Slimline Retainers and S/U Motors

[DynaSoar]

Slimline motors are not to be used with S/U motors without adding a rear thrust ring to the motor. I learned this the hard way. My Mirage's maiden flight ended drilling for oil in the Texcas cornfield.

The description and the instructions are not clear on this matter. They assume a person to have experience with RMS motors. Not a good assumption to make.

Ed at Giant Leap is fixing the description to make this clear. I know a lot of flights with S/U motors and Slimline's went fine. They apparently were lucky.

I'm going to do a bit of research and come up with a list of mods to make S/U motors safe to fly with a Slimline and share them here and with Ed for the instructions. In the mean time, pass the word. You could save someone from a needless loss.

 

[rstaff3]

I never would have thought to use it with a SU unless I added some sort of ring. A tape thrust ring probably would work.

 

[DynaSoar]

Originally posted by rstaff3
I never would have thought to use it with a SU unless I added some sort of ring. A tape thrust ring probably would work.

You never would have thought that unless you had experience with RMS motors. They have a rear thrust ring. If you'd never used one you wouldn't know about that, and that's the point.

I never would have thought to add a ring. The instructions said to use the spacer if there wasn't a thrust ring. This was an AT bird. It has a thrust ring glued in the motor tube, made from a piece of coupler tube with a spacer ring glued on the front. RMS motors have something on the aft end that goes by the same name as the thing that keeps the motor from shooting up through the rocket. The only hint in the instructions is misleading because it uses a term that means something else also.

 

[lalligood]

Originally posted by rstaff3
I never would have thought to use it with a SU unless I added some sort of ring. A tape thrust ring probably would work.

You're pretty much in the same boat when using SU motors with Aero Pack retainers too. Tape thrust rings have worked extremely well for me when I have used SU motors with my Aero Pack retainer.

Dynasoar,
Would I be correct in guessing that you had a motor block in the MMT tube but didn't have a thrust ring to hold the motor in place for ejection? Otherwise with no tape thrust ring you would have sent the motor up through the rocket (which never would've left the pad)...HEADS UP! Sorry to hear about that.

 

[DynaSoar]

Originally posted by lalligood
Dynasoar,
Would I be correct in guessing that you had a motor block in the MMT tube but didn't have a thrust ring to hold the motor in place for ejection? Otherwise with no tape thrust ring you would have sent the motor up through the rocket (which never would've left the pad)...HEADS UP! Sorry to hear about that.

Yeah, the thrust ring was in the motor mount. I set it forward to 11" so it could handle Ellis H and I S/U motors, but it was in there. Since the thrust ring was in there, according to the instructions I didn't need the spacer. There's just nothing in any description or instructions to lead one to think "the OTHER thrust ring".

The spacer ring does in fact fix the problem. And I had it with me all along, despite the fact that according to the instructions I didn't need it.