Saturday, October 12, 2019

Booster Bertha 2nd Stage Retainer Ring

In a comment from Boosted Bertha build Post #2, Openroad asked:
"I’m curious about how the engine retainer holds up on the sustainer - how many flights will it take for the booster motor’s ignition charge to “cook” the screw on retainer ring?"

Bernard Cawley answered and sent a picture via email:
"I have five flights on my Boosted Bertha. The sustainer's motor retainer ring is still serviceable - I'd guess it has 3-5 more flights in it before it won't fit well enough to be trusted. I have some of the 18mm retainers that are sold separately on hand, so I do have spares."

This is pretty much what I expected. It's interesting that the longer booster BT-20 tube and engine block at the top has directed the booster "flame" towards the center, there isn't any charring around the sides.
Estes does have replacement 18mm retainers on their website: CLICK HERE

Bernard Cawley gave additional information about the engine retainers in the comments below -  


  1. That directed flame bit is similar to the approach in the John Boren-designed accessory boosters (Booster-55, Booster-60 and the PSII booster for the Majestic/Ascender). It certainly seems to work - I'm 5 for 5 in second stage ignitions so far.

    As I noted (I think) in my email, the charring on the bottom of the ring isn't the real's that the threads in the ring have begun to warp a bit, so that it no longer screws on perfectly smoothly.

    Which leads to - the instructions have you use plastic cement to attach the portion glued to the motor tube. I've had both come loose. I reattached them with medium CA (it was a field repair at a launch several hours' drive from home) and so far that's holding OK.

  2. Also, there is enough "stuff" from the staging event ending up on the bottom of the sustainer that the interface between there and the stage coupler at the top of the booster needs to be cleaned up between flights so that the coupler doesn't get too tight.