I wan not sure about assembly, so I read the instructions several times before starting. After inserting the delay charge into the liner with the propellant grain, I test fit the liner into the casing. It was a tough fit, so I cleaned out the inside of the casing, and tried again. It was still a tough fit. So I test fit the other two liners and the were also a tough fit. At this point I figured a tough fit was normal. I pressed the liner into the casing as far as I could, which is almost flush with the outside of the casing. I cannot thread the end caps on. I also cannot remove the liner. it is stuck tight.


I don't know what I did wrong, and was wondering if it is normal for this tight of a fit?
Thanks ahead of time for your help.
Daniel Churchill

no it is not desirable to be that tight. there are a number of factors that might cause this. variations in manufacture of both the case and liner, the case might be on the lower side of spec for inside dia. and the liner on the high side. of the heat and humidity might cause the liner to 'swell'. usual fix* is to remove 1(one) layer of paper from the liner. this assumes that your case is clean and smooth on the inside.
Rex
*as suggested by aerotech.

Thanks for the quick reply Rex. I thought of the humidity issue, however the reloads were sealed, and we have had very low humidity here lately.
I plan on hitting the hardware store to get a dowel which closely matches the ID of the caseing so I can extract the liner without further damage.
Once it is removed from the casing, I will remove a layer of paper as you suggested.
Thanks again Rex!

swelling may have occurred at the factory, doesn't take much, and paper doesn't like to shrink back down . tis more of a challenge at times getting the larger liners(38mm) to fit the case, can't peel a phenolic liner. good luck and have fun,
Rex

Having to peel a layer off the liner is common on AT reloads, sometimes a layer may need to be removed from fuel grain, to fit inside liner also.

Some reloads come with separate instruction sheet explaining this.

Rule of thumb: how they go in = how they come out after firing. You just found this out...lol

Always check fit of grains into liner & liner into case.... before assembly.

Welome to the world of re-loadable motors!

PS: I cannot overemphasize how important it is to keep grease OFF the delay grain face. This [grease on delay] can prevent your ejection charge from firing.

Thanks Rex and Blackjack! I was going to grease the hell out of the casing. Now I think I will just use a little bit on the threads. I was going to use grey anti-seize grease. Is this okay? The motor did not come with any.

I now use Dow 111 high temp silicone grease on the threads and on the o-rings. For years I used petroleum jelly on my reloads. I never had a problem but some people may tell you not to use it. Whatever you use, apply only the thinnest of coatings. It doesn't require much and, as mentioned, you do not want to get grease on the delay element's faces. The lubrication on the rings helps ensure that they seat properly. I have even heard of people using spit on them. The only hard restriction that I know of is that you need to be careful that whatever you use on hybrids doesn't react with the gas. (I know the latter of off topic for this thread)

PS - I peeled the liner on an D24 reload this afternoon

blackjack2564 said:

PS: I cannot overemphasize how important it is to keep grease OFF the delay grain face. This [grease on delay] can prevent your ejection charge from firing.

Click to expand...

I have found an amazing way to bypass this issue.

SMALL DIAMETER DUAL DEPLOY!

Ok, not for everyone. But hey, at least with DD, if it fails it's your own fault.

Been playing phone tag with Aero-tech, and Carl caught me today. He's going to send me a replacement tube which I damaged. He said it was a tolerance stacking issue and was common on older reloads. I made a few suggestions on additions to their instructions for newbies like me.
Thanks everybody for your help!
Daniel

Received replacement tubes from Aero-tech today. Thanks for replacing the tubes I screwed up!!