Casing Failure Question

[Madison Alum]

Recently, I had an almost burn through on my 38/360 Rouse Tech casing. Outside of the casing was blistered and puckered out. Inside was indented. I had been having trouble with the casing in that the none of the reload liners I have been using with it would fit unless I peeled off the outside layer of paper. Also had to sand down the od of the forward and aft spacers to get them to fit into the casing.
First two launches with the casing went OK, but last one resulted in the problem.

Is it unusual for the reload liners not to fit into the casing (I am using AT reloads) without some sort of sanding or peeling?
Should I have sanded the liner instead of peeling off the outer layer?
Is the fact that I peeled off the outer layer of the liner the cause of the shortened life of the casing (I would assume you should expect to get more than 3 shots out of a casing)?

Thanks for your help.

 

[troj]

It happens once in a while -- paper tube tolerances are only "so good", plus environmental conditions affect it quite a bit.

If it's happening for all reloads on that particular case, I would guess you have a case that's a bit out of spec. The thing that really makes me question it is that you had to sand the insulators - that's one I've not heard of anyone having to do, before.

-Kevin

 

[rdbones]

I had this problem with two 54/2560 cases on the same flight (a cluster of 4) I contacted Aerotech and they replaced the cases. This is when they switched from the phenolic liners to the cardboard and the damage was right where the seal disk and liner met. They did switch back.

If you have the reload lot number and date of purchase contact the warranty department at AT and they should fix you up.

 

[Sailorbill]

1. Was this a new case? The ID may have been wrong from the factory.

2. Were all three of the reloads the same propellant? If they were different it might help prove #1.

3. How old were the reloads? In older reloads, like years old, the grains can sometimes swell.

4. If you have other reloads for this case you might want to measure them or at least try to insert them into another 38mm case to see if they are the problem.

5. Do this.Report a Malfunctioning Engine

6. Contact AT.

Peeling liners and grain covers is not unusual but needing to sand the the spacers is not something I have ever needed to do.

Good luck

 

[Madison Alum]

Thanks for your responses. I plan on taking the casing in to work Monday and get the ID measured. I'm not a big HP flyer, so this is the only 38mm casing I have for AT reloads. All three of the reloads that I have used with this casing were purchased last year and 2 of them were used last year, so the only info I have is on the one I used last weekend. This one was the only I I have launched. Maybe I should start keeping track of the lot info. I didn't have a problem getting the grains in the liners, just the liners and for and aft insulators into the casing, so the ID may be tight.
One other question I have is whether or not you should tape the grains together. I think it says to do so on the C slot grains, but I thought that was just to keep the slots aligned.
Thanks again,
John

 

[troj]

I didn't have a problem getting the grains in the liners, just the liners and for and aft insulators into the casing, so the ID may be tight.

Yep, when the liner is tight, or the case is off a smidge, I would expect the grains to still fit into the liner.

One other question I have is whether or not you should tape the grains together. I think it says to do so on the C slot grains, but I thought that was just to keep the slots aligned.

Whatever the instructions say to do. Going from memory (it's been a while), they do tell you to tape the grains -- the slots out of alignment will affect the burn.

-Kevin

 

[Madison Alum]

The RMS 29/40-120 instruction call for taping the grains together. I don't see any such instructions on the 38mm RMS reloads. I was just wondering if the extra lengtwise space in the liner allowed some grain separation and allowed the burn out along the face of the grain so the heat is on the inside of the the casing longer and almost directed, although for only a short period of time.

 

[RedMaxFlyer]

The RMS 29/40-120 instruction call for taping the grains together. I don't see any such instructions on the 38mm RMS reloads. I was just wondering if the extra lengtwise space in the liner allowed some grain separation and allowed the burn out along the face of the grain so the heat is on the inside of the the casing longer and almost directed, although for only a short period of time.

The two-grain 29/40-120 loads have you tape the grains together to ensure the slots remain aligned while you prep the rocket so that you can get the igniter up to the forward end of the motor. The tape is consumed shortly after ignition.

 

[Handeman]

I have a Dr Rocket 38mm case that is slightly under sized. On about 3 reloads, I needed to sand down the outside of the phenolic liner. The last time this happened, instead of sanding it down, I tried it in an Aerotech case. The liner that wouldn't fit the Dr Rocket case fit just fine in the Aerotech case, proving to me that my Dr Rocket is undersized. It's my understanding that Dr Rocket did not hold the same tolerances that Aerotech did, that's why they were cheaper. You may be running into the same issue with the Rouse-Tech case.

Since the case is trashed now, I would suggest replacing it with an Aerotech case, if you can find one.

 

[Madison Alum]

Reported the issue to Aerotech and they sent me a new casing. Hope to get it into the air in a couple of weeks in the Trident I I am building.