Sooting of aft closure threads on Aerotech 29mm RMS

[UhClem]

I have had a problem with two 29mm RMS Aerotech reloads I have flown. When disassembling the motor I have noticed sooting on the aft closure threads. On the last occasion it was an H180 reload and the sooting was so bad that a wrench was required to remove the aft closure. Examination of the aft 0-ring revealed that it had eroded.

I thought perhaps this was a personal problem but this last weekend at a launch another flyer approached with 29mm RMS case in hand and looking for a wrench. As I expected the aft closure was heavily sooted. (I think it was the H165R reload). Examination of the aft o-ring revealed no visible signs of erosion but one section did feel rough.

Has anyone else seen a problem with erosion of the aft o-ring or sooting of the aft closure threads in Aerotech 29mm RMS motors?

While this hasn't resulted in a serious problem yet I am concerned that it could eventually lead to a CATO.

 

[WillCarney]

What grease are you using.

I noticed a few times that with the redlines and other hot burning
propellant I got a little soot and O ring erosion. I used to use
vaseline as a lube but now I use a high temp DOW lube and do
not get any erosion on the o-rings or blow-by the rings causing
soot.

Try a better lube that might be your problem.

William

 

[Garoq]

Originally posted by WillCarney
What grease are you using.

I noticed a few times that with the redlines and other hot burning
propellant I got a little soot and O ring erosion. I used to use
vaseline as a lube but now I use a high temp DOW lube and do
not get any erosion on the o-rings or blow-by the rings causing
soot.

Try a better lube that might be your problem.

William

That could be it. Of course we also recommend Super Lube™ grease for RMS.

 

[UhClem]

Originally posted by WillCarney
What grease are you using.

I noticed a few times that with the redlines and other hot burning
propellant I got a little soot and O ring erosion. I used to use
vaseline as a lube but now I use a high temp DOW lube and do
not get any erosion on the o-rings or blow-by the rings causing
soot.

Try a better lube that might be your problem.

William

Interesting theory but it has a couple of problems.

The first is that I have been using the same o-ring lubricant since 1995 on everything from 24mm to 75mm reloads with no trouble until recently. I use either what came in the little white packet with the reload case or "Lube-Gel" from Radio Shack. These are both products of SuperLube and I suspect are identical. If the lubricant is at fault then why has this only occured recently?

The second is that the lubricant is not there to seal the case. It is there to prevent seizing of the o-ring as the closures are tightened. If the lubricant is called on to provided any sealing then the o-ring has failed.



As an interesting side note, I was watching Gary Rosenfield assemble several turbo K reloads back in 1996 when someone asked why he was using that tub of Slick-50 lubricant. The response was something to the effect of "Because I found it before I got to the Crisco". This tells me that the choice of lubricant is not critical.

 

[Garoq]

Originally posted by UhClem
Interesting theory but it has a couple of problems.

The first is that I have been using the same o-ring lubricant since 1995 on everything from 24mm to 75mm reloads with no trouble until recently. I use either what came in the little white packet with the reload case or "Lube-Gel" from Radio Shack. These are both products of SuperLube and I suspect are identical. If the lubricant is at fault then why has this only occured recently?

The second is that the lubricant is not there to seal the case. It is there to prevent seizing of the o-ring as the closures are tightened. If the lubricant is called on to provided any sealing then the o-ring has failed.

As an interesting side note, I was watching Gary Rosenfield assemble several turbo K reloads back in 1996 when someone asked why he was using that tub of Slick-50 lubricant. The response was something to the effect of "Because I found it before I got to the Crisco". This tells me that the choice of lubricant is not critical.

I don't remember that incident, but it was surely just an offhand remark. If it was a turbo reload I would have been using Krytox grease on the N2O-wetted components. On the other o-rings, the choice is not as critical. However, no one to my knowledge has really investigated the use of different o-ring lubricants with reloadable motors and quantified the results.

You're mostly right about the purpose of the lubricant. But it also fills in the microscopic pores in the sealing parts and helps prevents damage if the ring is forced over a rough surface or sharp edge.

Sooting in the threads is indicative of o-ring failure. It could be caused by any of the usual problems: lack of compression, contamination of the seal surface(s), damage to the o-ring, etc. Was there resistance during the last .030" of tightening the closure? If the liner was too short that could result in lack of compression of the seal.

 

[Batman]

What do you do if the liner is too short? That was the case on the last H128 I flew, unfortunately I assumed that I was being paranoid and flew it anyway. Somehow it caused an early ejection and a 3" zipper in my favorite rocket .

 

[Garoq]

Originally posted by Batman
What do you do if the liner is too short? That was the case on the last H128 I flew, unfortunately I assumed that I was being paranoid and flew it anyway. Somehow it caused an early ejection and a 3" zipper in my favorite rocket .

How short was it? The H128 liner is supposed to be 5.298" long.

The reload kit instructions state what is to be done if parts are missing or damaged, etc.